Synergistic gradient orbital coupling and work function engineering for high-efficiency hydrogen production via glycerol electrooxidation

Synergistic gradient orbital coupling and work function engineering for high-efficiency hydrogen production via glycerol electrooxidation | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 8 May 2025 V1 Latest version Share on Synergistic gradient orbital coupling and work function engineering for high-efficiency hydrogen production via glycerol electrooxidation Authors : Zhi-Yuan Feng , Jin-Chi Jiang , Biao Jin , and Long-Yue Meng 0000-0002-1860-4895 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174669020.02924729/v1 171 views 86 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The incorporation of rare earth metals into transition metal-based catalysts markedly improves their adsorption properties toward intermediates during coupled glycerol electro-oxidation and hydrogen evolution reactions. However, direct f-d electron hybridization often induces Fermi surface instability, limiting catalytic durability. To address this, we propose a novel strategy involving Dy and S co-doped NiMoO 4 , where 4f-2p-3d gradient orbital coupling is introduced alongside sulfur vacancies (Sv) via Ar plasma etching. This approach simultaneously reduces the catalyst’s work function and mitigates interfacial charge accumulation, yielding bouquet-like Dy-doped NiMoO 4 with abundant Sv (Sv/Dy-NiMoO 4 /NF). The optimized catalyst demonstrates remarkable performance in glycerol electrooxidation-coupled hydrogen production, achieving an exceptionally low hydrogen evolution overpotential of 29 mV at 10 mA cm -2 while simultaneously maintaining a cell voltage of just 1.39 V in membrane electrode assembly operation. This configuration provides a 260 mV reduction in potential compared to conventional overall water splitting, while additionally enabling the co-production of high-value formate as oxidation products. Experimental and theoretical analyses reveal that Sv optimize the electronic microenvironment, strengthening the adsorption of OH* and glycerol* intermediates. This work not only advances the design of high-efficiency electrocatalysts for energy-saving hydrogen production but also provides a sustainable route for co-producing valuable chemicals. Synergistic gradient orbital coupling and work function engineering for high-efficiency hydrogen production via glycerol electrooxidation Zhi-Yuan Feng 1 , Jin-Chi Jiang 1 , Biao Jin 2 ** , Long-Yue Meng 1* 1 Department of Chemistry, Yanbian University, Yanji, 133002, PR China 2 Analysis and Test Center, Yanbian University, Yanji, 133002, PR China Author Contact Information: * Corresponding author. E-mail address: [email protected] (L.Y. Meng). ** Co-corresponding author. E-mail address: jinbiao@ybu,edu,cn (B. Jin). Abstract: The incorporation of rare earth metals into transition metal-based catalysts markedly improves their adsorption properties toward intermediates during coupled glycerol electro-oxidation and hydrogen evolution reactions. However, direct f-d electron hybridization often induces Fermi surface instability, limiting catalytic durability. To address this, we propose a novel strategy involving Dy and S co-doped NiMoO₄, where 4f-2p-3d gradient orbital coupling is introduced alongside sulfur vacancies (Sv) via Ar plasma etching. This approach simultaneously reduces the catalyst’s work function and mitigates interfacial charge accumulation, yielding bouquet-like Dy-doped NiMoO₄ with abundant Sv (Sv/Dy-NiMoO₄/NF). The optimized catalyst demonstrates remarkable performance in glycerol electrooxidation-coupled hydrogen production, achieving an exceptionally low hydrogen evolution overpotential of 29 mV at 10 mA cm⁻² while simultaneously maintaining a cell voltage of just 1.39 V in membrane electrode assembly operation. This configuration provides a 260 mV reduction in potential compared to conventional overall water splitting, while additionally enabling the co-production of high-value formate as oxidation products. Experimental and theoretical analyses reveal that Sv optimize the electronic microenvironment, strengthening the adsorption of OH* and glycerol* intermediates. This work not only advances the design of high-efficiency electrocatalysts for energy-saving hydrogen production but also provides a sustainable route for co-producing valuable chemicals. Keywords: Gradient orbital coupling; S vacancies; Work function engineering ; Glycerol; H 2 generation Introduction The conversion of renewable biomass into high value-added chemicals presents a promising alternative to conventional fossil-derived products. Glycerol, a major by-product of biodiesel production, has experienced significant market accumulation, leading to a persistent global oversupply. Recognized as one of the top ten biomass-derived platform molecules by the U.S. Department of Energy, glycerol has attracted considerable attention for its potential in sustainable chemical synthesis [1-5]. Electrochemical conversion, in particular, stands out among various glycerol upgrading strategies due to its inherent advantages in sustainability and