Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting

Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting Honggang Fu, Zhijian Liang, Di Shen, Yao Wei, Fanfei Sun, Ying Xie, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4286568/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The electrocatalysts for high-energy consumed anodic oxygen evolution reaction (OER) especially in water splitting are generally prone to reconfiguration, so the dynamic structural evolution mechanisms should be deeply investigated. Herein, coral-like nanoarray assembled by nanosheets were synthesized via the layered effect of cobalt (Co) and the one-dimensional guiding effect of vanadium (V). The unique structure facilitates the full contact between active sites and electrolyte to enhance the electrocatalytic activity. The hydrogen evolution reaction (HER) and OER activity can be respectively promoted through modulating the electronic structure with nitrogen and phosphate anions. Thus, the assembled anion exchange membrane electrolyzer exhibits a direct current energy consumption of 4.31 kWh Nm –3 @250 mA cm –2 at 70°C. It only required 1.88 V voltage to achieve a current density of 500 mA cm –2 with excellent stability over 200 h. Operando synchrotron radiation and Bode phase angle analyses reveal that the dissolution of vanadium species makes the distorted Co-O octahedral to regular octahedral structure during OER, accompanying by a decrease of band gap and a shortening of the Co-Co bond length. Such a structural evolution plays as the key active site for the formation of oxygen-containing intermediates, thereby accelerating the reaction kinetics. Scientific community and society/Energy and society/Energy efficiency Scientific community and society/Energy and society/Energy supply and demand Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Sustainable alternatives to fossil fuels are significant for alleviating the increasingly severe situation of the energy crisis and global warming. Green hydrogen is widely considered to be a promising and clean fuel due to its high gravimetric energy density and environmentally friendly of combustion products. 1–3 Hydrogen generation via electrochemical water splitting is an auspicious strategy for the conversion and storage of renewable resources. 4–5 However, the efficiency of such clean energy technology and the scalable production of green hydrogen highly rely on exploring of cost-benefit and high-efficient electrocatalysts to promote the sluggish kinetics of both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Although precious metals Pt and Ir/Ru-based materials are considered as most advanced catalysts, the inherent scarcity and high-cost prevent the further commercial application of water splitting technology. 6–8 Anion exchange membrane (AEM) electrolysis water, as an emerging technology, combines the characteristics of proton exchange membrane (PEM) electrolysis water and alkaline (ALK) electrolysis water. It not only can quickly respond to renewable energy fluctuations like PEM, producing high-energy efficiency hydrogen gas, but also its operation in a slightly alkaline environment enables the utilization of transition metal-based catalysts. 9–11 Cobalt (Co)-based electrocatalysts have attracted considerable attention because of their tunable chemical reaction activity, high theoretical efficiency, thermodynamic stability and corrosion resistance in alkaline electrolyte. 12,13 Due to the limitation of the number of active sitesactive sites, most of the reported single-metal or single-component electrocatalysts exhibit confined effectiveness in facilitating reactions that involves both hydrogen- and oxygen-containing intermediates, such as * H, * O and * OOH. Alternatively, constructing three-dimensional (3D) structures orderly assembled from low-dimensional nanoscale structural units could provide plentiful active sites. Exploiting the epitaxial growth characteristics inherent in vanadium (V) oxides facilitates the construction of intricate 3D hierarchical porous micro-nano architectures. 14–16 Furthermore, the adsorption energy of intermediates can be precisely adjusted through the modulation of electronic structure of catalysts by different anions. Benefiting from the negatively charged nitrogen anions can weaken the strength of metal-H bond owing to the ensemble effect of metal nitrides, thereby optimizing the hydrogen adsorption and HER activity. 17–19 The stronger nucleophilicity of phosphate anions can act as the proton acceptors to facilitate the interfacial proton transfer, thus promoting the transformation of oxygen-containing intermediates for OER. 20–22 As such, intentionally constructing bimetallic Co-V electrocatalysts modulated by different anions is an effective strategy to simultaneously enhance the kinetics of HER and OER. Furthermore, transitional metal-based electrocatalysts, especially for Co species, always occur structural reconfiguration during the OER. However, most studies are primarily focused on utilizing theoretical calculations and off-line characterizations to explain the role of restructured configuration in enhancing activity. 23,24 Therefore, it is requisite to adopt advanced operando techniques to monitor the structural evolution of electrocatalysts and confirm the active sites for intermediates transformation, which is meaningful for the purposeful synthesis of water splitting electrocatalysts. Inspired by the above considerations, we employ a liquid phase self-assembly strategy to synthesize the coral-like Co 3 V 2 O 8 nanoarrays on the nickel foam substrate (CoVO@NF) based on the layered function of Co and the one-dimensional guidance of V. Such unique structure shows more active sites to enhance catalytic activity, while also providing sufficient space to mitigate changes in volume and stress to enhance the stability of catalyst. By a subsequent nitridation and phosphidation treatment, respectively, the obtained CoN/VN@NF and P-CoVO@NF exhibit well HER and OER activity with low overpotentials of 164 and 317 mV to achieve a large current density of 100 mA cm –2 , along with excellent stability for 10,000 cycles in 1.0 M KOH electrolyte. The assembled AEM electrolyzer shows a direct current energy consumption (W DC ) C of the is 4.31 kWh Nm –3 @250 mA cm –2 , closing to the international advanced level. Importantly, this system only needs a voltage of 1.88 and 1.98 V at the current densities of 500 and 1000 mA cm –2 , respectively. Operando synchrotron radiation discovers that the Co sites occur a structural evolution from the distorted octahedral to regular CoOOH octahedral structure during OER process. Operando Bode phase angle analyses further demonstrates that the phosphate anions modulation could enhance the charge transfer and deprotonation capabilities of the P-CoVO@NF, while the evolved CoOOH facilitates the formation of intermediates, thereby promoting the OER kinetics. Density functional theory (DFT) calculations demonstrate that the nitrogen anions could upward shifts the d-band center ( ɛ d ) of Co and V to optimize the adsorption energy of intermediates, as well as collaborating with the * OH adsorption site of V to accelerate the dissociation of water and improve HER activity. Conversely, P-O group induce the ɛ d of Co and V downward shifts, promoting the deprotonation of oxygen-containing intermediates during OER and simultaneously forming the CoOOH active center. Results Material characterizations Prior studies have shown that Co species tend to form lamellar structures, whereas V species are more inclined towards one-dimensional growth. Based on these bases, we have developed coral-like nanoarrays composed of nanosheets by utilizing the distinct behaviors of Co and V. As illustrated in Fig. 1 a, a liquid phase self-assembly method was employed to prepare coral-like interlaced cobalt vanadate nanosheet arrays precursor with the Co 3 V 2 O 8 phase supported on nickel foam substrate (CoVO/NF) (Supplementary Fig. 1). Indeed, the layered structure can be seen in the absence of V, while fibrous structure is obtained without using Co (Supplementary Fig. 2). It further proposed that Co is responsible for the stratification during catalyst growth, while V facilitates epitaxial growth. Subsequently, it underwent nitridation and phosphidation treatments to prepare CoN/VN@NF and P-CoVO@NF, respectively. To eliminate the interference from NF signals, the X-ray diffraction (XRD) characterizations of CoN/VN@NF and P-CoVO@NF are scraped from the NF substrates. As shown in Fig. 1 b, CoN/VN@NF primarily exhibits the hexagonal Co 2 N 0.67 phase and cubic VN phase. For P-CoVO@NF, the peaks still correspond to the cubic Co 3 V 2 O 8 phase as that of CoVO@NF, suggesting that phosphorus is incorporated in a doped form. The scanning electron microscopy (SEM) images in Fig. 1 c, d show that both the nitridation and phosphidation treatments maintain the coral-like nanosheet array structure, despite causing a rough surface. Such unique 3D micro-nano structures assembled by low-dimensional structures not only prevents the self-agglomeration during reaction processes to promote stability, but also furnishes an abundance of active sites to accelerate the electron transfer for enhancing electrocatalytic activity. Transmission electron microscopy (TEM) (Fig. 1 e) indicates that the nanosheet in CoN/VN@NF is composed of nanoparticles. It can increase the accessibility of the surface to allow the internal Co 2 N 0.67 -VN heterojunction directly contact with the reactants. High-resolution TEM (HRTEM) image shows clear lattice fringes and close contact between Co 2 N 0.67 (101) and VN (200) (Fig. 1 f), confirming the formation of heterojunction. The elemental mapping displays a uniform distribution of Co, V and N elements in CoN/VN@NF (Fig. 1 g). The obtained P-CoVO@NF represents overlapping nanosheets with the lattice fringes of Co 3 V 2 O 8 (122) plane (Fig. 1 h, i), while the uniform distribution of Co, V, O and P elements can be observed (Fig. 1 j). Additionally, an amorphous layer with a thickness of about 20 nm covers on the surface, and Fourier-transform infrared spectroscopy (FTIR) further proves the presence of P-O group (Supplementary Fig. 3). 25 Since phase transformation during OER process always involves bond-breaking, so the amorphous structure can more readily evolve than the crystalline structure. 26 The X-ray photoelectron spectroscopy (XPS) survey spectra indicate the presence of Co, V, N and O elements in CoN/VN@NF, while Co, V, P and O elements exist in P-CoVO@NF (Supplementary Fig. 4). As depicted in Fig. 2 a, the binding energies of Co 2p in CoN/VN@NF show a negative shift of 0.69 eV compared to CoVO@NF. Specially, the peaks at 779.73 and 795.95 eV of CoN/VN@NF respectively correspond to the Co 3+ in the Co 2p 3/2 and Co 2p 1/2 orbitals, while the peaks at 781.55 and 797.41 eV are assigned to Co 2+ . 27 The V 2p spectrum reveal two extra peaks after nitridation of CoVO@NF (Fig. 2 b). The peaks at 514.66 and 516.33 eV respectively attribute to V‒N‒O and V‒O bonds, indicating that the introduction of nitrogen anions results in the coupling between the electronic orbitals of Co and V with N atoms. 28 Besides, the V‒N bond located at 513.05 eV demonstrates the formation of metal nitride, which is further confirmed by the M‒N bond in N 1s spectrum (Fig. 2 c top). 29 For P-CoVO@NF, the Co 2p spectrum also exhibit the presence of Co 3+ at 780.02 and 795.95 eV, Co 2+ at 781.88 and 797.76 eV, while the peak at 516.3 eV in the V 2p spectrum ascribes to the V‒O bond. Compared to CoVO@NF, significant negative shifts in the Co 2p and V 2p peaks can be observed for P-CoVO@NF. Notably, the XPS spectrum reveals that the P predominantly exist in the form of P‒O bond at 133.71 eV, accompanying by a small amount of metal phosphide (Fig. 2 c bottom). 30 The P-O group with strong nucleophilicity could act as proton acceptor to activate surface oxygen during OER process. In addition to the oxygen vacancies (V O ) and metal‒oxygen (M‒O) peaks, an extra peak at 532.1 eV in the O 1s spectrum is attributed to the P-O bond (Supplementary Fig. 5). 31 X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) could provide accurate information of the valence states and coordination structures. As shown in Fig. 2 d, the position of the pre-edge absorption peak indicates the valence state order of Co as follows: CoN/VN@NF < P-CoVO@NF < CoVO@NF. The Fourier Transform (FT) EXAFS (FT-EXAFS) spectra for CoN/VN@NF and P-CoVO@NF implies that the introduction of nitrogen and P-O group respectively form the Co‒N and a small number of Co‒P coordinated structures (Fig. 2 e). The dominant peaks at 1.46 and 2.20 Å for CoN/VN@NF can be assigned to the first coordination shell of Co‒N/O bond and the inner coordination shell of Co‒Co bond (Supplementary Fig. 6 and Table 1), respectively. Compared with CoVO@NF, the decreased intensity of Co‒O bond at around 1.52 Å for P-CoVO@NF suggests a reduced average coordination number, indicating the formation of V O , which could enhance the electron transfer capability. Additionally, the small bulge at around 2.06 Å corresponds to the Co‒P bond. 32 Wavelet Transform (WT) is further recovered the coordination information of the first shell in both k-space and R space. After optimizing based on the Morlet wavelet, the Co K-edge WT-EXAFS of CoN/VN@NF and P-CoVO@NF respectively exhibit oscillations at 5.5 and 5.8 Å –1 correspond to Co‒N/O and Co‒O bonds (Fig. 2 f), whereas the minimal peak of Co‒P bond is difficult to be reflected. As shown in Fig. 2 g, the peak located at 5470 eV is designated as the 1s→3d transition of tetravalent V. 33 The weak pre-edge absorption peak in both CoN/VN@NF and P-CoVO@NF indicate that the introduction of anions transforms the low-coordinate VO 4 tetrahedra in CoVO@NF into high-coordinate V(N,O) 6 octahedra with higher symmetry. The pre-edge absorption peak gradually moves in the low energy direction from CoVO@NF to P-CoVO@NF and then to CoN/VN@NF, indicating that the oxidation state of V decreases due to the reduced oxygen content. Furthermore, the FT-EXAFS spectra of CoN/VN@NF exhibit four principal features below 6 Å (Fig. 2 h). Specially, the peaks at 1.63 and 2.42 Å correspond to the inner shell composed of six symmetric V‒N and V‒V bond, while the peaks near 3.70 and 4.45 Å are ascribed to the higher V‒N and V‒V shells, essentially consistent with the standard rock-salt structure of VN (Supplementary Fig. 7 and Table 2). 