Ce and S Co-Induced Oxygen Vacancies for Enhanced Alkaline Water Electrolysis

Ce and S Co-Induced Oxygen Vacancies for Enhanced Alkaline Water Electrolysis | 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 Research Article Ce and S Co-Induced Oxygen Vacancies for Enhanced Alkaline Water Electrolysis Ruxin Lei, Yufeng Zhang, Li Chen, Yuying Wu, Haitao Chen, Si Chen, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9258813/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 17 You are reading this latest preprint version Abstract Rational regulation of surface reconstruction and defect chemistry is crucial for developing high-performance non-noble-metal electrocatalysts toward the oxygen evolution reaction (OER). Herein, a Ce- and S-co-induced oxygen-vacancy strategy is developed to construct an ultrathin NiCeS nanosheet array grown in situ on nickel foam (NiCeS/NF) via a molten-salt route. Structural analyses reveal that NiCeS/NF features a multiphase Ni–Ce–S framework composed of sulfide, oxysulfide, and sulfate species, together with abundant heterointerfaces and defect-rich surface environments. Spectroscopic studies demonstrate that the synergistic coupling of Ce and S effectively redistributes the local electronic structure of Ni sites, enriches oxygen-deficient species, and accelerates electrochemical surface reconstruction into the active oxyhydroxide phase. Benefiting from the integrated structural and electronic modulation, NiCeS/NF exhibits outstanding OER performance in alkaline media, delivering a low overpotential of 187 mV at 10 mA cm − 2 , a small Tafel slope of 44.1 mV dec − 1 , and robust durability at 1000 mA cm − 2 for ≈ 400 h. This work provides an effective defect/interfacial engineering strategy for promoting alkaline water oxidation and offers insight into the cooperative role of rare-earth and sulfur species in reconstructive electrocatalysis. Ni-based electrocatalyst cerium and sulfur co-doping oxygen vacancies surface reconstruction oxygen evolution reaction alkaline water electrolysis Figures Figure 1 Figure 2 Figure 3 1. Introduction Hydrogen, as a clean energy carrier, possesses several prominent advantages, including high energy density, sustainability, stability and zero direct pollution [ 1 , 2 ]. It is widely regarded as one of the most promising candidates to partially replace fossil fuels in the 21st century. Compared with conventional fossil fuels, the utilization of hydrogen does not generate CO₂ or other greenhouse gases during combustion, and hydrogen can be integrated into diverse energy sectors such as transportation, industry and power storage. With the continuously growing global demand for sustainable energy, the application prospects of hydrogen as a green energy vector are highly anticipated. In particular, under the current worldwide push toward a low-carbon economy, the strategic importance of hydrogen is becoming increasingly prominent. Among various hydrogen production technologies, electrocatalytic water splitting is considered one of the most efficient and practically promising routes. This technology produces hydrogen and oxygen via the electrolysis of water and is compatible with high energy-conversion efficiency. However, the oxygen evolution reaction (OER) [ 3 ], as the anodic half-reaction in water splitting, involves a complex four-electron transfer process and is intrinsically sluggish in kinetics. This severely hampers the efficiency of water oxidation and thus limits the overall performance of water splitting. Consequently, the development of highly active and robust OER electrocatalysts—especially those capable of lowering the overpotential and accelerating the reaction rate—is crucial for enhancing the efficiency of water electrolysis [ 4 ]. To date, noble-metal-based catalysts, particularly Ru and Ir-containing materials, have delivered the highest OER activity. Nevertheless, their high cost and limited abundance severely hinder large-scale deployment. Therefore, it is imperative to develop non-noble-metal electrocatalysts that combine low cost with high activity and long-term stability. In recent years, a variety of transition-metal-based materials [ 5 ], including phosphides [ 6 ], sulfides [ 7 ], carbides, oxides [ 8 ], and selenides, have emerged as promising alternatives to noble metals because of their excellent catalytic performance, low cost, and environmental compatibility. Among them, transition-metal sulfides are especially attractive because their unique physicochemical properties, such as relatively low resistivity and favorable electrical conductivity, can endow them with high OER activity. For example, Xue et al. reported a W-doping-induced phase-transition strategy, in which a W–Ni 3 S 2 /Ni 7 S 6 heterojunction was constructed to markedly enhance catalytic performance [ 9 ]. The incorporation of W not only tailored the catalyst morphology, leading to the formation of uniform nanorod arrays, but also modulated the electronic structure of Ni, promoted the generation of a higher proportion of Ni 3+ species, and thereby activated the catalytic process. Meanwhile, the emergence of the new Ni₇S₆ phase further improved the intrinsic activity of the catalyst. Beyond transition-metal-sulfide engineering, the introduction of rare-earth elements provides an additional and powerful means of regulating the electronic structure of catalytic centers. Rare-earth elements possess distinctive 4f-electron characteristics. Their 4f orbitals are highly localized and energetically close to the 5d and 6s orbitals, enabling sensitive charge-transfer and valence-buffering effects when coordinated near transition-metal centers [ 10 – 12 ]. These elements can modulate the electron occupancy at metal sites and the metal–ligand covalency through valence fluctuations and oxygen-vacancy regulation, thereby influencing both the adsorption strength of key reaction intermediates and the preferred reaction pathway. Cerium-based systems are particularly representative. The reversible Ce³⁺/Ce⁴⁺ redox couple endows Ce with excellent oxygen storage/release capability and, through the generation or stabilization of near-surface oxygen vacancies, reshapes the local crystal field and band-edge positions. When Ce is coupled with Ni active sites, the Ni–O–Ce bridge can induce directional charge compensation, resulting in moderate de-electronation of the Ni 3d band, enhanced metal–ligand hybridization, and optimized interactions with critical intermediates such as *OH, *O, and *OOH [ 13 ]. This electronic redistribution not only facilitates the electrochemical reconstruction from Ni(OH)₂ to the active NiOOH phase, but also provides an oxygen-vacancy/oxygen-refilling channel for lattice-oxygen-involved pathways, thereby lowering the OER energy barrier from both kinetic and thermodynamic perspectives. In parallel with such rare-earth-induced electronic regulation, sulfur incorporation can further amplify interfacial and charge-transport effects. Sulfur coordination enhances the intrinsic electrical conductivity and carrier density of the precatalyst, reduces the interfacial charge-transfer resistance, and accelerates self-reconstruction during the initial stages of anodic polarization, thereby enabling the rapid formation of a hydroxyl-rich, defect-rich, and electronically well-coupled amorphous active layer [ 14 , 15 ]. As polarization proceeds, part of the sulfur species undergo leaching and S–O exchange, leading to the formation of a surface shell containing sulfate species. This shell can stabilize key intermediates such as *OOH through hydrogen-bonding and electrostatic interactions, thereby lowering the free-energy barrier for the *O → *OOH step [ 16 , 17 ]. In this context, rare-earth elements and sulfur play complementary roles at the same interface: rare-earth species serve as electronic buffers and oxygen-vacancy regulators, whereas sulfur enhances conductivity and stabilizes reaction intermediates. Together, they reshape the adsorption-energy landscape and reconstruction pathway around transition-metal centers, rendering the catalytic interface more favorable for the OER [ 18 ]. In this work, we report a Ce- and S-co-doped Ni-based electrocatalyst (NiCeS/NF) supported on nickel foam, and systematically evaluate its structure and electrocatalytic performance using a suite of physicochemical and electrochemical techniques. Comparative studies with related catalysts demonstrate that NiCeS/NF exhibits superior OER performance, characterized by a low overpotential and excellent durability. These results highlight the substantial potential of Ce and S co-doping as an effective strategy to synergistically boost the catalytic activity and stability of non-noble-metal OER electrocatalysts. 