energy efficiency. The glycerol electro-oxidation reaction (GOR) exhibits a notably lower theoretical oxidation potential compared to the oxygen evolution reaction (OER), while simultaneously enabling the selective production of valuable oxidation products such as formic acid, glycolic acid, and glyceric acid. This approach not only facilitates the valorization of glycerol but also integrates with the hydrogen evolution reaction (HER), substantially reducing the operational voltage required for hydrogen production. Consequently, it enhances the economic viability of hydrogen generation compared to conventional water electrolysis [6-11]. Of particular industrial relevance among GOR-derived products is formic acid, which serves not only as a potential fuel for direct formic acid fuel cells but also as a versatile platform chemical in the synthesis of pesticides, pharmaceuticals, and dyes. Despite these advantages, existing electrocatalysts for glycerol oxidation often suffer from suboptimal selectivity and Faradaic efficiency, primarily due to competing oxygen evolution. Thus, the development of high-performance electrocatalysts with enhanced product selectivity and reaction efficiency remains a critical challenge in advancing practical glycerol electro-oxidation systems coupled with hydrogen production [12-17]. Noble metals exhibit outstanding catalytic activity for the electrooxidation of organic substrates, including glycerol, demonstrating high selectivity toward C3 products at low applied potentials. However, their practical application is hindered by two major drawbacks: a propensity for overoxidation to CO 2 at higher potentials and their inherently limited natural abundance, which results in prohibitively high costs [18,19]. Consequently, significant research efforts have focused on developing transition metal-based alternatives, particularly sulfides, phosphides, oxides, and nitrides, as bifunctional catalysts for combined HER and organic electrooxidation [20-22]. NiMoO 4 has emerged as a promising bimetallic oxide catalyst, where Ni incorporation effectively modulates Mo-H bond strength to facilitate hydrogen desorption. However, its practical application is constrained by intrinsically poor electrical conductivity [23,24]. To address this limitation, strategic co-doping with metal and nonmetal elements has been employed to optimize local electronic environments. Rare earth elements, with their distinctive 4f electron configurations, enable effective orbital hybridization with transition metal 3d orbitals, while simultaneously enhancing material conductivity without compromising structural stability. This principle was demonstrated by Huang et al., who achieved significant electronic modulation of Ni sites in Ni-MOF through Dy doping, resulting in enhanced intermediate adsorption and accelerated OER kinetics [25].Complementary nonmetal doping, particularly with sulfur, offers additional benefits: (1) its low electronegativity promotes surface charge separation, creating abundant active sites; (2) facilitates electron density redistribution at metal centers [26,27]; and (3) critically, the S 2p orbitals mediate between rare earth 4f and transition metal 3d orbitals, stabilizing the Fermi surface against the destabilizing effects of direct f-d hybridization. Complementary to doping strategies, defect engineering has proven to be an effective approach for activating catalytic sites, with the introduction of anionic vacancies being particularly impactful due to the preferential redistribution of localized electrons from the vacancies to neighboring metal centers. This electron transfer mechanism serves to optimize the adsorption energetics of reactive intermediates during catalytic processes. Ar plasma treatment has emerged as a powerful technique for precisely engineering such lattice defects while simultaneously modulating the electronic band structure of materials [28,29]. Through controlled plasma etching, the strategic creation of vacancies at optimal concentrations yields multiple synergistic benefits: the material’s work function is significantly reduced, charge transfer kinetics are enhanced, and undesirable interfacial charge accumulation is mitigated. These combined effects effectively weaken the trapping of hydrogen intermediates (H*) at the interface while promoting favorable hydrogen spillover phenomena, ultimately leading to improved catalytic performance. Inspired by the above principles, we developed an innovative approach for modulating material work function through Ar plasma etching. The synthesis involved in situ growth of Dy-doped NiMoO 4 bouquet-like nanostructures on nickel foam (NF) via hydrothermal method, followed by sequential S doping through vapor deposition and controlled generation of sulfur vacancies via Ar plasma treatment. This sophisticated fabrication process enabled the redistribution of localized electrons from the vacancies to adjacent metal centers, thereby optimizing the electronic microenvironment while significantly lowering the material’s work function. The resulting Sv/Dy-NiMoO 4 /NF catalyst demonstrated exceptional performance, achieving a