34 For P-CoVO@NF, the strongest V‒O bond is located at 1.62 Å rather than the 1.12 Å for CoVO@NF, attributing to the P incorporation causes the stretching of V‒O bond within Co 3 V 2 O 8 lattice. Such local structural variant makes the V‒O bond easily to break, resulting in the dissolution of V during OER process, thus promoting the reconstruction of Co species. As the WT-EXAFS illustrated in Fig. 2 i, the highest intensity peaks for CoN/VN@NF and P-CoVO@NF in the first coordination shell are ascribed to the V‒N and V‒O bonds at 7.50 and 6.20 Å –1 , respectively. The k-value for the V‒O bond in P-CoVO@NF is much higher than the CoVO@NF (6.20 vs. 4.81 Å –1 ), revealing that the V‒O bond is stretched by the P incorporation. Electrochemical performance HER performance. The HER activity was evaluated in 1.0 M KOH by a three-electrode system, and the commercial 20% Pt/C catalyst loaded on NF (denoted as Pt/C@NF) was also tested. As displayed in Fig. 3 a, CoN/VN@NF requires overpotentials of only 55 mV and 164 mV at the current densities of 10 mA cm –2 ( η 10 ) and 100 mA cm –2 ( η 100 ), respectively. It is significantly better than CoVO@NF (93 and 204 mV) and P-CoVO@NF (84 and 197 mV), approaching commercial 20% Pt/C (17 and 129 mV) (Fig. 3 b). Notably, CoN/VN@NF also exhibits outstanding HER activity over the recently reported non-precious metal electrocatalysts (Supplementary Table 3). The highest current response of CoN/VN@NF is attributed to the introduced nitrogen atom can increase the d-electron density of metal, resulting in a redistribution of the density of states near the Fermi level ( E F ) and generating a similar electronic structure as that of precious metal. The poor HER activity of nitride NF substrate indicates a negligible contribution to electrocatalytic activity (Supplementary Fig. 8). Compared to CoVO@NF and P-CoVO@NF, the lower Tafel slope value of 53 mV dec –1 for CoN/VN@NF inidicates a faster kinetics (Fig. 3 c), which also suggests the Volmer-Heyrovsky mechanism of CoN/VN@NF towards HER. 35 The Nyquist plots collected by electrochemical impedance spectroscopy (EIS) and the double-layer capacitance ( C dl ) values show that CoN/VN@NF displays the smallest charge transfer resistance and much more active sites (Fig. 3 d,e and Supplementary Fig. 9). After normalizing by the ECSA values, CoN/VN@NF still exhibit largest current density ( J ECSA ) (Supplementary Fig. 10), further confirming the outstanding intrinsic activity. Moreover, CoN/VN@NF shows a turnover frequency (TOF) value of 1.16 s –1 at 0.2 V, which is significantly higher than CoVO@NF (0.50 s –1 ) and P-CoVO@NF (0.54 s –1 ) (Supplementary Fig. 11). It maintains the higher level across the entire range of applied potentials, further provinging the rapid kinetics of CoN/VN@NF. Durability is another crucial criterion for assessing the potential application of electrocatalyst. As depicted in Fig. 3 f, the CoN/VN@NF maintains its initial activity without significant degradation after 10,000 continuous cyclic voltammetry (CV) cycles. It also can stably operate for over 100 h at a current density of 100 mA cm –2 , further confirming the superior stability of CoN/VN@NF (inset of Fig. 3 f). After stability test, it preserves the original coral-like nanoarray structure, while the binding energies of Co and V in the XPS spectra show slightly variation (Supplementary Fig. 12). It reveals that the stable surface chemical state of CoN/VN@NF is conductive to long-term operation. OER performance. The OER activity was also investigated in alkaline electrolyte, and the commercial RuO 2 catalyst supported on NF (denoted as RuO 2 @NF) was studied for comparison. As presented in Fig. 3 g, the P-CoVO@NF performs much better OER activity than the compared catalysts. The P-CoVO@NF only requires the overpotentials of 296 and 317 mV to deliver the current densities of 50 and 100 mA cm –2 , respectively, much lower than CoVO@NF (341 and 373 mV), CoN/VN@NF (389 and 425 mV) and RuO 2 @NF (376 and 420 mV) (Fig. 3 h). Significantly, the activity exceeds most of the reported transition metal based electrocatalysts (Supplementary Table 4). As displayed in Fig. 3 i, the P-CoVO@NF possesses the lowest Tafel slope value of 77 mV dec –1 than CoVO@NF (152 mV dec –1 ), CoN/VN@NF (133 mV dec –1 ) and RuO 2 @NF (138 mV dec –1 ). Generally, the Tafel slope value for OER increases with the enhanced coverage of * O under the site-isolation model. 36 Consequently, the enhanced activity of P-CoVO@NF, suggested by the lowest Tafel slope value, may be due to the accelerated kinetics of * O transformation. Additionally, the higher conductivity of P-CoVO@NF facilitates charge transfer, thereby enhancing OER activity (Fig. 3 j). Moreover, the OER activity of NF substrate after phosphating is not well, so the activity of the substrate can be negligible (Supplementary Fig. 13). P-CoVO@NF exhibits outstanding intrinsic OER activity with a moderate ECSA value and a J ECSA value about 9 times higher than that of CoN/VN@NF at 1.55 V (Fig. 3 k and Supplementary Fig. 14–15). The TOF value of P-CoVO@NF is 0.17 s –1 at an overpotential of 300 mV, approximately 5.7 times as that of CoN/VN@NF (Supplementary Fig. 16), further proving the higher intrinsic activity of P-CoVO@NF. Durability test shows that no noticeable activity decay is observed after 100 h at 100 mA cm –2 (Fig. 3 l). Furthermore, only a slight decay is noted after 10,000 continuous CV cycles, while the intensity of the oxidation peak increases because extra metal species could be oxidized during OER process. After the stability test, the surface of P-CoVO@NF were covered with thinner nanosheets as confirmed by SEM images (Supplementary Fig. 17). OER Mechanism Generally, the metal species on the surface of catalysts undergo in-situ reconstruction during OER process. The operando Bode plots indicate that the charge transfer signals at different characteristic frequencies can be divided into two areas (Fig. 4 a-c). Specially, the electron transfer response in the inner layer of the catalyst occurs at the high-frequency range of 10 2 −10 4 Hz, whereas the charge transfer response at the catalyst/electrolyte interface is observed at the low-frequency range of 10 − 2 −10 2 Hz. 37 Compared with CoVO@NF and CoN/VN@NF, the P-CoVO@NF exhibits lower peaks in both high and low frequency ranges, and these peaks decrease more rapidly with the increasing potential. It indicates a faster oxidation of intermediates and deprotonation of * OOH for P-CoVO@NF, revealing the much better OER activity. 38 The Nyquist plots in Supplementary Fig. 18 are fitted based on a hypothetical equivalent circuit model composed of three parts (Fig. 4 d). In detail, the R s stands for the electrolyte resistance. The first parallel circuit involves constant phase element (CPE 1 ) and resistance ( R CEOR ) related to the electron transfer from the inner layer of catalyst to the reaction interface, and the CEOR represents the surface reconstruction of catalyst during OER. The second parallel circuit includes a constant phase element (CPE 2 ) and resistance ( R OER ) associated with the charge transfer of interface reaction. 39 Relatively, the smallest R CEOR value of P-CoVO@NF implies the easier oxidization and reconstruction (Supplementary Table 5). At the low potential range of 1.20 ~ 1.45 V, the R OER values of P-CoVO@NF and CoVO@NF drop sharply but still large, manifesting that the catalysts only occur rapid structural changes. The R OER value of P-CoVO@NF approaches zero when the potential exceeds 1.45 V indicates the occurrence of OER process, whereas it starts at above 1.5 V for CoN/VN@NF (Fig. 4 e). It further uncovers the superior OER kinetics and intrinsic activity of P-CoVO@NF. Hence, the regulation of P-O can improve the utilization rate of * OH, endowing P-CoVO@NF with faster charge transfer and deprotonation capability, while the self-reconstructed interface facilitates to OER acitivity. Operando XAFS was further employed to investigate the structure change of Co sites during OER. As depicted in Fig. 4 f, the Co K-edge absorption of P-CoVO@NF is situated between CoO and CoOOH at an open-circuit potential (OCP), indicating that the oxidation state of Co is between + 2 and + 3. When the potential promotes from 1.20 to 1.50 V, the Co K-edge gradually shifts towards higher energy, suggesting the increase of Co valence state. The valence states of Co under different applied potentials are further quantified by analyzing the first derivative of absorption edge. 40,41 As displayed in Fig. 4 g, the oxidation state of Co gradually increases from + 2.31 at OCP to + 2.69 at 1.20 V, then to + 2.71 at 1.30 V and + 2.76 at 1.40 V. When the voltage exceeds the oxygen evolution potential, the charge on the catalyst surface is insufficient to further oxidize Co, which causes electrons to escape from the surface oxygen and results in the formation of O 2 . Simultaneously, cobalt species undergo surface reconstruction, and its oxidation state eventually rises to + 3.31 at 1.5 V. It can be inferred that the OER occurs at the potential range of 1.4‒1.5 V, consistent with the above Bode phase angle analyses. Moreover, the Co sites exhibit stronger attraction to O 2p electrons at a high potential, benefiting to the deprotonation of M‒OH. 42 Consequently, Co sites with higher oxidation states enhance the adsorption of OH ‒ ions to form Co‒OH, thereby reducing the required potential for deprotonation and generating more reactive oxygen species to promote OER activity. Figure 4 h and Supplementary Fig. 19 displays the changes of coordination structures for the surface Co species. At OCP, the peak at 1.5 Å is associated with the single scattering path of Co‒O bond, as well as the Co‒Co (d-Oh) from distorted octahedral (tetrahedral-like) coordination structure is located at 2.8 Å. Upon increasing the potential to 1.2 V, a new peak of Co‒Co (r-Oh) at 2.4 Å originated from regular octahedral coordination structure (Supplementary Table 6). This generates a shift from high-spin Co 2+ to low-spin Co 3+ and the decrease of band gap from 0.615 eV to 0 eV, resulting in a high conductivity and well OER activity 43 (Fig. 4 i). Furthermore, the V 2p XPS spectra show almost no change except for the decreased intensity, implying the partial V dissolution during OER (Fig. 4 j and Supplementary Table 7). The positive shift of Co 2p spectrum along with the increased area of Co 3+ peak again indicates the elevated oxidation state for cobalt species (Supplementary Fig. 20). The solution after OER was analyzed by performing Inductively coupled plasma-mass spectrometry (ICP-MS). The content of Co are negligible, whereas V is detected with content of 7.5 µg mL − 1 (Supplementary Table 8), further ascertaining that a small amount of V leaches into solution during OER. The dissolution of V creates vacancies in the Co 3 V 2 O 8 lattice, which could provide sufficient space to promote such a configurational transformation. The evoluted oxygen-bridged octahedral center is similar to the local environment of Co‒(O)OH, making the Co site benefits to the adsorption of oxygen species, and then oxidation and structural reconfiguration. As the potential further increases, the peak intensity of Co‒O begins to decline, which possibly ascribes to the electrons removal from CoOOH, leading to the protons generation and subsequent O 2 release. Additionally, the decline in the peak height of the Co-O bond indicates the formation of V O during the OER process, which in turn enhances the adsorption of intermediate species and the rate of electron conduction in the materials. Furthermore, the relative intensity of P 2p spectrum decreases, accompanied by the disappearance of metal phosphides. The O 1s spectrum presented shows an increase in V O after stability test, which maybe facilitates the adsorption and desorption of intermediates (Supplementary Fig. 21). The presence of O‒H bond is attributed to the in-situ reconstructed CoOOH, originating from the surface metal phosphides decompose into PO x and CoOOH. Besides, a portion of V‒O bond will break at a high potential, and the PO x ions dissolve from Co‒PO x , thus creating pathway to allow more metal sites contact with the OH ‒ ions in the electrolyte to form CoOOH. The evoluted CoOOH can provide effective active sites to lower the reaction barrier and accelerate the reaction process. Raman spectroscopy was conducted to reveal the variation of the chemical composition after OER test. As shown in Fig. 4 k, P-CoVO@NF displays O − V−O bond at 816 cm ‒1 and V − O bond at 988 cm ‒1 . 44 Moreover, the stretching vibrations of Co − O−V bond originated from the presence of V O , can be split into the doublet peaks at 280 and 334 cm –1 . The peaks at 660 and 943 cm –1 are respectively attributed to the A 1g vibrational modes of Co-O and O − P−O bonds. 45 After CV cycles test, the characteristic peaks of Co 3 V 2 O 8 disappear, while the new peaks emerge at 468 and 548 cm ‒1 respectively belong to the E g and F 2g vibrational modes of CoOOH. Theory calculations The electronic charge distribution of CoVO@NF, CoN/VN@NF and P-CoVO@NF models based on DFT calculations are shown in Fig. 5 a-c and Supplementary Table 9. It can be concluded that the charge of both Co and V atoms follows this order: CoVO@NF > P-CoVO@NF > CoN/VN@NF. Therefore, both nitrogen and phosphate anions regulation promote the electron density around Co and V atoms. Additionally, the nitrogen anion could generate a stronger electron coupling interaction with metals compared to P-O group, resulting in a lower charge distribution, which matches well with the above XPS and XANES analyses. For CoN/VN@NF, the electron accumulation at the nitrogen site is more conducive to the capture of hydrogen protons, thereby promoting HER activity. In contrast, the phosphorus site in P-CoVO@NF exhibits higher positive charge, which is benefitical to adsorb hydroxyl groups. Based on these results, we will consider nitrogen site as the adsorption site for * H in CoN/VN@NF, while the phosphorus site as the adsorption site for * OH in P-CoVO@NF in the subsequent computational processes of HER. Moreover, the CoVO@NF, CoN/VN@NF and P-CoVO@NF models exhibit a continuous density of states (DOS) near the E F (Fig. 5 d), suggesting the narrow band gaps and excellent conductivity. The ɛ d values of Co in CoVO@NF, CoN/VN@NF and P-CoVO@NF are ‒1.23, ‒1.09 and ‒1.43 eV, respectively, while the corresponding values of V are ‒0.08, ‒0.02 and ‒0.17 eV (Fig. 5 e,f). Relatively, the Co and V in CoN/VN@NF model show the highest electron density and the ɛ d values are much closer to the E F , leading to stronger ntermediates adsorption and efficient electron transfer. The Co and V in P-CoVO@NF model exhibit a moderate electron density with the furthest ɛ d values from E F , suggesting a higher occupancy of antibonding states, which weakens the intermediates adsorption and facilitates the subsequent reaction steps. 