2. Experimental Section 2.1 Chemicals and Materials KOH (95%) and Ce(NO₃)₃·6H₂O were purchased from Macklin, while Ni(NO₃)₃·6H₂O was obtained from Chengdu Jinshan, and potassium thiocyanate was acquired from Beijing Inokai. Nickel foam was supplied by Kunshan Guangjiayuan New Materials Co., Ltd. All chemicals used in this study were of analytical grade and did not require further purification. Deionized water was used throughout the experimental procedures. 2.2 Synthesis of Samples The nickel foam (NF) was cleaned with anhydrous ethanol in an ultrasonic bath to obtain a clean surface. A 20 mL glass bottle was charged with 3 g of Ni(NO₃)₃·6H₂O, 2.17 g of Ce(NO₃)₃·6H₂O, and 1 g of potassium thiocyanate. After reacting at 120°C in an oven for 2 hours, NiCeS/NF was obtained. For comparison, NiCe/NF was prepared by reacting 3 g of Ni(NO₃)₃·6H₂O and 2.17 g of Ce(NO₃)₃·6H₂O under the same conditions. NiS/NF was synthesized by adding only 3 g of Ni(NO₃)₃·6H₂O and 1 g of potassium thiocyanate. CeS/NF was prepared by adding only 2.17 g of Ce(NO₃)₃·6H₂O and 1 g of potassium thiocyanate, with all other conditions remaining the same. 2.3 Characterization The crystallographic phases of the samples were analyzed using X-ray diffraction (XRD) with a Bruker diffractometer. The microstructure and morphology were examined by field emission scanning electron microscopy (SEM, Zeiss Supra, Carl Zeiss), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and energy-dispersive X-ray spectroscopy (EDX) using a 200 kV FEI Tecnai G2 F20 field-emission TEM. The chemical composition and valence states of the samples were analyzed by X-ray photoelectron spectroscopy (XPS, AXIS Ultra DLD, Kratos Analytical Ltd.). Electron paramagnetic resonance (EPR) measurements were performed at 77 K using a Bruker A300-10/12 spectrometer. 2.4 Electrochemical Measurements The synthesized catalyst (1 cm × 1 cm) was used as the working electrode (WE), with a Hg/HgO (1 M KOH) electrode and a platinum sheet (1 cm × 1 cm) serving as the reference and counter electrodes, respectively. The measured potential was converted to the reversible hydrogen electrode (RHE) scale. Cyclic voltammetry (CV) was performed at a scan rate of 30 mV/s in 1.0 M KOH for 30 cycles to activate the samples. Linear sweep voltammetry (LSV) was carried out at a scan rate of 5 mV/s under the same conditions to record the polarization curves. Electrochemical impedance spectroscopy (EIS) was measured in the frequency range of 10⁻² to 10⁵ Hz. The electrochemical active surface area (ECSA) was evaluated by CV in the narrow non-faradaic electrochemical window at different scan rates (100 to 200 mV/s) to assess the double-layer capacitance. Long-term stability tests were conducted using chronoamperometry at an initial current density of 1000 mA cm⁻² in 1.0 M KOH to evaluate the durability of the catalysts. 3. Results and Discussion 3.1 Structural and Morphological Characterizations Using nickel nitrate, cerium nitrate, and potassium thiocyanate as precursors, ultrathin three-dimensional NiCeS nanosheets were grown in situ on nickel foam (NF) via a molten-salt method. X-ray diffraction (XRD) was used to determine the phase composition and multiphase characteristics of the as-prepared sample. As shown in Fig. 1 a, the diffraction peaks at 25.43°, 26.67°, 29.06°, and 30.70° are assigned to the (1 1 1) plane of Ce 2 S 3 (PDF#21–0189), the (0 0 4) plane of Ce(SO 4 ) 2 (PDF#22–0546), the (1 0 1) plane of Ce 2 O 2 S (PDF#26-1085), and the (− 2 1 2) plane of Ni x S 6 (PDF#51–0718), respectively. These results confirm the formation of a Ni–Ce–S multiphase framework composed of sulfide, oxysulfide, and sulfate phases on the NF surface. The formation of these phases originates from the decomposition and rearrangement of SCN − in the molten-salt medium. This process generates S 2− /S x 2− species together with sulfur–oxygen intermediates, driving the simultaneous formation of sulfide, oxysulfide, and sulfate phases. The molten-salt medium lowers the barriers for nucleation and phase evolution, resulting in intimate coupling of the different phases within the nanosheet framework. This multiphase architecture creates abundant heterointerfaces and defect sites, which regulate charge distribution and provide adsorption sites for reaction intermediates during electrochemical reactions.[ 19 ]. The morphology and elemental distribution of NiCeS/NF, NiCe/NF, NiS/NF, CeS/NF, and bare NF were characterized using SEM, TEM, and EDS. The SEM results show that in the NiCeS/NF sample, a large number of ultra-thin nanosheets grow uniformly and densely in a vertical/inclined orientation on the surface of the three-dimensional porous nickel foam framework (Fig. 1 b), forming an open and interconnected 3D sheet network. This structure is beneficial for electrolyte infiltration and active site exposure. In contrast, NiCe/NF exhibits a dense honeycomb-like sheet structure (Figure S1 ), and comparison between the two demonstrates that the introduction of sulfur causes the nanosheets to form a densely stacked structure, significantly increasing the specific surface area and enhancing the catalyst’s interaction with the electrolyte. To further analyze its fine structure, TEM and HRTEM analyses were performed on NiCeS/NF. The low magnification TEM image (Fig. 1 c) shows that the material consists of numerous interconnected and partially stacked ultra-thin nanosheets, forming hierarchical porous channels. This thin and cross-linked structure helps shorten the charge/ion diffusion path and promote interfacial electron transfer. HRTEM images reveal distinguishable lattice fringes, with a lattice spacing of approximately 0.22 nm attributed to the Ni x S₆ (-2 2 4) plane and a spacing of 0.21 nm corresponding to the (0 4 2) plane of Ce(SO₄)₂ (Fig. 1 d). EDS mapping confirms that Ni, Ce, S, and O elements are evenly distributed within the composite catalyst layer (Fig. 1 e-f), with atomic ratios of 26.0:1.9:1.4:70.7 (Figure S2 and Table S1 ), indicating the successful formation of a multi-element synergistic system. The selected area electron diffraction (SAED) pattern shows clear concentric diffraction rings, which are attributed to the (2 2 2), (0 1 8) planes of Ni x S₆ and the (2 0 4) plane of Ce₂O₂S (Figure S3). This further confirms the polycrystalline nature of the material, where randomly oriented nanocrystals and interconnected sheet-like pores together form a conductive backbone and high-speed mass transport network. These results collectively indicate that the molten salt method promotes the synergistic regulation of Ni, Ce, and S at the nickel foam interface, leading to the formation of ultra-thin nanosheet structures with multi-element coupling, thereby laying a structural foundation for enhancing its electrocatalytic performance. To clarify the surface electronic structure and interfacial coupling of the as-prepared catalyst, X-ray photoelectron spectroscopy (XPS) was carried out. As shown in Fig. 2 a, the survey spectrum of NiCeS/NF displays clear signals of Ni, Ce, S, and O, confirming the successful incorporation of these elements on the NF surface. High-resolution Ni 2p spectra show that the Ni²⁺ 2p 3/2 peak of NiCeS/NF is located at 856.25 eV and is positively shifted relative to that of the Ni-containing reference sample (Fig. 2 b). This shift indicates a decrease in the electron density around the Ni sites, revealing interfacial charge redistribution induced by the coupling of Ni, Ce, and S species. As a result, the Ni centers in NiCeS/NF exhibit a more electron-deficient electronic state and a modified local coordination environment. Such electronic modulation is favorable for the anodic oxidation of Ni species and thus facilitates the formation of the active NiOOH phase under operating conditions. [ 20 , 21 ] The Ce 3d spectrum provides further evidence for the electronic interaction between Ce and the Ni-based framework. Compared with the reference sample, NiCeS/NF shows an increased Ce 3+ /Ce 4+ ratio together with a