remarkably low HER overpotential of merely 29 mV at 10 mA cm -2 , attributable to the synergistic effects of 4f-2p-3d gradient orbital coupling, precise electronic structure modulation, and reduced work function. Impressively, the catalyst maintained stable performance over 100 hours of continuous water electrolysis with minimal activity degradation. Furthermore, when coupled with GOR, the system required 260 mV lower potential at 10 mA cm −2 while simultaneously producing valuable formic acid as a co-product. Comprehensive experimental characterization combined with density functional theory (DFT) calculations revealed that the engineered sulfur vacancies played a pivotal role in work function reduction and enhanced adsorption of key reaction intermediates. This work establishes a novel paradigm for designing cost-effective electrocatalysts through plasma-induced vacancy engineering, offering new perspectives for developing integrated systems that combine efficient hydrogen production with value-added chemical synthesis. Results and discussion 2.1. Synthesis and Characterization of Sv/Dy–NiMoO 4 /NF Figure 1a shows the preparation process of bouquet-like Sv/Dy–NiMoO 4 /NF. First, Dy-doped NiMoO 4 was grown in situ on the NF surface using a hydrothermal method. Ni 2+ and MoO 4 2− were electrostatically adsorbed on the NF surface and formed a vertical prismatic nanoarray of NiMoO 4 . In the subsequent Dy doping process, flowers were formed on top of NiMoO 4 , yielding Dy–NiMoO 4 . Dy–NiMoO 4 was doped with S by chemical vapor deposition, and S vacancies were constructed by Ar plasma etching, yielding Sv/Dy–NiMoO 4 /NF. The typical morphologies and structures of the prepared catalysts were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM images show that NiMoO 4 /NF had the morphology of a prismatic array with a regular and uniform distribution (Figure S1). Each individual prism was approximately 500 nm in size with a very smooth surface. The unique three-dimensional array structure promotes full contact between the electrode and electrolyte solution and accelerates the mass transfer efficiency. Figure 1b–d show the flower-like morphology and structure of Sv/Dy–NiMoO 4 /NF, with micro-flowers of about 2 µm in size appearing at the top of NiMoO 4 /NF. This bouquet-like array structure provides a higher electroactive surface area, enhances charge/mass transfer, and promotes the rapid desorption of bubbles from the catalyst surface, increasing catalytic reactivity. The TEM results further confirmed that the catalyst was mainly composed of rods and flowers (Figure 1e and f), and high-resolutio n TEM (HR-TEM) showed many defects in the lattice fringes, suggesting the formation of vacancies on the catalyst surface after etching with Ar plasma (Figure 1g). The results in Figure S2 show lattice fringes of 0.245 and 0.294 nm, corresponding to the (201) and (330) crystal planes of NiMoO 4 , respectively, and a partially amorphous morphology was produced under the influence of S doping. The Fourier transform further confirmed the presence of vacancies. Figure S3 shows a TEM image of the micro-flower at the tip of NiMoO 4 , which had partial lattice stripes and a large number of amorphous states. The addition of Dy will cause the distortion of the lattice structure of the original NiMoO 4 and affect the growth pattern of the material, thus forming a flower-like structure. Figure 1h shows the linear scanning of the yellow dotted line in Figure 1f. The intensity of S was slightly higher than those of Ni, Mo, and O, confirming that the NiMoO 4 phase was successfully doped with S. The intensity of Dy was very low, mainly because the selected part mainly consisted of NiMoO 4 nanorods, whereas Dy was mainly distributed in the flowery part. In addition, energy-dispersive X-ray spectroscopy (EDS) mapping analysis (Figure 1i) was performed to prove the coexistence and uniform distribution of Ni, Mo, O, S, and Dy. The results indicated the successful doping of Dy and S and further confirmed that Dy was mainly distributed in the flowery part. The crystal structures of NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF, and Sv/Dy–NiMoO 4 /NF were investigated by X-ray diffraction (XRD). As shown in Figure 2a, three strong diffraction peaks are observed at 44.8°, 52.2°, and 76.6°, which are assigned to the (111), (200), and (220) facets of the NF, respectively. In addition to the strong diffraction peaks of NF, the sample also exhibited crystalline phase of NiMoO 4 , identified based on PDF #45-0142. The diffraction peak shifted 0.2° to a lower Angle after Dy doping, which was attributed to the lattice distortion caused by the large ionic radius of Dy. S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF showed significant decreases in the intensity of the diffraction peaks, which is attributed to the introduction of S to the lattice of NiMoO 4 , resulting in the transformation of part of the material from crystalline to amorphous in structure [30]. Owing to the high sensitivity of electron paramagnetic resonance (EPR) to unpaired electrons in the materials, the defect structures