46 Based on the hydrogen binding energy (HBE) theory, the * H Gibbs free energy (Δ G *H ) for CoN/VN@NF (‒0.23 eV) is much closer to zero indicates the promoted HER activity (Supplementary Fig. 22‒24). Moreover, the water dissociation serves as the rate-determining step (RDS) for both CoVO@NF and P-CoVO@NF models, whereas the water adsorption is the RDS for CoN/VN@NF model (Fig. 5 g and Supplementary Fig. 25). The energy barrier values of RDS demonstrate that the Co site is the active site for CoVO@NF and P-CoVO@NF models, while V site is beneficial to the * OH adsorption for CoN/VN@NF model. Besides, the exothermic water dissociation of CoN/VN@NF model suggests its excellent HER activity. To identify the active sites for OER, the P, V and Co sites in P-CoVO@NF model are respectively selected as the active sites, in which the Co site exhibits the lowest energy barrier for the RDS (Supplementary Fig. 26–29). Specially, the RDS of P-CoVO@NF model is the formation of * OOH with an energy barrier of 1.76 eV (Fig. 5 h), significantly lower than CoVO@NF of 2.62 eV and CoN/VN@NF of 1.92 eV ( * O formation step is the RDS). It is concluded that the formation of strongly nucleophilic P-O group greatly enhance the interfacial proton transfer, thereby reducing the energy barrier for the formation of * O and promoting the conversion rate of intermediates. The weaker electron coupling effect of P-O group can lower the adsorption strength of oxygen-containing intermediates and accelerate the deprotonation of * OH, thus enhancing the OER kinetics. Since the cobalt species in P-CoVO@NF gradually reconstructs into cobalt hydroxide during OER, so the P-CoOOH model was also built (inset of Fig. 5 i). The Co site in P-CoOOH model has a much more positive charge of 0.92 e, and the ɛ d value of ‒1.38 eV is closer to the E F compared to P-CoVO@NF (Supplementary Fig. 30), indicating the stronger adsorption of oxygen-containing intermediates. Furthermore, the Δ G of oxygen-containing intermediates at the Co site in P-CoOOH is obviously decreased (Fig. 5 i and Supplementary Fig. 31), while the formation of * OOH is identified as the RDS. Specifically, the difference between Δ G *O and Δ G *OOH at the Co site in P-CoOOH is 1.68 eV, which is lower than P-CoVO@NF, indicating a thermodynamically favorable OER process of P-CoOOH. The charge configuration analyses indicate that the increase of Co valence state after reconstructing induces a pseudo-electrophobic effect, thereby reducing the positive charge on the O atom as well as the negative charge on the H atom in * OH. It reveals that the O‒H bond in * OH is easy to cleavage under the attack of OH ‒ ions, benefitting to the formation of * OOH. Therefore, such a structural reconfiguration could promote OER kinectics. We further utilize CoN/VN@NF as cathode and P-CoVO@NF as anode for overall water splitting by an H‒type electrolytic cell separated with an exchange membrane. The P-CoVO@NF(+)||CoN/VN@NF(‒) system only requires a voltage of 1.43 V to achieve a current density of 10 mA cm ‒2 , whereas a higher voltage of 1.62 V is needed for RuO 2 @NF(+)||PtC@NF(‒) system (Supplementary Fig. 32). Importantly, a 1.75 V voltage for P-CoVO@NF(+)||CoN/VN@NF(‒) system could drive a large current of 100 mA cm ‒2 . The outstanding performance is comparable to the reported advanced electrocatalysts (Supplementary Table 10). It also displays a prominent durability without obvious attenuation current density for 100 h (Supplementary Fig. 33). The Faradaic efficiency was measured by the H–type electrolytic cell with collection device of the evolved H 2 and O 2 gases (Supplementary Fig. 34). The obtained volume ratio of H 2 :O 2 is about 2:1 at a current density of 40 mA cm − 2 , and the P-CoVO@NF(+)||CoN/VN@NF(‒) system exhibits a Faraday efficiency of near 100% (Supplementary Fig. 35). The P-CoVO@NF//CoN/VN@NF system also can be driven by a 1.45 V solar cell (Supplementary Fig. 36). The H 2 and O 2 gases are conspicuously generated on the cathode and anode, respectively, further manifesting the potential for converting low-voltage electrical energy originated from solar energy into chemical energy. Furthermore, we also assembled an AEM electrolyzer to evaluate the practice application of catalysts. The P-CoVO@NF and CoN/VN@NF were respectively used as the anode and cathode with the AEM made of industrial fluorocarbon acid resin film (Fig. 6 a). The electrolyzer was tested within the temperature range of 25 to 70°C using 1 M KOH electrolyte, and it could be concluded that the voltage and total cell resistance decreased with the working temperature increased (Fig. 6 b,c). At 70°C, a voltage of 1.88 V was able to drive a current density of 500 mA cm − 2 , while a voltage of 1.98 V achieved a current density of 1000 mA cm –2 , outperforming most of the advanced non-precious metal-based electrocatalysts. 47,48 The W DC was calculated to be 4.31 kWh Nm –3 @250 mA cm –2 , approaching the international forefront in terms of efficiency. Additionally, the electrolyzer attaining an high energy conversion efficiency of 78.7% under an operational current density of 500 mA cm –2 , as well as excellent stability over a span of 200 hours (Fig. 6 d). This can be attributed to the construction of 3D micro-nano structures and the occurrence of surface restructuring. The results suggest that the optimized nanostructure design of P-CoVO@NF and CoN/VN@NF could serve as potential applications is commercial AEM systems. Discussion The nitrogen and phosphate anions are respectively utilized to accurately modulate the electronic structures of coral-like Co-V bimetallic nanoarrays electrocatalysts, thereby enabling superior performance in HER, OER and AEM electrolyzer. The layered effect of Co and the epitaxial growth of V are key to the formation of such unique structure. Furthermore, the nitrogen anions could upregulate the ɛ d of Co and V to optimize the energy barrier of intermediation for improving HER activity. The phosphate anions downregulate the corresponding ɛ d to favor the deprotonation of oxygen-containing intermediates during OER as well as forming the CoOOH active center with high valence states and low band gaps, thereby improving the conductivity and the adsorption capacity of intermediates. Besides, the Co-O undergo an in-situ structural reconfiguration from distorted octahedron to regular octahedron during OER process, which could facilitate the reaction kinetics and the formation of intermediates. The phosphate anions modulation can accelerate the charge transfer and deprotonation capabilities of the electrocatalyst, thus enhancing the OER activity. Our work provides an effective modulation strategy and new insights into the structural evolution mechanisms of electrocatalysts, contributing to a better understanding of their design and synthesis for sustainable energy storage and conversion applications. Methods Chemicals Cobalt chloride hexahydrate (CoCl 2 ·6H 2 O), ammomium metavanadate (NH 4 VO 3 ) were purchased from Aladdin Chemical Reagent Co., Ltd. Sodium hypophosphite (NaH 2 PO 2 ) was purchased from Rhawn Chemical Reagent Co., Ltd. Ethanol, acetone and hydrochloric acid were purchased from Tianjin Fuyu Chemical Reagent Co., Ltd. Commercial Ni foam (NF) was purchased from Kunshan Jiayisheng Electronics Co. Ltd. All of the reagents are of analytical grade and directly used without further purification. Deionized water was used in the experiments. Synthesis of CoVO@NF Typically, a Ni foam (NF) substrate with a size of 3 × 4 cm was washed in 3 M HCl for 5 min to remove surface oxides, then it was respectively ultrasonicated in acetone and ethanol for 30 minutes. Subsequently, 0.36 mmol of CoCl 2 ·6H 2 O and 1.44 mmol of NH 4 VO 3 were dissolved into 80 mL of deionized water under stirring. After adjusting the pH value of the solution approximately 4, a piece of treated NF was dipped for 1 h. Then, it was transferred into a 100 mL Teflon-lined stainless steel autoclave and heated at 160°C for 8 h, so the coral-like interlaced Co 3 V 2 O 8 nanosheet arrays precursor supported on NF substrate was prepared (denoted as CoVO@NF). Synthesis of CoN/VN@NF The CoN/VN@NF was synthesized by pyrolyzing the CoVO@NF precursor at 600°C for 2 h under NH 3 ambient with a heating rate of 5°C min − 1 . To assess the effect of the NF substrate on HER activity, the same nitriding treatment were applied to NF for synthesis of NFN. Synthesis of P-CoVO@NF Typically, 1.5 g of NaH 2 PO 2 powder and CoVO@NF precursor were positioned upstream and downstream of the quartz tube, respectively. Prior to pyrolysis, nitrogen was purged for 30 min to eliminate any residual air. Then, it was heated to 450°C for 2 h with a heating rate of 2°C min − 1 to prepare P-CoVO@NF. Also, the same phosphating process were adopted to NF to prepare NFP for comparison. Characterizations X-ray diffraction (XRD) analyses were conducted using a Bruker D8 Advance X-ray diffractometer equipped with Cu K α radiation. Grazing Incidence X-Ray Diffraction (GI-XRD) measurements were performed on a Bruker D8 Venture DUO microsourced single-crystal X-ray diffractometer, equipped with a Photon III detector and Cu-Diamond X-ray sources (λ = 1.5406 Å). SEM images were obtained by utilizing a Hitachi S-4800 instrument, operating at an accelerating voltage of 15 kV. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and EDS elemental mapping images were captured by using a JEM-2100 electron microscope (JEOL, Japan) operating at an acceleration voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) was conducted on a VG ESCALABMK II system using Mg-K α radiation (1253.6 eV). Raman spectroscopic measurements were performed utilizing a Jobin Yvon HR 800 micro-Raman system with 457.9 nm excitation. Fourier transform infrared spectra (FT-IR) in the range of 400–4000 cm − 1 were recorded using a PE Spectrum One B IR spectrometer with KBr pellets. Inductively coupled plasma emission spectroscopy (ICP-MS) was used to determine the metal content in the electrolyte after the stability test (Thermo Fisher ICP-MS RQ). The extended X-ray absorption fine structure (EXAFS) analysis was carried out at beam line BL14W1 of the Shanghai Synchrotron Radiation Facility (SSRF) in China, utilizing a Si (111) double crystal monochromator. All spectra were aligned, normalized, and fitted using IFEFFIT-based software. Electrochemical Measurements All the electrochemical tests in 1.0 M KOH electrolyte at room temperature by a three-electrode configuration. The electrode material with a size of 1 × 1.5 cm 2 served as the working electrode, while the Hg/HgO electrode and graphite rod were employed as the reference and counter electrodes, respectively. For all measurements, the final potential was calibrated based on the Nernst equation for a reversible hydrogen electrode (RHE): E RHE = E Hg/HgO + 0.098 V + 0.059 pH. Tafel plots were calculated by the polarization curves. Cyclic voltammetry (CV) curves were recorded by different scan rates from 5 to 25 mV s ‒1 to determine the double layer capacitance ( C dl ). All the linear sweep voltammetry (LSV) curves are obtained by 85% IR compensation. Electrochemical impedance spectroscopy (EIS) was performed on LSV curves corresponding to a potential of 10 mA cm ‒2 , over a frequency range of 0.01 to 100,000 Hz. Potential cycling stability was examined through continuous CV curves at a scan rate of 100 mV s ‒1 . Additionally, the chronoamperometry test was conducted at a desired potential of 100 mA cm ‒2 for 100 h. The Faraday efficiency of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was determined by comparing the experimental and theoretical amounts of H 2 and O 2 . Gas analysis was performed using the drain method in a closed H-type electrolyzer under the chronoamperometry test at 40 mA cm ‒2 for 60 min. The theoretical H 2 amount was calculated as follows. $$\text{n}\left({\text{H}}_{\text{2}}\right)\text{= }\frac{\text{Q}}{\text{nF}}$$ 1 where Q is the charge through the electrode, n(H 2 ) is the number of moles of hydrogen produced, F is Faraday constant of 96,485 C mol ‒1 , and n is the number of transferred electrons during the water splitting (2 for HER). The theoretical amount of O 2 is calculated the same as that for H 2 except n = 4. The turnover frequency (TOF) of the catalyst was calculated using the following equation based on previous reports. $$\text{TOF= }\frac{\text{Total Hydrogen Turn Overs/}{\text{cm}}^{\text{2}}\text{geometric area}}{\text{Surface Sits /}{\text{cm}}^{\text{2}}\text{ geometric area}}$$ 2 The number of total hydrogen turn overs can be determined from the current density using the following equation: The total number of effective surface sites was calculated by the following equation: $$\frac{\text{Surface sites}}{{\text{cm}}^{\text{2}}\text{ geometric area}}\text{ = }\frac{\text{ Surface sites (flat standard)}}{{\text{cm}}^{\text{2}}\text{ geometric area}}\text{ × Roughness factor}$$ where the roughness factor (R f ) can be determined by the C dl , and we assume 60 µF cm ‒2 for the specific capacitance of a flat electrode provided by previous reports. The surface sites of 2 × 10 15 for the flat standard electrode was used for previous results. All electrochemical measurements were performed on a CHI660E electrochemical workstation, except for the EIS tests. EIS data were collected via Autolab PGSTAT302N (Eco Chemie, Utrecht, The Netherlands). AEM Electrolyzer Preparation and Measurement The AEM (Mainz hydrogen energy), which consists of a current collector (eTM-3060PC), MEA type reactor (serpentine channel), Anion exchange membrane (Fumasep FAA-3-PK-130), working electrodes (CoN/VN@NF||P-CoVO@NF). Prior to use, the anion exchange membrane should be soaked in a 1 M KOH solution for 24 hours. Within the AEM electrolyzer system, the 1 M KOH solution is provided to both the cathode and anode at a flow rate of 40 mL/min at various temperatures. The water splitting performance is determined by measuring the LSV curves within a range of 1.0 to 2.0 V at a scan rate of 5 mV/s. For durability testing, the AEM system operates at a constant potential of 1.88 V for 150 hours. EIS measurements are conducted at a voltage of 1.88 V within a frequency range of 10 kHz to 0.01 Hz, with an amplitude of 10 mV. The formula for calculating direct current energy consumption (W DC ) is: $${\text{W}}_{\text{DC}}\text{ = }\frac{\text{IVt × }\frac{\text{1}}{\text{1000}}}{\text{4.18×}{\text{10}}^{\text{-4}}\text{×It}{\text{η}}_{\text{e}}}\text{ }\text{=}\text{ }\frac{V}{0.418{\eta }_{e}}$$ where I is the cell current through the electrode, V is the cell voltage, t is time, η e is current efficiency. Theoretical calculations Density Functional Theory (DFT) simulations were performed using the Cambridge Sequential Total Energy Package (CASTEP) module implemented in Material Studio. The electronic exchange and correlation effects were described using the Perdew-Burke-Ernzerhof (PBE) functional, a generalized gradient approximation (GGA). In consideration of the specific situations of theoretical calculations, Co 3 N was utilized instead of Co 2 N 0.67 . To simplify the calculations, a four-layer Co 3 N (101) slab and a three-layer VN (200) slab were chosen as the surface slab supercells. For the P-CoVO model, part of the vanadium atoms were replaced by P atoms after geometry optimization, followed by a series of calculations. Population analysis was performed using the Mulliken scheme, and a plane-wave energy cutoff of 400 eV was employed. The Brillouin zone sampling was carried out using a (2×3×6) Monkhorst-Pack grid, and a vacuum layer of 15 Å was added to the supercell to prevent interaction between individual periodic images. Geometry optimization was repeated until the total energy tolerance reached 1×10 ‒5 eV and the changes in force on the atoms were less than 0.03 eV Å ‒1 . The Gibbs free energy can be expressed as: $$\text{ΔG }\text{= ΔE + ΔZPE }\text{–}\text{ TΔS}$$ 3 where ΔE is the reaction energy calculated by the DFT methods. ΔZPE and TΔS are the thermodynamic corrections of zero-point-energy (ZPE) and entropy (S) derived from the vibrational partitions function at 298.15 K, respectively. As the entropy of hydrogen in the absorbed state is negligible, ∆S can be calculated as ‒1/2S 0 H 2 . Therefore, the Gibbs free energy of H * can be taken as: $$\text{Δ}{\text{G}}_{{\text{H}}^{\text{*}}}\text{ = Δ}{\text{E}}_{{\text{H}}^{\text{*}}}\text{ + 0.24 eV}$$ 4 The adsorption energy on the surfaces of catalysts was calculated by using equation: $$\text{ΔE = }{\text{E}}_{\text{total }}\text{–}\text{ }{\text{E}}_{\text{surface}} \text{– }{\text{E}}_{\text{absorbate}}$$ 5 where E total , E surface , and E absorbate are the total energy of the adsorption state system, the total energy of the pure surface, and the total energy of intermediate, respectively. The OER process could occur include four elementary steps: \(\text{O}{\text{H}}^{\text{–}}\text{→ O}{\text{H}}^{\text{*}}\text{+ }{\text{e}}^{\text{–}}\) ΔG 1 \(\text{O}{\text{H}}^{\text{–}}\text{+ O}{\text{H}}^{\text{*}}\text{→ }{\text{H}}_{\text{2}}\text{O +}{\text{O}}^{\text{*}}\text{+ }{\text{e}}^{\text{–}}\) ΔG 2 \(\text{O}{\text{H}}^{\text{–}}\text{+ }{\text{O}}^{\text{*}}\text{→ }{\text{H}}_{\text{2}}\text{O +}{\text{ OOH}}^{\text{*}}\text{+ }{\text{e}}^{\text{–}}\) ΔG 3 \(\text{OO}{\text{H}}^{\text{*}}\text{+ }{\text{OH}}^{\text{–}}\text{→ }{\text{O}}_{\text{2}}\text{ +}{\text{H}}_{\text{2}}\text{O+ }{\text{e}}^{\text{–}}\) ΔG 4 The overpotential (η) can be obtained from the Gibbs free energy differences at each step: $$\text{η}\text{ = max}\left(\text{Δ}{\text{G}}_{\text{1}}\text{, Δ}{\text{G}}_{\text{2}}\text{, Δ}{\text{G}}_{\text{3}}\text{, Δ}{\text{G}}_{\text{4}}\right)\text{/}\text{e }\text{– }\text{1.23 V}$$ 6 Declarations Data Availability The authors declare that all data supporting the findings of this study are available in the article and its Supplementary Information. Acknowledgements We gratefully acknowledge the support of this research by the National Key R&D Program of China (2023YFA1507204), the National Natural Science Foundation of China (U20A20250, 22179034), the Natural Science Foundation of Heilongjiang Province (ZD2023B002). Competing interests The authors declare no conflict of interest. Additional information Supplementary Information Correspondence and requests for materials should be addressed to Lei Wang or Honggang Fu. