High-Interface Alkalinity Induced by Intercalated Squaric Acid Anions for 700 Hours of Oxygen Evolution at 3 A cm−2

High-Interface Alkalinity Induced by Intercalated Squaric Acid Anions for 700 Hours of Oxygen Evolution at 3 A cm−2 | 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 High-Interface Alkalinity Induced by Intercalated Squaric Acid Anions for 700 Hours of Oxygen Evolution at 3 A cm −2 Bin Zhang, Ruo-Yao Fan, Shanshan Lu, Fuli Wang, Yu-Sheng Zhang, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5261089/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Apr, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract The corrosive acidic interfacial microenvironment caused by rapid multistep deprotonation of the alkaline oxygen evolution reaction (OER) in industrial high-current water electrolysis is one of the key problems limiting activity and stability. Some functional anions derived from electrocatalysis exhibit special functionalities in modulating the catalytic interface microenvironment, but this matter has not received adequate attention in academic discussions. The coordinated squaric acid molecule is revealed to undergo a dissolve-reintercalation process in the alkaline OER, leading to its eventual stabilization within the Fe-doped NiOOH interlayer in the form of squaric acid anions (Sq 2− ) (NiFe-SQ/NF-R). This intercalated Sq 2− stabilizes OH − through multiple hydrogen bond interactions, which is conducive to maintaining high catalytic interface alkalinity. Hence, the interfacial acidification of the prepared NiFe-SQ/NF-R in the alkaline OER process is significantly inhibited, resulting in a tenfold increase in its catalytic durability (from 65 to 700 hours) when exposed to a high current density of 3.0 A cm − 2 , as opposed to traditional NiFe-LDH/NF-R materials. This derived functional anion guarantees the enduring performance of the NiFe-derived electrocatalyst under high current densities by controlling the interfacial alkalinity. Physical sciences/Chemistry/Electrochemistry/Electrocatalysis Physical sciences/Chemistry/Green chemistry/Sustainability Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction With the rapid expansion of the hydrogen energy industry and the wide application of large-scale water electrolysers, 1 – 3 the microenvironmental effect between the electrode and electrolyte interface 4 , 5 in industrial-scale devices has significantly increased. In large-scale, high-current and compact water electrolysis systems, the relationships between the influence of special material transformation pathways, ion conduction modes and interfacial molecule/ion interactions on the local microenvironment of electrodes and their catalytic performance remain unexplored. Further regulation of the dynamic interface microenvironment will help to increase the selectivity and reaction rate of some catalytic processes, which provides new ideas for further improving the activity and stability of electrocatalysts. Ni-Fe-based (oxy)hydroxide stands out as a widely favoured electrocatalyst for the OER under alkaline conditions. 6 – 8 Numerous endeavors have been undertaken to bolster its catalytic performance through methods such as element doping 9 – 11 , morphology manipulation 12 , 13 , strain adjustment 14 , and various other approaches. However, the catalytic interface microenvironment can also have a drastic effect on the apparent catalytic performance. 15 , 16 The focus on the catalyst in the microstructure design alone may prove insufficient to fulfil the demands of practical application requirements. In the violent reaction process of high-current water electrolysis, the multistep deprotonation of the alkaline OER initiates the rapid formation and local accumulation of H + , resulting in the formation of an acidic interfacial microenvironment. This local acidic microenvironment is strongly corrosive to the metal site of Ni-Fe-based (oxy)hydroxide, posing a challenge to enhancing its performance and durability. 17 – 19 As a consequence, promoting the swift transformation and consumption of H + is essential for addressing the abovementioned acid corrosion issue, ensuring favourable alkalinity at the anode interface and further enhancing catalytic activity and stability, particularly during large-current electrolysis operations. While some studies have demonstrated that breaking down Ni-Fe layered double hydroxides (NiFe-LDH) into ultrathin nanosheets 20 or initiating element leaching to loosen the catalyst's outer layer 21 can promote the diffusion of OH − as a proton acceptor to slow the formation of a local acidic microenvironment, the challenge now lies in quickly and adequately consuming such a large amount of H + under a large current. Recent studies by Ranit Ram show that defect structures induced by selectively dissolved WO 4 2− ions can trap and preserve H 2 O and OH − , thus prolonging the catalytic activity of OER electrocatalysts under acidic conditions. 22 Motivated by this discovery, our research aims to incorporate specific functional compounds known as "intermediaries" to stabilize OH − at the electrochemical interface, addressing the challenge of anodic acidification in high-current alkaline OER processes. In this study, we prepared Sq 2− -modified Fe-doped NiOOH as a derived catalytically active layer to drive alkaline OER catalytic processes with ampere-scale currents. Owing to the spatial volume effect of Sq 2− , the increase in the layer spacing of Fe-doped NiOOH promotes the effective diffusion of OH − , which increases the concentration of OH − near the active sites and thus enhances the catalytic activity. The intercalation-adsorbed Sq 2− has been found to stabilize OH − at the interface through multiple hydrogen bonding interactions, thereby preserving high interface alkalinity, which plays a critical role in prolonging the catalytic lifespan, particularly in instances of high current densities. Thus, the NiFe-SQ/NF-R electrode created in this research exhibits an exceptionally low overpotential of 284 mV to reach 1.0 A cm − 2 and demonstrates a remarkably large current stability surpassing 700 hours at 3.0 A cm − 2 . This work demonstrates the feasibility of using the stabilization effect of functional anions on OH − to maintain high anode interface alkalinity and improve catalytic activity and stability, paving the way for the innovative design of large-scale current OER electrocatalysts for industrial applications. Results Structural Design and Characterization The importance of designing more stable large-current OER electrocatalysts from the perspective of improving the local anode alkalinity or weakening the acidic interfacial microenvironment has not been widely recognized, and there is a lack of comprehensive research and literature in this area. Therefore, to further prolong the actual service life and increase the current resistance of anode electrocatalysts in large current industrial water electrolysers, an effective strategy and innovative mechanisms for designing catalyst structures on the basis of real interfacial microenvironments are urgently needed. We are dedicated to developing a more practical Ni-Fe-based alkaline OER electrocatalyst by focusing on improving its activity and stability at large current densities. Our efforts involved creating a consolidated integrated anode using nickel foam (NF) as the self-supporting base and etched substrate. 23 , 24 As illustrated in Fig. 1 a, the Ni-Fe bimetallic squarate-based coordination polymer (NiFe-SQ/NF) was synthesized through a one-step hydrothermal process involving in situ etching of NF with the help of an acidic environment facilitated by SQ, an Fe(NO 3 ) 3 ●9H 2 O, and a polyvinyl pyrrolidone (PVP) solution (Supplementary Table 1). Additional detailed synthesis procedures and reaction equations for the etching processes can be found in the experimental methods section and in the notes section of Supplementary Fig. 1. As shown in Fig. 1 b, NiFe-SQ/NF exhibited a distinct cuboid angular stack structure, growing uniformly and closely on the initially smooth NF surface (Supplementary Fig. 2). The scanning electron microscopy (SEM)-mapping images show that Fe, Ni, O and C are uniformly distributed on the surface of NiFe-SQ/NF (Supplementary Fig. 3). The analysis conducted via inductively coupled plasma‒optical emission spectroscopy (ICP‒OES) revealed that the ratio of iron to nickel in the NiFe-SQ/NF sample was approximately 0.39 (Supplementary Table 2). The typical square structure of the squarate-based coordination polymer is only achievable through the inclusion of ferric nitrate during the synthesis process (Supplementary Fig. 4), which highlights the importance of the purple Fe-based complex and acidic conditions in facilitating the production of NiFe-SQ/NF. The samples synthesized without ferric nitrate (Ni-SQ/NF-R) had poor catalytic activity (Supplementary Fig. 5). X-ray diffraction (XRD) analysis of NiFe-SQ/NF reveals distinctive peaks associated with the Ni-Fe coordination polymer (NiFe(H 2 O) 2 (C 4 O 4 )) 25 – 27 and metallic Ni (JCPDS no. 96-210-0644) (Supplementary Fig. 6), suggesting a straightforward phase composition. Then, cyclic voltammetry (CV) was utilized to initiate the rapid surface electrochemical reconstruction activation process of NiFe-SQ/NF, and NiFe-SQ/NF-R was obtained. Only the peaks of metal Ni were detected in the XRD pattern of NiFe-SQ/NF-R, which may be attributed to the presence of numerous amorphous metal hydroxide/hydroxyl oxide species within the surface reconfigurable layer. Alkaline hydrolysis occurs on the surface of NiFe-SQ/NF during electrochemical anodic activation treatment, causing some Sq 2− to run off and creating a net-like fissure structure in NiFe-SQ/NF-R (Fig. 1 c). These fissures act as beneficial micron-scale channels that increase gas release and electrolyte flux at the electrode surface, particularly under large current conditions. A comparison of the water contact angles of the NiFe-SQ/NF and NiFe-SQ/NF-R surfaces reveals that the electrochemical activation treatment shifts the catalytic surface from hydrophobic to superhydrophilic (Supplementary Fig. 7), promoting rapid wetting and electrolyte diffusion on the electrode. In Supplementary Fig. 8, the SEM maps of NiFe-SQ/NF-R show no significant elemental aggregation, indicating that the electrochemical treatment only excites the superficial species without changing the main structure. SEM images of the NiFe-SQ/NF-R sample cross-sections after the OER show that the square catalyst is closely bound to the outer surface of the nickel foam (Supplementary Fig. 9). This self-etching growth strategy ensures strong adhesion at the interface between the catalyst and substrate. The electrochemical oxidation reconstruction and dissolution of the squaric acid ligand were carried out simultaneously. The dissolution of squaric acid results in an increased presence of defects in the restructured framework (NiFe-SQ/NF-R), which in turn accelerate the reconstruction process. 28 , 29 To illustrate this phenomenon, a comparison was conducted between the electrolyte after CV activation and the KOH solution of Sq 2− , revealing that they have similar Raman characteristic peaks attributed to Sq 2− (Supplementary Fig. 10). 30 , 31 To further investigate the more subtle structural transformation of NiFe-SQ/NF during electrochemical activation, we performed an in-depth examination of the sample via spherical aberration-corrected transmission electron microscopy (AC-TEM). Specifically, in Fig. 1 d, short and disordered lattice fringes can be observed in the outer reconstructed layer of NiFe-SQ/NF-R, which are attributed to metallic hydroxyl oxides. More comprehensive AC-TEM images of NiFe-SQ/NF-R are shown in Supplementary Fig. 11. Following the formation of this special crystalline‒amorphous composite layer, the reconstruction process can be terminated quickly, serving as a protective barrier for the internal coordination polymerization structure. The selected-area electron diffraction (SAED) pattern (Supplementary Fig. 12) for NiFe-SQ/NF-R exhibits similar structural information that matches that of r -NiOOH (JCPDS no. 00-006-0075). Under the same test conditions, NiFe-LDH/NF-R exhibits a longer-range ordered distribution of the (1 0 1) crystal plane (Supplementary Fig. 13), which corresponds to its XRD pattern (JCPDS no. 00-040-0215, Supplementary Fig. 14). The NiFe-LDH/NF composite discussed in this study was prepared via a conventional hydrothermal method. 32 , 33 The in situ Raman analysis reveal that NiFe-LDH/NF undergoes a reconstruction process under the excitation of an oxidation current, leading to the gradual transformation of Ni(OH) 2 (455, 530 cm − 1 ) into (Fe-doped) NiOOH (475, 550 cm − 1 ) (Supplementary Fig. 15). These findings indicate that NiFe-LDH/NF and NiFe-SQ/NF produce similar NiOOH components after electrochemical reconstruction, which are recognized as active species of the OER. The standard spacing of NiOOH (1 0 5) crystal faces is typically measured at 0.209 nm according to the statistical data (JCPDF no. 00-006-0075). However, our actual observations show that the (1 0 5) crystal face of unintercalated NiOOH produced by electrochemical activation is slightly smaller at 0.205 nm under identical test conditions (Supplementary Fig. 16). The small difference from the standard values can be attributed to inevitable structural strain induced by electrochemical activation during the preparation process. The presence of Sq 2− insertion leads to a noticeable broadening of the (1 0 5) crystal face of NiOOH, which is measured at 0.210 nm, as indicated by the blue frame in Fig. 1 e and f, compared with the NiOOH (1 0 5) crystal face without Sq 2− (0.205 nm). At the same time, the NiOOH in situ Raman characteristic peaks of NiFe-SQ/NF also show a peak shift caused by intercalated Sq 2− (Supplementary Fig. 17). The results above demonstrate that the Sq 2− intercalation-modified Fe-doped NiOOH obtained by electrochemical directional reconstruction results in a larger layer space (Fig. 1 g), serving as a wide electrolyte diffusion channel and an ideal reaction region. The element mapping images of NiFe-SQ/NF-R under high-resolution AC-TEM reveal a homogeneous distribution of Ni, Fe, O, and C (Fig. 1 h-l), suggesting that the electrochemical activation treatment does not lead to phase segregation of the catalytic components. Electrocatalytic oxygen evolution performance The electrochemical properties of all the samples in the standard three-electrode and membrane electrode systems were investigated in depth. Purified KOH was used as the electrolyte during the test. Supplementary Fig. 18 shows that the ultrafast surface reconstruction process driven by electrochemistry allows the catalytic surface to achieve a state of relative equilibrium after ten cycles of activation, resulting in consistent and stable catalytic properties. In Fig. 2 a, NiFe-SQ/NF-R demonstrates desirable overpotentials of 259 mV and 284 mV to achieve current densities of 500 mA cm − 2 and 1000 mA cm − 2, positioning it as a leading electrocatalyst for efficient OER at large current levels, which are lower than those of NiFe-LDH/NF-R (Fig. 2 d). On the basis of the previously mentioned results, we believe that such excellent catalytic properties are due to micron-scale transport channels, wider layer spaces, and faster catalytic reaction kinetics, which are caused by Sq 2− intercalation. Comparative experiments (Supplementary Fig. 19) were carried out to confirm the limited influence of Sq 2− adsorption at the catalytic interface on the catalytic performance of the OER. The increase in Sq 2− did not result in a noteworthy increase in the oxidation current, which also proves that Sq 2− is not further oxidized in an alkaline environment. Upon comparing the linear sweep voltammetry (LSV) curves of NiFe-SQ/NF-R and NiFe-LDH/NF-R, NiFe-SQ/NF-R exhibits notably larger Ni 2+ /Ni 3+ oxidation peaks, suggesting that the intercalation effect of Sq 2− can promote the formation and stabilization of NiOOH. 