of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF were studied in detail using EPR. Vacancy defects can be divided into metallic and nonmetallic types, which can be distinguished by analyzing the spectral splitting factor ( g -factor). In general, a g -factor close to 2.0 indicates a nonmetallic vacancy, while a value of approximately 2.1 indicates a metallic vacancy [31]. Figure 2b shows that the g -factor was 2.005, indicating the presence of a large number of nonmetallic vacancies in the catalyst after Ar plasma etching. The Raman spectra show a comparison of the catalysts before and after the construction of S vacancies. After the construction of the S vacancies, the strength of the Ni–S bond significantly decreased, and a redshift occurred (Figure 2c). This may be because the formation of an S vacancy by removing some S alters the lattice vibration between the Ni and S atoms, resulting in a reduction in peak strength. Moreover, the introduction of S vacancies leads to the coordination of the surrounding Ni, forming a new Ni–S bond, and the bond length and angle change, showing a redshift in the peak position. As shown in Figure 2d and e, the water contact angle and bubble contact angle are 28° and 142.6°, respectively, indicating that Sv/Dy–NiMoO 4 /NF has excellent hydrophilicity and hydrophobicity, which not only increases contact between Sv/Dy–NiMoO 4 /NF and the electrolyte solution but also improves the mass transfer efficiency. Furthermore, it allows the bubble to move quickly away from its surface, preventing the coverage of active sites [32]. In addition, ultraviolet photoelectron spectroscopy (UPS) was used to measure the work functions of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. The work function of S/Dy–NiMoO 4 /NF is 4.11 eV, and that of Sv/Dy–NiMoO 4 /NF is 4.02 eV. This indicates that after the construction of the S vacancies, electrons are more easily transferred from the catalyst interior to the surface, which promotes electron exchange with the reactants and reduces the accumulation of charge at the catalyst interface, thus weakening H* capture at the interface. This is conducive to interface hydrogen overflow and achieves faster reaction kinetics [33]. To further verify the chemical state of the catalyst surface, NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF, and Sv/Dy–NiMoO 4 /NF were analyzed using X-ray photoelectron spectroscopy (XPS). Figure S4a and 4b show the valence state changes of the elements before and after Dy doping, respectively. After Dy doping, Ni moves in the direction of high binding energy. The 4 f 9 electron configuration of Dy with multiple unfilled 4 f orbitals can act as a 3 d orbital electron acceptor for Ni and regulate the central electronic state of Ni; this f – d hybridization induces strong Dy–Ni interactions. The Mo 3 d spectrum of NiMoO 4 shows two strong peaks, confirming that Mo is in the Mo 6+ state. After doping with Dy, the binding energy of Mo exhibits a slight negative shift, indicating that electrons are present at the Mo site. Figure 3a–d show the changes in the chemical states before and after the construction of S vacancies. As shown in Figure 3a, S/Dy–NiMoO 4 /NF shows three characteristic peaks of 162.5, 163.8, and 169.3 eV, which are attributed to S 2– 2 p 3/2 , S 2– 2 p 1/2 , and S–O, respectively, proving the successful doping of S. In Sv/Dy–NiMoO 4 /NF, the content of S 2– 2 p 1/2 was significantly increased, corresponding to low-coordination S, indicating the successful construction of S vacancies. At the same time, the S–O content increased significantly, possibly because the formation of S vacancies changed the chemical environment of the surrounding atoms to increase the electron density and thus the strength of the S–O bond [34] . S is enriched on the surface of the material, and the surface S is preferentially removed during etching, resulting in a significant increase in the surface S vacancies concentration. O forms a stronger ionic bond with the metal (Mo-O-Ni), so O is more stable in the catalyst, preferentially forming an S vacancy rather than an O vacancy during etching. Figure 3b shows that the S/Dy–NiMoO 4 /NF high-resolution Ni 2 p spectrum is deconvolved into two spin-orbit peaks with wide satellite peaks at 879.1 and 861.0 eV, respectively. The peaks at 874.6 and 856.2 eV are attributed to the hypervalent Ni 3+ species. The two peaks at 871.3 and 853.8 eV are attributed to Ni 2+ . After the construction of the S vacancies, the Ni 2+ /Ni 3+ ratio increased significantly, and the residual electrons of the S vacancies were transferred to the Ni site, resulting in a change in the electronic environment of the Ni site, which optimized the adsorption and deionization of water. Compared to Dy–NiMoO 4 /NF, the valence states of Mo 4+ and Mo 5+ appeared in the 3 d spectrum of Mo in S/Dy–NiMoO 4 /NF (Figure 3c), whereas the oxidation state of Mo increased after the construction of S vacancies, and the species contents of Mo 4+ and Mo 5+ decreased significantly. The high-resolution Dy 4 d spectrum of S/Dy–NiMoO 4 /NF shows two characteristic peaks at 153.8 and 156.9 eV corresponding to Dy 4 d 1/2 and Dy 