weakened characteristic Ce 4+ feature at around 917.7 eV (Fig. 2 c), indicating partial reduction of Ce 4+ to Ce 3+ . This result suggests that Ce in NiCeS/NF is stabilized in a more defect-rich electronic state through interfacial coupling with the Ni-containing phase. The coexistence of Ce³⁺ and Ce⁴⁺ is also associated with the formation of oxygen-deficient environments, which help regulate local charge balance and promote surface reconstruction during the electrochemical process [ 13 ]. In contrast, the stronger Ce⁴⁺ signature in CeS/NF indicates that, without coupling to Ni species, Ce tends to remain in a more oxidized surface state. The high-resolution S 2p spectra further reveal the chemical state of sulfur in the different samples (Fig. 2 d). For NiCeS/NF, the peaks located at 162.8 and 164.1 eV are assigned to the S 2p₃/₂ and S 2p₁/₂ components of metal–S species, respectively, while the peak at 169.0 eV is attributed to oxidized sulfur species (S–O). Similar features are also observed in NiS/NF and CeS/NF. Specifically, the S 2p signals of NiS/NF appear at 163.1 and 164.4 eV, with the oxidized sulfur peak located at 168.8 eV, whereas CeS/NF shows the corresponding peaks at 162.9, 164.3, and 168.7 eV. The coexistence of metal–S and S–O species confirms that sulfur is present in both reduced and oxidized forms in all three samples. Compared with NiS/NF and CeS/NF, the sulfur species in NiCeS/NF show distinct binding-energy shifts, indicating that the simultaneous incorporation of Ni and Ce alters the local electronic structure around sulfur through interfacial coupling [ 22 ]. These results suggest that sulfur in NiCeS/NF contributes not only to the construction of the sulfide framework, but also to the regulation of the surface chemical environment. The coexistence of reduced sulfur and oxidized sulfur species is closely related to the surface reconstruction behavior under anodic conditions, where sulfide species promote precursor activation, while surface S–O species help stabilize the oxygenated interfacial environment during OER [ 23 ]. The O 1s spectrum can be deconvoluted into three components corresponding to lattice oxygen (M–O), hydroxyl species (M–OH), and adsorbed water (H₂O) (Fig. 2 e). Compared with the reference samples, the M–O component of NiCeS/NF shifts to lower binding energy, indicating a redistributed surface electronic structure and a more polarized metal–oxygen environment. This feature is consistent with the strengthened interfacial electronic coupling among Ni, Ce, and S species, and reflects the increased structural flexibility of the surface oxygen framework, which is favorable for electrochemical reconstruction. Electron paramagnetic resonance (EPR) measurements further support the defect-rich nature of NiCeS/NF. The signal at g ≈ 2.003 is characteristic of oxygen vacancies and trapped surface electrons. The signal intensity follows the order NiCeS/NF > CeS/NF > NiS/NF > NiCe/NF (Fig. 2 f), indicating that the coexistence of Ni, Ce, and S leads to the highest defect concentration among all samples. Combined with the XPS results, this finding demonstrates that sulfur introduction promotes defect generation, while Ce species help stabilize the defect-rich local environment through valence regulation. Therefore, the synergistic coupling of Ni, Ce, and S induces charge redistribution, enriches oxygen-deficient sites, and accelerates surface reconstruction, together accounting for the enhanced electrocatalytic activity of NiCeS/NF [ 24 ]. 3.2 Oxygen Evolution Performances To further confirm the impact of the optimally reconstructed NiCeS/NF on OER activity, linear sweep voltammetry (LSV) was conducted using 1 M KOH in a standard three-electrode setup. A 90% iR compensation was applied to the raw data to eliminate ohmic losses and accurately reflect the inherent properties of the electrocatalysts. At a current density of 0.1 mA cm⁻², the onset potential followed this order: NiCeS/NF (0.16 V) < CeS/NF (0.18 V) < NiS/NF (0.21 V) < NiCe/NF (0.22 V) (Figure S4). Since the onset potential is independent of the number of accessible active sites or kinetic factors, this data highlights the intrinsic activity of NiCeS/NF. In the reverse linear sweep voltammetry (LSV) test, the NiCeS@NF catalyst displayed a distinct anodic peak at 1.25 V, which is attributed to the reduction of high-valent metal species in the catalyst (Fig. 3 a). This phenomenon indicates that NiCeS@NF can effectively facilitate the reduction of high-valent metal species during the OER process, thereby enhancing catalytic activity. At a current density of 10 mA cm − 2 , NiCeS/NF required only a 187 mV overpotential, which is significantly lower than NiCe (241 mV), NiS/NF (248 mV), and CeS/NF (278 mV). This performance improvement, particularly at lower overpotentials, suggests that the NiCeS@NF catalyst exhibits significantly superior intrinsic activity in the OER process compared to the other catalysts (Fig. 3 b). The advantage of low overpotential becomes more pronounced at higher currents, making it closer to real-world applications, and the catalyst remains unaffected by redox signals within the relevant potential window, highlighting NiCeS/NF as a promising candidate for industrial water oxidation. Next, the surface reconstruction dynamics and OER process were investigated. The Tafel slope evaluation revealed that NiCeS/NF has a Tafel slope of only 44.1 mV dec⁻¹, which is lower than NiCe/NF (46.7 mV dec⁻¹), NiS/NF (61.7 mV dec⁻¹), and CeS/NF (123.9 mV dec⁻¹) (Fig. 3 c). This further demonstrates that doping with Ce and S shifts the rate-determining step from the first electron transfer reaction to the third electron transfer reaction (MO + OH⁻ → MOOH + e⁻) [ 25 ]. For well-performing catalysts, the more reverse rate-determining steps, the more effective the catalytic activity. The exposure of active sites was estimated through the double-layer capacitance (C dl ), with values of 2.36 mF cm − 2 , 2.26 mF cm − 2 , 2.02 mF cm − 2 , and 2.23 mF cm − 2 for NiCeS/NF, NiCe/NF, NiS/NF, and CeS/NF, respectively (Fig. 3 d). This indicates that NiCeS/NF has a slightly higher electrochemical surface area, providing more surface sites available for OER. This result corroborates the characteristic of NiCeS/NF to undergo easier reconstruction into a hydroxyl-rich, high-defect density NiOOH high-activity phase during anodic polarization. Electrochemical impedance spectroscopy (EIS) revealed the fastest electron transfer capability of NiCeS/NF. The circles in the EIS plots represent the size of the charge transfer resistance (R ct ), where a smaller diameter indicates lower R ct [ 26 ], corresponding to faster charge transfer in the electrochemical process. The R ct value for NiCeS/NF was 3.72 Ω, significantly lower than NiCe/NF (11.15 Ω), NiS/NF (8.52 Ω), and CeS/NF (18.13 Ω) (Fig. 3 e). This indicates that NiCeS/NF exhibits faster charge transfer at the interface during the OER process, further illustrating the positive role of Ce and S co-doping in enhancing OER performance, facilitating easier metal oxidation, and boosting OER activity. Further EIS measurements were conducted to analyze the related kinetic properties. Durability is a mandatory criterion for the practical application of electrocatalysts. The long-term stability of NiCeS@NF was evaluated using chronoamperometry at a current density of 1000 mA cm⁻². As shown in Fig. 3 f, NiCeS@NF showed no significant decline in activity during the approximately 400 hours of testing, demonstrating exceptional durability, which surpasses that of most OER catalysts (Table S2). During this period, the current density exhibited only minor fluctuations, primarily due to changes in electrolyte concentration, supplementation, and environmental temperature. This outstanding lifespan emphasizes the great potential of NiCeS@NF for sustained performance in industrial applications. 