34 , 35 The reduced Tafel slope observed for NiFe-SQ/NF-R (50 mV dec − 1 ) (Fig. 2 b) indicates that the presence of intercalated adsorbed Sq 2− enhances the catalytic reaction kinetics. The interfacial charge transfer capability of the samples was assessed via electrochemical impedance spectroscopy (EIS). NiFe-SQ/NF-R exhibited the smallest charge transfer resistance (R ct ) (Fig. 2 c), which suggests that the interlayer Sq 2− facilitates rapid transfer of the interface charge to enhance the OER. The electrochemical active surface area (ECSA) of NiFe-SQ/NF-R (99.75 cm 2 ) and NiFe-LDH/NF-R (46.00 cm 2 ) were determined from their CV curves at different sweep speeds (Supplementary Fig. 20a-c). Analysis of the polarization curves normalized by the ECSA reveals that NiFe-SQ/NF-R demonstrates superior intrinsic catalytic activity (Supplementary Fig. 20d). The Faradaic efficiency is calculated by measuring the volume of oxygen produced by NiFe-SQ/NF-R during electrolysis (drainage method). The experimental findings, illustrated in Supplementary Fig. 21, exhibit a notable proximity between the observed data and the theoretical values derived from Faradaic's principles of electrolysis. This yields a Faradaic efficiency nearing 96%, suggesting that the increased current density stems from the OER process. In other words, the outstanding alkaline OER performance of NiFe-SQ/NF-R is mainly attributed to the intercalation of Sq 2− , which promotes increased NiOOH generation, increases the number of OH − diffusion channels, expedites interfacial electron transfer, and provides excellent intrinsic catalytic activity. The CoFe-SQ/CF-R and Fe-SQ/IF-R samples were effectively synthesized through similar methods using cobalt foam (CF) and iron foam (IF) (Supplementary Fig. 22). Our proposed synthesis method has been validated for universal applicability, making it well suited for widespread industrial implementation. The multistep chronopotentiometry (CP) step test diagram illustrates that NiFe-SQ/NF-R can adjust to fluctuating current (Supplementary Fig. 23a). Additionally, NiFe-SQ/NF-R can maintain stable catalytic performance for more than 100 h at consistent current densities of 100 mA cm − 2 and 500 mA cm − 2 (Supplementary Fig. 23b) while retaining its original catalytic structure even after this duration (Supplementary Fig. 23c-f). The catalytic activities of NiFe-SQ/NF-R and NiFe-LDH/NF-R were evaluated at different temperatures (Supplementary Fig. 24a and b) because of the observed increase in the local temperature near the anode under high current density conditions. The findings revealed a considerable increase in the catalytic activity of both compounds with increasing temperature. To mitigate the influence of temperature, rigorous measures were taken to maintain a consistent temperature via a temperature-equalizing apparatus during high-current assessments. Analysis of the Arrhenius plot indicated that NiFe-SQ/NF-R exhibited a lower apparent electrochemical activation energy (Ea) 36 than did NiFe-LDH/NF-R (Supplementary Fig. 24c). Further examination was conducted on the long-term stability of NiFe-SQ/NF-R and NiFe-LDH/NF-R when subjected to a persistent large current density of 3.0 A cm − 2 . As depicted in Fig. 2 e, conventional NiFe-LDH/NF-R can only endure approximately 65 hours of CP testing at 3.0 A cm − 2 , whereas NiFe-SQ/NF-R exhibits remarkable stability for more than 700 hours. After observing the surface morphology of the electrocatalysts before and after the large-current stability test via SEM, despite undergoing 700 h of high-current testing, the surface structure of NiFe-SQ/NF-R does not exhibit significant dissolution or large areas falling off, which is a stark difference from the incomplete catalytic surface of NiFe-LDH/NF-R after 65 h of testing (illustration of Fig. 2 e). While some potassium salt deposits are visible on the surface of NiFe-SQ/NF-R during the drying process, altering its morphology is not expected to greatly impact its stability. In addition, under industry-relevant conditions (30 wt% KOH, 60°C), NiFe-SQ/NF-R also exhibits lower battery voltages and better stability than typical NiFe-LDH/NF-R (Supplementary Fig. 25). Under simulated industrial conditions, the NiFe-SQ/NF-R we prepared is comparable to other reported excellent catalytic electrodes (Supplementary Table 3). Therefore, the sudden deactivation of NiFe-LDH/NF-R is due mainly to structural collapse and surface degradation caused by the acidic interfacial microenvironment. Building upon the preceding characterization findings, the distinctive function of intercalated Sq 2− in maintaining high interface alkalinity results in the preservation of the structural integrity of NiFe-SQ/NF-R, notably enhancing its stability under high-current conditions. Next, we integrated NiFe-SQ/NF-R as a self-supporting anode into an anion exchange membrane water electrolyzer (AEMWE) to investigate the comprehensive performance of water electrolysis. Notably, Fig. 2 f shows that the NiFe-SQ/NF-R electrode outperforms the NiFe-LDH/NF-R electrode, operating at a lower cell voltage of 2.13 V to achieve a large current of 3.0 A cm − 2 , compared with the requirement of 2.44 V for NiFe-LDH/NF-R. Compared with findings in other studies, the utilization of AEMWE to attain such elevated levels of current density represents a cutting-edge approach (Fig. 2 g and Supplementary Table 4). AEMWE combined with NiFe-SQ/NF-R demonstrates stability at a high current density of 1.0 A cm − 2 , suggesting promising application prospects within membrane electrode systems (Supplementary Fig. 26). Structural source of long-term stability for high currents. The strong dissolution tendency of Fe elements in the OER process is also an important factor affecting the stability of OER electrocatalysts. 37 , 38 Consequently, a meticulous analysis of the electronic environment and coordination configuration of NiFe-SQ/NF-R was carried out via X − ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure energy spectrum (XAFS) methods. The results depicted in Fig. 3 a illustrate a slight shift in the Ni 2+ 2 p 3/2 and Ni 3+ 2 p 3/2 peaks between NiFe-SQ/NF-R and NiFe-LDH/NF-R, implying a close resemblance of the electronic configuration surrounding the Ni sites in both. Nonetheless, discernible distinctions were observed in the environments of the Fe sites. In the K -edge XANES spectrum of Fe, compared with that of NiFe-LDH/NF-R, the preedge peak intensity of NiFe-SQ/NF-R is significantly greater, indicating that there are coordination vacancies near the Fe sites 39 (Fig. 3 b). The wavelet transform (WT) contour map of NiFe-SQ/NF-R illustrates unique coordination features linked to Fe-O and Fe-M (Fig. 3 c). In more detail, the K -edge extended X-ray absorption fine structure (EXAFS) spectra of Fe show that the characteristic peaks attributed to both the Fe-O (1.5 Å) and Fe-M (2.7 Å) shells in NiFe-SQ/NF-R show significant downwards trends (Fig. 3 d). Upon examination, it is determined that the coordination number in proximity to the Fe sites within NiFe-SQ/NF-R is notably lower than that near the Fe sites in NiFe-LDH/NF-R (Supplementary Table 5). This disparity is linked to the emergence of vacancies surrounding the Fe site, as the electron paramagnetic resonance (EPR) results show that the signal strength of NiFe-SQ/NF-R is significantly stronger than that of NiFe-LDH/NF-R under the same conditions (Supplementary Fig. 27). The detailed analytical fitting procedures are depicted in Supplementary Fig. 28. The removal of squaric acid ligands from the primary framework results in an increased presence of vacant sites in the hydroxyl oxide derivatives obtained through reconstruction. These vacancies can buffer the lattice distortion of the Fe site to reduce the dissolution tendency of Fe, thereby preventing phase segregation of Fe. 35 Therefore, the presence of coordination vacancies within NiFe-SQ/NF-R plays a pivotal role in safeguarding the integrity of the Fe sites, thereby significantly contributing to its superior stability. In addition to the coordination environment, the dynamic evolution of the catalytic structure and electrode interface microenvironment also greatly influences the catalytic behavior of metal centers. This research delves into a detailed examination of the electrochemical structure evolution and interface microenvironment formation mechanism of NiFe-SQ/NF-R and NiFe-LDH/NF-R through in situ Raman and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Under alkaline conditions, the diffusion of OH − dominates the Ni(OH) 2 +OH − ↔NiOOH + H 2 O + e − reaction. By applying the Randles–Sevick equation, the effect of the scanning rate on the oxidation peak current density was investigated (Fig. 4 a) 40 . The results show that NiFe-SQ/NF-R has improved OH − diffusion kinetics, which is a key element in facilitating the generation of NiOOH and improving catalytic activity. Considering the structural features of NiFe-SQ/NF-R, it is reasonable to speculate that the swift OH − diffusion capability stems from the external micron-scale channel structure and the increased interlamellar spacing resulting from internal Sq 2− intercalation. In Fig. 4 b, the initial NiFe-SQ/NF structure displays a prominent peak at 1492 cm − 1 , which is indicative of structural C − O bonds (O − C−C − O str ) and represents saturated coordination between SQ and the metal center. Following the CV-driven electrochemical reconstruction process, the O − C−C − O str peak vanished from the catalytic surface, whereas a new O − C−C − O ad associated with Sq 2− emerged at approximately 1560 cm − 1 41, 42 . The wide peak at approximately 3300 cm − 1 is associated with the O − H stretching vibration pattern of asymmetric hydrogen bonds resulting from the interaction of OH − with adsorbed Sq 2− . The magnitude of these peaks increases proportionally to the level of activation, as the incorporation of Sq 2− leads to a gradual expansion of the Fe-doped NiOOH layer, facilitating enhanced interlayer diffusion and the steady presence of more OH − . Even after conducting 20 CV activation scans, the peaks at 1560 cm − 1 and 3300 cm − 1 remained present, suggesting stable intercalation and adsorption of Sq 2− between the layers of the sample. In the CV activation process of NiFe-LDH/NF, no significant change in the peak at approximately 3300 cm − 1 (Supplementary Fig. 29) was found, but the peaks of NiFe-SQ/NF-R were significantly enhanced during activation, further highlighting the important role of Sq 2− in stabilizing OH − . The structural evolution of NiFe-SQ/NF during the electrochemical reconstruction process can be deduced as follows: the alkali hydrolysis process first disrupts the coordination bond between the SQ ligand and the metal center, enabling the uncoordinated C − O group to establish an anchoring effect with OH − through hydrogen bonding. In addition, Sq 2− interacts with M-OH (M: Fe or Ni) at the metal-catalyzed interface to create adsorption-bonded O − C−C − O ad for a stable interlayer insertion. The analysis of the ATR-FTIR data further validates the evolution process of the structure, supporting previous findings from spherical aberration electron microscopy. We employed an improved in situ Raman electrochemical cell to accurately examine the interfacial H 2 O/OH − structure near the electrode surface. Three different hydrogen-bonded water structures are deconvolved: 4 − HBŸH 2 O (~ 3200 cm − 1 ), 3 − HBŸH 2 O/OH − (~ 3400 cm − 1 ) and 0 − HBŸH 2 O (~ 3600 cm − 1 ). 22,43,44 Sq 2− , with four uncoordinated O*, is able to form more complex hydrogen bond interactions with interfacial H 2 O and OH − to regulate the interfacial water structure. This resulte in distinct O‒H stretching patterns in the NiFe-SQ/NF-R samples in contrast to those in the NiFe-LDH/NF-R samples (Fig. 4 c and d). As shown in Supplementary Fig. 30, the ratios of 4-HBŸH 2 O and 3-HBŸH 2 O at the NiFe-SQ/NF interface consistently increased with prolonged testing duration, whereas they notably decreased at the NiFe-LDH/NF interface. These results suggest that the inserted Sq 2− has the ability to regulate interfacial water and capture OH − , which is conducive to alleviating local acidification during the OER. Changes in the interface alkalinity of NiFe-SQ/NF and NiFe-LDH/NF were observed through in situ Raman spectroscopy, utilizing the phosphoric acid-sensitive pH characteristics. The principle of this method is that as the pH increases, the phosphate species can undergo the conversion of H 3 PO 4 → H 2 PO 4 − → HPO 4 2− → PO 4 3− (illustration of Fig. 5 a). 