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. 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Supplementary Files SupportingInformation.docx Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4286568","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":296826542,"identity":"4fb828be-64ee-4679-906f-f72062e19f2d","order_by":0,"name":"Honggang Fu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyUlEQVRIiWNgGAWjYBAC9gYeBoYPDBJAJmMDcVp4DvAwMM4gWQszD0kO45HIPfzats0ij4H/cNuDHwx2crqELOORyEuzzm2TKGaQSGw37GFINjY7QECLvUSOmXHOGYnEBgnGNgkehgOJ2whp4QFpsQBp4T/YJvmHSC3GjxkqgFoYEtukibOF540ZY0+FRDGbBFCLjAERfuFhzzH+8MOgLo+f//gzyTcVdnIEtQABGygeE9jAbAPCykGA+QNIC3FqR8EoGAWjYEQCAC8tOG19OWd7AAAAAElFTkSuQmCC","orcid":"","institution":"Heilongjiang University","correspondingAuthor":true,"prefix":"","firstName":"Honggang","middleName":"","lastName":"Fu","suffix":""},{"id":296826543,"identity":"fef67032-938e-4641-b300-030837581d24","order_by":1,"name":"Zhijian Liang","email":"","orcid":"","institution":"Heilongjiang University","correspondingAuthor":false,"prefix":"","firstName":"Zhijian","middleName":"","lastName":"Liang","suffix":""},{"id":296826544,"identity":"9b249ca9-837f-42cf-82fa-a5714e781978","order_by":2,"name":"Di Shen","email":"","orcid":"","institution":"Heilongjiang University","correspondingAuthor":false,"prefix":"","firstName":"Di","middleName":"","lastName":"Shen","suffix":""},{"id":296826545,"identity":"ad35e7b7-7413-4173-aece-1e72cd8398ff","order_by":3,"name":"Yao Wei","email":"","orcid":"","institution":"Shanghai Institute of Applied Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Yao","middleName":"","lastName":"Wei","suffix":""},{"id":296826546,"identity":"4530d33b-f951-4b18-965c-05e1341a2165","order_by":4,"name":"Fanfei Sun","email":"","orcid":"","institution":"China Shanghai Synchrotron Radiation Facility, Zhangjiang National Laboratory, Shanghai Institute of Applied Physics, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Fanfei","middleName":"","lastName":"Sun","suffix":""},{"id":296826547,"identity":"f3d40f23-dc74-43b5-b0b9-7b31e53cc1d3","order_by":5,"name":"Ying Xie","email":"","orcid":"","institution":"Heilongjiang University","correspondingAuthor":false,"prefix":"","firstName":"Ying","middleName":"","lastName":"Xie","suffix":""},{"id":296826548,"identity":"3a67e9dd-dd40-4935-a576-3a9359fa1c94","order_by":6,"name":"Lei Wang","email":"","orcid":"https://orcid.org/0000-0002-0624-5098","institution":"Heilongjiang University","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2024-04-18 09:15:33","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4286568/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4286568/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":55762609,"identity":"e6937a67-95b9-4677-b18b-ee0852e6250e","added_by":"auto","created_at":"2024-05-02 19:21:23","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":6547943,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of catalysts. a\u003c/strong\u003e Synthetic scheme and \u003cstrong\u003eb\u003c/strong\u003e XRD patterns of CoN/VN@NF and P-CoVO@NF. SEM images of \u003cstrong\u003ec\u003c/strong\u003e CoN/VN@NF and \u003cstrong\u003ed \u003c/strong\u003eP-CoVO@NF. \u003cstrong\u003ee\u003c/strong\u003e TEM, \u003cstrong\u003ef\u003c/strong\u003e HRTEM images and \u003cstrong\u003eg\u003c/strong\u003e EDX elemental mappings of CoN/VN@NF. \u003cstrong\u003eh\u003c/strong\u003e TEM, \u003cstrong\u003ei\u003c/strong\u003e HRTEM images and \u003cstrong\u003ej\u003c/strong\u003e EDX elemental mappings of of P-CoVO@NF.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/0802e25584af69d11d5b109a.png"},{"id":55762608,"identity":"930963e9-1f06-4784-850d-c37696bef489","added_by":"auto","created_at":"2024-05-02 19:21:23","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3113025,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXPS and XAS characterizations of catalysts.\u003c/strong\u003e XPS spectra of \u003cstrong\u003ea\u003c/strong\u003e Co 2p and \u003cstrong\u003eb\u003c/strong\u003e V 2p for CoVO@NF, CoN/VN@NF and P-CoVO@NF. \u003cstrong\u003ec\u003c/strong\u003e XPS spectra of N 1s for CoN/VN@NF (top), P 2p for P-CoVO@NF (bottom). \u003cstrong\u003ed\u003c/strong\u003e Normalized Co K-edge XANES, \u003cstrong\u003ee\u003c/strong\u003e FT-EXAFS spectra and \u003cstrong\u003ef\u003c/strong\u003e Co K-edge WT-EXAFS contour plots of CoVO@NF, CoN/VN@NF, P-CoVO@NF and Co foil. \u003cstrong\u003eg\u003c/strong\u003e Normalized V K-edge XANES, \u003cstrong\u003eh\u003c/strong\u003e FT-EXAFS spectra and \u003cstrong\u003ei\u003c/strong\u003e V K-edge WT-EXAFS contour plots of CoVO@NF, CoN/VN@NF, P-CoVO@NF and V foil.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/41a3890a11920c3121c151d2.png"},{"id":55762606,"identity":"b52bdfbd-e97e-4479-8ede-99f06d1272d8","added_by":"auto","created_at":"2024-05-02 19:21:23","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1780125,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectrochemical performance of catalysts.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e HER polarization curves, \u003cstrong\u003eb\u003c/strong\u003e overpotentials at the current densities of 10 and 100 mA cm\u003csup\u003e‒2\u003c/sup\u003e, and \u003cstrong\u003ec\u003c/strong\u003e Tafel plots of CoVO@NF, CoN/VN@NF, P-CoVO@NF, Pt/C@NF and NF. \u003cstrong\u003ed\u003c/strong\u003e Nyquist plots at η=10 mV and \u003cstrong\u003ee\u003c/strong\u003e the capacitive current at 0.05 V as a function of scan rate for CoVO@NF, CoN/VN@NF and P-CoVO@NF. \u003cstrong\u003ef\u003c/strong\u003e Polarization curves of CoN/VN@NF before and after 10000 cycles; inset is the chronoamperometry curve for 100 h. \u003cstrong\u003eg\u003c/strong\u003e OER polarization curves, \u003cstrong\u003eh\u003c/strong\u003e overpotentials at the current densities of 50 and 100 mA cm\u003csup\u003e‒2\u003c/sup\u003e, and \u003cstrong\u003ei\u003c/strong\u003e Tafel plots of CoVO@NF, CoN/VN@NF, P-CoVO@NF, RuO\u003csub\u003e2\u003c/sub\u003e@NF and NF. \u003cstrong\u003ej\u003c/strong\u003e Nyquist plots at \u003cem\u003eη\u003c/em\u003e=50 mV and \u003cstrong\u003ek\u003c/strong\u003e the capacitive current at 0.05 V as a function of the scan rate for CoVO@NF, CoN/VN@NF and P-CoVO@NF. \u003cstrong\u003el\u003c/strong\u003e Polarization curves of CoN/VN@NF before and after 10000 cycles; inset is the chronoamperometry curve for 100 h. All the tests are carried out in 1.0 M KOH.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/22c2809a5be364b492a28fc0.png"},{"id":55762610,"identity":"b52b8ff3-8a41-474e-80fc-910121371978","added_by":"auto","created_at":"2024-05-02 19:21:23","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":4652938,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eIn situ and operando characterizations of P-CoVO@NF in alkaline solutions. \u003c/strong\u003eOperando Bode phase angle plots for \u003cstrong\u003ea\u003c/strong\u003e CoVO@NF, \u003cstrong\u003eb\u003c/strong\u003e CoN/VN@NF and\u003cstrong\u003e c\u003c/strong\u003e P-CoVO@NF catalysts. \u003cstrong\u003ed\u003c/strong\u003e Electrical equivalent circuit model for analyzing the interfacial charge transfer. \u003cstrong\u003ee\u003c/strong\u003e The fitting results of the CEOR and OER resistance at different potentials for CoVO@NF, CoN/VN@NF and P-CoVO@NF. \u003cstrong\u003ef\u003c/strong\u003e Operando Co K-edge XANES measurements of P-CoVO@NF under electrocatalytic reaction conditions. \u003cstrong\u003eg\u003c/strong\u003e Calculated Co valence state based on 4f by using an integral method. \u003cstrong\u003eh\u003c/strong\u003e Corresponding Co K-edge FT-EXAFS spectra of P-CoVO@NF.\u003cstrong\u003e i\u003c/strong\u003e Models and energy band structure of P-Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e bulk and P-CoOOH bulk, where cyan, yellow, pink, red and white spheres represent Co, V, P, O and H atoms, respectively. Characterizations of P-CoVO@NF before and after OER test: \u003cstrong\u003ej\u003c/strong\u003e XPS spectra of V 2p, \u003cstrong\u003ek\u003c/strong\u003e Raman spectra.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/45dfb47067a853404a10e725.png"},{"id":55762985,"identity":"9670434d-7fde-4026-8cdc-61490bc545f4","added_by":"auto","created_at":"2024-05-02 19:29:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":4526283,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical calculations of catalysts.\u003c/strong\u003e The electronic charge distribution of \u003cstrong\u003ea\u003c/strong\u003e CoN/VN@NF, \u003cstrong\u003eb\u003c/strong\u003e CoVO@NF and \u003cstrong\u003ec\u003c/strong\u003e P-CoVO@NF models, where cyan, yellow, bule, pink and red spheres represent Co, V, N, P and O atoms, respectively. \u003cstrong\u003ed\u003c/strong\u003e Total density of states, partial density of state for \u003cstrong\u003ee\u003c/strong\u003e Co and \u003cstrong\u003ef\u003c/strong\u003e V, free energy diagrams of \u003cstrong\u003eg\u003c/strong\u003e HER and \u003cstrong\u003eh\u003c/strong\u003e OER processes for CoVO@NF, CoN/VN@NF and P-CoVO@NF models. (i) Free energy diagram of OER process on Co site for P-CoOOH@NF, inset is the electronic charge distribution for each atom in P-CoOOH@NF.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/104bc8de20dcc72095a13af7.png"},{"id":55762611,"identity":"f7981f65-23e6-42e2-b590-b7cb027e3c4a","added_by":"auto","created_at":"2024-05-02 19:21:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3231193,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eWater splitting performance for AEM electrolyzer. a\u003c/strong\u003e Schematic illustration of AEM electrolyzer. \u003cstrong\u003eb\u003c/strong\u003e Polarization curves and \u003cstrong\u003ec\u003c/strong\u003e Nyquist plots for AEM electrolyzer at different cell temperatures. \u003cstrong\u003ed\u003c/strong\u003e Stability test at cell potential of 1.88 V for 200 h; inset is photograph of the AEM electrolyzer.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/efe511fca174a8f3990f300b.png"},{"id":56904915,"identity":"843c035d-36ad-4c48-8266-3b9e64227246","added_by":"auto","created_at":"2024-05-22 03:18:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":22872460,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/bbf9dcb3-de61-4605-ab4a-d55cc81f0e4a.pdf"},{"id":55762613,"identity":"4922aaab-e446-4850-9aed-ed2e800f7c95","added_by":"auto","created_at":"2024-05-02 19:21:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":52514614,"visible":true,"origin":"","legend":"\u003cp\u003eVanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4286568/v1/f1dbce3eeb456e48c789eb03.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSustainable alternatives to fossil fuels are significant for alleviating the increasingly severe situation of the energy crisis and global warming. Green hydrogen is widely considered to be a promising and clean fuel due to its high gravimetric energy density and environmentally friendly of combustion products.\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e Hydrogen generation via electrochemical water splitting is an auspicious strategy for the conversion and storage of renewable resources.\u003csup\u003e4\u0026ndash;5\u003c/sup\u003e However, the efficiency of such clean energy technology and the scalable production of green hydrogen highly rely on exploring of cost-benefit and high-efficient electrocatalysts to promote the sluggish kinetics of both cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Although precious metals Pt and Ir/Ru-based materials are considered as most advanced catalysts, the inherent scarcity and high-cost prevent the further commercial application of water splitting technology.\u003csup\u003e6\u0026ndash;8\u003c/sup\u003e Anion exchange membrane (AEM) electrolysis water, as an emerging technology, combines the characteristics of proton exchange membrane (PEM) electrolysis water and alkaline (ALK) electrolysis water. It not only can quickly respond to renewable energy fluctuations like PEM, producing high-energy efficiency hydrogen gas, but also its operation in a slightly alkaline environment enables the utilization of transition metal-based catalysts.\u003csup\u003e9\u0026ndash;11\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eCobalt (Co)-based electrocatalysts have attracted considerable attention because of their tunable chemical reaction activity, high theoretical efficiency, thermodynamic stability and corrosion resistance in alkaline electrolyte.\u003csup\u003e12,13\u003c/sup\u003e Due to the limitation of the number of active sitesactive sites, most of the reported single-metal or single-component electrocatalysts exhibit confined effectiveness in facilitating reactions that involves both hydrogen- and oxygen-containing intermediates, such as \u003csup\u003e*\u003c/sup\u003eH, \u003csup\u003e*\u003c/sup\u003eO and \u003csup\u003e*\u003c/sup\u003eOOH. Alternatively, constructing three-dimensional (3D) structures orderly assembled from low-dimensional nanoscale structural units could provide plentiful active sites. Exploiting the epitaxial growth characteristics inherent in vanadium (V) oxides facilitates the construction of intricate 3D hierarchical porous micro-nano architectures.\u003csup\u003e14\u0026ndash;16\u003c/sup\u003e Furthermore, the adsorption energy of intermediates can be precisely adjusted through the modulation of electronic structure of catalysts by different anions. Benefiting from the negatively charged nitrogen anions can weaken the strength of metal-H bond owing to the ensemble effect of metal nitrides, thereby optimizing the hydrogen adsorption and HER activity.\u003csup\u003e17\u0026ndash;19\u003c/sup\u003e The stronger nucleophilicity of phosphate anions can act as the proton acceptors to facilitate the interfacial proton transfer, thus promoting the transformation of oxygen-containing intermediates for OER.\u003csup\u003e20\u0026ndash;22\u003c/sup\u003e As such, intentionally constructing bimetallic Co-V electrocatalysts modulated by different anions is an effective strategy to simultaneously enhance the kinetics of HER and OER. Furthermore, transitional metal-based electrocatalysts, especially for Co species, always occur structural reconfiguration during the OER. However, most studies are primarily focused on utilizing theoretical calculations and off-line characterizations to explain the role of restructured configuration in enhancing activity.