4. Conclusion In this work, we have constructed a Ce- and S-co-doped Ni-based electrocatalyst (NiCeS/NF) via a molten-salt-assisted in situ growth strategy, forming ultra-thin, interconnected nanosheets and a Ni–Ce–S multi-phase framework on nickel foam. Structural and spectroscopic analyses reveal strong electronic and defect coupling among Ni, Ce and S. The Ni–O–Ce motifs, enriched Ce³⁺–V O pairs, and coexisting sulfide/sulfate species jointly promote rapid surface reconstruction into a hydroxyl-rich, defect-rich NiCeOOH shell and optimize the adsorption of key OER intermediates. Benefiting from this synergistic structure–electronic–defect regulation, NiCeS/NF delivers an overpotential of 187 mV at 10 mA cm⁻², a low Tafel slope of 44.1 mV dec⁻¹, the smallest charge-transfer resistance (3.72 Ω), and robust operation at 1000 mA cm⁻² for ~400 h with negligible activity decay. These results demonstrate that Ce and S co-doping is an effective strategy to simultaneously enhance activity and durability of non-noble-metal OER catalysts and provide useful guidance for the rational design of advanced electrocatalysts for alkaline water electrolysis. Declarations Corresponding Author Yachao Zhu, ICGM, CNRS, Université de Montpellier, Montpellier, France. Institute of Future Technology, Southwest Jiaotong University, Chengdu 610031, China. [email protected] Jie Deng, School of Architecture and Civil Engineering, Chengdu University, Chengdu, China. College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University, Chengdu, 610106, China. Institute for Advanced Study, Chengdu University, Chengdu,610106, China. [email protected] Si Chen, Sichuan Institute of Product Quality Supervision and Inspection, Chengdu, China. [email protected] Authors Ruxin Lei, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，Chengdu, China. Yufeng Zhang, School of Architecture and Civil Engineering, Chengdu University, Chengdu, China. Li Chen, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China. Yuying Wu, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China. Haitao Chen, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China. Author Contributions Ruxin Lei contributed equally as first authors by designing the study, conducting experiments, analysing data, and drafting the manuscript. Jie Deng, Yachao Zhu, and Si Chen served as corresponding authors, providing overall supervision, project management, and final manuscript revision. Yufeng Zhang, Li Chen, Yuying Wu, Haitao Chen participated in performing experiments, data analysis, literature review, and revising specific sections of the manuscript. All authors discussed the results and approved the final version for publication. Notes The authors declare no competing financial interest. Acknowledgements This work was supported by projects of Longquanyi new economy and technology plan (2024LQRD0012) and by projects of Administration for State Market Supervision Administration (No.2024MK114) and by Central Government-Guided Special Fund for Local Science and Technology Development in Sichuan Province (2024ZYD0302). 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Zhong, Highly Efficient Oxygen Evolution by a Thermocatalytic Process Cascaded Electrocatalysis Over Sulfur‐Treated Fe‐Based Metal–Organic‐Frameworks, Advanced Energy Materials 10 (2020) 2000184. https://doi.org/10.1002/aenm.202000184. S. Chakraborty, S. Marappa, S. Agarwal, D. Bagchi, A. Rao, C.P. Vinod, S.C. Peter, A. Singh, M. Eswaramoorthy, Improvement in Oxygen Evolution Performance of NiFe Layered Double Hydroxide Grown in the Presence of 1T-Rich MoS 2 , ACS Appl. Mater. Interfaces 14 (2022) 31951–31961. https://doi.org/10.1021/acsami.2c06210. S. Zhou, C. Chen, J. Xia, L. Li, X. Qian, F.-X. Yin, G. He, Q. Chen, H. Chen, FeN 4 S 1 Single-Atom Sites Anchored on Three-Dimensional Porous Carbon for Highly Efficient and Durable Oxygen Electrocatalysis, ACS Nano 18 (2024) 32995–33004. https://doi.org/10.1021/acsnano.4c15410. X. Wang, J. Li, Q. Xue, X. Han, C. Xing, Z. Liang, P. Guardia, Y. Zuo, R. Du, L. Balcells, J. Arbiol, J. Llorca, X. Qi, A. Cabot, Sulfate-Decorated Amorphous–Crystalline Cobalt-Iron Oxide Nanosheets to Enhance O–O Coupling in the Oxygen Evolution Reaction, ACS Nano 17 (2023) 825–836. https://doi.org/10.1021/acsnano.2c12029. Y. Chen, L. Dong, S. Jia, Q. Zhang, L. Liu, Z. Liu, Z. Zhang, K. Yue, Y. Cheng, D. Li, Z. Zhu, Y. Wang, Superhydrophilic S‐NiFe LDH by Room Temperature Synthesis for Enhanced Alkaline Water/Seawater Oxidation at Large Current Densities, Small 21 (2025) 2409499. https://doi.org/10.1002/smll.202409499. M. Li, H. Li, X. Jiang, M. Jiang, X. Zhan, G. Fu, J.-M. Lee, Y. Tang, Gd-induced electronic structure engineering of a NiFe-layered double hydroxide for efficient oxygen evolution, J. Mater. Chem. A 9 (2021) 2999–3006. https://doi.org/10.1039/D0TA10740A. Y. Xue, J. Zhao, L. Huang, Y.-R. Lu, A. Malek, G. Gao, Z. Zhuang, D. Wang, C.T. Yavuz, X. Lu, Stabilizing ruthenium dioxide with cation-anchored sulfate for durable oxygen evolution in proton-exchange membrane water electrolyzers, Nat Commun 14 (2023) 8093. https://doi.org/10.1038/s41467-023-43977-7. S. Xu, S. Feng, Y. Yu, D. Xue, M. Liu, C. Wang, K. Zhao, B. Xu, J.-N. Zhang, Dual-site segmentally synergistic catalysis mechanism: boosting CoFeSx nanocluster for sustainable water oxidation, Nat Commun 15 (2024) 1720. https://doi.org/10.1038/s41467-024-45700-6. J. He, A. Bhargav, A. Manthiram, High-Energy-Density, Long-Life Lithium–Sulfur Batteries with Practically Necessary Parameters Enabled by Low-Cost Fe–Ni Nanoalloy Catalysts, ACS Nano 15 (2021) 8583–8591. https://doi.org/10.1021/acsnano.1c00446. M. Karpuraranjith, Y. Chen, B. Wang, J. Ramkumar, D. Yang, K. Srinivas, W. Wang, W. Zhang, R. Manigandan, Hierarchical ultrathin layered MoS2@NiFe2O4 nanohybrids as a bifunctional catalyst for highly efficient oxygen evolution and organic pollutant degradation, Journal of Colloid and Interface Science 592 (2021) 385–396. https://doi.org/10.1016/j.jcis.2021.02.062. N. Zhang, X. Liu, H. Zhong, W. Liu, D. Bao, J. Zeng, D. Wang, C. Ma, X. Zhang, Local Oxygen Vacancy‐Mediated Oxygen Exchange for Active and Durable Acidic Water Oxidation, Angewandte Chemie 137 (2025) e202503246. https://doi.org/10.1002/ange.202503246. Y. Yang, S. Wei, Y. Li, D. Guo, H. Liu, L. Liu, Effect of cobalt doping-regulated crystallinity in nickel-iron layered double hydroxide catalyzing oxygen evolution, Applied Catalysis B: Environmental 314 (2022) 121491. https://doi.org/10.1016/j.apcatb.2022.121491. C. Wan, J. Jin, X. Wei, S. Chen, Y. Zhang, T. Zhu, H. Qu, Inducing the SnO2-based electron transport layer into NiFe LDH/NF as efficient catalyst for OER and methanol oxidation reaction, Journal of Materials Science & Technology 124 (2022) 102–108. https://doi.org/10.1016/j.jmst.2022.01.022. Y. Qi, Y. Zhang, L. Yang, Y. Zhao, Y. Zhu, H. Jiang, C. Li, Insights into the activity of nickel boride/nickel heterostructures for efficient methanol electrooxidation, Nat Commun 13 (2022) 4602. https://doi.org/10.1038/s41467-022-32443-5. Y. Ma, H. Du, S. Zheng, Z. Zhou, H. Zhang, Y. Ma, S. Passerini, Y. Wu, High-Entropy Approach vs. Traditional Doping Strategy for Layered Oxide Cathodes in Alkali-Metal-Ion Batteries: A Comparative Study, Energy Storage Materials 79 (2025) 104295. https://doi.org/10.1016/j.ensm.2025.104295. Additional Declarations No competing interests reported. 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University","correspondingAuthor":false,"prefix":"","firstName":"Yufeng","middleName":"","lastName":"Zhang","suffix":""},{"id":617366297,"identity":"dcd66175-733a-4663-b37d-435e27df8217","order_by":2,"name":"Li Chen","email":"","orcid":"","institution":"Chengdu University，Chengdu","correspondingAuthor":false,"prefix":"","firstName":"Li","middleName":"","lastName":"Chen","suffix":""},{"id":617366300,"identity":"c0b964cb-3ed1-4656-856f-57e99e9b0b44","order_by":3,"name":"Yuying Wu","email":"","orcid":"","institution":"Chengdu University，Chengdu","correspondingAuthor":false,"prefix":"","firstName":"Yuying","middleName":"","lastName":"Wu","suffix":""},{"id":617366301,"identity":"46179f09-5d95-434f-96a8-2c5da4ee02f2","order_by":4,"name":"Haitao Chen","email":"","orcid":"","institution":"Chengdu University，Chengdu","correspondingAuthor":false,"prefix":"","firstName":"Haitao","middleName":"","lastName":"Chen","suffix":""},{"id":617366303,"identity":"ef41a0d5-a0fe-473a-a893-194fd4170bf8","order_by":5,"name":"Si Chen","email":"","orcid":"","institution":"Sichuan Institute of Product Quality Supervision and Inspection","correspondingAuthor":false,"prefix":"","firstName":"Si","middleName":"","lastName":"Chen","suffix":""},{"id":617366306,"identity":"a4de5af5-52c9-445d-a489-c24936f6d6aa","order_by":6,"name":"Yachao Zhu","email":"","orcid":"","institution":"Southwest Jiaotong