45 The electrolyte with a phosphate compound served as a pH probe during in situ Raman analysis. Through the correspondence between the characteristic Raman vibration peak of the phosphate species and pH, we can establish a linear relationship between pH and the vibration peak. This monitoring is crucial for understanding the local acidification microenvironment of Ni-Fe-based layered materials during anode testing, which is a significant issue that impacts activity and stability, particularly under high current density testing conditions. During in situ testing, spectral data were collected at 4-minute intervals under a consistent current density of 10 mA cm − 2 in a solution of KOH and phosphoric acid at pH 12. By observing the variation in the characteristic peaks of PO 4 (936 cm − 1 ), PO 3 (990 cm − 1 ) and P(OH) (857 cm − 1 ), we obtain the local pH values of NiFe-LDH/NF and NiFe-SQ/NF. A low vibrational transition energy leads to a weak peak signal of P(OH). Nevertheless, this minimal effect does not hinder the formulation of conclusions. Rapid reduction of the local pH from 12 to 8 in NiFe-LDH/NF was accomplished within a short duration of 12 min (Fig. 5 a). This provides direct evidence that the layered structure of NiFe-LDH tends to promote an acidic microenvironment, pinpointing a key factor contributing to its limited large current stability. Surprisingly, during the initial 52 minutes of the examination, the regional pH of NiFe-SQ/NF remains constant at 12, which then transitions to 11 by the 56th minute (Fig. 5 b), with its acidification rate at the interface notably lagging behind that of NiFe-LDH (Fig. 5 d). The primary factor contributing to this outcome is the tendency of the intercalation-adsorbed Sq 2− to trap and stabilize OH − . In Fig. 5 c, two peaks at approximately 1554 and 1640 cm − 1 are identified, which are attributed to the asymmetric C–O vibrations ((M-)C–O and C = O) of adsorbed Sq 2− (O − C−C − O ad ), respectively. Over time, these peaks demonstrated a slight tendency toward augmentation, suggesting an increase in the presence of Sq 2− adsorbed within the layers with increasing reconstruction process. Therefore, the presence of intercalated adsorbed Sq 2− is pivotal in maintaining localized interface alkalinity, thereby significantly prolonging the catalytic lifespan by tenfold under high currents of 3.0 A cm − 2 . As shown in Fig. 5 e, the above analysis clearly reveals that the sluggish surface acidification rate of NiFe-SQ/NF stems from two key factors. First, in terms of surface structure composition, the dispersed micron-scale diffusion channels and expanded layer spacing directly facilitated the internal diffusion of OH − and the outwards transfer of H + . Second, when considering internal structural groups, Sq 2− as "intermediaries", is adept at trapping and steadying OH − , thereby expediting the conversion of H + and consequently delaying the emergence of a localized acidic microenvironment, thus sustaining increased interface alkalinity. In short, this regulatory mechanism of interface alkalinity is particularly important for optimizing the local interfacial microenvironment under harsh conditions characterized by a high current. The theoretical source of enhanced catalytic activity The increase in catalytic activity through the internal mechanism of interlaminar Sq 2− anions was further investigated via spin polarization density functional theory (DFT) calculations. The peaks corresponding to Ni(OH) 2 (455, 530 cm − 1 ) and NiOOH (476, 553 cm − 1 ) are evident in Fig. 6 a, suggesting that NiFe-SQ/NF underwent surface restructuring to facilitate the formation of NiOOH, a notably potent species. The electrochemical reconstruction processes of NiFe-LDH/NF and NiFe-SQ/NF led to the formation of Fe-doped NiOOH (Fe-NiOOH(NiFe-LDH/NF-R)) and Fe-doped NiOOH with intercalated Sq 2− (Fe-NiOOH(Sq 2− )(NiFe-SQ/NF-R)), respectively, which served as the primary active layers. After a rounded analysis, it is clear that the model architecture harbors promising active sites denoted as Ni − O−Fe − O−Ni and Ni − O−Ni − O−Ni. As shown in Supplementary Fig. 31, computational assessments were conducted to determine the optimal OER pathways for Fe-NiOOH(Sq 2− ) (NiFe-SQ/NF-R) and Fe-NiOOH(NiFe-LDH/NF-R) at these designated active sites. For the Ni − O−Fe − O−Ni site in Fig. 6 b, the rate-determining step (RDS) of the OER is the transition from *O to *OOH, and the barrier is reduced from 3.37 eV to 2.76 eV through the incorporation of Sq 2− anions. This is because interlayer Sq 2− increases the effective concentration of OH − near the active site through multiple hydrogen bonds interacting with OH − , which facilitates the formation of key *OOH intermediates. Additionally, the deprotonation barrier of the *OOH step in Fe-NiOOH(Sq 2− ) (NiFe-SQ/NF-R) is notably lower at 0.01 eV than that in Fe-NiOOH(NiFe-LDH/NF-R), which is 1.07 eV. This result indicates that Sq 2− significantly accelerates the *OOH dehydrogenation process because both the unpaired O* sites and the captured OH − serve as proton acceptors to ensure the efficiency of the deprotonation process. In this study, the predominant active site for the OER was identified as the Ni − O−Fe − O−Ni site. This site is proposed to enable an Sq 2− led efficient pathway, which supports the activation and stabilization of *OOH intermediates and assists in their deprotonation. Consequently, this mechanism reduces the reaction energy barrier and increases the catalytic effectiveness. Upon examination of the density of states (DOS) images, it was noted that the electron state density of Fe-NiOOH(Sq 2− ) (NiFe-SQ/NF-R) surpasses that of Fe-NiOOH(NiFe-LDH/NF-R) at the Fermi level, suggesting that the intercalated Sq 2− plays a significant role in enhancing the electron transport efficiency (Fig. 6 c). The electron state density of Fe within Fe-NiOOH(Sq 2− ) (NiFe-SQ/NF-R) is notably lower than that of Fe in Fe-NiOOH(NiFe-LDH/NF-R) across a wide energy range. This observed disparity suggests a reduction in the electron cloud density surrounding the Fe orbital subsequent to the Sq 2− intercalation procedure. This is consistent with the conclusion drawn from the differential charge density map (Supplementary Fig. 32). The orbital state densities of Fe and O in Fe-NiOOH(Sq 2− ) (NiFe-SQ/NF-R) demonstrate closer overlapping resonances, leading to stronger electron interactions. 34 , 46 Consequently, our as-designed NiFe-SQ/NF-R catalytic interface facilitates a comprehensive improvement in the catalytic activity for the OER. Conclusion In summary, we present a novel approach for controlling the local alkalinity of the interfacial microenvironment under large current conditions by incorporating steadily adsorbed Sq 2− anions between the layers of Fe-doped NiOOH. Intercalated Sq 2− facilitates the activation and stabilization of *OOH intermediates and assists in their deprotonation, thereby increasing their catalytic activity. The captured OH − , which acts as a potent proton receptor, facilitates the rapid consumption of H + , postponing the formation of acidic microenvironments and thereby bolstering the durability of the material when subjected to high-current conditions. As a result, the NiFe-SQ/NF-R demonstrates a lower overpotential (284 mV at 1.0 A cm − 2 ), a decreased Tafel slope (50 mV dec − 1 ), and reliable long-term stability (700 hours under 3.0 A cm − 2 ). This research successfully incorporated functional ligand-derived anions into layered materials, leading to enhanced performance in OER materials by minimizing the local acidic microenvironment and maintaining high interfacial alkalinity, especially under large current conditions. Methods Materials. Ferric nitrate nonahydrate (Fe(NO 3 ) 3 ●9H 2 O), nickel nitrate hexahydrate (Ni(NO 3 ) 2 ·6H 2 O), cobaltous nitrate hexahydrate (Co(NO 3 ) 2 ·6H 2 O), polyvinylpyrrolidone (PVP, K30), ammonium fluoride (NH 4 F), urea (CO(NH 2 ) 2 ), acetone (CH 3 COCH 3 ), ethanol (C 2 H 5 OH), hydrochloric acid (HCl, 36%~38%) and potassium hydroxide (KOH) were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid, C 4 H 2 O 4 ) was acquired from Macklin Chemical Reagent Co., Ltd., Shanghai, China. Nickel foam (NF) (aperture: 110 ppi, thickness: 1.5 mm) was obtained from Kunshan Lvchuang Electronic Technology Co., Ltd. Pt/C (20 wt%, Macklin Chemical Reagent Co. Ltd.) and Nafion (5 wt%, Sigma‒Aldrich) were also used. Deionized water was used in all the experiments. All the chemicals used in this study were of analytical grade and were used without further purification. Synthesis of NiFe-SQ/NF-R. NF (2.5 cm*3.5 cm*1.5 mm) was initially subjected to ultrasonic cleaning in acetone, hydrochloric acid (1 M), and ethanol, each for 15 minutes. Thorough removal of oxides and organic residues from the NF surfaces played a crucial role in the preparation of the electrocatalysts for this study. The NF was subsequently placed in a solution comprising 0.3000 g of PVP, 2.5 mmol of squaric acid, 0.5 mmol of Fe(NO 3 ) 3 ●9H 2 O, and 30 mL of deionized water. The mixture was subsequently transferred to a 100 mL Teflon vessel sealed with a stainless autoclave, heated to 120°C, and maintained for 6 hours. The resulting dark green NiFe-SQ/NF sample was obtained after rinsing with deionized water and drying in a vacuum oven at 60°C. Finally, NiFe-SQ/NF underwent electrochemical activation in 1 M KOH to yield NiFe-SQ/NF-R. The specific activation process involved cyclic voltammetry in a standard three-electrode configuration, with a scanning range of 0 − 1.488 V vs. RHE, a scanning rate of 10 mV s − 1 , and a total of 10 cycles. Synthesis of NiFe-LDH/NF-R. The process of synthesizing NiFe-LDH/NF-R closely mirrors that of NiFe-SQ/NF-R, differing primarily in replacing the solution with 1.0 mmol of Ni(NO 3 ) 2 ●6H 2 O, 0.5 mmol of Fe(NO 3 ) 3 ●9H 2 O, 2.5 mmol of NH 4 F, 6 mmol of CO(NH 2 ) 2 , and 30 mL of deionized water. Structural characterization. The crystal phase of the catalyst was analysed via X-ray diffraction (XRD) with Cu Kα radiation ( λ = 1.54 Å) on a Rigaku D/max-2500 pc apparatus. The morphological characteristics of the samples were examined by scanning electron microscopy (SEM) with a Hitachi S-4800 instrument. The elemental composition and distribution of the catalyst were evaluated via energy dispersive spectroscopy (EDS) in conjunction with a Hitachi S-4800 instrument. The powder samples were dissolved in dilute acid for inductively coupled plasma‒optical emission spectroscopy (ICP‒OES) (Agilent 5110 (OES)) to obtain the exact contents of Fe and Ni. Electron paramagnetic resonance (EPR) data were collected on a German-Bruker-A300 spectrometer. Spherical aberration-corrected transmission electron microscopy (AC − TEM) images and elemental maps were obtained via an aberration − corrected transmission electron microscope (Titan Themis Cubed G2 300) operating at 300 kV. The contact angle of ultrapure water on the electrode was measured at room temperature by employing a dynamic contact angle system (JC2000C1). X − ray photoelectron spectroscopy (XPS) data were calibrated to the C 1 s peak energy of 284.8 eV via a Thermo Fisher Scientific II spectrometer equipped with an Al Kα source (1486.6 eV). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was conducted with a BRUKER ALPHA II infrared spectrometer. In situ Raman spectroscopy was performed in electrolytes of KOH and H 3 PO 4 at pH 12 using the samples and platinum wire as the working and counter electrodes, respectively. The laser excitation wavelength used during the measurements was 532 nm, a constant current density of 10 mA cm − 2 was maintained by the electrochemical workstation, and spectral data were collected every 4 minutes. The X-ray absorption fine structure energy spectrum (XAFS) was obtained at the Shanghai Synchrotron Radiation BL13SSW station (SSRF, 3.5 GeV, 220 mA, Si(111) twin). Data acquisition is carried out via a small detector under environmental conditions. The Athena module in the IFEFFIT package is used for standard XAFS data processing. Electrochemical measurements. This investigation examined the performance of various electrocatalysts in the OER utilizing a standard three-electrode configuration in an alkaline environment (KOH) with a GamryInterface 3000E workstation. The synthesized electrocatalysts (1.0 cm 2 ), a Pt sheet and a mercury oxide electrode were used as the working electrode, opposite electrode and reference electrode, respectively. All potentials were converted to the reversible hydrogen electrode (RHE) via the following equation: Linear sweep voltammetry (LSV) was carried out at a rate of 5.0 mV s − 1 with manual iR compensation, unless otherwise stated. Specifically, the resistance of the system is tested first and then compensated manually at a value of 95%. Electrochemical impedance spectroscopy (EIS) tests spanned a frequency range of 10 5 -0.1 Hz at 1.48 V vs. RHE. The large current performance and stability were evaluated via a GamryInterface 5000E workstation assisted by stirring and automatic circulation refill devices. Membrane electrode measurement. NiFe-SQ/NF-R (1.0 cm 2 ) and Pt/C (1.0 cm 2 , 0.5 mg cm − 2 ) were used as the anode (OER) and cathode (HER), respectively. KOH (1 M) was circulated through the membrane electrode at a flow rate of 50 mL min − 1 . The full-cell OER performance of the AEM was evaluated on a GamryInterface 5000E workstation at 25°C. Density functional theory calculations. Spin-polarized density functional theory (DFT) calculations were conducted employing the Vienna ab initio simulation package (VASP) to explore the alkaline OER. The calculations were carried out via the projector augmented wave method with a cut-off energy of 400 eV and the Perdew–Burke–Ernzerhof functional. To consider the impact of the 3 d electrons of the Ni and Fe atoms, the DFT + U method was utilized, with effective U values of 5.5 eV 47 and 5.3 eV 48 , respectively. Moreover, the DFT-D3 method was applied to correct for the influence of the 3 d electrons of Ni atoms and van der Waals interactions. 49 This study involved cleaving two layers of NiOOH (0 0 1) facets with a vacuum layer of 20 Å and incorporating 16% of the Ni atoms substituted with Fe atoms to form the Fe-doped NiOOH (Fe-NiOOH(NiFe-LDH/NF-R)) model. Furthermore, Sq 2− was introduced between the layers to create Fe-doped NiOOH with an intercalated Sq 2− (Fe-NiOOH(Sq 2− )(NiFe-SQ/NF-R)) model. All the models underwent full relaxation with an energy convergence criterion of 10 − 5 eV and a force convergence criterion of 0.02 eV Å −1 . The Γ point was utilized in the K-point mesh, and the adsorption energy (E ads ) was computed via formula 2. E total , E substrate and E adsorbate represent the energies of the adsorption structure, substrate and adsorbate, respectively. The free energies were calculated via the following formula 3: G , E DFT , ZPE and TS represent the free energy, energy from DFT calculations, zero-point energy and entropic contributions, respectively. Declarations Data availability The data that support the plots within this paper are available from the corresponding author upon reasonable request. The source data underlying Figs. 2 −6 are provided as a Source Data file. Source data are provided with this paper. Competing interests The authors declare no competing interests. Author contributions B.D. and Y.C. conceived the paper and directed the research. R.F., F.W. and Y.Z. designed and carried out the experiments. S.L. contributed to the in situ Raman spectra. D.B. and Y.C. performed the density functional theory calculations. B.Z. provide discussion and sorted the writing ideas. R.F. wrote the paper. D.B. and B.Z. revised the manuscript with comments from all the authors. Acknowledgments This work is financially supported by the National Natural Science Foundation of China (52174283 and 52274308) and an innovation fund project for graduate students of China University of Petroleum (East China) supported by "the Fundamental Research Funds for the Central Universities" (No. 24CX04022A). We acknowledge beamline BL13SSW at the Shanghai Synchrotron Radiation Facility for XAFS experimental support. References Oener SZ, Foster MJ, Boettcher SW (2020) Accelerating water dissociation in bipolar membranes and for electrocatalysis. 