\u003csup\u003e23,24\u003c/sup\u003e Therefore, it is requisite to adopt advanced operando techniques to monitor the structural evolution of electrocatalysts and confirm the active sites for intermediates transformation, which is meaningful for the purposeful synthesis of water splitting electrocatalysts.\u003c/p\u003e \u003cp\u003eInspired by the above considerations, we employ a liquid phase self-assembly strategy to synthesize the coral-like Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e nanoarrays on the nickel foam substrate (CoVO@NF) based on the layered function of Co and the one-dimensional guidance of V. Such unique structure shows more active sites to enhance catalytic activity, while also providing sufficient space to mitigate changes in volume and stress to enhance the stability of catalyst. By a subsequent nitridation and phosphidation treatment, respectively, the obtained CoN/VN@NF and P-CoVO@NF exhibit well HER and OER activity with low overpotentials of 164 and 317 mV to achieve a large current density of 100 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, along with excellent stability for 10,000 cycles in 1.0 M KOH electrolyte. The assembled AEM electrolyzer shows a direct current energy consumption (W\u003csub\u003eDC\u003c/sub\u003e)\u003csub\u003eC\u003c/sub\u003e of the is 4.31 kWh Nm\u003csup\u003e\u0026ndash;3\u003c/sup\u003e@250 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, closing to the international advanced level. Importantly, this system only needs a voltage of 1.88 and 1.98 V at the current densities of 500 and 1000 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, respectively. Operando synchrotron radiation discovers that the Co sites occur a structural evolution from the distorted octahedral to regular CoOOH octahedral structure during OER process. Operando Bode phase angle analyses further demonstrates that the phosphate anions modulation could enhance the charge transfer and deprotonation capabilities of the P-CoVO@NF, while the evolved CoOOH facilitates the formation of intermediates, thereby promoting the OER kinetics. Density functional theory (DFT) calculations demonstrate that the nitrogen anions could upward shifts the d-band center (\u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e) of Co and V to optimize the adsorption energy of intermediates, as well as collaborating with the \u003csup\u003e*\u003c/sup\u003eOH adsorption site of V to accelerate the dissociation of water and improve HER activity. Conversely, P-O group induce the \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e of Co and V downward shifts, promoting the deprotonation of oxygen-containing intermediates during OER and simultaneously forming the CoOOH active center.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003eMaterial characterizations\u003c/h2\u003e\n\u003cp\u003ePrior studies have shown that Co species tend to form lamellar structures, whereas V species are more inclined towards one-dimensional growth. Based on these bases, we have developed coral-like nanoarrays composed of nanosheets by utilizing the distinct behaviors of Co and V. As illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea, a liquid phase self-assembly method was employed to prepare coral-like interlaced cobalt vanadate nanosheet arrays precursor with the Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e phase supported on nickel foam substrate (CoVO/NF) (Supplementary Fig.\u0026nbsp;1). Indeed, the layered structure can be seen in the absence of V, while fibrous structure is obtained without using Co (Supplementary Fig.\u0026nbsp;2). It further proposed that Co is responsible for the stratification\u0026nbsp;during catalyst growth, while V facilitates epitaxial growth. Subsequently, it underwent nitridation and phosphidation treatments to prepare CoN/VN@NF and P-CoVO@NF, respectively. To eliminate the interference from NF signals, the X-ray diffraction (XRD) characterizations of CoN/VN@NF and P-CoVO@NF are scraped from the NF substrates. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb, CoN/VN@NF primarily exhibits the hexagonal Co\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e0.67\u003c/sub\u003e phase and cubic VN phase. For P-CoVO@NF, the peaks still correspond to the cubic Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e phase as that of CoVO@NF, suggesting that phosphorus is incorporated in a doped form. The scanning electron microscopy (SEM) images in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec, d show that both the nitridation and phosphidation treatments maintain the coral-like nanosheet array structure, despite causing a rough surface. Such unique 3D micro-nano structures assembled by low-dimensional structures not only prevents the self-agglomeration during reaction processes to promote stability, but also furnishes an abundance of active sites to accelerate the electron transfer for enhancing electrocatalytic activity. Transmission electron microscopy (TEM) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ee) indicates that the nanosheet in CoN/VN@NF is composed of nanoparticles. It can increase the accessibility of the surface to allow the internal Co\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e0.67\u003c/sub\u003e-VN heterojunction directly contact with the reactants. High-resolution TEM (HRTEM) image shows clear lattice fringes and close contact between Co\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e0.67\u003c/sub\u003e (101) and VN (200) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ef), confirming the formation of heterojunction. The elemental mapping displays a uniform distribution of Co, V and N elements in CoN/VN@NF (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eg). The obtained P-CoVO@NF represents overlapping nanosheets with the lattice fringes of Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e (122) plane (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eh, i), while the uniform distribution of Co, V, O and P elements can be observed (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ej). Additionally, an amorphous layer with a thickness of about 20 nm covers on the surface, and Fourier-transform infrared spectroscopy (FTIR) further proves the presence of P-O group (Supplementary Fig.\u0026nbsp;3).\u003csup\u003e25\u003c/sup\u003e Since phase transformation during OER process always involves bond-breaking, so the amorphous structure can more readily evolve than the crystalline structure.\u003csup\u003e26\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eThe X-ray photoelectron spectroscopy (XPS) survey spectra indicate the presence of Co, V, N and O elements in CoN/VN@NF, while Co, V, P and O elements exist in P-CoVO@NF (Supplementary Fig.\u0026nbsp;4). As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea, the binding energies of Co 2p in CoN/VN@NF show a negative shift of 0.69 eV compared to CoVO@NF. Specially, the peaks at 779.73 and 795.95 eV of CoN/VN@NF respectively correspond to the Co\u003csup\u003e3+\u003c/sup\u003e in the Co 2p\u003csub\u003e3/2\u003c/sub\u003e and Co 2p\u003csub\u003e1/2\u003c/sub\u003e orbitals, while the peaks at 781.55 and 797.41 eV are assigned to Co\u003csup\u003e2+\u003c/sup\u003e.\u003csup\u003e27\u003c/sup\u003e The V 2p spectrum reveal two extra peaks after nitridation of CoVO@NF (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). The peaks at 514.66 and 516.33 eV respectively attribute to V‒N‒O and V‒O bonds, indicating that the introduction of nitrogen anions results in the coupling between the electronic orbitals of Co and V with N atoms.\u003csup\u003e28\u003c/sup\u003e Besides, the V‒N bond located at 513.05 eV demonstrates the formation of metal nitride, which is further confirmed by the M‒N bond in N 1s spectrum (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec top). \u003csup\u003e29\u003c/sup\u003e For P-CoVO@NF, the Co 2p spectrum also exhibit the presence of Co\u003csup\u003e3+\u003c/sup\u003e at 780.02 and 795.95 eV, Co\u003csup\u003e2+\u003c/sup\u003e at 781.88 and 797.76 eV, while the peak at 516.3 eV in the V 2p spectrum ascribes to the V‒O bond. Compared to CoVO@NF, significant negative shifts in the Co 2p and V 2p peaks can be observed for P-CoVO@NF. Notably, the XPS spectrum reveals that the P predominantly exist in the form of P‒O bond at 133.71 eV, accompanying by a small amount of metal phosphide (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec bottom).\u003csup\u003e30\u003c/sup\u003e The P-O group with strong nucleophilicity could act as proton acceptor to activate surface oxygen during OER process. In addition to the oxygen vacancies (V\u003csub\u003eO\u003c/sub\u003e) and metal‒oxygen (M‒O) peaks, an extra peak at 532.1 eV in the O 1s spectrum is attributed to the P-O bond (Supplementary Fig.\u0026nbsp;5).\u003csup\u003e31\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eX-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) could provide accurate information of the valence states and coordination structures. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed, the position of the pre-edge absorption peak indicates the valence state order of Co as follows: CoN/VN@NF\u0026thinsp;\u0026lt;\u0026thinsp;P-CoVO@NF\u0026thinsp;\u0026lt;\u0026thinsp;CoVO@NF. The Fourier Transform (FT) EXAFS (FT-EXAFS) spectra for CoN/VN@NF and P-CoVO@NF implies that the introduction of nitrogen and P-O group respectively form the Co‒N and a small number of Co‒P coordinated structures (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee). The dominant peaks at 1.46 and 2.20 \u0026Aring; for CoN/VN@NF can be assigned to the first coordination shell of Co‒N/O bond and the inner coordination shell of Co‒Co bond (Supplementary Fig.\u0026nbsp;6 and Table\u0026nbsp;1), respectively. Compared with CoVO@NF, the decreased intensity of Co‒O bond at around 1.52 \u0026Aring; for P-CoVO@NF suggests a reduced average coordination number, indicating the formation of V\u003csub\u003eO\u003c/sub\u003e, which could enhance the electron transfer capability. Additionally, the small bulge at around 2.06 \u0026Aring; corresponds to the Co‒P bond.\u003csup\u003e32\u003c/sup\u003e Wavelet Transform (WT) is further recovered the coordination information of the first shell in both k-space and R space. After optimizing based on the Morlet wavelet, the Co K-edge WT-EXAFS of CoN/VN@NF and P-CoVO@NF respectively exhibit oscillations at 5.5 and 5.8 \u0026Aring;\u003csup\u003e\u0026ndash;1\u003c/sup\u003e correspond to Co‒N/O and Co‒O bonds (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef), whereas the minimal peak of Co‒P bond is difficult to be reflected.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg, the peak located at 5470 eV is designated as the 1s\u0026rarr;3d transition of tetravalent V.\u003csup\u003e33\u003c/sup\u003e The weak pre-edge absorption peak in both CoN/VN@NF and P-CoVO@NF indicate that the introduction of anions transforms the low-coordinate VO\u003csub\u003e4\u003c/sub\u003e tetrahedra in CoVO@NF into high-coordinate V(N,O)\u003csub\u003e6\u003c/sub\u003e octahedra with higher symmetry. The pre-edge absorption peak gradually moves in the low energy direction from CoVO@NF to P-CoVO@NF and then to CoN/VN@NF, indicating that the oxidation state of V decreases due to the reduced oxygen content. Furthermore, the FT-EXAFS spectra of CoN/VN@NF exhibit four principal features below 6 \u0026Aring; (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eh). Specially, the peaks at 1.63 and 2.42 \u0026Aring; correspond to the inner shell composed of six symmetric V‒N and V‒V bond, while the peaks near 3.70 and 4.45 \u0026Aring; are ascribed to the higher V‒N and V‒V shells, essentially consistent with the standard rock-salt structure of VN (Supplementary Fig.\u0026nbsp;7 and Table\u0026nbsp;2).\u003csup\u003e34\u003c/sup\u003e For P-CoVO@NF, the strongest V‒O bond is located at 1.62 \u0026Aring; rather than the 1.12 \u0026Aring; for CoVO@NF, attributing to the P incorporation causes the stretching of V‒O bond within Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e lattice. Such local structural variant makes the V‒O bond easily to break, resulting in the dissolution of V during OER process, thus promoting the reconstruction of Co species. As the WT-EXAFS illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ei, the highest intensity peaks for CoN/VN@NF and P-CoVO@NF in the first coordination shell are ascribed to the V‒N and V‒O bonds at 7.50 and 6.20 \u0026Aring;\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, respectively. The k-value for the V‒O bond in P-CoVO@NF is much higher than the CoVO@NF (6.20 vs. 4.81 \u0026Aring;\u003csup\u003e\u0026ndash;1\u003c/sup\u003e), revealing that the V‒O bond is stretched by the P incorporation.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003eElectrochemical performance\u003c/h2\u003e\n\u003cp\u003e\u003cstrong\u003eHER performance.\u003c/strong\u003e The HER activity was evaluated in 1.0 M KOH by a three-electrode system, and the commercial 20% Pt/C catalyst loaded on NF (denoted as Pt/C@NF) was also tested. As displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea, CoN/VN@NF requires overpotentials of only 55 mV and 164 mV at the current densities of 10 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e (\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e10\u003c/sub\u003e) and 100 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e (\u003cem\u003e\u0026eta;\u003c/em\u003e\u003csub\u003e100\u003c/sub\u003e), respectively. It is significantly better than CoVO@NF (93 and 204 mV) and P-CoVO@NF (84 and 197 mV), approaching commercial 20% Pt/C (17 and 129 mV) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb). Notably, CoN/VN@NF also exhibits outstanding HER activity over the recently reported non-precious metal electrocatalysts (Supplementary Table\u0026nbsp;3). The highest current response of CoN/VN@NF is attributed to the introduced nitrogen atom can increase the d-electron density of metal, resulting in a redistribution of the density of states near the Fermi level (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e) and generating a similar electronic structure as that of precious metal. The poor HER activity of nitride NF substrate indicates a negligible contribution to electrocatalytic activity (Supplementary Fig.\u0026nbsp;8).\u003c/p\u003e\n\u003cp\u003eCompared to CoVO@NF and P-CoVO@NF, the lower Tafel slope value of 53 mV dec\u003csup\u003e\u0026ndash;1\u003c/sup\u003e for CoN/VN@NF inidicates a faster kinetics (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec), which also suggests the Volmer-Heyrovsky mechanism of CoN/VN@NF towards HER.\u003csup\u003e35\u003c/sup\u003e The Nyquist plots collected by electrochemical impedance spectroscopy (EIS) and the double-layer capacitance (\u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e) values show that CoN/VN@NF displays the smallest charge transfer resistance and much more active sites (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed,e and Supplementary Fig.\u0026nbsp;9). After normalizing by the ECSA values, CoN/VN@NF still exhibit largest current density (\u003cem\u003eJ\u003c/em\u003e\u003csub\u003eECSA\u003c/sub\u003e) (Supplementary Fig.