4 d 5/2 , respectively, and the chemical state of Dy did not change significantly after the construction of S vacancies (Figure 3d). The electronic interactions in Sv/Dy-NiMoO₄/NF were systematically investigated. In the absence of Dy, the t ₂g orbitals of Ni remain fully occupied, resulting in strong electronic repulsion within the Ni-S-Ni moiety. However, upon Dy incorporation, Dy hybridizes with the 3d orbitals of Ni and the 2p orbitals of S, establishing 4f-2p-3d orbital coupling (Figure 3e). This interaction facilitates electron redistribution, where Dy acts as an electron acceptor, effectively mitigating electronic repulsion and optimizing the d-band center. Consequently, the modified electronic structure enhances the adsorption of reaction intermediates, significantly improving the electrocatalytic performance in the water splitting process. 2.2. Electrocatalytic performance of Sv/Dy–NiMoO 4 /NF The electrocatalytic activity of Sv/Dy–NiMoO 4 /NF was investigated using a typical three-electrode configuration containing 1.0 M KOH. At first, the HER properties of catalysts with different Ar plasma etching times were compared. With an etching time of 7.5 min, the catalyst showed excellent HER properties and an ultra-low overpotential (Figure S5). The linear-sweep voltammetry (LSV) curve in Figure 4a shows that Sv/Dy–NiMoO 4 /NF had significant HER catalytic activity, and a current density of 10 mA cm −2 was achieved at an overpotential of only 29 mV. This performance was better than that of NiMoO 4 /NF (252 mV), Dy–NiMoO 4 /NF (225 mV), and S/Dy–NiMoO 4 /NF (125 mV), as well as that of commercial Pt/C catalysts; the prepared catalyst still showed excellent performance under the high current density used in industrial production. Furthermore, Sv/Dy–NiMoO 4 /NF shows an extremely low Tafel slope of 36.9 mV dec −1 , with fast kinetic characteristics in the HER process (Figure 4b). Generally, HER involves two adsorption/desorption processes. The Tafel slope values corresponding to the adsorption (Volmer) step are approximately 120 mV dec −1 , and the Tafel slope values corresponding to the Heyrovsky and Tafel desorption steps are 40 and 30 mV dec −1 , respectively. Therefore, Sv/Dy–NiMoO 4 /NF followed Volmer–Tafel kinetics. The electrochemically active surface area (ECSA) of each sample is expressed by the double-layer capacitance ( C dl ) (Figure S6). Compared to NiMoO 4 /NF (1.3 mF cm −2 ), Dy–NiMoO 4 /NF (2.5 mF cm −2 ) and S/Dy–NiMoO 4 /NF (119.3 mF cm −2 ), Sv/Dy–NiMoO 4 /NF had larger ECSAs (54.2 mF cm −2 ). The exposure of more active sites resulted in a higher HER activity (Figure 4c). In addition, electrochemical impedance spectroscopy (EIS) was performed (Figure 4d) to determine the electron transfer dynamics between the electrolyte and electrode. After S doping, the hybrid p – d – f orbitals changed the electron-state density of the material, resulting in a significant decrease in the resistance. After the construction of S vacancies, the resistance value of 0.9 Ω was almost metallic, indicating that the Sv/Dy–NiMoO 4 /NF catalyst had rapid charge-transfer characteristics. Stability is an important parameter for evaluating the performance of catalysts in electrochemical reactions. As shown in Figure 4e, after 20 h of electrolysis, the current density changed only slightly, indicating excellent stability. Compared with some recently published work on HER electrocatalysts, the prepared Sv/ Dy-NiM O O 4 /NF showed advantages (Figure 4f and Table S1). Owing to its slow kinetics and high thermodynamic barrier, the actual oxidation potential of the OER is much higher than the theoretical decomposition voltage of water (1.23 V); the OER accounts for most of the energy consumption in water splitting. The theoretical oxidation potential of glycerol is low. To reduce the battery voltage required for water decomposition, a glycerol-coupled water electrolysis system was constructed using the GOR to replace the OER. First, the GOR performances of NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF, and Sv/Dy–NiMoO 4 /NF were compared in electrolytes containing 1 M KOH and 0.1 M glycerol. As shown in Figure 5a, Sv/Dy–NiMoO 4 /NF required an overpotential of only 1.34 V to achieve a current density of 10 mA cm −2 and had a very low Tafel slope of 43.6 mV dec −1 , indicating that the catalyst has good kinetics in the GOR (Figure 5b). The GOR and OER properties of Sv/Dy–NiMoO 4 /NF were compared, and the GOR had a potential drive 160 mV less than that of the OER at a current density of 10 mA cm −2 (Figure 5c). Because the GOR would not occur at a very low potential, while the OER would compete at a high potential and affect the Faraday efficiency of the product, the potential range of 1.30–1.50 V was selected for 1 h of electrolysis. By comparing the nuclear magnetic resonance hydrogen spectrum ( 1 H NMR) of the products obtained at different potentials, the product was identified as mainly formic acid (Figure 5d). At a voltage of 1.30 V, the GOR did not occur; therefore, almost no formic acid was formed. As the voltage increased, the Faraday efficiency of formic acid gradually increased, reaching