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ACS Catal 7:5329–5339 Zhou LY, Cao SB, Zhang LL, Xiang G, Zeng XF, Chu GW, Chen JF (2022) Quantitatively evaluating activity and number of catalytic sites on metal oxide for ammonium perchlorate decomposition. AIChE J 68:e17582 Grimme S, Antony J, Ehrlich S, Krieg H (2010) A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J Chem Phys 132:154104 Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.pdf Sourcedata.xlsx Source data underlying Figs. 2-6 Cite Share Download PDF Status: Published Journal Publication published 10 Apr, 2025 Read the published version in Nature Communications → 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. 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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-5261089","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":417865196,"identity":"da1f8a4f-f9fc-4043-ab43-23f1d4d77318","order_by":0,"name":"Bin Zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAy0lEQVRIiWNgGAWjYBACAwYeEGXDwNgApHhI0JImQbKWwxJgHlFazPnPHvxc8Ot8HfOMBMYHb9sY5M0JabFsOJcsPbPvtgTjjARmw7ltDIY7Gwg57GCPgTRvD1gLmzRvG0OCwQFCWg7zGP/m7TkH0sL+mzgtx3jMpHl+HADbwkyUFsseHjNr3oZkycaeh82Sc85JGG4gpMWc/4zxbZ4/dvyG7ckHP7wps5EnaAsYMLYxMBg2gCNTghj1IPCHgUGeWLWjYBSMglEw8gAADxE8LaFiNyQAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0003-0542-1819","institution":"Tianjin University","correspondingAuthor":true,"prefix":"","firstName":"Bin","middleName":"","lastName":"Zhang","suffix":""},{"id":417865197,"identity":"62db77db-2dc4-4530-8a52-89a6601b6208","order_by":1,"name":"Ruo-Yao Fan","email":"","orcid":"","institution":"China University of Petroleum (East China)","correspondingAuthor":false,"prefix":"","firstName":"Ruo-Yao","middleName":"","lastName":"Fan","suffix":""},{"id":417865198,"identity":"30132e7b-4a88-41b1-90b1-27459e0e3944","order_by":2,"name":"Shanshan Lu","email":"","orcid":"","institution":"Tianjin University","correspondingAuthor":false,"prefix":"","firstName":"Shanshan","middleName":"","lastName":"Lu","suffix":""},{"id":417865199,"identity":"3eedebd8-78ba-4f8c-9537-4fc773896365","order_by":3,"name":"Fuli Wang","email":"","orcid":"","institution":"China University of Petroluem Huadong-Qingdao Campus","correspondingAuthor":false,"prefix":"","firstName":"Fuli","middleName":"","lastName":"Wang","suffix":""},{"id":417865200,"identity":"73029b7a-ee82-47b3-b2bf-1a57fd22292a","order_by":4,"name":"Yu-Sheng Zhang","email":"","orcid":"","institution":"China University of Petroleum (East China)","correspondingAuthor":false,"prefix":"","firstName":"Yu-Sheng","middleName":"","lastName":"Zhang","suffix":""},{"id":417865201,"identity":"5daa44b2-35cf-4a17-861f-310d3bc54d8f","order_by":5,"name":"Mirabbos Hojamberdiev","email":"","orcid":"","institution":"Technische Universität Berlin","correspondingAuthor":false,"prefix":"","firstName":"Mirabbos","middleName":"","lastName":"Hojamberdiev","suffix":""},{"id":417865202,"identity":"2aadef05-349d-455a-a03a-3754b5a94ced","order_by":6,"name":"Yongming Chai","email":"","orcid":"","institution":"State Key Laboratory of Heavy Oil Processing, Key Laboratory of Catalysis, China National Petroleum Corp. (CNPC) China University of Petroleum (East China), Qingdao 266555, P. R. China.","correspondingAuthor":false,"prefix":"","firstName":"Yongming","middleName":"","lastName":"Chai","suffix":""},{"id":417865203,"identity":"55732333-7dec-4307-91a7-69890b5850f0","order_by":7,"name":"Bin Dong","email":"","orcid":"https://orcid.org/0000-0002-4817-6289","institution":"China University of Petroleum (East China)","correspondingAuthor":false,"prefix":"","firstName":"Bin","middleName":"","lastName":"Dong","suffix":""}],"badges":[],"createdAt":"2024-10-14 12:25:51","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5261089/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5261089/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-025-58623-7","type":"published","date":"2025-04-10T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":77322452,"identity":"c65b21b2-a1fa-4c1c-81d6-663658ec1ac4","added_by":"auto","created_at":"2025-02-27 11:49:18","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":35353248,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSynthesis strategy and physical characterization of NiFe-SQ/NF-R. a\u003c/strong\u003e Diagram of the preparation process of NiFe-SQ/NF-R.\u003cstrong\u003e \u003c/strong\u003eSEM images of \u003cstrong\u003eb\u003c/strong\u003e NiFe-SQ/NF and \u003cstrong\u003ec\u003c/strong\u003e NiFe-SQ/NF-R. \u003cstrong\u003ed\u003c/strong\u003e AC-TEM images with color processing of NiFe-SQ/NF-R (taken from the square morphology region. ). \u003cstrong\u003ee \u003c/strong\u003eAC-TEM image of NiFe-SQ/NF-R. \u003cstrong\u003ef\u003c/strong\u003e Corresponding autocorrelated lattice fringe pattern of NiOOH(Sq\u003csup\u003e2−\u003c/sup\u003e) (1 0 5). \u003cstrong\u003eg\u003c/strong\u003e Structure diagram of Fe-doped NiOOH(Sq\u003csup\u003e2−\u003c/sup\u003e). \u003cstrong\u003eh\u003c/strong\u003e HAADF TEM image and \u003cstrong\u003ei-l \u003c/strong\u003eelemental mappings of Ni, Fe, O, and C elements for NiFe-SQ/NF-R.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/75b727845e9641e051c0b1ac.png"},{"id":77322449,"identity":"ac03dadc-42ea-4da7-8be4-9e12a8f62a6a","added_by":"auto","created_at":"2025-02-27 11:49:18","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3072883,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEnhanced catalytic activity and stability of the OER at high currents. a\u003c/strong\u003e LSV curves for NiFe-SQ/NF-R, NiFe-LDH/NF-R, and NF-R in 1 M KOH at a scan rate of 5.0 mV s\u003csup\u003e−1\u003c/sup\u003e. \u003cstrong\u003eb\u003c/strong\u003e Corresponding Tafel slopes. \u003cstrong\u003ec\u003c/strong\u003e Nyquist diagrams of NiFe-SQ/NF-R, NiFe-LDH/NF-R, and NF-R at a constant potential of 1.48 V vs. RHE. \u003cstrong\u003ed \u003c/strong\u003eOverpotentials of NiFe-SQ/NF-R and NiFe-LDH/NF-R at 100 mA cm\u003csup\u003e−2\u003c/sup\u003e, 500 mA cm\u003csup\u003e−2 \u003c/sup\u003eand 1000 mA cm\u003csup\u003e−2\u003c/sup\u003e. \u003cstrong\u003ee\u003c/strong\u003e Long-term CP test (without iR compensation) of the samples at a current density of 3.0 A cm\u003csup\u003e−2\u003c/sup\u003e. \u003cstrong\u003ef\u003c/strong\u003e Polarization curves of the assembled NiFe-SQ/NF-R(+) || Pt/C(−) and NiFe-LDH/NF-R(+) || Pt/C(−) AEMWEs. \u003cstrong\u003eg\u003c/strong\u003e Comparison of the maximum current density provided by other non-noble metal-based materials used as PEMWE anodes.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/f9be5400bb37f86cb0e5dc1f.png"},{"id":77321149,"identity":"d7e1f4ae-7fa4-4044-9126-a2e5145abdcb","added_by":"auto","created_at":"2025-02-27 11:33:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1929817,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eLow-saturation coordination configuration of Fe sites in NiFe-SQ/NF-R. a \u003c/strong\u003eXPS spectra of NiFe-LDH/NF-R and NiFe-SQ/NF-R. \u003cstrong\u003eb\u003c/strong\u003eFe \u003cem\u003eK\u003c/em\u003e-edge XANES spectra for NiFe-LDH/NF-R and NiFe-SQ/NF-R.\u003cstrong\u003e c\u003c/strong\u003e Wavelet transform of Fe-\u003cem\u003eK\u003c/em\u003e-edge EXAFS data of NiFe-SQ/NF-R. \u003cstrong\u003ed\u003c/strong\u003e FT-EXAFS curves at the Fe \u003cem\u003eK\u003c/em\u003e-edge collected for NiFe-LDH/NF-R and NiFe-SQ/NF-R.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/dec081a39becfe769299c79e.png"},{"id":77323439,"identity":"4ddd67a4-bc9a-49f2-aa5d-a7411d35d6bc","added_by":"auto","created_at":"2025-02-27 11:57:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5462142,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSuperior OH\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e−\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e diffusion, trapping and stabilization capabilities of NiFe-SQ/NF-R. a\u003c/strong\u003e LSV curves of NiFe-SQ/NF-R at different sweep speeds. \u003cstrong\u003eb\u003c/strong\u003e Contour plots of the ATR-FTIR data of NiFe-SQ/NF after different numbers of CV scan cycles. In situ Raman spectra of the water structures of \u003cstrong\u003ec\u003c/strong\u003e NiFe-SQ/NF and \u003cstrong\u003ed\u003c/strong\u003e NiFe-LDH/NF.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/5d5fe3c55d760399f9586f6d.png"},{"id":77322217,"identity":"347cc47e-fb48-457a-9dd3-a2e8782fec8d","added_by":"auto","created_at":"2025-02-27 11:41:18","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":6249850,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRegulatory mechanism of intercalated Sq\u003c/strong\u003e\u003csup\u003e\u003cstrong\u003e2−\u003c/strong\u003e\u003c/sup\u003e\u003cstrong\u003e on the interface alkalinity. \u003c/strong\u003eIn situ Raman spectra of \u003cstrong\u003ea\u003c/strong\u003e NiFe-LDH/NF and \u003cstrong\u003eb\u003c/strong\u003e NiFe-SQ/NF in a solution of KOH and phosphoric acid at pH 12. The illustration shows the structural transformation of phosphates at different pH values. \u003cstrong\u003ec\u003c/strong\u003e In situ Raman spectra of NiFe-SQ/NF with background correction. \u003cstrong\u003ed\u003c/strong\u003e Changes in the interface pH with test time. \u003cstrong\u003ee\u003c/strong\u003e Schematic illustration of the intercalated Sq\u003csup\u003e2−\u003c/sup\u003e trapping OH\u003csup\u003e− \u003c/sup\u003eto induce a highly alkaline interface.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/dcefa5ecac58de7962595c05.png"},{"id":77321151,"identity":"a99ee675-3d76-42ea-9096-1c0b6484d8b4","added_by":"auto","created_at":"2025-02-27 11:33:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":2757964,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical verification of improved OER catalytic activity.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e In situ Raman spectra of NiFe-SQ/NF. \u003cstrong\u003eb\u003c/strong\u003e Gibbs free energy diagrams of Fe-NiOOH(Sq\u003csup\u003e2−\u003c/sup\u003e)(NiFe-SQ/NF-R) and Fe-NiOOH(NiFe-LDH/NF-R) at the Ni−O−Fe−O−Ni sites and Ni−O−Ni−O−Ni sites. \u003cstrong\u003ec\u003c/strong\u003e DOS of Fe-NiOOH(Sq\u003csup\u003e2−\u003c/sup\u003e) (NiFe-SQ/NF-R) and Fe-NiOOH(NiFe-LDH/NF-R).\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/67c36cbe05aaa42711c460a0.png"},{"id":80372765,"identity":"56fd9d38-760c-4545-b66d-695985240ffc","added_by":"auto","created_at":"2025-04-11 07:10:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":53631213,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/f0f5bdd7-9a0d-4589-82da-0b4d4c086003.pdf"},{"id":77322213,"identity":"0e4f842f-2157-411f-b078-8b4abdd07f02","added_by":"auto","created_at":"2025-02-27 11:41:17","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4040606,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/11a067087d8250a09949a87c.pdf"},{"id":77321158,"identity":"6133d0f4-8f1a-425f-a264-dbe5ce426879","added_by":"auto","created_at":"2025-02-27 11:33:18","extension":"xlsx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":9626636,"visible":true,"origin":"","legend":"\u003cp\u003eSource data underlying Figs. 2-6\u003c/p\u003e","description":"","filename":"Sourcedata.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-5261089/v1/505739640d3a640f4d7e10bd.xlsx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eHigh-Interface Alkalinity Induced by Intercalated Squaric Acid Anions for 700 Hours of Oxygen Evolution at 3 A cm\u003csup\u003e−2\u003c/sup\u003e\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eWith the rapid expansion of the hydrogen energy industry and the wide application of large-scale water electrolysers,\u003csup\u003e\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e the microenvironmental effect between the electrode and electrolyte interface\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e in industrial-scale devices has significantly increased. In large-scale, high-current and compact water electrolysis systems, the relationships between the influence of special material transformation pathways, ion conduction modes and interfacial molecule/ion interactions on the local microenvironment of electrodes and their catalytic performance remain unexplored. Further regulation of the dynamic interface microenvironment will help to increase the selectivity and reaction rate of some catalytic processes, which provides new ideas for further improving the activity and stability of electrocatalysts.\u003c/p\u003e \u003cp\u003eNi-Fe-based (oxy)hydroxide stands out as a widely favoured electrocatalyst for the OER under alkaline conditions.\u003csup\u003e\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e Numerous endeavors have been undertaken to bolster its catalytic performance through methods such as element doping\u003csup\u003e\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, morphology manipulation\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e, strain adjustment\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, and various other approaches. However, the catalytic interface microenvironment can also have a drastic effect on the apparent catalytic performance.\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e The focus on the catalyst in the microstructure design alone may prove insufficient to fulfil the demands of practical application requirements. In the violent reaction process of high-current water electrolysis, the multistep deprotonation of the alkaline OER initiates the rapid formation and local accumulation of H\u003csup\u003e+\u003c/sup\u003e, resulting in the formation of an acidic interfacial microenvironment. This local acidic microenvironment is strongly corrosive to the metal site of Ni-Fe-based (oxy)hydroxide, posing a challenge to enhancing its performance and durability.