\u0026nbsp;10), further confirming the outstanding intrinsic activity. Moreover, CoN/VN@NF shows a turnover frequency (TOF) value of 1.16 s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at 0.2 V, which is significantly higher than CoVO@NF (0.50 s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) and P-CoVO@NF (0.54 s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) (Supplementary Fig.\u0026nbsp;11). It maintains the higher level across the entire range of applied potentials, further provinging the rapid kinetics of CoN/VN@NF.\u003c/p\u003e\n\u003cp\u003eDurability is another crucial criterion for assessing the potential application of electrocatalyst. As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef, the CoN/VN@NF maintains its initial activity without significant degradation after 10,000 continuous cyclic voltammetry (CV) cycles. It also can stably operate for over 100 h at a current density of 100 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, further confirming the superior stability of CoN/VN@NF (inset of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef). After stability test, it preserves the original coral-like nanoarray structure, while the binding energies of Co and V in the XPS spectra show slightly variation (Supplementary Fig.\u0026nbsp;12). It reveals that the stable surface chemical state of CoN/VN@NF is conductive to long-term operation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOER performance.\u003c/strong\u003e The OER activity was also investigated in alkaline electrolyte, and the commercial RuO\u003csub\u003e2\u003c/sub\u003e catalyst supported on NF (denoted as RuO\u003csub\u003e2\u003c/sub\u003e@NF) was studied for comparison. As presented in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eg, the P-CoVO@NF performs much better OER activity than the compared catalysts. The P-CoVO@NF only requires the overpotentials of 296 and 317 mV to deliver the current densities of 50 and 100 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, respectively, much lower than CoVO@NF (341 and 373 mV), CoN/VN@NF (389 and 425 mV) and RuO\u003csub\u003e2\u003c/sub\u003e@NF (376 and 420 mV) (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eh). Significantly, the activity exceeds most of the reported transition metal based electrocatalysts (Supplementary Table\u0026nbsp;4). As displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ei, the P-CoVO@NF possesses the lowest Tafel slope value of 77 mV dec\u003csup\u003e\u0026ndash;1\u003c/sup\u003e than CoVO@NF (152 mV dec\u003csup\u003e\u0026ndash;1\u003c/sup\u003e), CoN/VN@NF (133 mV dec\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) and RuO\u003csub\u003e2\u003c/sub\u003e@NF (138 mV dec\u003csup\u003e\u0026ndash;1\u003c/sup\u003e). Generally, the Tafel slope value for OER increases with the enhanced coverage of \u003csup\u003e*\u003c/sup\u003eO under the site-isolation model.\u003csup\u003e36\u003c/sup\u003e Consequently, the enhanced activity of P-CoVO@NF, suggested by the lowest Tafel slope value, may be due to the accelerated kinetics of \u003csup\u003e*\u003c/sup\u003eO transformation. Additionally, the higher conductivity of P-CoVO@NF facilitates charge transfer, thereby enhancing OER activity (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ej). Moreover, the OER activity of NF substrate after phosphating is not well, so the activity of the substrate can be negligible (Supplementary Fig.\u0026nbsp;13).\u003c/p\u003e\n\u003cp\u003eP-CoVO@NF exhibits outstanding intrinsic OER activity with a moderate ECSA value and a \u003cem\u003eJ\u003c/em\u003e\u003csub\u003eECSA\u003c/sub\u003e value about 9 times higher than that of CoN/VN@NF at 1.55 V (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ek and Supplementary Fig.\u0026nbsp;14\u0026ndash;15). The TOF value of P-CoVO@NF is 0.17 s\u003csup\u003e\u0026ndash;1\u003c/sup\u003e at an overpotential of 300 mV, approximately 5.7 times as that of CoN/VN@NF (Supplementary Fig.\u0026nbsp;16), further proving the higher intrinsic activity of P-CoVO@NF. Durability test shows that no noticeable activity decay is observed after 100 h at 100 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003el). Furthermore, only a slight decay is noted after 10,000 continuous CV cycles, while the intensity of the oxidation peak increases because extra metal species could be oxidized during OER process. After the stability test, the surface of P-CoVO@NF were covered with thinner nanosheets as confirmed by SEM images (Supplementary Fig.\u0026nbsp;17).\u003c/p\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003eOER Mechanism\u003c/h2\u003e\n\u003cp\u003eGenerally, the metal species on the surface of catalysts undergo in-situ reconstruction during OER process. The operando Bode plots indicate that the charge transfer signals at different characteristic frequencies can be divided into two areas (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea-c). Specially, the electron transfer response in the inner layer of the catalyst occurs at the high-frequency range of 10\u003csup\u003e2\u003c/sup\u003e\u0026minus;10\u003csup\u003e4\u003c/sup\u003e Hz, whereas the charge transfer response at the catalyst/electrolyte interface is observed at the low-frequency range of 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u0026minus;10\u003csup\u003e2\u003c/sup\u003e Hz.\u003csup\u003e37\u003c/sup\u003e Compared with CoVO@NF and CoN/VN@NF, the P-CoVO@NF exhibits lower peaks in both high and low frequency ranges, and these peaks decrease more rapidly with the increasing potential. It indicates a faster oxidation of intermediates and deprotonation of \u003csup\u003e*\u003c/sup\u003eOOH for P-CoVO@NF, revealing the much better OER activity.\u003csup\u003e38\u003c/sup\u003e The Nyquist plots in Supplementary Fig.\u0026nbsp;18 are fitted based on a hypothetical equivalent circuit model composed of three parts (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed). In detail, the \u003cem\u003eR\u003c/em\u003e\u003csub\u003es\u003c/sub\u003e stands for the electrolyte resistance. The first parallel circuit involves constant phase element (CPE\u003csub\u003e1\u003c/sub\u003e) and resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eCEOR\u003c/sub\u003e) related to the electron transfer from the inner layer of catalyst to the reaction interface, and the CEOR represents the surface reconstruction of catalyst during OER. The second parallel circuit includes a constant phase element (CPE\u003csub\u003e2\u003c/sub\u003e) and resistance (\u003cem\u003eR\u003c/em\u003e\u003csub\u003eOER\u003c/sub\u003e) associated with the charge transfer of interface reaction.\u003csup\u003e39\u003c/sup\u003e Relatively, the smallest \u003cem\u003eR\u003c/em\u003e\u003csub\u003eCEOR\u003c/sub\u003e value of P-CoVO@NF implies the easier oxidization and reconstruction (Supplementary Table\u0026nbsp;5). At the low potential range of 1.20\u0026thinsp;~\u0026thinsp;1.45 V, the \u003cem\u003eR\u003c/em\u003e\u003csub\u003eOER\u003c/sub\u003e values of P-CoVO@NF and CoVO@NF drop sharply but still large, manifesting that the catalysts only occur rapid structural changes. The \u003cem\u003eR\u003c/em\u003e\u003csub\u003eOER\u003c/sub\u003e value of P-CoVO@NF approaches zero when the potential exceeds 1.45 V indicates the occurrence of OER process, whereas it starts at above 1.5 V for CoN/VN@NF (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee). It further uncovers the superior OER kinetics and intrinsic activity of P-CoVO@NF. Hence, the regulation of P-O can improve the utilization rate of \u003csup\u003e*\u003c/sup\u003eOH, endowing P-CoVO@NF with faster charge transfer and deprotonation capability, while the self-reconstructed interface facilitates to OER acitivity.\u003c/p\u003e\n\u003cp\u003eOperando XAFS was further employed to investigate the structure change of Co sites during OER. As depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ef, the Co K-edge absorption of P-CoVO@NF is situated between CoO and CoOOH at an open-circuit potential (OCP), indicating that the oxidation state of Co is between +\u0026thinsp;2 and +\u0026thinsp;3. When the potential promotes from 1.20 to 1.50 V, the Co K-edge gradually shifts towards higher energy, suggesting the increase of Co valence state. The valence states of Co under different applied potentials are further quantified by analyzing the first derivative of absorption edge.\u003csup\u003e40,41\u003c/sup\u003e As displayed in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eg, the oxidation state of Co gradually increases from +\u0026thinsp;2.31 at OCP to +\u0026thinsp;2.69 at 1.20 V, then to +\u0026thinsp;2.71 at 1.30 V and +\u0026thinsp;2.76 at 1.40 V. When the voltage exceeds the oxygen evolution potential, the charge on the catalyst surface is insufficient to further oxidize Co, which causes electrons to escape from the surface oxygen and results in the formation of O\u003csub\u003e2\u003c/sub\u003e. Simultaneously, cobalt species undergo surface reconstruction, and its oxidation state eventually rises to +\u0026thinsp;3.31 at 1.5 V. It can be inferred that the OER occurs at the potential range of 1.4‒1.5 V, consistent with the above Bode phase angle analyses. Moreover, the Co sites exhibit stronger attraction to O 2p electrons at a high potential, benefiting to the deprotonation of M‒OH.\u003csup\u003e42\u003c/sup\u003e Consequently, Co sites with higher oxidation states enhance the adsorption of OH\u003csup\u003e‒\u003c/sup\u003e ions to form Co‒OH, thereby reducing the required potential for deprotonation and generating more reactive oxygen species to promote OER activity. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eh and Supplementary Fig.\u0026nbsp;19 displays the changes of coordination structures for the surface Co species. At OCP, the peak at 1.5 \u0026Aring; is associated with the single scattering path of Co‒O bond, as well as the Co‒Co (d-Oh) from distorted octahedral (tetrahedral-like) coordination structure is located at 2.8 \u0026Aring;. Upon increasing the potential to 1.2 V, a new peak of Co‒Co (r-Oh) at 2.4 \u0026Aring; originated from regular octahedral coordination structure (Supplementary Table\u0026nbsp;6). This generates a shift from high-spin Co\u003csup\u003e2+\u003c/sup\u003e to low-spin Co\u003csup\u003e3+\u003c/sup\u003e and the decrease of band gap from 0.615 eV to 0 eV, resulting in a high conductivity and well OER activity\u003csup\u003e43\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ei). Furthermore, the V 2p XPS spectra show almost no change except for the decreased intensity, implying the partial V dissolution during OER (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ej and Supplementary Table\u0026nbsp;7). The positive shift of Co 2p spectrum along with the increased area of Co\u003csup\u003e3+\u003c/sup\u003e peak again indicates the elevated oxidation state for cobalt species (Supplementary Fig.\u0026nbsp;20). The solution after OER was analyzed by performing Inductively coupled plasma-mass spectrometry (ICP-MS). The content of Co are negligible, whereas V is detected with content of 7.5 \u0026micro;g mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Supplementary Table\u0026nbsp;8), further ascertaining that a small amount of V leaches into solution during OER. The dissolution of V creates vacancies in the Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e lattice, which could provide sufficient space to promote such a configurational transformation. The evoluted oxygen-bridged octahedral center is similar to the local environment of Co‒(O)OH, making the Co site benefits to the adsorption of oxygen species, and then oxidation and structural reconfiguration. As the potential further increases, the peak intensity of Co‒O begins to decline, which possibly ascribes to the electrons removal from CoOOH, leading to the protons generation and subsequent O\u003csub\u003e2\u003c/sub\u003e release. Additionally, the decline in the peak height of the Co-O bond indicates the formation of V\u003csub\u003eO\u003c/sub\u003e during the OER process, which in turn enhances the adsorption of intermediate species and the rate of electron conduction in the materials.\u003c/p\u003e\n\u003cp\u003eFurthermore, the relative intensity of P 2p spectrum decreases, accompanied by the disappearance of metal phosphides. The O 1s spectrum presented shows an increase in V\u003csub\u003eO\u003c/sub\u003e after stability test, which maybe facilitates the adsorption and desorption of intermediates (Supplementary Fig.\u0026nbsp;21). The presence of O‒H bond is attributed to the in-situ reconstructed CoOOH, originating from the surface metal phosphides decompose into PO\u003csub\u003ex\u003c/sub\u003e and CoOOH. Besides, a portion of V‒O bond will break at a high potential, and the PO\u003csub\u003ex\u003c/sub\u003e ions dissolve from Co‒PO\u003csub\u003ex\u003c/sub\u003e, thus creating pathway to allow more metal sites contact with the OH\u003csup\u003e‒\u003c/sup\u003e ions in the electrolyte to form CoOOH. The evoluted CoOOH can provide effective active sites to lower the reaction barrier and accelerate the reaction process. Raman spectroscopy was conducted to reveal the variation of the chemical composition after OER test. As shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ek, P-CoVO@NF displays O\u0026thinsp;\u0026minus;\u0026thinsp;V\u0026minus;O bond at 816 cm\u003csup\u003e‒1\u003c/sup\u003e and V\u0026thinsp;\u0026minus;\u0026thinsp;O bond at 988 cm\u003csup\u003e‒1\u003c/sup\u003e.\u003csup\u003e44\u003c/sup\u003e Moreover, the stretching vibrations of Co\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;V bond originated from the presence of V\u003csub\u003eO\u003c/sub\u003e, can be split into the doublet peaks at 280 and 334 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. The peaks at 660 and 943 cm\u003csup\u003e\u0026ndash;1\u003c/sup\u003e are respectively attributed to the \u003cem\u003eA\u003c/em\u003e\u003csub\u003e1g\u003c/sub\u003e vibrational modes of Co-O and O\u0026thinsp;\u0026minus;\u0026thinsp;P\u0026minus;O bonds.\u003csup\u003e45\u003c/sup\u003e After CV cycles test, the characteristic peaks of Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e disappear, while the new peaks emerge at 468 and 548 cm\u003csup\u003e‒1\u003c/sup\u003e respectively belong to the \u003cem\u003eE\u003c/em\u003e\u003csub\u003eg\u003c/sub\u003e and \u003cem\u003eF\u003c/em\u003e\u003csub\u003e2g\u003c/sub\u003e vibrational modes of CoOOH.