University","correspondingAuthor":false,"prefix":"","firstName":"Yachao","middleName":"","lastName":"Zhu","suffix":""},{"id":617366308,"identity":"a74082c8-d5fe-46fc-9bb0-1e55a9b872b2","order_by":7,"name":"Jie Deng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYDCCA0AsYcAgx8CQAGSxkaDFmEQtQJDYQLQWvuO9h19YFNik97fnGDB8KDvMwD+7Ab8WyTPn0iwkDNJyZ5x5Y8A449xhBok7B/BrMbiRY2YgYXA4d4NEjgEzb9thBgOJBAJa7r8BafmfbgDS8pcoLTd4jB9IGBxIAGthJEaL5JkcM2AgJxvOOPOs4GDPuXQeiRsEtPAdP2P8WeKPnTx/e/LGBz/KrOX4ZxDQAgRs0hJQ1gEg5iGoHgiYP34gRtkoGAWjYBSMXAAAggZC0yam+lsAAAAASUVORK5CYII=","orcid":"","institution":"Chengdu University，Chengdu","correspondingAuthor":true,"prefix":"","firstName":"Jie","middleName":"","lastName":"Deng","suffix":""}],"badges":[],"createdAt":"2026-03-29 12:39:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9258813/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9258813/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106403475,"identity":"b74b1738-5627-4c3d-9a0c-21aab3849f5a","added_by":"auto","created_at":"2026-04-08 09:14:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1044154,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD pattern of NiCeS/NF, (b) SEM image of NiCeS/NF, (c) TEM image of NiCeS/NF, (d) The HRTEM image of NiCeS/NF, (e-f) Elemental mapping of NiCeS/NF.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9258813/v1/b2ec146dfbf252664ac50e8f.png"},{"id":106403594,"identity":"3dd16047-0908-4845-b1ed-2b8950c539bf","added_by":"auto","created_at":"2026-04-08 09:14:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":357835,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The survey XPS spectra of NiCeS/NF, (b) High-resolution XPS spectra of Ni 2p, (c) High-resolution XPS spectra of Ce 3d, (d) High-resolution XPS spectra of S 2p, (e) High-resolution XPS spectra of O 1s (f) EPR spectra of each sample.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9258813/v1/6c5057ef364f126516f5ff67.png"},{"id":106357873,"identity":"2d5f550d-2efc-48f6-8408-09ae76ec5e9f","added_by":"auto","created_at":"2026-04-07 19:15:35","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":290901,"visible":true,"origin":"","legend":"\u003cp\u003e(a) LSV curves with iR compensation, (b) Overpotential at 10, 50, and 100 mA cm\u003csup\u003e-2\u003c/sup\u003e, (c) Tafel slopes for each sample, (d) Double-layer capacitance, (e) Nyquist plots for each sample, (f) Long-term i−t curve of NiCeS/NF.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-9258813/v1/8891b39e5e3dc889e54889b5.png"},{"id":106405895,"identity":"e2a1868c-8ad2-4482-b428-65748942bb0c","added_by":"auto","created_at":"2026-04-08 09:28:58","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2068856,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9258813/v1/3ffeb8cd-a264-40f0-af4f-531bd6e6af03.pdf"},{"id":106357870,"identity":"3df033e0-2827-461f-9800-3d42f207e78f","added_by":"auto","created_at":"2026-04-07 19:15:35","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2281284,"visible":true,"origin":"","legend":"","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-9258813/v1/241d5a6931e81777911ae5f9.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Ce and S Co-Induced Oxygen Vacancies for Enhanced Alkaline Water Electrolysis","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHydrogen, as a clean energy carrier, possesses several prominent advantages, including high energy density, sustainability, stability and zero direct pollution [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. It is widely regarded as one of the most promising candidates to partially replace fossil fuels in the 21st century. Compared with conventional fossil fuels, the utilization of hydrogen does not generate CO₂ or other greenhouse gases during combustion, and hydrogen can be integrated into diverse energy sectors such as transportation, industry and power storage. With the continuously growing global demand for sustainable energy, the application prospects of hydrogen as a green energy vector are highly anticipated. In particular, under the current worldwide push toward a low-carbon economy, the strategic importance of hydrogen is becoming increasingly prominent. Among various hydrogen production technologies, electrocatalytic water splitting is considered one of the most efficient and practically promising routes. This technology produces hydrogen and oxygen via the electrolysis of water and is compatible with high energy-conversion efficiency. However, the oxygen evolution reaction (OER) [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], as the anodic half-reaction in water splitting, involves a complex four-electron transfer process and is intrinsically sluggish in kinetics. This severely hampers the efficiency of water oxidation and thus limits the overall performance of water splitting. Consequently, the development of highly active and robust OER electrocatalysts\u0026mdash;especially those capable of lowering the overpotential and accelerating the reaction rate\u0026mdash;is crucial for enhancing the efficiency of water electrolysis [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo date, noble-metal-based catalysts, particularly Ru and Ir-containing materials, have delivered the highest OER activity. Nevertheless, their high cost and limited abundance severely hinder large-scale deployment. Therefore, it is imperative to develop non-noble-metal electrocatalysts that combine low cost with high activity and long-term stability. In recent years, a variety of transition-metal-based materials [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], including phosphides [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], sulfides [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], carbides, oxides [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], and selenides, have emerged as promising alternatives to noble metals because of their excellent catalytic performance, low cost, and environmental compatibility. Among them, transition-metal sulfides are especially attractive because their unique physicochemical properties, such as relatively low resistivity and favorable electrical conductivity, can endow them with high OER activity. For example, Xue et al. reported a W-doping-induced phase-transition strategy, in which a W\u0026ndash;Ni\u003csub\u003e3\u003c/sub\u003eS\u003csub\u003e2\u003c/sub\u003e/Ni\u003csub\u003e7\u003c/sub\u003eS\u003csub\u003e6\u003c/sub\u003e heterojunction was constructed to markedly enhance catalytic performance [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The incorporation of W not only tailored the catalyst morphology, leading to the formation of uniform nanorod arrays, but also modulated the electronic structure of Ni, promoted the generation of a higher proportion of Ni\u003csup\u003e3+\u003c/sup\u003e species, and thereby activated the catalytic process. Meanwhile, the emergence of the new Ni₇S₆ phase further improved the intrinsic activity of the catalyst.\u003c/p\u003e \u003cp\u003eBeyond transition-metal-sulfide engineering, the introduction of rare-earth elements provides an additional and powerful means of regulating the electronic structure of catalytic centers. Rare-earth elements possess distinctive 4f-electron characteristics. Their 4f orbitals are highly localized and energetically close to the 5d and 6s orbitals, enabling sensitive charge-transfer and valence-buffering effects when coordinated near transition-metal centers [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. These elements can modulate the electron occupancy at metal sites and the metal\u0026ndash;ligand covalency through valence fluctuations and oxygen-vacancy regulation, thereby influencing both the adsorption strength of key reaction intermediates and the preferred reaction pathway. Cerium-based systems are particularly representative. The reversible Ce\u0026sup3;⁺/Ce⁴⁺ redox couple endows Ce with excellent oxygen storage/release capability and, through the generation or stabilization of near-surface oxygen vacancies, reshapes the local crystal field and band-edge positions. When Ce is coupled with Ni active sites, the Ni\u0026ndash;O\u0026ndash;Ce bridge can induce directional charge compensation, resulting in moderate de-electronation of the Ni 3d band, enhanced metal\u0026ndash;ligand hybridization, and optimized interactions with critical intermediates such as *OH, *O, and *OOH [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This electronic redistribution not only facilitates the electrochemical reconstruction from Ni(OH)₂ to the active NiOOH phase, but also provides an oxygen-vacancy/oxygen-refilling channel for lattice-oxygen-involved pathways, thereby lowering the OER energy barrier from both kinetic and thermodynamic perspectives.