\u003csup\u003e\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e As a consequence, promoting the swift transformation and consumption of H\u003csup\u003e+\u003c/sup\u003e is essential for addressing the abovementioned acid corrosion issue, ensuring favourable alkalinity at the anode interface and further enhancing catalytic activity and stability, particularly during large-current electrolysis operations.\u003c/p\u003e \u003cp\u003eWhile some studies have demonstrated that breaking down Ni-Fe layered double hydroxides (NiFe-LDH) into ultrathin nanosheets\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e or initiating element leaching to loosen the catalyst's outer layer\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e can promote the diffusion of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e as a proton acceptor to slow the formation of a local acidic microenvironment, the challenge now lies in quickly and adequately consuming such a large amount of H\u003csup\u003e+\u003c/sup\u003e under a large current. Recent studies by Ranit Ram show that defect structures induced by selectively dissolved WO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e ions can trap and preserve H\u003csub\u003e2\u003c/sub\u003eO and OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, thus prolonging the catalytic activity of OER electrocatalysts under acidic conditions.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Motivated by this discovery, our research aims to incorporate specific functional compounds known as \"intermediaries\" to stabilize OH\u003csup\u003e\u0026minus;\u003c/sup\u003e at the electrochemical interface, addressing the challenge of anodic acidification in high-current alkaline OER processes.\u003c/p\u003e \u003cp\u003eIn this study, we prepared Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e-modified Fe-doped NiOOH as a derived catalytically active layer to drive alkaline OER catalytic processes with ampere-scale currents. Owing to the spatial volume effect of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e, the increase in the layer spacing of Fe-doped NiOOH promotes the effective diffusion of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, which increases the concentration of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e near the active sites and thus enhances the catalytic activity. The intercalation-adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e has been found to stabilize OH\u003csup\u003e\u0026minus;\u003c/sup\u003e at the interface through multiple hydrogen bonding interactions, thereby preserving high interface alkalinity, which plays a critical role in prolonging the catalytic lifespan, particularly in instances of high current densities. Thus, the NiFe-SQ/NF-R electrode created in this research exhibits an exceptionally low overpotential of 284 mV to reach 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and demonstrates a remarkably large current stability surpassing 700 hours at 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. This work demonstrates the feasibility of using the stabilization effect of functional anions on OH\u003csup\u003e\u0026minus;\u003c/sup\u003e to maintain high anode interface alkalinity and improve catalytic activity and stability, paving the way for the innovative design of large-scale current OER electrocatalysts for industrial applications.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStructural Design and Characterization\u003c/h2\u003e \u003cp\u003eThe importance of designing more stable large-current OER electrocatalysts from the perspective of improving the local anode alkalinity or weakening the acidic interfacial microenvironment has not been widely recognized, and there is a lack of comprehensive research and literature in this area. Therefore, to further prolong the actual service life and increase the current resistance of anode electrocatalysts in large current industrial water electrolysers, an effective strategy and innovative mechanisms for designing catalyst structures on the basis of real interfacial microenvironments are urgently needed. We are dedicated to developing a more practical Ni-Fe-based alkaline OER electrocatalyst by focusing on improving its activity and stability at large current densities. Our efforts involved creating a consolidated integrated anode using nickel foam (NF) as the self-supporting base and etched substrate.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e As illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the Ni-Fe bimetallic squarate-based coordination polymer (NiFe-SQ/NF) was synthesized through a one-step hydrothermal process involving in situ etching of NF with the help of an acidic environment facilitated by SQ, an Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e●9H\u003csub\u003e2\u003c/sub\u003eO, and a polyvinyl pyrrolidone (PVP) solution (Supplementary Table\u0026nbsp;1). Additional detailed synthesis procedures and reaction equations for the etching processes can be found in the experimental methods section and in the notes section of Supplementary Fig.\u0026nbsp;1. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, NiFe-SQ/NF exhibited a distinct cuboid angular stack structure, growing uniformly and closely on the initially smooth NF surface (Supplementary Fig.\u0026nbsp;2). The scanning electron microscopy (SEM)-mapping images show that Fe, Ni, O and C are uniformly distributed on the surface of NiFe-SQ/NF (Supplementary Fig.\u0026nbsp;3). The analysis conducted via inductively coupled plasma‒optical emission spectroscopy (ICP‒OES) revealed that the ratio of iron to nickel in the NiFe-SQ/NF sample was approximately 0.39 (Supplementary Table\u0026nbsp;2). The typical square structure of the squarate-based coordination polymer is only achievable through the inclusion of ferric nitrate during the synthesis process (Supplementary Fig.\u0026nbsp;4), which highlights the importance of the purple Fe-based complex and acidic conditions in facilitating the production of NiFe-SQ/NF. The samples synthesized without ferric nitrate (Ni-SQ/NF-R) had poor catalytic activity (Supplementary Fig.\u0026nbsp;5). X-ray diffraction (XRD) analysis of NiFe-SQ/NF reveals distinctive peaks associated with the Ni-Fe coordination polymer (NiFe(H\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e(C\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e))\u003csup\u003e\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e and metallic Ni (JCPDS no. 96-210-0644) (Supplementary Fig.\u0026nbsp;6), suggesting a straightforward phase composition. Then, cyclic voltammetry (CV) was utilized to initiate the rapid surface electrochemical reconstruction activation process of NiFe-SQ/NF, and NiFe-SQ/NF-R was obtained. Only the peaks of metal Ni were detected in the XRD pattern of NiFe-SQ/NF-R, which may be attributed to the presence of numerous amorphous metal hydroxide/hydroxyl oxide species within the surface reconfigurable layer. Alkaline hydrolysis occurs on the surface of NiFe-SQ/NF during electrochemical anodic activation treatment, causing some Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e to run off and creating a net-like fissure structure in NiFe-SQ/NF-R (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec). These fissures act as beneficial micron-scale channels that increase gas release and electrolyte flux at the electrode surface, particularly under large current conditions. A comparison of the water contact angles of the NiFe-SQ/NF and NiFe-SQ/NF-R surfaces reveals that the electrochemical activation treatment shifts the catalytic surface from hydrophobic to superhydrophilic (Supplementary Fig.\u0026nbsp;7), promoting rapid wetting and electrolyte diffusion on the electrode. In Supplementary Fig.\u0026nbsp;8, the SEM maps of NiFe-SQ/NF-R show no significant elemental aggregation, indicating that the electrochemical treatment only excites the superficial species without changing the main structure. SEM images of the NiFe-SQ/NF-R sample cross-sections after the OER show that the square catalyst is closely bound to the outer surface of the nickel foam (Supplementary Fig.\u0026nbsp;9). This self-etching growth strategy ensures strong adhesion at the interface between the catalyst and substrate.\u003c/p\u003e \u003cp\u003eThe electrochemical oxidation reconstruction and dissolution of the squaric acid ligand were carried out simultaneously. The dissolution of squaric acid results in an increased presence of defects in the restructured framework (NiFe-SQ/NF-R), which in turn accelerate the reconstruction process.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e To illustrate this phenomenon, a comparison was conducted between the electrolyte after CV activation and the KOH solution of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e, revealing that they have similar Raman characteristic peaks attributed to Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;10).\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e To further investigate the more subtle structural transformation of NiFe-SQ/NF during electrochemical activation, we performed an in-depth examination of the sample via spherical aberration-corrected transmission electron microscopy (AC-TEM). Specifically, in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, short and disordered lattice fringes can be observed in the outer reconstructed layer of NiFe-SQ/NF-R, which are attributed to metallic hydroxyl oxides. More comprehensive AC-TEM images of NiFe-SQ/NF-R are shown in Supplementary Fig.\u0026nbsp;11. Following the formation of this special crystalline‒amorphous composite layer, the reconstruction process can be terminated quickly, serving as a protective barrier for the internal coordination polymerization structure. The selected-area electron diffraction (SAED) pattern (Supplementary Fig.\u0026nbsp;12) for NiFe-SQ/NF-R exhibits similar structural information that matches that of \u003cem\u003er\u003c/em\u003e-NiOOH (JCPDS no. 00-006-0075). Under the same test conditions, NiFe-LDH/NF-R exhibits a longer-range ordered distribution of the (1 0 1) crystal plane (Supplementary Fig.\u0026nbsp;13), which corresponds to its XRD pattern (JCPDS no. 00-040-0215, Supplementary Fig.\u0026nbsp;14). The NiFe-LDH/NF composite discussed in this study was prepared via a conventional hydrothermal method.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe in situ Raman analysis reveal that NiFe-LDH/NF undergoes a reconstruction process under the excitation of an oxidation current, leading to the gradual transformation of Ni(OH)\u003csub\u003e2\u003c/sub\u003e (455, 530 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) into (Fe-doped) NiOOH (475, 550 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) (Supplementary Fig.\u0026nbsp;15). These findings indicate that NiFe-LDH/NF and NiFe-SQ/NF produce similar NiOOH components after electrochemical reconstruction, which are recognized as active species of the OER. The standard spacing of NiOOH (1 0 5) crystal faces is typically measured at 0.209 nm according to the statistical data (JCPDF no. 00-006-0075). However, our actual observations show that the (1 0 5) crystal face of unintercalated NiOOH produced by electrochemical activation is slightly smaller at 0.205 nm under identical test conditions (Supplementary Fig.\u0026nbsp;16). The small difference from the standard values can be attributed to inevitable structural strain induced by electrochemical activation during the preparation process. The presence of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e insertion leads to a noticeable broadening of the (1 0 5) crystal face of NiOOH, which is measured at 0.210 nm, as indicated by the blue frame in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee and f, compared with the NiOOH (1 0 5) crystal face without Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (0.205 nm). At the same time, the NiOOH in situ Raman characteristic peaks of NiFe-SQ/NF also show a peak shift caused by intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;17). The results above demonstrate that the Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e intercalation-modified Fe-doped NiOOH obtained by electrochemical directional reconstruction results in a larger layer space (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg), serving as a wide electrolyte diffusion channel and an ideal reaction region. The element mapping images of NiFe-SQ/NF-R under high-resolution AC-TEM reveal a homogeneous distribution of Ni, Fe, O, and C (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eh-l), suggesting that the electrochemical activation treatment does not lead to phase segregation of the catalytic components.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eElectrocatalytic oxygen evolution performance\u003c/h3\u003e\n\u003cp\u003eThe electrochemical properties of all the samples in the standard three-electrode and membrane electrode systems were investigated in depth. Purified KOH was used as the electrolyte during the test. Supplementary Fig.\u0026nbsp;18 shows that the ultrafast surface reconstruction process driven by electrochemistry allows the catalytic surface to achieve a state of relative equilibrium after ten cycles of activation, resulting in consistent and stable catalytic properties. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, NiFe-SQ/NF-R demonstrates desirable overpotentials of 259 mV and 284 mV to achieve current densities of 500 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 1000 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2,\u003c/sup\u003e positioning it as a leading electrocatalyst for efficient OER at large current levels, which are lower than those of NiFe-LDH/NF-R (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). On the basis of the previously mentioned results, we believe that such excellent catalytic properties are due to micron-scale transport channels, wider layer spaces, and faster catalytic reaction kinetics, which are caused by Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e intercalation. Comparative experiments (Supplementary Fig.