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003eTheory calculations\u003c/h2\u003e\n\u003cp\u003eThe electronic charge distribution of CoVO@NF, CoN/VN@NF and P-CoVO@NF models based on DFT calculations are shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea-c and Supplementary Table\u0026nbsp;9. It can be concluded that the charge of both Co and V atoms follows this order: CoVO@NF\u0026thinsp;\u0026gt;\u0026thinsp;P-CoVO@NF\u0026thinsp;\u0026gt;\u0026thinsp;CoN/VN@NF. Therefore, both nitrogen and phosphate anions regulation promote the electron density around Co and V atoms. Additionally, the nitrogen anion could generate a stronger electron coupling interaction with metals compared to P-O group, resulting in a lower charge distribution, which matches well with the above XPS and XANES analyses. For CoN/VN@NF, the electron accumulation at the nitrogen site is more conducive to the capture of hydrogen protons, thereby promoting HER activity. In contrast, the phosphorus site in P-CoVO@NF exhibits higher positive charge, which is benefitical to adsorb hydroxyl groups. Based on these results, we will consider nitrogen site as the adsorption site for \u003csup\u003e*\u003c/sup\u003eH in\u0026nbsp;CoN/VN@NF, while the phosphorus site as the adsorption site for \u003csup\u003e*\u003c/sup\u003eOH in P-CoVO@NF in the subsequent computational processes of HER. Moreover, the CoVO@NF, CoN/VN@NF and P-CoVO@NF models exhibit a continuous density of states (DOS) near the \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed), suggesting the narrow band gaps and excellent conductivity. The \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e values of Co in CoVO@NF, CoN/VN@NF and P-CoVO@NF are ‒1.23, ‒1.09 and ‒1.43 eV, respectively, while the corresponding values of V are ‒0.08, ‒0.02 and ‒0.17 eV (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee,f). Relatively, the Co and V in CoN/VN@NF model show the highest electron density and the \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e values are much closer to the \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e, leading to stronger ntermediates adsorption and efficient electron transfer. The Co and V in P-CoVO@NF model exhibit a moderate electron density with the furthest \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e values from \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e, suggesting a higher occupancy of antibonding states, which weakens the intermediates adsorption and facilitates the subsequent reaction steps.\u003csup\u003e46\u003c/sup\u003e Based on the hydrogen binding energy (HBE) theory, the\u003csup\u003e*\u003c/sup\u003eH Gibbs free energy (\u0026Delta;\u003cem\u003eG\u003c/em\u003e\u003csub\u003e*H\u003c/sub\u003e) for CoN/VN@NF (‒0.23 eV) is much closer to zero indicates the promoted HER activity (Supplementary Fig.\u0026nbsp;22‒24). Moreover, the water dissociation serves as the rate-determining step (RDS) for both CoVO@NF and P-CoVO@NF models, whereas the water adsorption is the RDS for CoN/VN@NF model (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eg and Supplementary Fig.\u0026nbsp;25). The energy barrier values of RDS demonstrate that the Co site is the active site for CoVO@NF and P-CoVO@NF models, while V site is beneficial to the \u003csup\u003e*\u003c/sup\u003eOH adsorption for CoN/VN@NF model. Besides, the exothermic water dissociation of CoN/VN@NF model suggests its excellent HER activity.\u003c/p\u003e\n\u003cp\u003eTo identify the active sites for OER, the P, V and Co sites in P-CoVO@NF model are respectively selected as the active sites, in which the Co site exhibits the lowest energy barrier for the RDS (Supplementary Fig.\u0026nbsp;26\u0026ndash;29). Specially, the RDS of P-CoVO@NF model is the formation of \u003csup\u003e*\u003c/sup\u003eOOH with an energy barrier of 1.76 eV (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eh), significantly lower than CoVO@NF of 2.62 eV and CoN/VN@NF of 1.92 eV (\u003csup\u003e*\u003c/sup\u003eO formation step is the RDS). It is concluded that the formation of strongly nucleophilic P-O group greatly enhance the interfacial proton transfer, thereby reducing the energy barrier for the formation of \u003csup\u003e*\u003c/sup\u003eO and promoting the conversion rate of intermediates. The weaker electron coupling effect of P-O group can lower the adsorption strength of oxygen-containing intermediates and accelerate the deprotonation of \u003csup\u003e*\u003c/sup\u003eOH, thus enhancing the OER kinetics. Since the cobalt species in P-CoVO@NF gradually reconstructs into cobalt hydroxide during OER, so the P-CoOOH model was also built (inset of Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ei). The Co site in P-CoOOH model has a much more positive charge of 0.92 e, and the \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e value of ‒1.38 eV is closer to the \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e compared to P-CoVO@NF (Supplementary Fig.\u0026nbsp;30), indicating the stronger adsorption of oxygen-containing intermediates. Furthermore, the \u0026Delta;\u003cem\u003eG\u003c/em\u003e of oxygen-containing intermediates at the Co site in P-CoOOH is obviously decreased (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ei and Supplementary Fig.\u0026nbsp;31), while the formation of \u003csup\u003e*\u003c/sup\u003eOOH is identified as the RDS. Specifically, the difference between \u0026Delta;\u003cem\u003eG\u003c/em\u003e\u003csub\u003e*O\u003c/sub\u003e and \u0026Delta;\u003cem\u003eG\u003c/em\u003e\u003csub\u003e*OOH\u003c/sub\u003e at the Co site in P-CoOOH is 1.68 eV, which is lower than P-CoVO@NF, indicating a thermodynamically favorable OER process of P-CoOOH. The charge configuration analyses indicate that the increase of Co valence state after reconstructing induces a pseudo-electrophobic effect, thereby reducing the positive charge on the O atom as well as the negative charge on the H atom in \u003csup\u003e*\u003c/sup\u003eOH. It reveals that the O‒H bond in \u003csup\u003e*\u003c/sup\u003eOH is easy to cleavage under the attack of OH\u003csup\u003e‒\u003c/sup\u003e ions, benefitting to the formation of \u003csup\u003e*\u003c/sup\u003eOOH. Therefore, such a structural reconfiguration could promote OER kinectics.\u003c/p\u003e\n\u003cp\u003eWe further utilize CoN/VN@NF as cathode and P-CoVO@NF as anode for overall water splitting by an H‒type electrolytic cell separated with an exchange membrane. The P-CoVO@NF(+)||CoN/VN@NF(‒) system only requires a voltage of 1.43 V to achieve a current density of 10 mA cm\u003csup\u003e‒2\u003c/sup\u003e, whereas a higher voltage of 1.62 V is needed for RuO\u003csub\u003e2\u003c/sub\u003e@NF(+)||PtC@NF(‒) system (Supplementary Fig.\u0026nbsp;32). Importantly, a 1.75 V voltage for P-CoVO@NF(+)||CoN/VN@NF(‒) system could drive a large current of 100 mA cm\u003csup\u003e‒2\u003c/sup\u003e. The outstanding performance is comparable to the reported advanced electrocatalysts (Supplementary Table\u0026nbsp;10). It also displays a prominent durability without obvious attenuation current density for 100 h (Supplementary Fig.\u0026nbsp;33). The Faradaic efficiency was measured by the H\u0026ndash;type electrolytic cell with collection device of the evolved H\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e gases (Supplementary Fig.\u0026nbsp;34). The obtained volume ratio of H\u003csub\u003e2\u003c/sub\u003e:O\u003csub\u003e2\u003c/sub\u003e is about 2:1 at a current density of 40 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and the P-CoVO@NF(+)||CoN/VN@NF(‒) system exhibits a Faraday efficiency of near 100% (Supplementary Fig.\u0026nbsp;35). The P-CoVO@NF//CoN/VN@NF system also can be driven by a 1.45 V solar cell (Supplementary Fig.\u0026nbsp;36). The H\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e gases are conspicuously generated on the cathode and anode, respectively, further manifesting the potential for converting low-voltage electrical energy originated from solar energy into chemical energy. Furthermore, we also assembled an AEM electrolyzer to evaluate the practice application of catalysts. The P-CoVO@NF and CoN/VN@NF were respectively used as the anode and cathode with the AEM made of industrial fluorocarbon acid resin film (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea). The electrolyzer was tested within the temperature range of 25 to 70\u0026deg;C using 1 M KOH electrolyte, and it could be concluded that the voltage and total cell resistance decreased with the working temperature increased (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb,c). At 70\u0026deg;C, a voltage of 1.88 V was able to drive a current density of 500 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, while a voltage of 1.98 V achieved a current density of 1000 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, outperforming most of the advanced non-precious metal-based electrocatalysts.\u003csup\u003e47,48\u003c/sup\u003e The W\u003csub\u003eDC\u003c/sub\u003e was calculated to be 4.31 kWh Nm\u003csup\u003e\u0026ndash;3\u003c/sup\u003e@250 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, approaching the international forefront in terms of efficiency. Additionally, the electrolyzer attaining an high energy conversion efficiency of 78.7% under an operational current density of 500 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e, as well as excellent stability over a span of 200 hours (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ed). This can be attributed to the construction of 3D micro-nano structures and the occurrence of surface restructuring. The results suggest that the optimized nanostructure design of P-CoVO@NF and CoN/VN@NF could serve as potential applications is commercial AEM systems.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe nitrogen and phosphate anions are respectively utilized to accurately modulate the electronic structures of coral-like Co-V bimetallic nanoarrays electrocatalysts, thereby enabling superior performance in HER, OER and AEM electrolyzer. The layered effect of Co and the epitaxial growth of V are key to the formation of such unique structure. Furthermore, the nitrogen anions could upregulate the \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e of Co and V to optimize the energy barrier of intermediation for improving HER activity. The phosphate anions downregulate the corresponding \u003cem\u003eɛ\u003c/em\u003e\u003csub\u003ed\u003c/sub\u003e to favor the deprotonation of oxygen-containing intermediates during OER as well as forming the CoOOH active center with high valence states and low band gaps, thereby improving the conductivity and the adsorption capacity of intermediates. Besides, the Co-O undergo an in-situ structural reconfiguration from distorted octahedron to regular octahedron during OER process, which could facilitate the reaction kinetics and the formation of intermediates. The phosphate anions modulation can accelerate the charge transfer and deprotonation capabilities of the electrocatalyst, thus enhancing the OER activity. Our work provides an effective modulation strategy and new insights into the structural evolution mechanisms of electrocatalysts, contributing to a better understanding of their design and synthesis for sustainable energy storage and conversion applications.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003eChemicals\u003c/h2\u003e\n \u003cp\u003eCobalt chloride hexahydrate (CoCl\u003csub\u003e2\u003c/sub\u003e·6H\u003csub\u003e2\u003c/sub\u003eO), ammomium metavanadate (NH\u003csub\u003e4\u003c/sub\u003eVO\u003csub\u003e3\u003c/sub\u003e) were purchased from Aladdin Chemical Reagent Co., Ltd. Sodium hypophosphite (NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e) was purchased from Rhawn Chemical Reagent Co., Ltd. Ethanol, acetone and hydrochloric acid were purchased from Tianjin Fuyu Chemical Reagent Co., Ltd. Commercial Ni foam (NF) was purchased from Kunshan Jiayisheng Electronics Co. Ltd. All of the reagents are of analytical grade and directly used without further purification. Deionized water was used in the experiments.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003eSynthesis of CoVO@NF\u003c/h2\u003e\n \u003cp\u003eTypically, a Ni foam (NF) substrate with a size of 3 × 4 cm was washed in 3 M HCl for 5 min to remove surface oxides, then it was respectively ultrasonicated in acetone and ethanol for 30 minutes. Subsequently, 0.36 mmol of CoCl\u003csub\u003e2\u003c/sub\u003e·6H\u003csub\u003e2\u003c/sub\u003eO and 1.44 mmol of NH\u003csub\u003e4\u003c/sub\u003eVO\u003csub\u003e3\u003c/sub\u003e were dissolved into 80 mL of deionized water under stirring. After adjusting the pH value of the solution approximately 4, a piece of treated NF was dipped for 1 h. Then, it was transferred into a 100 mL Teflon-lined stainless steel autoclave and heated at 160°C for 8 h, so the coral-like interlaced Co\u003csub\u003e3\u003c/sub\u003eV\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e8\u003c/sub\u003e nanosheet arrays precursor supported on NF substrate was prepared (denoted as CoVO@NF).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003eSynthesis of CoN/VN@NF\u003c/h2\u003e\n \u003cp\u003eThe CoN/VN@NF was synthesized by pyrolyzing the CoVO@NF precursor at 600°C for 2 h under NH\u003csub\u003e3\u003c/sub\u003e ambient with a heating rate of 5°C min\u003csup\u003e− 1\u003c/sup\u003e. To assess the effect of the NF substrate on HER activity, the same nitriding treatment were applied to NF for synthesis of NFN.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003eSynthesis of P-CoVO@NF\u003c/h2\u003e\n \u003cp\u003eTypically, 1.5 g of NaH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e2\u003c/sub\u003e powder and CoVO@NF precursor were positioned upstream and downstream of the quartz tube, respectively. Prior to pyrolysis, nitrogen was purged for 30 min to eliminate any residual air. Then, it was heated to 450°C for 2 h with a heating rate of 2°C min\u003csup\u003e− 1\u003c/sup\u003e to prepare P-CoVO@NF. Also, the same phosphating process were adopted to NF to prepare NFP for comparison.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003eCharacterizations\u003c/h2\u003e\n \u003cp\u003eX-ray diffraction (XRD) analyses were conducted using a Bruker D8 Advance X-ray diffractometer equipped with Cu K\u003csub\u003eα\u003c/sub\u003e radiation. Grazing Incidence X-Ray Diffraction (GI-XRD) measurements were performed on a Bruker D8 Venture DUO microsourced single-crystal X-ray diffractometer, equipped with a Photon III detector and Cu-Diamond X-ray sources (λ = 1.5406 Å). SEM images were obtained by utilizing a Hitachi S-4800 instrument, operating at an accelerating voltage of 15 kV. Transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and EDS elemental mapping images were captured by using a JEM-2100 electron microscope (JEOL, Japan) operating at an acceleration voltage of 200 kV. X-ray photoelectron spectroscopy (XPS) was conducted on a VG ESCALABMK II system using Mg-K\u003csub\u003eα\u003c/sub\u003e radiation (1253.6 eV). Raman spectroscopic measurements were performed utilizing a Jobin Yvon HR 800 micro-Raman system with 457.9 nm excitation. Fourier transform infrared spectra (FT-IR) in the range of 400–4000 cm\u003csup\u003e− 1\u003c/sup\u003e were recorded using a PE Spectrum One B IR spectrometer with KBr pellets. Inductively coupled plasma emission spectroscopy (ICP-MS) was used to determine the metal content in the electrolyte after the stability test (Thermo Fisher ICP-MS RQ). The extended X-ray absorption fine structure (EXAFS) analysis was carried out at beam line BL14W1 of the Shanghai Synchrotron Radiation Facility (SSRF) in China, utilizing a Si (111) double crystal monochromator. All spectra were aligned, normalized, and fitted using IFEFFIT-based software.