\u003c/p\u003e \u003cp\u003eIn parallel with such rare-earth-induced electronic regulation, sulfur incorporation can further amplify interfacial and charge-transport effects. Sulfur coordination enhances the intrinsic electrical conductivity and carrier density of the precatalyst, reduces the interfacial charge-transfer resistance, and accelerates self-reconstruction during the initial stages of anodic polarization, thereby enabling the rapid formation of a hydroxyl-rich, defect-rich, and electronically well-coupled amorphous active layer [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. As polarization proceeds, part of the sulfur species undergo leaching and S\u0026ndash;O exchange, leading to the formation of a surface shell containing sulfate species. This shell can stabilize key intermediates such as *OOH through hydrogen-bonding and electrostatic interactions, thereby lowering the free-energy barrier for the *O \u0026rarr; *OOH step [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In this context, rare-earth elements and sulfur play complementary roles at the same interface: rare-earth species serve as electronic buffers and oxygen-vacancy regulators, whereas sulfur enhances conductivity and stabilizes reaction intermediates. Together, they reshape the adsorption-energy landscape and reconstruction pathway around transition-metal centers, rendering the catalytic interface more favorable for the OER [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this work, we report a Ce- and S-co-doped Ni-based electrocatalyst (NiCeS/NF) supported on nickel foam, and systematically evaluate its structure and electrocatalytic performance using a suite of physicochemical and electrochemical techniques. Comparative studies with related catalysts demonstrate that NiCeS/NF exhibits superior OER performance, characterized by a low overpotential and excellent durability. These results highlight the substantial potential of Ce and S co-doping as an effective strategy to synergistically boost the catalytic activity and stability of non-noble-metal OER electrocatalysts.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals and Materials\u003c/h2\u003e \u003cp\u003eKOH (95%) and Ce(NO₃)₃\u0026middot;6H₂O were purchased from Macklin, while Ni(NO₃)₃\u0026middot;6H₂O was obtained from Chengdu Jinshan, and potassium thiocyanate was acquired from Beijing Inokai. Nickel foam was supplied by Kunshan Guangjiayuan New Materials Co., Ltd. All chemicals used in this study were of analytical grade and did not require further purification. Deionized water was used throughout the experimental procedures.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Synthesis of Samples\u003c/h2\u003e \u003cp\u003eThe nickel foam (NF) was cleaned with anhydrous ethanol in an ultrasonic bath to obtain a clean surface. A 20 mL glass bottle was charged with 3 g of Ni(NO₃)₃\u0026middot;6H₂O, 2.17 g of Ce(NO₃)₃\u0026middot;6H₂O, and 1 g of potassium thiocyanate. After reacting at 120\u0026deg;C in an oven for 2 hours, NiCeS/NF was obtained. For comparison, NiCe/NF was prepared by reacting 3 g of Ni(NO₃)₃\u0026middot;6H₂O and 2.17 g of Ce(NO₃)₃\u0026middot;6H₂O under the same conditions. NiS/NF was synthesized by adding only 3 g of Ni(NO₃)₃\u0026middot;6H₂O and 1 g of potassium thiocyanate. CeS/NF was prepared by adding only 2.17 g of Ce(NO₃)₃\u0026middot;6H₂O and 1 g of potassium thiocyanate, with all other conditions remaining the same.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Characterization\u003c/h2\u003e \u003cp\u003eThe crystallographic phases of the samples were analyzed using X-ray diffraction (XRD) with a Bruker diffractometer. The microstructure and morphology were examined by field emission scanning electron microscopy (SEM, Zeiss Supra, Carl Zeiss), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), and energy-dispersive X-ray spectroscopy (EDX) using a 200 kV FEI Tecnai G2 F20 field-emission TEM. The chemical composition and valence states of the samples were analyzed by X-ray photoelectron spectroscopy (XPS, AXIS Ultra DLD, Kratos Analytical Ltd.). Electron paramagnetic resonance (EPR) measurements were performed at 77 K using a Bruker A300-10/12 spectrometer.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Electrochemical Measurements\u003c/h2\u003e \u003cp\u003eThe synthesized catalyst (1 cm \u0026times; 1 cm) was used as the working electrode (WE), with a Hg/HgO (1 M KOH) electrode and a platinum sheet (1 cm \u0026times; 1 cm) serving as the reference and counter electrodes, respectively. The measured potential was converted to the reversible hydrogen electrode (RHE) scale. Cyclic voltammetry (CV) was performed at a scan rate of 30 mV/s in 1.0 M KOH for 30 cycles to activate the samples. Linear sweep voltammetry (LSV) was carried out at a scan rate of 5 mV/s under the same conditions to record the polarization curves. Electrochemical impedance spectroscopy (EIS) was measured in the frequency range of 10⁻\u0026sup2; to 10⁵ Hz. The electrochemical active surface area (ECSA) was evaluated by CV in the narrow non-faradaic electrochemical window at different scan rates (100 to 200 mV/s) to assess the double-layer capacitance. Long-term stability tests were conducted using chronoamperometry at an initial current density of 1000 mA cm⁻\u0026sup2; in 1.0 M KOH to evaluate the durability of the catalysts.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Structural and Morphological Characterizations\u003c/h2\u003e \u003cp\u003eUsing nickel nitrate, cerium nitrate, and potassium thiocyanate as precursors, ultrathin three-dimensional NiCeS nanosheets were grown in situ on nickel foam (NF) via a molten-salt method. X-ray diffraction (XRD) was used to determine the phase composition and multiphase characteristics of the as-prepared sample. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, the diffraction peaks at 25.43\u0026deg;, 26.67\u0026deg;, 29.06\u0026deg;, and 30.70\u0026deg; are assigned to the (1 1 1) plane of Ce\u003csub\u003e2\u003c/sub\u003eS\u003csub\u003e3\u003c/sub\u003e (PDF#21\u0026ndash;0189), the (0 0 4) plane of Ce(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (PDF#22\u0026ndash;0546), the (1 0 1) plane of Ce\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003eS (PDF#26-1085), and the (\u0026minus;\u0026thinsp;2 1 2) plane of Ni\u003csub\u003ex\u003c/sub\u003eS\u003csub\u003e6\u003c/sub\u003e (PDF#51\u0026ndash;0718), respectively. These results confirm the formation of a Ni\u0026ndash;Ce\u0026ndash;S multiphase framework composed of sulfide, oxysulfide, and sulfate phases on the NF surface. The formation of these phases originates from the decomposition and rearrangement of SCN\u003csup\u003e\u0026minus;\u003c/sup\u003e in the molten-salt medium. This process generates S\u003csup\u003e2\u0026minus;\u003c/sup\u003e/S\u003csub\u003ex\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e species together with sulfur\u0026ndash;oxygen intermediates, driving the simultaneous formation of sulfide, oxysulfide, and sulfate phases. The molten-salt medium lowers the barriers for nucleation and phase evolution, resulting in intimate coupling of the different phases within the nanosheet framework. This multiphase architecture creates abundant heterointerfaces and defect sites, which regulate charge distribution and provide adsorption sites for reaction intermediates during electrochemical reactions.[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe morphology and elemental distribution of NiCeS/NF, NiCe/NF, NiS/NF, CeS/NF, and bare NF were characterized using SEM, TEM, and EDS. The SEM results show that in the NiCeS/NF sample, a large number of ultra-thin nanosheets grow uniformly and densely in a vertical/inclined orientation on the surface of the three-dimensional porous nickel foam framework (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb), forming an open and interconnected 3D sheet network. This structure is beneficial for electrolyte infiltration and active site exposure. In contrast, NiCe/NF exhibits a dense honeycomb-like sheet structure (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), and comparison between the two demonstrates that the introduction of sulfur causes the nanosheets to form a densely stacked structure, significantly increasing the specific surface area and enhancing the catalyst\u0026rsquo;s interaction with the electrolyte.