\u0026nbsp;19) were carried out to confirm the limited influence of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e adsorption at the catalytic interface on the catalytic performance of the OER. The increase in Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e did not result in a noteworthy increase in the oxidation current, which also proves that Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e is not further oxidized in an alkaline environment. Upon comparing the linear sweep voltammetry (LSV) curves of NiFe-SQ/NF-R and NiFe-LDH/NF-R, NiFe-SQ/NF-R exhibits notably larger Ni\u003csup\u003e2+\u003c/sup\u003e/Ni\u003csup\u003e3+\u003c/sup\u003e oxidation peaks, suggesting that the intercalation effect of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e can promote the formation and stabilization of NiOOH.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e The reduced Tafel slope observed for NiFe-SQ/NF-R (50 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb) indicates that the presence of intercalated adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e enhances the catalytic reaction kinetics. The interfacial charge transfer capability of the samples was assessed via electrochemical impedance spectroscopy (EIS). NiFe-SQ/NF-R exhibited the smallest charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), which suggests that the interlayer Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e facilitates rapid transfer of the interface charge to enhance the OER. The electrochemical active surface area (ECSA) of NiFe-SQ/NF-R (99.75 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) and NiFe-LDH/NF-R (46.00 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) were determined from their CV curves at different sweep speeds (Supplementary Fig.\u0026nbsp;20a-c). Analysis of the polarization curves normalized by the ECSA reveals that NiFe-SQ/NF-R demonstrates superior intrinsic catalytic activity (Supplementary Fig.\u0026nbsp;20d). The Faradaic efficiency is calculated by measuring the volume of oxygen produced by NiFe-SQ/NF-R during electrolysis (drainage method). The experimental findings, illustrated in Supplementary Fig.\u0026nbsp;21, exhibit a notable proximity between the observed data and the theoretical values derived from Faradaic's principles of electrolysis. This yields a Faradaic efficiency nearing 96%, suggesting that the increased current density stems from the OER process. In other words, the outstanding alkaline OER performance of NiFe-SQ/NF-R is mainly attributed to the intercalation of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e, which promotes increased NiOOH generation, increases the number of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e diffusion channels, expedites interfacial electron transfer, and provides excellent intrinsic catalytic activity. The CoFe-SQ/CF-R and Fe-SQ/IF-R samples were effectively synthesized through similar methods using cobalt foam (CF) and iron foam (IF) (Supplementary Fig.\u0026nbsp;22). Our proposed synthesis method has been validated for universal applicability, making it well suited for widespread industrial implementation.\u003c/p\u003e \u003cp\u003eThe multistep chronopotentiometry (CP) step test diagram illustrates that NiFe-SQ/NF-R can adjust to fluctuating current (Supplementary Fig.\u0026nbsp;23a). Additionally, NiFe-SQ/NF-R can maintain stable catalytic performance for more than 100 h at consistent current densities of 100 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 500 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;23b) while retaining its original catalytic structure even after this duration (Supplementary Fig.\u0026nbsp;23c-f). The catalytic activities of NiFe-SQ/NF-R and NiFe-LDH/NF-R were evaluated at different temperatures (Supplementary Fig.\u0026nbsp;24a and b) because of the observed increase in the local temperature near the anode under high current density conditions. The findings revealed a considerable increase in the catalytic activity of both compounds with increasing temperature. To mitigate the influence of temperature, rigorous measures were taken to maintain a consistent temperature via a temperature-equalizing apparatus during high-current assessments. Analysis of the Arrhenius plot indicated that NiFe-SQ/NF-R exhibited a lower apparent electrochemical activation energy (Ea)\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e than did NiFe-LDH/NF-R (Supplementary Fig.\u0026nbsp;24c). Further examination was conducted on the long-term stability of NiFe-SQ/NF-R and NiFe-LDH/NF-R when subjected to a persistent large current density of 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee, conventional NiFe-LDH/NF-R can only endure approximately 65 hours of CP testing at 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, whereas NiFe-SQ/NF-R exhibits remarkable stability for more than 700 hours. After observing the surface morphology of the electrocatalysts before and after the large-current stability test via SEM, despite undergoing 700 h of high-current testing, the surface structure of NiFe-SQ/NF-R does not exhibit significant dissolution or large areas falling off, which is a stark difference from the incomplete catalytic surface of NiFe-LDH/NF-R after 65 h of testing (illustration of Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). While some potassium salt deposits are visible on the surface of NiFe-SQ/NF-R during the drying process, altering its morphology is not expected to greatly impact its stability. In addition, under industry-relevant conditions (30 wt% KOH, 60\u0026deg;C), NiFe-SQ/NF-R also exhibits lower battery voltages and better stability than typical NiFe-LDH/NF-R (Supplementary Fig.\u0026nbsp;25). Under simulated industrial conditions, the NiFe-SQ/NF-R we prepared is comparable to other reported excellent catalytic electrodes (Supplementary Table\u0026nbsp;3). Therefore, the sudden deactivation of NiFe-LDH/NF-R is due mainly to structural collapse and surface degradation caused by the acidic interfacial microenvironment. Building upon the preceding characterization findings, the distinctive function of intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e in maintaining high interface alkalinity results in the preservation of the structural integrity of NiFe-SQ/NF-R, notably enhancing its stability under high-current conditions. Next, we integrated NiFe-SQ/NF-R as a self-supporting anode into an anion exchange membrane water electrolyzer (AEMWE) to investigate the comprehensive performance of water electrolysis. Notably, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef shows that the NiFe-SQ/NF-R electrode outperforms the NiFe-LDH/NF-R electrode, operating at a lower cell voltage of 2.13 V to achieve a large current of 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, compared with the requirement of 2.44 V for NiFe-LDH/NF-R. Compared with findings in other studies, the utilization of AEMWE to attain such elevated levels of current density represents a cutting-edge approach (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg and Supplementary Table\u0026nbsp;4). AEMWE combined with NiFe-SQ/NF-R demonstrates stability at a high current density of 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, suggesting promising application prospects within membrane electrode systems (Supplementary Fig.\u0026nbsp;26).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eStructural source of long-term stability for high currents.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe strong dissolution tendency of Fe elements in the OER process is also an important factor affecting the stability of OER electrocatalysts.\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e,\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e Consequently, a meticulous analysis of the electronic environment and coordination configuration of NiFe-SQ/NF-R was carried out via X\u0026thinsp;\u0026minus;\u0026thinsp;ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure energy spectrum (XAFS) methods. The results depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea illustrate a slight shift in the Ni\u003csup\u003e2+\u003c/sup\u003e 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e and Ni\u003csup\u003e3+\u003c/sup\u003e 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e peaks between NiFe-SQ/NF-R and NiFe-LDH/NF-R, implying a close resemblance of the electronic configuration surrounding the Ni sites in both. Nonetheless, discernible distinctions were observed in the environments of the Fe sites. In the \u003cem\u003eK\u003c/em\u003e-edge XANES spectrum of Fe, compared with that of NiFe-LDH/NF-R, the preedge peak intensity of NiFe-SQ/NF-R is significantly greater, indicating that there are coordination vacancies near the Fe sites\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The wavelet transform (WT) contour map of NiFe-SQ/NF-R illustrates unique coordination features linked to Fe-O and Fe-M (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). In more detail, the \u003cem\u003eK\u003c/em\u003e-edge extended X-ray absorption fine structure (EXAFS) spectra of Fe show that the characteristic peaks attributed to both the Fe-O (1.5 \u0026Aring;) and Fe-M (2.7 \u0026Aring;) shells in NiFe-SQ/NF-R show significant downwards trends (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). Upon examination, it is determined that the coordination number in proximity to the Fe sites within NiFe-SQ/NF-R is notably lower than that near the Fe sites in NiFe-LDH/NF-R (Supplementary Table\u0026nbsp;5). This disparity is linked to the emergence of vacancies surrounding the Fe site, as the electron paramagnetic resonance (EPR) results show that the signal strength of NiFe-SQ/NF-R is significantly stronger than that of NiFe-LDH/NF-R under the same conditions (Supplementary Fig.\u0026nbsp;27). The detailed analytical fitting procedures are depicted in Supplementary Fig.\u0026nbsp;28. The removal of squaric acid ligands from the primary framework results in an increased presence of vacant sites in the hydroxyl oxide derivatives obtained through reconstruction. These vacancies can buffer the lattice distortion of the Fe site to reduce the dissolution tendency of Fe, thereby preventing phase segregation of Fe.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e Therefore, the presence of coordination vacancies within NiFe-SQ/NF-R plays a pivotal role in safeguarding the integrity of the Fe sites, thereby significantly contributing to its superior stability.\u003c/p\u003e \u003cp\u003eIn addition to the coordination environment, the dynamic evolution of the catalytic structure and electrode interface microenvironment also greatly influences the catalytic behavior of metal centers. This research delves into a detailed examination of the electrochemical structure evolution and interface microenvironment formation mechanism of NiFe-SQ/NF-R and NiFe-LDH/NF-R through in situ Raman and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Under alkaline conditions, the diffusion of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e dominates the Ni(OH)\u003csub\u003e2\u003c/sub\u003e+OH\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026harr;NiOOH\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;e\u003csup\u003e\u0026minus;\u003c/sup\u003e reaction. By applying the Randles\u0026ndash;Sevick equation, the effect of the scanning rate on the oxidation peak current density was investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea)\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe results show that NiFe-SQ/NF-R has improved OH\u003csup\u003e\u0026minus;\u003c/sup\u003e diffusion kinetics, which is a key element in facilitating the generation of NiOOH and improving catalytic activity. Considering the structural features of NiFe-SQ/NF-R, it is reasonable to speculate that the swift OH\u003csup\u003e\u0026minus;\u003c/sup\u003e diffusion capability stems from the external micron-scale channel structure and the increased interlamellar spacing resulting from internal Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e intercalation. In Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, the initial NiFe-SQ/NF structure displays a prominent peak at 1492 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is indicative of structural C\u0026thinsp;\u0026minus;\u0026thinsp;O bonds (O\u0026thinsp;\u0026minus;\u0026thinsp;C\u0026minus;C\u0026thinsp;\u0026minus;\u0026thinsp;O\u003csub\u003estr\u003c/sub\u003e) and represents saturated coordination between SQ and the metal center. Following the CV-driven electrochemical reconstruction process, the O\u0026thinsp;\u0026minus;\u0026thinsp;C\u0026minus;C\u0026thinsp;\u0026minus;\u0026thinsp;O\u003csub\u003estr\u003c/sub\u003e peak vanished from the catalytic surface, whereas a new O\u0026thinsp;\u0026minus;\u0026thinsp;C\u0026minus;C\u0026thinsp;\u0026minus;\u0026thinsp;O\u003csub\u003ead\u003c/sub\u003e associated with Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e emerged at approximately 1560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1 41,\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. The wide peak at approximately 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is associated with the O\u0026thinsp;\u0026minus;\u0026thinsp;H stretching vibration pattern of asymmetric hydrogen bonds resulting from the interaction of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e with adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e. The magnitude of these peaks increases proportionally to the level of activation, as the incorporation of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e leads to a gradual expansion of the Fe-doped NiOOH layer, facilitating enhanced interlayer diffusion and the steady presence of more OH\u003csup\u003e\u0026minus;\u003c/sup\u003e. Even after conducting 20 CV activation scans, the peaks at 1560 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e remained present, suggesting stable intercalation and adsorption of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e between the layers of the sample. In the CV activation process of NiFe-LDH/NF, no significant change in the peak at approximately 3300 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Supplementary Fig.