a maximum of 92.7% at 1.45 V and decreasing at 1.50 V, owing to competition with the OER. High-performance ion chromatography (IC) was used to quantify the reaction product and reveal the ability of the GOR catalyzed by Sv/Dy–NiMoO 4 /NF to produce formic acid (Figure 5e and f) [35]. The composition of the product was analyzed hourly using the chronocurrent method at a voltage of 1.45 V. In the continuous electrolytic process, the main reaction product was formic acid. The formic acid product was quantitatively analyzed using the standard curve method, and its content reached 137.6 mg/L after 5 h. In addition, 1 H NMR analysis of the products obtained hourly during electrolysis showed that the glycerol content gradually decreased and the formic acid content gradually increased over time, which is consistent with the IC results, indicating that the GOR process catalyzed by Sv/Dy–NiMoO 4 /NF had strong selectivity for formic acid (Figure S7). Because Sv/Dy–NiMoO 4 /NF exhibited excellent HER, OER, and GOR properties, it was used in an integrated overall water splitting (OWS) system and a glycerol electrooxidation-coupled hydrogen evolution two-electrode system with alkaline electrolytes. The LSV curve intuitively shows that Sv/Dy–NiMoO 4 /NF in the glycerol electrooxidation-coupled hydrogen evolution system significantly reduces the voltage compared to that in the OWS system, and the potential drive is reduced by 236 mV at a current density of 100 mA cm −2 (Figure S8). In addition, the Faraday efficiency of Sv/Dy–NiMoO 4 /NF in OWS was measured, and the drainage method of the H-type electrolytic cell was used as a visual parameter to evaluate the efficiencies of H 2 and O 2 production by the anode and cathode. As shown in Figure S9, the ratio of H 2 to O 2 was approximately 2:1, consistent with the theoretical value, and the Faraday efficiency of H 2 production reached 98.8%. Changes in the surface chemical state of Sv/Dy–NiMoO 4 /NF after the HER and GOR tests were analyzed using XPS. As shown in Figure S10a, the high-resolution Ni 2 p spectrum shows that after the HER, the content of Ni 3+ increased and that of Ni 0 disappeared. After the GOR test, Ni was only slightly oxidized, and the content of Ni 0 decreased, indicating that HER activity is more inclined to occur at the Ni site. The Mo 3 d spectra show that slight oxidation occurred after both the HER and GOR, and the content of Mo 4+ and Mo 5+ decreased (Figure S10b). Figure S10c and d show the S 2 p and Dy 4 d spectra, respectively. The HER and GOR tests caused few obvious changes, and only a small reduction in the S–O bond appeared, which may arise from *OH attacking the S–O bond during electrocatalysis, resulting in a decrease in bond strength. The morphologies of the catalysts after the GOR testing were characterized using SEM and TEM. As shown in Figure S11 and S12, the morphology of Sv/Dy–NiMoO 4 /NF showed no obvious changes, proving the excellent stability of the catalyst. These results indicate that Sv/Dy–NiMoO 4 /NF exhibited excellent catalytic ability in both the three-electrode and two-electrode systems; however, its suitability for industrial production requires further evaluation. An alkaline anion-exchange membrane electrolyzer device was assembled using the membrane electrode assembly, as shown in Figure S13. Sv/ Dy-NiMoO 4 /NF was used as cathode and anode, the size was 1*1*0.05 cm, and the flow rate of peristaltic pump was 150 ml/min. A voltage of only 1.39 V was required to reach a current density of 10 mA cm −2 in 1 M KOH + glycerol, whereas a voltage of 1.65 V was required to drive OWS. Therefore, the proposed strategy of using Sv/Dy–NiMoO 4 /NF in glycerol electrooxidation-assisted hydrogenolysis has potential applicability for industrial production. 2.3. In situ operando characterization Operando characterization is important for understanding the mechanisms involved in catalytic reactions. In situ EIS was used to analyze the electrochemical kinetic behavior of the Sv/Dy–NiMoO 4 /NF interface with the electrolyte in the OER and GOR systems, and the corresponding Bode plots are shown in Figure 6a and 6b. Generally, the phase angle peak in the low-frequency region is related to the resistance of the interface reaction, while that in the high-frequency region represents the electrooxidation of the catalyst. In the OER system with 1 M KOH, Sv/Dy–NiMoO 4 /NF was 1.50 V versus a reversible hydrogen electrode (RHE), and a clear transition peak was observed in the low-frequency region, indicating the initiation of OER [36]. When 0.1 M glycerol was added to the reaction system, Sv/Dy–NiMoO 4 /NF was 1.35 V versus RHE. An obvious transition peak was observed in the low-frequency region before the GOR process began, indicating that glycerol can cause a negative shift in the radio potential, which is consistent with the results of 1 H NMR. To investigate the phase evolution of Sv/Dy–NiMoO 4 /NF during GOR and the actual reaction site, the Sv/Dy–NiMoO 4 /NF changes in the OER and GOR systems were measured by in situ Raman spectroscopy in the range of 1.2–1.75 V versus the RHE potential. As shown in Figure 6c, with