\u003c/p\u003e \u003cp\u003eTo further analyze its fine structure, TEM and HRTEM analyses were performed on NiCeS/NF. The low magnification TEM image (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec) shows that the material consists of numerous interconnected and partially stacked ultra-thin nanosheets, forming hierarchical porous channels. This thin and cross-linked structure helps shorten the charge/ion diffusion path and promote interfacial electron transfer. HRTEM images reveal distinguishable lattice fringes, with a lattice spacing of approximately 0.22 nm attributed to the Ni\u003csub\u003ex\u003c/sub\u003eS₆ (-2 2 4) plane and a spacing of 0.21 nm corresponding to the (0 4 2) plane of Ce(SO₄)₂ (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). EDS mapping confirms that Ni, Ce, S, and O elements are evenly distributed within the composite catalyst layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee-f), with atomic ratios of 26.0:1.9:1.4:70.7 (Figure S2 and Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), indicating the successful formation of a multi-element synergistic system. The selected area electron diffraction (SAED) pattern shows clear concentric diffraction rings, which are attributed to the (2 2 2), (0 1 8) planes of Ni\u003csub\u003ex\u003c/sub\u003eS₆ and the (2 0 4) plane of Ce₂O₂S (Figure S3). This further confirms the polycrystalline nature of the material, where randomly oriented nanocrystals and interconnected sheet-like pores together form a conductive backbone and high-speed mass transport network. These results collectively indicate that the molten salt method promotes the synergistic regulation of Ni, Ce, and S at the nickel foam interface, leading to the formation of ultra-thin nanosheet structures with multi-element coupling, thereby laying a structural foundation for enhancing its electrocatalytic performance.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo clarify the surface electronic structure and interfacial coupling of the as-prepared catalyst, X-ray photoelectron spectroscopy (XPS) was carried out. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the survey spectrum of NiCeS/NF displays clear signals of Ni, Ce, S, and O, confirming the successful incorporation of these elements on the NF surface. High-resolution Ni 2p spectra show that the Ni\u0026sup2;⁺ 2p\u003csub\u003e3/2\u003c/sub\u003e peak of NiCeS/NF is located at 856.25 eV and is positively shifted relative to that of the Ni-containing reference sample (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). This shift indicates a decrease in the electron density around the Ni sites, revealing interfacial charge redistribution induced by the coupling of Ni, Ce, and S species. As a result, the Ni centers in NiCeS/NF exhibit a more electron-deficient electronic state and a modified local coordination environment. Such electronic modulation is favorable for the anodic oxidation of Ni species and thus facilitates the formation of the active NiOOH phase under operating conditions. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] The Ce 3d spectrum provides further evidence for the electronic interaction between Ce and the Ni-based framework. Compared with the reference sample, NiCeS/NF shows an increased Ce\u003csup\u003e3+\u003c/sup\u003e/Ce\u003csup\u003e4+\u003c/sup\u003e ratio together with a weakened characteristic Ce\u003csup\u003e4+\u003c/sup\u003e feature at around 917.7 eV (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), indicating partial reduction of Ce\u003csup\u003e4+\u003c/sup\u003e to Ce\u003csup\u003e3+\u003c/sup\u003e. This result suggests that Ce in NiCeS/NF is stabilized in a more defect-rich electronic state through interfacial coupling with the Ni-containing phase. The coexistence of Ce\u0026sup3;⁺ and Ce⁴⁺ is also associated with the formation of oxygen-deficient environments, which help regulate local charge balance and promote surface reconstruction during the electrochemical process [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In contrast, the stronger Ce⁴⁺ signature in CeS/NF indicates that, without coupling to Ni species, Ce tends to remain in a more oxidized surface state. The high-resolution S 2p spectra further reveal the chemical state of sulfur in the different samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). For NiCeS/NF, the peaks located at 162.8 and 164.1 eV are assigned to the S 2p₃/₂ and S 2p₁/₂ components of metal\u0026ndash;S species, respectively, while the peak at 169.0 eV is attributed to oxidized sulfur species (S\u0026ndash;O). Similar features are also observed in NiS/NF and CeS/NF. Specifically, the S 2p signals of NiS/NF appear at 163.1 and 164.4 eV, with the oxidized sulfur peak located at 168.8 eV, whereas CeS/NF shows the corresponding peaks at 162.9, 164.3, and 168.7 eV. The coexistence of metal\u0026ndash;S and S\u0026ndash;O species confirms that sulfur is present in both reduced and oxidized forms in all three samples. Compared with NiS/NF and CeS/NF, the sulfur species in NiCeS/NF show distinct binding-energy shifts, indicating that the simultaneous incorporation of Ni and Ce alters the local electronic structure around sulfur through interfacial coupling [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. These results suggest that sulfur in NiCeS/NF contributes not only to the construction of the sulfide framework, but also to the regulation of the surface chemical environment. The coexistence of reduced sulfur and oxidized sulfur species is closely related to the surface reconstruction behavior under anodic conditions, where sulfide species promote precursor activation, while surface S\u0026ndash;O species help stabilize the oxygenated interfacial environment during OER [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The O 1s spectrum can be deconvoluted into three components corresponding to lattice oxygen (M\u0026ndash;O), hydroxyl species (M\u0026ndash;OH), and adsorbed water (H₂O) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). Compared with the reference samples, the M\u0026ndash;O component of NiCeS/NF shifts to lower binding energy, indicating a redistributed surface electronic structure and a more polarized metal\u0026ndash;oxygen environment. This feature is consistent with the strengthened interfacial electronic coupling among Ni, Ce, and S species, and reflects the increased structural flexibility of the surface oxygen framework, which is favorable for electrochemical reconstruction.\u003c/p\u003e \u003cp\u003eElectron paramagnetic resonance (EPR) measurements further support the defect-rich nature of NiCeS/NF. The signal at g\u0026thinsp;\u0026asymp;\u0026thinsp;2.003 is characteristic of oxygen vacancies and trapped surface electrons. The signal intensity follows the order NiCeS/NF\u0026thinsp;\u0026gt;\u0026thinsp;CeS/NF\u0026thinsp;\u0026gt;\u0026thinsp;NiS/NF\u0026thinsp;\u0026gt;\u0026thinsp;NiCe/NF (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef), indicating that the coexistence of Ni, Ce, and S leads to the highest defect concentration among all samples. Combined with the XPS results, this finding demonstrates that sulfur introduction promotes defect generation, while Ce species help stabilize the defect-rich local environment through valence regulation. Therefore, the synergistic coupling of Ni, Ce, and S induces charge redistribution, enriches oxygen-deficient sites, and accelerates surface reconstruction, together accounting for the enhanced electrocatalytic activity of NiCeS/NF [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Oxygen Evolution Performances\u003c/h2\u003e \u003cp\u003eTo further confirm the impact of the optimally reconstructed NiCeS/NF on OER activity, linear sweep voltammetry (LSV) was conducted using 1 M KOH in a standard three-electrode setup. A 90% iR compensation was applied to the raw data to eliminate ohmic losses and accurately reflect the inherent properties of the electrocatalysts. At a current density of 0.1 mA cm⁻\u0026sup2;, the onset potential followed this order: NiCeS/NF (0.16 V)\u0026thinsp;\u0026lt;\u0026thinsp;CeS/NF (0.18 V)\u0026thinsp;\u0026lt;\u0026thinsp;NiS/NF (0.21 V) \u0026lt; NiCe/NF (0.22 V) (Figure S4). Since the onset potential is independent of the number of accessible active sites or kinetic factors, this data highlights the intrinsic activity of NiCeS/NF. In the reverse linear sweep voltammetry (LSV) test, the NiCeS@NF catalyst displayed a distinct anodic peak at 1.25 V, which is attributed to the reduction of high-valent metal species in the catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). This phenomenon indicates that NiCeS@NF can effectively facilitate the reduction of high-valent metal species during the OER process, thereby enhancing catalytic activity.