\u0026nbsp;29) was found, but the peaks of NiFe-SQ/NF-R were significantly enhanced during activation, further highlighting the important role of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e in stabilizing OH\u003csup\u003e\u0026minus;\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe structural evolution of NiFe-SQ/NF during the electrochemical reconstruction process can be deduced as follows: the alkali hydrolysis process first disrupts the coordination bond between the SQ ligand and the metal center, enabling the uncoordinated C\u0026thinsp;\u0026minus;\u0026thinsp;O group to establish an anchoring effect with OH\u003csup\u003e\u0026minus;\u003c/sup\u003e through hydrogen bonding. In addition, Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e interacts with M-OH (M: Fe or Ni) at the metal-catalyzed interface to create adsorption-bonded O\u0026thinsp;\u0026minus;\u0026thinsp;C\u0026minus;C\u0026thinsp;\u0026minus;\u0026thinsp;O\u003csub\u003ead\u003c/sub\u003e for a stable interlayer insertion. The analysis of the ATR-FTIR data further validates the evolution process of the structure, supporting previous findings from spherical aberration electron microscopy. We employed an improved in situ Raman electrochemical cell to accurately examine the interfacial H\u003csub\u003e2\u003c/sub\u003eO/OH\u003csup\u003e\u0026minus;\u003c/sup\u003e structure near the electrode surface. Three different hydrogen-bonded water structures are deconvolved: 4\u0026thinsp;\u0026minus;\u0026thinsp;HB\u0026#159;H\u003csub\u003e2\u003c/sub\u003eO (~\u0026thinsp;3200 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), 3\u0026thinsp;\u0026minus;\u0026thinsp;HB\u0026#159;H\u003csub\u003e2\u003c/sub\u003eO/OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (~\u0026thinsp;3400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and 0\u0026thinsp;\u0026minus;\u0026thinsp;HB\u0026#159;H\u003csub\u003e2\u003c/sub\u003eO (~\u0026thinsp;3600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003csup\u003e22,43,44\u003c/sup\u003e Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e, with four uncoordinated O*, is able to form more complex hydrogen bond interactions with interfacial H\u003csub\u003e2\u003c/sub\u003eO and OH\u003csup\u003e\u0026minus;\u003c/sup\u003e to regulate the interfacial water structure. This resulte in distinct O‒H stretching patterns in the NiFe-SQ/NF-R samples in contrast to those in the NiFe-LDH/NF-R samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and d). As shown in Supplementary Fig.\u0026nbsp;30, the ratios of 4-HB\u0026#159;H\u003csub\u003e2\u003c/sub\u003eO and 3-HB\u0026#159;H\u003csub\u003e2\u003c/sub\u003eO at the NiFe-SQ/NF interface consistently increased with prolonged testing duration, whereas they notably decreased at the NiFe-LDH/NF interface. These results suggest that the inserted Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e has the ability to regulate interfacial water and capture OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, which is conducive to alleviating local acidification during the OER.\u003c/p\u003e \u003cp\u003eChanges in the interface alkalinity of NiFe-SQ/NF and NiFe-LDH/NF were observed through in situ Raman spectroscopy, utilizing the phosphoric acid-sensitive pH characteristics. The principle of this method is that as the pH increases, the phosphate species can undergo the conversion of H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e \u0026rarr; H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026rarr; HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e \u0026rarr; PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026minus;\u003c/sup\u003e (illustration of Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea).\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e The electrolyte with a phosphate compound served as a pH probe during in situ Raman analysis. Through the correspondence between the characteristic Raman vibration peak of the phosphate species and pH, we can establish a linear relationship between pH and the vibration peak. This monitoring is crucial for understanding the local acidification microenvironment of Ni-Fe-based layered materials during anode testing, which is a significant issue that impacts activity and stability, particularly under high current density testing conditions. During in situ testing, spectral data were collected at 4-minute intervals under a consistent current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e in a solution of KOH and phosphoric acid at pH 12. By observing the variation in the characteristic peaks of PO\u003csub\u003e4\u003c/sub\u003e (936 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), PO\u003csub\u003e3\u003c/sub\u003e (990 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and P(OH) (857 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), we obtain the local pH values of NiFe-LDH/NF and NiFe-SQ/NF. A low vibrational transition energy leads to a weak peak signal of P(OH). Nevertheless, this minimal effect does not hinder the formulation of conclusions. Rapid reduction of the local pH from 12 to 8 in NiFe-LDH/NF was accomplished within a short duration of 12 min (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea). This provides direct evidence that the layered structure of NiFe-LDH tends to promote an acidic microenvironment, pinpointing a key factor contributing to its limited large current stability.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSurprisingly, during the initial 52 minutes of the examination, the regional pH of NiFe-SQ/NF remains constant at 12, which then transitions to 11 by the 56th minute (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb), with its acidification rate at the interface notably lagging behind that of NiFe-LDH (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed). The primary factor contributing to this outcome is the tendency of the intercalation-adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e to trap and stabilize OH\u003csup\u003e\u0026minus;\u003c/sup\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec, two peaks at approximately 1554 and 1640 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are identified, which are attributed to the asymmetric C\u0026ndash;O vibrations ((M-)C\u0026ndash;O and C\u0026thinsp;=\u0026thinsp;O) of adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (O\u0026thinsp;\u0026minus;\u0026thinsp;C\u0026minus;C\u0026thinsp;\u0026minus;\u0026thinsp;O\u003csub\u003ead\u003c/sub\u003e), respectively. Over time, these peaks demonstrated a slight tendency toward augmentation, suggesting an increase in the presence of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e adsorbed within the layers with increasing reconstruction process. Therefore, the presence of intercalated adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e is pivotal in maintaining localized interface alkalinity, thereby significantly prolonging the catalytic lifespan by tenfold under high currents of 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee, the above analysis clearly reveals that the sluggish surface acidification rate of NiFe-SQ/NF stems from two key factors. First, in terms of surface structure composition, the dispersed micron-scale diffusion channels and expanded layer spacing directly facilitated the internal diffusion of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e and the outwards transfer of H\u003csup\u003e+\u003c/sup\u003e. Second, when considering internal structural groups, Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e as \"intermediaries\", is adept at trapping and steadying OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, thereby expediting the conversion of H\u003csup\u003e+\u003c/sup\u003e and consequently delaying the emergence of a localized acidic microenvironment, thus sustaining increased interface alkalinity. In short, this regulatory mechanism of interface alkalinity is particularly important for optimizing the local interfacial microenvironment under harsh conditions characterized by a high current.\u003c/p\u003e\n\u003ch3\u003eThe theoretical source of enhanced catalytic activity\u003c/h3\u003e\n\u003cp\u003eThe increase in catalytic activity through the internal mechanism of interlaminar Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e anions was further investigated via spin polarization density functional theory (DFT) calculations. The peaks corresponding to Ni(OH)\u003csub\u003e2\u003c/sub\u003e (455, 530 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and NiOOH (476, 553 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) are evident in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, suggesting that NiFe-SQ/NF underwent surface restructuring to facilitate the formation of NiOOH, a notably potent species. The electrochemical reconstruction processes of NiFe-LDH/NF and NiFe-SQ/NF led to the formation of Fe-doped NiOOH (Fe-NiOOH(NiFe-LDH/NF-R)) and Fe-doped NiOOH with intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e)(NiFe-SQ/NF-R)), respectively, which served as the primary active layers. After a rounded analysis, it is clear that the model architecture harbors promising active sites denoted as Ni\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Fe\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Ni and Ni\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Ni\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Ni. As shown in Supplementary Fig.\u0026nbsp;31, computational assessments were conducted to determine the optimal OER pathways for Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R) and Fe-NiOOH(NiFe-LDH/NF-R) at these designated active sites. For the Ni\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Fe\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Ni site in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, the rate-determining step (RDS) of the OER is the transition from *O to *OOH, and the barrier is reduced from 3.37 eV to 2.76 eV through the incorporation of Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e anions. This is because interlayer Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e increases the effective concentration of OH\u003csup\u003e\u0026minus;\u003c/sup\u003e near the active site through multiple hydrogen bonds interacting with OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, which facilitates the formation of key *OOH intermediates. Additionally, the deprotonation barrier of the *OOH step in Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R) is notably lower at 0.01 eV than that in Fe-NiOOH(NiFe-LDH/NF-R), which is 1.07 eV. This result indicates that Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e significantly accelerates the *OOH dehydrogenation process because both the unpaired O* sites and the captured OH\u003csup\u003e\u0026minus;\u003c/sup\u003e serve as proton acceptors to ensure the efficiency of the deprotonation process. In this study, the predominant active site for the OER was identified as the Ni\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Fe\u0026thinsp;\u0026minus;\u0026thinsp;O\u0026minus;Ni site. This site is proposed to enable an Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e led efficient pathway, which supports the activation and stabilization of *OOH intermediates and assists in their deprotonation. Consequently, this mechanism reduces the reaction energy barrier and increases the catalytic effectiveness. Upon examination of the density of states (DOS) images, it was noted that the electron state density of Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R) surpasses that of Fe-NiOOH(NiFe-LDH/NF-R) at the Fermi level, suggesting that the intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e plays a significant role in enhancing the electron transport efficiency (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec). The electron state density of Fe within Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R) is notably lower than that of Fe in Fe-NiOOH(NiFe-LDH/NF-R) across a wide energy range. This observed disparity suggests a reduction in the electron cloud density surrounding the Fe orbital subsequent to the Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e intercalation procedure. This is consistent with the conclusion drawn from the differential charge density map (Supplementary Fig.\u0026nbsp;32). The orbital state densities of Fe and O in Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R) demonstrate closer overlapping resonances, leading to stronger electron interactions.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e Consequently, our as-designed NiFe-SQ/NF-R catalytic interface facilitates a comprehensive improvement in the catalytic activity for the OER.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we present a novel approach for controlling the local alkalinity of the interfacial microenvironment under large current conditions by incorporating steadily adsorbed Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e anions between the layers of Fe-doped NiOOH. Intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e facilitates the activation and stabilization of *OOH intermediates and assists in their deprotonation, thereby increasing their catalytic activity. The captured OH\u003csup\u003e\u0026minus;\u003c/sup\u003e, which acts as a potent proton receptor, facilitates the rapid consumption of H\u003csup\u003e+\u003c/sup\u003e, postponing the formation of acidic microenvironments and thereby bolstering the durability of the material when subjected to high-current conditions. As a result, the NiFe-SQ/NF-R demonstrates a lower overpotential (284 mV at 1.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), a decreased Tafel slope (50 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and reliable long-term stability (700 hours under 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). This research successfully incorporated functional ligand-derived anions into layered materials, leading to enhanced performance in OER materials by minimizing the local acidic microenvironment and maintaining high interfacial alkalinity, especially under large current conditions.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eMaterials.\u003c/strong\u003e Ferric nitrate nonahydrate (Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e●9H\u003csub\u003e2\u003c/sub\u003eO), nickel nitrate hexahydrate (Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), cobaltous nitrate hexahydrate (Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO), polyvinylpyrrolidone (PVP, K30), ammonium fluoride (NH\u003csub\u003e4\u003c/sub\u003eF), urea (CO(NH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e), acetone (CH\u003csub\u003e3\u003c/sub\u003eCOCH\u003csub\u003e3\u003c/sub\u003e), ethanol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH), hydrochloric acid (HCl, 36%~38%) and potassium hydroxide (KOH) were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid, C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e) was acquired from Macklin Chemical Reagent Co., Ltd., Shanghai, China. Nickel foam (NF) (aperture: 110 ppi, thickness: 1.5 mm) was obtained from Kunshan Lvchuang Electronic Technology Co., Ltd. Pt/C (20 wt%, Macklin Chemical Reagent Co. Ltd.) and Nafion (5 wt%, Sigma‒Aldrich) were also used. Deionized water was used in all the experiments. All the chemicals used in this study were of analytical grade and were used without further purification.