an increase in the potential, the MoO 2 2− peak at 358 cm −1 gradually decreased in strength, almost disappearing at high potentials; the strength of the M–O bond indicated by the peaks at 827, 864, and 942 cm −1 also gradually decreased. This is because, in the OER process, the Sv/Dy–NiMoO 4 /NF surface was oxidized, resulting in M–O bond breakage. With an increase in potential, the oxidation effect was enhanced, promoting M–O bond breakage. Under the action of an electric field, MoO 2 2− was detached from the Sv/Dy–NiMoO 4 /NF surface and entered the electrolyte solution (Figure 6c) [37]. In the GOR system, the glycerol adsorbed on the catalyst surface changed the surface properties of the catalyst and covered the active sites, thus inhibiting the Raman signal of the M–O bond. With increasing potential, the GOR reaction intensity increased, the glycerol adsorption layer on the Sv/Dy–NiMoO 4 /NF surface was destroyed, and the M–O bonds were re-exposed. At this time, glycerol was gradually converted into formic acid, and the local environment of the Sv/Dy–NiMoO 4 /NF surface changed, leading to an increase in the Raman activity of the M–O bonds (Figure 6d). To monitor the oxidation pathway of glycerol during the GOR process, in situ electrochemical IR spectroscopy of glycerol was performed at different electrolysis times on Sv/Dy–NiMoO 4 /NF at a potential of 1.45 V vs. RHE. The signal located at 1076 cm −1 corresponded to the ethanoic acid reaction, and the characteristic peak at 1226 cm −1 assigned to glyceraldehyde suggested a GOR process that first generates glyceraldehyde via the oxidation of the terminal hydroxyl group. In addition, the two characteristic peaks at 1350 and 1381 cm −1 corresponded to the O–C–O symmetric stretching vibrations of the carboxylate, and the signal at 1585 cm −1 indicated an O–C–O antisymmetric stretching vibration that was enhanced by the generation of formate. The bending vibration of OH supplied from the KOH electrolyte had a persistent characteristic peak at 1662 cm −1 , which contributed to the GOR. As the reaction time increased, further oxidation of formate may have occurred, reflected by a weak asymmetric stretching vibration of CO 2 at 2364 cm −1 [14, 15]. Based on the above results and previous reports, the possible reaction pathways for glycerol on the Sv/Dy–NiMoO 4 /NF surface were hypothesized as follows. First, the hydroxyl group at the end of glycerol was oxidized to produce glyceraldehyde, which was further oxidized as an intermediate to produce glycolic acid. The oxidation of glyceraldehyde could be divided into two steps: glyceraldehyde underwent C–C bond cleavage to generate ethanoic acid and formate, and ethanoic acid then underwent C–C bond cleavage to generate formate. 2.4. DFT calculations To explore the intrinsic relationship between water and glycerol molecules, as well as electrocatalytic activity, S/Dy–NiMoO 4 /NF was selected as the model, and electron redistribution in S/Dy–NiMoO 4 /NF was realized by constructing S vacancies. In addition, DFT calculations were performed according to the crystal structure. As shown in Figure 7a and b, after the introduction of S vacancies, electrons were depleted in the Ni 3 d and S 2 p overlapping regions and accumulated on Ni-S-Dy atoms (yellow and blue represent electron accumulation and consumption, respectively), and S vacancies caused significant electron redistribution in the crystal. From the density of states, it can be seen that the D-band centers of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF were −1.92 eV and −1.73 eV from the Fermi level, respectively. These are close to the Fermi level, indicating that the degree of anti-bonding orbital occupation was reduced and the bonding effect was enhanced. This is beneficial for strengthening the electronic coupling between the metal sites on the catalyst surface and the intermediates of water and glycerol oxidation, thus promoting the HER and GOR processes (Figure 7c and d) [12] . To clarify the ability of electrons to be liberated from the catalyst surface before and after the construction of S vacancies, the work functions of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF were calculated to be 5.50 and 5.56 eV, respectively, indicating that etching with Ar plasma led to a decrease in the work function. This is consistent with the UPS (Figure 7e and f). Figure 7g and h show the adsorption energies of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF for OH* and Gly*, respectively. After the introduction of S vacancies, the adsorption energy of *OH increased from −0.72 eV to −1.01 eV, indicating the presence of more OH groups on the surface of the catalyst. Meanwhile, the adsorption energy of Gly* increased from −2.24 eV to −2.48 eV, which further indicated that the introduction of S vacancies contributed to the interaction of water and glycerol and enhanced the performance of HER and OER. The performance of HER was evaluated by the Gibbs free energy (ΔG H* ) of hydrogen adsorption. As shown in Figure 7i, the ΔG H* of Mo, Ni, S and S vacancies atoms on the surface of Sv/Dy–NiMoO 4 /NF were –1.05, 0.18, -0.43 and -0.25 