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003eElectrochemical Measurements\u003c/h2\u003e\n \u003cp\u003eAll the electrochemical tests in 1.0 M KOH electrolyte at room temperature by a three-electrode configuration. The electrode material with a size of 1 × 1.5 cm\u003csup\u003e2\u003c/sup\u003e served as the working electrode, while the Hg/HgO electrode and graphite rod were employed as the reference and counter electrodes, respectively. For all measurements, the final potential was calibrated based on the Nernst equation for a reversible hydrogen electrode (RHE): \u003cem\u003eE\u003c/em\u003e\u003csub\u003eRHE\u003c/sub\u003e = \u003cem\u003eE\u003c/em\u003e\u003csub\u003eHg/HgO\u003c/sub\u003e + 0.098 V + 0.059 pH. Tafel plots were calculated by the polarization curves. Cyclic voltammetry (CV) curves were recorded by different scan rates from 5 to 25 mV s\u003csup\u003e‒1\u003c/sup\u003e to determine the double layer capacitance (\u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e). All the linear sweep voltammetry (LSV) curves are obtained by 85% IR compensation. Electrochemical impedance spectroscopy (EIS) was performed on LSV curves corresponding to a potential of 10 mA cm\u003csup\u003e‒2\u003c/sup\u003e, over a frequency range of 0.01 to 100,000 Hz. Potential cycling stability was examined through continuous CV curves at a scan rate of 100 mV s\u003csup\u003e‒1\u003c/sup\u003e. Additionally, the chronoamperometry test was conducted at a desired potential of 100 mA cm\u003csup\u003e‒2\u003c/sup\u003e for 100 h. The Faraday efficiency of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was determined by comparing the experimental and theoretical amounts of H\u003csub\u003e2\u003c/sub\u003e and O\u003csub\u003e2\u003c/sub\u003e. Gas analysis was performed using the drain method in a closed H-type electrolyzer under the chronoamperometry test at 40 mA cm\u003csup\u003e‒2\u003c/sup\u003e for 60 min. The theoretical H\u003csub\u003e2\u003c/sub\u003e amount was calculated as follows.\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ1\" class=\"mathdisplay\"\u003e$$\\text{n}\\left({\\text{H}}_{\\text{2}}\\right)\\text{= }\\frac{\\text{Q}}{\\text{nF}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere Q is the charge through the electrode, n(H\u003csub\u003e2\u003c/sub\u003e) is the number of moles of hydrogen produced, F is Faraday constant of 96,485 C mol\u003csup\u003e‒1\u003c/sup\u003e, and n is the number of transferred electrons during the water splitting (2 for HER). The theoretical amount of O\u003csub\u003e2\u003c/sub\u003e is calculated the same as that for H\u003csub\u003e2\u003c/sub\u003e except n = 4.\u003c/p\u003e\n \u003cp\u003eThe turnover frequency (TOF) of the catalyst was calculated using the following equation based on previous reports.\u003c/p\u003e\n \u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ2\" class=\"mathdisplay\"\u003e$$\\text{TOF= }\\frac{\\text{Total Hydrogen Turn Overs/}{\\text{cm}}^{\\text{2}}\\text{geometric area}}{\\text{Surface Sits /}{\\text{cm}}^{\\text{2}}\\text{ geometric area}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe number of total hydrogen turn overs can be determined from the current density using the following equation:\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\"\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eThe total number of effective surface sites was calculated by the following equation:\u003c/p\u003e\n \u003cdiv id=\"Equb\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equb\" class=\"mathdisplay\"\u003e$$\\frac{\\text{Surface sites}}{{\\text{cm}}^{\\text{2}}\\text{ geometric area}}\\text{ = }\\frac{\\text{ Surface sites (flat standard)}}{{\\text{cm}}^{\\text{2}}\\text{ geometric area}}\\text{ × Roughness factor}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere the roughness factor (R\u003csub\u003ef\u003c/sub\u003e) can be determined by the \u003cem\u003eC\u003c/em\u003e\u003csub\u003edl\u003c/sub\u003e, and we assume 60 µF cm\u003csup\u003e‒2\u003c/sup\u003e for the specific capacitance of a flat electrode provided by previous reports. The surface sites of 2 × 10\u003csup\u003e15\u003c/sup\u003e for the flat standard electrode was used for previous results. All electrochemical measurements were performed on a CHI660E electrochemical workstation, except for the EIS tests. EIS data were collected via Autolab PGSTAT302N (Eco Chemie, Utrecht, The Netherlands).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003eAEM Electrolyzer Preparation and Measurement\u003c/h2\u003e\n \u003cp\u003eThe AEM (Mainz hydrogen energy), which consists of a current collector (eTM-3060PC), MEA type reactor (serpentine channel), Anion exchange membrane (Fumasep FAA-3-PK-130), working electrodes (CoN/VN@NF||P-CoVO@NF). Prior to use, the anion exchange membrane should be soaked in a 1 M KOH solution for 24 hours. Within the AEM electrolyzer system, the 1 M KOH solution is provided to both the cathode and anode at a flow rate of 40 mL/min at various temperatures. The water splitting performance is determined by measuring the LSV curves within a range of 1.0 to 2.0 V at a scan rate of 5 mV/s. For durability testing, the AEM system operates at a constant potential of 1.88 V for 150 hours. EIS measurements are conducted at a voltage of 1.88 V within a frequency range of 10 kHz to 0.01 Hz, with an amplitude of 10 mV. The formula for calculating direct current energy consumption (W\u003csub\u003eDC\u003c/sub\u003e) is:\u003c/p\u003e\n \u003cdiv id=\"Equc\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equc\" class=\"mathdisplay\"\u003e$${\\text{W}}_{\\text{DC}}\\text{ = }\\frac{\\text{IVt × }\\frac{\\text{1}}{\\text{1000}}}{\\text{4.18×}{\\text{10}}^{\\text{-4}}\\text{×It}{\\text{η}}_{\\text{e}}}\\text{ }\\text{=}\\text{ }\\frac{V}{0.418{\\eta }_{e}}$$\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere I is the cell current through the electrode, V is the cell voltage, t is time, \u003cem\u003eη\u003c/em\u003e\u003csub\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sub\u003e is current efficiency.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003eTheoretical calculations\u003c/h2\u003e\n \u003cp\u003eDensity Functional Theory (DFT) simulations were performed using the Cambridge Sequential Total Energy Package (CASTEP) module implemented in Material Studio. The electronic exchange and correlation effects were described using the Perdew-Burke-Ernzerhof (PBE) functional, a generalized gradient approximation (GGA). In consideration of the specific situations of theoretical calculations, Co\u003csub\u003e3\u003c/sub\u003eN was utilized instead of Co\u003csub\u003e2\u003c/sub\u003eN\u003csub\u003e0.67\u003c/sub\u003e. To simplify the calculations, a four-layer Co\u003csub\u003e3\u003c/sub\u003eN (101) slab and a three-layer VN (200) slab were chosen as the surface slab supercells. For the P-CoVO model, part of the vanadium atoms were replaced by P atoms after geometry optimization, followed by a series of calculations. Population analysis was performed using the Mulliken scheme, and a plane-wave energy cutoff of 400 eV was employed. The Brillouin zone sampling was carried out using a (2×3×6) Monkhorst-Pack grid, and a vacuum layer of 15 Å was added to the supercell to prevent interaction between individual periodic images. Geometry optimization was repeated until the total energy tolerance reached 1×10\u003csup\u003e‒5\u003c/sup\u003e eV and the changes in force on the atoms were less than 0.03 eV Å\u003csup\u003e‒1\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eThe Gibbs free energy can be expressed as:\u003c/p\u003e\n \u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ3\" class=\"mathdisplay\"\u003e$$\\text{ΔG }\\text{= ΔE + ΔZPE }\\text{–}\\text{ TΔS}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere ΔE is the reaction energy calculated by the DFT methods. ΔZPE and TΔS are the thermodynamic corrections of zero-point-energy (ZPE) and entropy (S) derived from the vibrational partitions function at 298.15 K, respectively. As the entropy of hydrogen in the absorbed state is negligible, ∆S can be calculated as ‒1/2S\u003csub\u003e0\u003c/sub\u003e H\u003csub\u003e2\u003c/sub\u003e. Therefore, the Gibbs free energy of H\u003csup\u003e*\u003c/sup\u003e can be taken as:\u003c/p\u003e\n \u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ4\" class=\"mathdisplay\"\u003e$$\\text{Δ}{\\text{G}}_{{\\text{H}}^{\\text{*}}}\\text{ = Δ}{\\text{E}}_{{\\text{H}}^{\\text{*}}}\\text{ + 0.24 eV}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe adsorption energy on the surfaces of catalysts was calculated by using equation:\u003c/p\u003e\n \u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ5\" class=\"mathdisplay\"\u003e$$\\text{ΔE = }{\\text{E}}_{\\text{total }}\\text{–}\\text{ }{\\text{E}}_{\\text{surface}} \\text{– }{\\text{E}}_{\\text{absorbate}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere E\u003csub\u003etotal\u003c/sub\u003e, E\u003csub\u003esurface\u003c/sub\u003e, and E\u003csub\u003eabsorbate\u003c/sub\u003e are the total energy of the adsorption state system, the total energy of the pure surface, and the total energy of intermediate, respectively.\u003c/p\u003e\n \u003cp\u003eThe OER process could occur include four elementary steps:\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\text{O}{\\text{H}}^{\\text{–}}\\text{→ O}{\\text{H}}^{\\text{*}}\\text{+ }{\\text{e}}^{\\text{–}}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e ΔG\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\text{O}{\\text{H}}^{\\text{–}}\\text{+ O}{\\text{H}}^{\\text{*}}\\text{→ }{\\text{H}}_{\\text{2}}\\text{O +}{\\text{O}}^{\\text{*}}\\text{+ }{\\text{e}}^{\\text{–}}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e ΔG\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\text{O}{\\text{H}}^{\\text{–}}\\text{+ }{\\text{O}}^{\\text{*}}\\text{→ }{\\text{H}}_{\\text{2}}\\text{O +}{\\text{ OOH}}^{\\text{*}}\\text{+ }{\\text{e}}^{\\text{–}}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e ΔG\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u0026nbsp;\u003cspan class=\"mathinline\"\u003e\\(\\text{OO}{\\text{H}}^{\\text{*}}\\text{+ }{\\text{OH}}^{\\text{–}}\\text{→ }{\\text{O}}_{\\text{2}}\\text{ +}{\\text{H}}_{\\text{2}}\\text{O+ }{\\text{e}}^{\\text{–}}\\)\u003c/span\u003e\u0026nbsp;\u003c/span\u003e ΔG\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003eThe overpotential (η) can be obtained from the Gibbs free energy differences at each step:\u003c/p\u003e\n \u003cdiv id=\"Equ6\" class=\"Equation\"\u003e\n \u003cdiv id=\"FileID_Equ6\" class=\"mathdisplay\"\u003e$$\\text{η}\\text{ = max}\\left(\\text{Δ}{\\text{G}}_{\\text{1}}\\text{, Δ}{\\text{G}}_{\\text{2}}\\text{, Δ}{\\text{G}}_{\\text{3}}\\text{, Δ}{\\text{G}}_{\\text{4}}\\right)\\text{/}\\text{e }\\text{– }\\text{1.23 V}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e6\u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that all data supporting the findings of this study are available in the article and its Supplementary Information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe gratefully acknowledge the support of this research by the National Key R\u0026amp;D Program of China (2023YFA1507204), the National Natural Science Foundation of China (U20A20250, 22179034), the Natural Science Foundation of Heilongjiang Province (ZD2023B002).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary Information\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespondence\u003c/strong\u003e and requests for materials should be addressed to Lei Wang or Honggang Fu.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePublisher\u0026rsquo;s note\u003c/strong\u003e Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eOpen Access\u003c/strong\u003e This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article\u0026rsquo;s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article\u0026rsquo;s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view acopyofthislicence, visit http://creativecommons.org/ licenses/by/4.0/.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eContributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eL.W. and H.F. conceived the idea. Z.L. performed the experiments. D.S. and Y.X. performed the DFT calculations studies. Y.W. and F.S. tested the operando EXAFS experiment and analyzed all the XANES and EXAFS data. L.W. designed and revised the structure and logic of the manuscript. Z.L., L.W., and H.F. wrote the manuscript with input from all co-authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSun, F. et al. Energy-Saving Hydrogen Production by Chlorine-Free Hybrid Seawater Splitting Coupling Hydrazine Degradation. \u003cem\u003eNat\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e\u003cem\u003e Commun\u003c/em\u003e\u003cem\u003e.\u003c/em\u003e \u003cstrong\u003e12\u003c/strong\u003e, 4182 (2021).\u003c/li\u003e\n\u003cli\u003eFan, R. L. et al. Ultrastable Electrocatalytic Seawater Splitting at Ampere-Level Current Density. \u003cem\u003eNat. Sustain\u003c/em\u003e. \u003cstrong\u003e7\u003c/strong\u003e, 158‒167 (2024).\u003c/li\u003e\n\u003cli\u003eKosmala, T. et al. Operando Visualization of the Hydrogen Evolution Reaction with Atomic-Scale Precision at Different Metal\u0026ndash;Graphene Interfaces. \u003cem\u003eNat. 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Energy Mater\u003c/em\u003e. \u003cstrong\u003e13\u003c/strong\u003e, 2203595 (2023).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4286568/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4286568/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe electrocatalysts for high-energy consumed anodic oxygen evolution reaction (OER) especially in water splitting are generally prone to reconfiguration, so the dynamic structural evolution mechanisms should be deeply investigated. Herein, coral-like nanoarray assembled by nanosheets were synthesized via the layered effect of cobalt (Co) and the one-dimensional guiding effect of vanadium (V). The unique structure facilitates the full contact between active sites and electrolyte to enhance the electrocatalytic activity. The hydrogen evolution reaction (HER) and OER activity can be respectively promoted through modulating the electronic structure with nitrogen and phosphate anions. Thus, the assembled anion exchange membrane electrolyzer exhibits a direct current energy consumption of 4.31 kWh Nm\u003csup\u003e\u0026ndash;3\u003c/sup\u003e@250 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e at 70\u0026deg;C. It only required 1.88 V voltage to achieve a current density of 500 mA cm\u003csup\u003e\u0026ndash;2\u003c/sup\u003e with excellent stability over 200 h. Operando synchrotron radiation and Bode phase angle analyses reveal that the dissolution of vanadium species makes the distorted Co-O octahedral to regular octahedral structure during OER, accompanying by a decrease of band gap and a shortening of the Co-Co bond length. Such a structural evolution plays as the key active site for the formation of oxygen-containing intermediates, thereby accelerating the reaction kinetics.\u003c/p\u003e","manuscriptTitle":"Vanadium Dissolution Eliminate the Lattice Distortion of Co-O Octahedron during Oxygen Evolution for Water Splitting","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-02 19:21:18","doi":"10.21203/rs.3.rs-4286568/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d9d84c58-30cb-46e2-89eb-ad973dbb3a34","owner":[],"postedDate":"May 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":31308053,"name":"Scientific community and society/Energy and society/Energy efficiency"},{"id":31308054,"name":"Scientific community and society/Energy and society/Energy supply and demand"}],"tags":[],"updatedAt":"2024-05-22T03:10:27+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-02 19:21:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4286568","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4286568","identity":"rs-4286568","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}