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis of NiFe-SQ/NF-R.\u003c/strong\u003e NF (2.5 cm*3.5 cm*1.5 mm) was initially subjected to ultrasonic cleaning in acetone, hydrochloric acid (1 M), and ethanol, each for 15 minutes. Thorough removal of oxides and organic residues from the NF surfaces played a crucial role in the preparation of the electrocatalysts for this study. The NF was subsequently placed in a solution comprising 0.3000 g of PVP, 2.5 mmol of squaric acid, 0.5 mmol of Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e●9H\u003csub\u003e2\u003c/sub\u003eO, and 30 mL of deionized water. The mixture was subsequently transferred to a 100 mL Teflon vessel sealed with a stainless autoclave, heated to 120\u0026deg;C, and maintained for 6 hours. The resulting dark green NiFe-SQ/NF sample was obtained after rinsing with deionized water and drying in a vacuum oven at 60\u0026deg;C. Finally, NiFe-SQ/NF underwent electrochemical activation in 1 M KOH to yield NiFe-SQ/NF-R. The specific activation process involved cyclic voltammetry in a standard three-electrode configuration, with a scanning range of 0\u0026thinsp;\u0026minus;\u0026thinsp;1.488 V vs. RHE, a scanning rate of 10 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a total of 10 cycles.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSynthesis of NiFe-LDH/NF-R.\u003c/strong\u003e The process of synthesizing NiFe-LDH/NF-R closely mirrors that of NiFe-SQ/NF-R, differing primarily in replacing the solution with 1.0 mmol of Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e●6H\u003csub\u003e2\u003c/sub\u003eO, 0.5 mmol of Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e●9H\u003csub\u003e2\u003c/sub\u003eO, 2.5 mmol of NH\u003csub\u003e4\u003c/sub\u003eF, 6 mmol of CO(NH\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, and 30 mL of deionized water.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStructural characterization.\u003c/strong\u003e The crystal phase of the catalyst was analysed via X-ray diffraction (XRD) with Cu K\u0026alpha; radiation (\u003cem\u003e\u0026lambda;\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1.54 \u0026Aring;) on a Rigaku D/max-2500 pc apparatus. The morphological characteristics of the samples were examined by scanning electron microscopy (SEM) with a Hitachi S-4800 instrument. The elemental composition and distribution of the catalyst were evaluated via energy dispersive spectroscopy (EDS) in conjunction with a Hitachi S-4800 instrument. The powder samples were dissolved in dilute acid for inductively coupled plasma‒optical emission spectroscopy (ICP‒OES) (Agilent 5110 (OES)) to obtain the exact contents of Fe and Ni. Electron paramagnetic resonance (EPR) data were collected on a German-Bruker-A300 spectrometer. Spherical aberration-corrected transmission electron microscopy (AC\u0026thinsp;\u0026minus;\u0026thinsp;TEM) images and elemental maps were obtained via an aberration\u0026thinsp;\u0026minus;\u0026thinsp;corrected transmission electron microscope (Titan Themis Cubed G2 300) operating at 300 kV. The contact angle of ultrapure water on the electrode was measured at room temperature by employing a dynamic contact angle system (JC2000C1). X\u0026thinsp;\u0026minus;\u0026thinsp;ray photoelectron spectroscopy (XPS) data were calibrated to the C 1\u003cem\u003es\u003c/em\u003e peak energy of 284.8 eV via a Thermo Fisher Scientific II spectrometer equipped with an Al K\u0026alpha; source (1486.6 eV). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was conducted with a BRUKER ALPHA II infrared spectrometer. In situ Raman spectroscopy was performed in electrolytes of KOH and H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e at pH 12 using the samples and platinum wire as the working and counter electrodes, respectively. The laser excitation wavelength used during the measurements was 532 nm, a constant current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was maintained by the electrochemical workstation, and spectral data were collected every 4 minutes. The X-ray absorption fine structure energy spectrum (XAFS) was obtained at the Shanghai Synchrotron Radiation BL13SSW station (SSRF, 3.5 GeV, 220 mA, Si(111) twin). Data acquisition is carried out via a small detector under environmental conditions. The Athena module in the IFEFFIT package is used for standard XAFS data processing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical measurements.\u003c/strong\u003e This investigation examined the performance of various electrocatalysts in the OER utilizing a standard three-electrode configuration in an alkaline environment (KOH) with a GamryInterface 3000E workstation. The synthesized electrocatalysts (1.0 cm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e), a Pt sheet and a mercury oxide electrode were used as the working electrode, opposite electrode and reference electrode, respectively. All potentials were converted to the reversible hydrogen electrode (RHE) via the following equation:\u003c/p\u003e\n\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\u003cimg src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img174064621931.png\" style=\"text-align: start; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: medium; font-family: \u0026quot;\u0026quot;;\"\u003e\u003cbr\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eLinear sweep voltammetry (LSV) was carried out at a rate of 5.0 mV s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with manual iR compensation, unless otherwise stated. Specifically, the resistance of the system is tested first and then compensated manually at a value of 95%. Electrochemical impedance spectroscopy (EIS) tests spanned a frequency range of 10\u003csup\u003e5\u003c/sup\u003e-0.1 Hz at 1.48 V vs. RHE. The large current performance and stability were evaluated via a GamryInterface 5000E workstation assisted by stirring and automatic circulation refill devices.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMembrane electrode measurement.\u003c/strong\u003e NiFe-SQ/NF-R (1.0 cm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) and Pt/C (1.0 cm\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, 0.5 mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) were used as the anode (OER) and cathode (HER), respectively. KOH (1 M) was circulated through the membrane electrode at a flow rate of 50 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The full-cell OER performance of the AEM was evaluated on a GamryInterface 5000E workstation at 25\u0026deg;C.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDensity functional theory calculations.\u003c/strong\u003e Spin-polarized density functional theory (DFT) calculations were conducted employing the Vienna ab initio simulation package (VASP) to explore the alkaline OER. The calculations were carried out via the projector augmented wave method with a cut-off energy of 400 eV and the Perdew\u0026ndash;Burke\u0026ndash;Ernzerhof functional. To consider the impact of the 3\u003cem\u003ed\u003c/em\u003e electrons of the Ni and Fe atoms, the DFT\u0026thinsp;+\u0026thinsp;U method was utilized, with effective U values of 5.5 eV\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e and 5.3 eV\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e, respectively. Moreover, the DFT-D3 method was applied to correct for the influence of the 3\u003cem\u003ed\u003c/em\u003e electrons of Ni atoms and van der Waals interactions.\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e This study involved cleaving two layers of NiOOH (0 0 1) facets with a vacuum layer of 20 \u0026Aring; and incorporating 16% of the Ni atoms substituted with Fe atoms to form the Fe-doped NiOOH (Fe-NiOOH(NiFe-LDH/NF-R)) model. Furthermore, Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e was introduced between the layers to create Fe-doped NiOOH with an intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e (Fe-NiOOH(Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e)(NiFe-SQ/NF-R)) model. All the models underwent full relaxation with an energy convergence criterion of 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV and a force convergence criterion of 0.02 eV \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e. The \u0026Gamma; point was utilized in the K-point mesh, and the adsorption energy (E\u003csub\u003eads\u003c/sub\u003e) was computed via formula 2.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img1740646201.png\" style=\"text-align: start; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: medium; font-family: \u0026quot;\u0026quot;;\"\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eE\u003c/em\u003e \u003csub\u003etotal\u003c/sub\u003e, \u003cem\u003eE\u003c/em\u003e\u003csub\u003esubstrate\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003eadsorbate\u003c/sub\u003e represent the energies of the adsorption structure, substrate and adsorbate, respectively. The free energies were calculated via the following formula 3:\u003c/p\u003e\n\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\u003cimg src=\"https://myfiles.space/user_files/127393_c7e80a1c9bb65875/127393_custom_files/img1740646294.png\" style=\"text-align: start; color: rgb(0, 0, 0); background-color: rgb(255, 255, 255); font-size: medium; font-family: \u0026quot;\u0026quot;;\"\u003e\u003cbr\u003e\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cem\u003eG\u003c/em\u003e, \u003cem\u003eE\u003c/em\u003e\u003csub\u003eDFT\u003c/sub\u003e, \u003cem\u003eZPE\u003c/em\u003e and \u003cem\u003eTS\u003c/em\u003e represent the free energy, energy from DFT calculations, zero-point energy and entropic contributions, respectively.\u003c/p\u003e\n "},{"header":"Declarations","content":" \u003ch2\u003eData availability\u003c/h2\u003e\n \u003cp\u003eThe data that support the plots within this paper are available from the corresponding author upon reasonable request. The source data underlying Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026minus;6 are provided as a Source Data file. Source data are provided with this paper.\u003c/p\u003e\n \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e \u003cp\u003eB.D. and Y.C. conceived the paper and directed the research. R.F., F.W. and Y.Z. designed and carried out the experiments. S.L. contributed to the in situ Raman spectra. D.B. and Y.C. performed the density functional theory calculations. B.Z. provide discussion and sorted the writing ideas. R.F. wrote the paper. D.B. and B.Z. revised the manuscript with comments from all the authors.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work is financially supported by the National Natural Science Foundation of China (52174283 and 52274308) and an innovation fund project for graduate students of China University of Petroleum (East China) supported by \"the Fundamental Research Funds for the Central Universities\" (No. 24CX04022A). We acknowledge beamline BL13SSW at the Shanghai Synchrotron Radiation Facility for XAFS experimental support.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eOener SZ, Foster MJ, Boettcher SW (2020) Accelerating water dissociation in bipolar membranes and for electrocatalysis. 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AIChE J 68:e17582\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrimme S, Antony J, Ehrlich S, Krieg H (2010) A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H-Pu. J Chem Phys 132:154104\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5261089/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5261089/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe corrosive acidic interfacial microenvironment caused by rapid multistep deprotonation of the alkaline oxygen evolution reaction (OER) in industrial high-current water electrolysis is one of the key problems limiting activity and stability. Some functional anions derived from electrocatalysis exhibit special functionalities in modulating the catalytic interface microenvironment, but this matter has not received adequate attention in academic discussions. The coordinated squaric acid molecule is revealed to undergo a dissolve-reintercalation process in the alkaline OER, leading to its eventual stabilization within the Fe-doped NiOOH interlayer in the form of squaric acid anions (Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e) (NiFe-SQ/NF-R). This intercalated Sq\u003csup\u003e2\u0026minus;\u003c/sup\u003e stabilizes OH\u003csup\u003e\u0026minus;\u003c/sup\u003e through multiple hydrogen bond interactions, which is conducive to maintaining high catalytic interface alkalinity. Hence, the interfacial acidification of the prepared NiFe-SQ/NF-R in the alkaline OER process is significantly inhibited, resulting in a tenfold increase in its catalytic durability (from 65 to 700 hours) when exposed to a high current density of 3.0 A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, as opposed to traditional NiFe-LDH/NF-R materials. This derived functional anion guarantees the enduring performance of the NiFe-derived electrocatalyst under high current densities by controlling the interfacial alkalinity.\u003c/p\u003e","manuscriptTitle":"High-Interface Alkalinity Induced by Intercalated Squaric Acid Anions for 700 Hours of Oxygen Evolution at 3 A cm−2","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-27 11:33:13","doi":"10.21203/rs.3.rs-5261089/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"61108e61-e4a0-4b43-b680-e662781e90ff","owner":[],"postedDate":"February 27th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":44954102,"name":"Physical sciences/Chemistry/Electrochemistry/Electrocatalysis"},{"id":44954103,"name":"Physical sciences/Chemistry/Green chemistry/Sustainability"}],"tags":[],"updatedAt":"2025-04-11T07:09:58+00:00","versionOfRecord":{"articleIdentity":"rs-5261089","link":"https://doi.org/10.1038/s41467-025-58623-7","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2025-04-10 04:00:00","publishedOnDateReadable":"April 10th, 2025"},"versionCreatedAt":"2025-02-27 11:33:13","video":"","vorDoi":"10.1038/s41467-025-58623-7","vorDoiUrl":"https://doi.org/10.1038/s41467-025-58623-7","workflowStages":[]},"version":"v1","identity":"rs-5261089","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5261089","identity":"rs-5261089","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}