eV, respectively. ΔG H* at the Ni site was closer to 0 eV, indicating that the Ni site was the main active site on the Sv/Dy–NiMoO 4 /NF surface. In addition, ΔG H* at the S site in S/Dy–NiMoO 4 /NF was −0.43 eV, and the introduction of S vacancies reduced ΔG H* at the S site, showing good H* adsorption/desorption kinetics for HER. Conclusion Sv/Dy–NiMoO 4 /NF bouquet-like array structures were prepared by Dy doping and introducing S vacancies with Ar plasma for catalytic GOR to produce high-value-added formates, and GOR and HER were coupled to achieve the efficient production of H 2 . Benefiting from the formation of 4 f –2 p –3 d gradient orbital coupling and the reduction of the work functions, excellent HER activity (a 29 mV overpotential at 10 mA cm −2 ) and GOR performance (1.34 V vs. RHE at 10 mA cm −2 ) were obtained. The membrane electrode assembly with Sv/Dy–NiMoO 4 /NF as the anode and cathode provided a current density of 10 mA cm −2 at a cell voltage of 1.39 V, 260 mV lower than the voltage necessary for OWS. DFT calculations showed that Sv/Dy–NiMoO 4 /NF had good adsorption energy for *OH and *Gly, and good H* adsorption/desorption kinetics were realized through the introduction of S vacancies. This study realizes the simultaneous production of high value-added chemicals and clean energy and provides sufficient guidance for the design of novel transition-metal catalysts and promoting hydrogen production from biomass oxidation coupling. Acknowledgments： This study was supported by grants from the National Natural Science Foundation of China (22166034); the Project of Development and Reform Commission of Jilin Province (China) (2024C020-6) and the Higher Education Discipline Innovation Project (111 Project, D18012). Conflicts of Interest: The authors declare no conflict of interest. Author statement: Zhi-Yuan Feng is responsible for paper writing and testing; Jin-Chi Jiang is responsible for data processing; Biao Jin is responsible for the nuclear magnetic testing of products, Long-Yue Meng is responsible for scheme design and analysis. 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(i) Element mapping images of Sv/Dy–NiMoO 4 /NF. Figure 2 (a) XRD patterns of NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. (b) EPR spectra of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. (c) Raman spectrum of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. (d) Contact angle of Sv/Dy–NiMoO 4 /NF. (e) Bubble contact angle of Sv/Dy–NiMoO 4 /NF. (f) UPS spectrum of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. Figure 3 (a) High-resolution of S 2p spectra, (b) Ni 2p spectra, (c) Mo 3d spectra and (d) Dy 4d spectra in S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. (e) The schematic diagram of 4f-2p-3d electron interaction in Sv/Dy–NiMoO 4 /NF. Figure 4 (a) LSVs of NF, NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF, Sv/Dy–NiMoO 4 /NF and Pt/C for catalyzing HER at a scanning rate of 5 mV s −1 in 1 M KOH in three-electrode system. (b) Tafel plots and (c) C dl values at different scanning rates of all studied electrocatalysts. (d) Nyquist plots of all studied electrocatalysts. (e) Chronoamperometry i-t curve of 20 h for HER in three-electrode system. (f) Compared of overpotential at 10 mA cm –2 of the Sv/Dy–NiMoO 4 /NF catalyst with the recently reported catalyst. Figure 5 (a) LSVs of NF, NiMoO 4 /NF, Dy–NiMoO 4 /NF, S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF for catalyzing GOR at a scanning rate of 5 mV s −1 in 1 M KOH in three-electrode system. (b) Tafel plots of all studied electrocatalysts. (c) LSVs of the Sv/Dy–NiMoO 4 /NF for OER and GOR in three-electrode system. (d) 1 H NMR spectrums of solutions obtained after GOR for 1 h under the potential of 1.30 V, 1.35 V, 1.40 V, 1.45 V and 1.50 V, respectively. (e) The evolution of IC chromatograms as a function of electrolyzing time. (f) Standard IC chromatograms and the corresponding calibration curves of formate. Figure 6 (a) Bode phase plots of Sv/Dy–NiMoO 4 /NF electrode at various potentials in 1.0 M KOH and (b) 1.0 M KOH with 0.1 M GLY. (c) In situ Raman spectra of Sv/Dy–NiMoO 4 /NF electrode at various potentials in 1.0 M KOH and (b) 1.0 M KOH with 0.1 M GLY. Figure 7 The atomic structure models and the three-dimensional charge density of (a) S/Dy–NiMoO 4 /NF and (b) Sv/Dy–NiMoO 4 /NF. Total and projected DOS for (c) S/Dy–NiMoO 4 /NF and (d) Sv/Dy–NiMoO 4 /NF. The computed work functions of (e) S/Dy–NiMoO 4 /NF and (f) Sv/Dy–NiMoO 4 /NF. Adsorption energy of (g) OH* and (h) Gly* on S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF. (i) The Gibbs free energy diagrams for HER on Mo, Ni site of Sv/Dy–NiMoO 4 /NF, and S site of S/Dy–NiMoO 4 /NF and Sv/Dy–NiMoO 4 /NF, H* denotes the adsorbed hydrogen intermediate. 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Synergistic gradient orbital coupling and work function engineering for high-efficiency hydrogen production via glycerol electrooxidation. Authorea . 08 May 2025. DOI: https://doi.org/10.22541/au.174669020.02924729/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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