\u003c/p\u003e \u003cp\u003eAt a current density of 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, NiCeS/NF required only a 187 mV overpotential, which is significantly lower than NiCe (241 mV), NiS/NF (248 mV), and CeS/NF (278 mV). This performance improvement, particularly at lower overpotentials, suggests that the NiCeS@NF catalyst exhibits significantly superior intrinsic activity in the OER process compared to the other catalysts (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The advantage of low overpotential becomes more pronounced at higher currents, making it closer to real-world applications, and the catalyst remains unaffected by redox signals within the relevant potential window, highlighting NiCeS/NF as a promising candidate for industrial water oxidation. Next, the surface reconstruction dynamics and OER process were investigated. The Tafel slope evaluation revealed that NiCeS/NF has a Tafel slope of only 44.1 mV dec⁻\u0026sup1;, which is lower than NiCe/NF (46.7 mV dec⁻\u0026sup1;), NiS/NF (61.7 mV dec⁻\u0026sup1;), and CeS/NF (123.9 mV dec⁻\u0026sup1;) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). This further demonstrates that doping with Ce and S shifts the rate-determining step from the first electron transfer reaction to the third electron transfer reaction (MO\u0026thinsp;+\u0026thinsp;OH⁻ \u0026rarr; MOOH\u0026thinsp;+\u0026thinsp;e⁻) [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. For well-performing catalysts, the more reverse rate-determining steps, the more effective the catalytic activity. The exposure of active sites was estimated through the double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e), with values of 2.36 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, 2.26 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, 2.02 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, and 2.23 mF cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for NiCeS/NF, NiCe/NF, NiS/NF, and CeS/NF, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). This indicates that NiCeS/NF has a slightly higher electrochemical surface area, providing more surface sites available for OER. This result corroborates the characteristic of NiCeS/NF to undergo easier reconstruction into a hydroxyl-rich, high-defect density NiOOH high-activity phase during anodic polarization.\u003c/p\u003e \u003cp\u003eElectrochemical impedance spectroscopy (EIS) revealed the fastest electron transfer capability of NiCeS/NF. The circles in the EIS plots represent the size of the charge transfer resistance (R\u003csub\u003ect\u003c/sub\u003e), where a smaller diameter indicates lower R\u003csub\u003ect\u003c/sub\u003e [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], corresponding to faster charge transfer in the electrochemical process. The R\u003csub\u003ect\u003c/sub\u003e value for NiCeS/NF was 3.72 Ω, significantly lower than NiCe/NF (11.15 Ω), NiS/NF (8.52 Ω), and CeS/NF (18.13 Ω) (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee). This indicates that NiCeS/NF exhibits faster charge transfer at the interface during the OER process, further illustrating the positive role of Ce and S co-doping in enhancing OER performance, facilitating easier metal oxidation, and boosting OER activity. Further EIS measurements were conducted to analyze the related kinetic properties. Durability is a mandatory criterion for the practical application of electrocatalysts. The long-term stability of NiCeS@NF was evaluated using chronoamperometry at a current density of 1000 mA cm⁻\u0026sup2;. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef, NiCeS@NF showed no significant decline in activity during the approximately 400 hours of testing, demonstrating exceptional durability, which surpasses that of most OER catalysts (Table S2). During this period, the current density exhibited only minor fluctuations, primarily due to changes in electrolyte concentration, supplementation, and environmental temperature. This outstanding lifespan emphasizes the great potential of NiCeS@NF for sustained performance in industrial applications.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, we have constructed a Ce- and S-co-doped Ni-based electrocatalyst (NiCeS/NF) via a molten-salt-assisted in situ growth strategy, forming ultra-thin, interconnected nanosheets and a Ni\u0026ndash;Ce\u0026ndash;S multi-phase framework on nickel foam. Structural and spectroscopic analyses reveal strong electronic and defect coupling among Ni, Ce and S. The Ni\u0026ndash;O\u0026ndash;Ce motifs, enriched Ce\u0026sup3;⁺\u0026ndash;V\u003csub\u003eO\u003c/sub\u003e pairs, and coexisting sulfide/sulfate species jointly promote rapid surface reconstruction into a hydroxyl-rich, defect-rich NiCeOOH shell and optimize the adsorption of key OER intermediates. Benefiting from this synergistic structure\u0026ndash;electronic\u0026ndash;defect regulation, NiCeS/NF delivers an overpotential of 187 mV at 10 mA cm⁻\u0026sup2;, a low Tafel slope of 44.1 mV dec⁻\u0026sup1;, the smallest charge-transfer resistance (3.72 \u0026Omega;), and robust operation at 1000 mA cm⁻\u0026sup2; for ~400 h with negligible activity decay. These results demonstrate that Ce and S co-doping is an effective strategy to simultaneously enhance activity and durability of non-noble-metal OER catalysts and provide useful guidance for the rational design of advanced electrocatalysts for alkaline water electrolysis.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCorresponding Author\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eYachao Zhu, ICGM, CNRS, Universit\u0026eacute; de Montpellier, Montpellier, France. Institute of Future Technology, Southwest Jiaotong University, Chengdu 610031, China. [email protected]\u003c/p\u003e\n\u003cp\u003eJie Deng, School of Architecture and Civil Engineering, Chengdu University, Chengdu, China. College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University, Chengdu, 610106, China. Institute for Advanced Study, Chengdu University, Chengdu,610106, China. [email protected]\u003c/p\u003e\n\u003cp\u003eSi Chen, Sichuan Institute of Product Quality Supervision and Inspection, Chengdu, China. [email protected]\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRuxin Lei, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，Chengdu, China.\u003c/p\u003e\n\u003cp\u003eYufeng Zhang, School of Architecture and Civil Engineering, Chengdu University, Chengdu, China.\u003c/p\u003e\n\u003cp\u003eLi Chen, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China.\u003c/p\u003e\n\u003cp\u003eYuying Wu, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China.\u003c/p\u003e\n\u003cp\u003eHaitao Chen, College of Food and Biological Engineering and College of Chemistry and Chemical Engineering, Chengdu University，China.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eRuxin Lei contributed equally as first authors by designing the study, conducting experiments, analysing data, and drafting the manuscript. Jie Deng, Yachao Zhu, and Si Chen served as corresponding authors, providing overall supervision, project management, and final manuscript revision. Yufeng Zhang, Li Chen, Yuying Wu, Haitao Chen participated in performing experiments, data analysis, literature review, and revising specific sections of the manuscript. All authors discussed the results and approved the final version for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNotes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing financial interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by projects of Longquanyi new economy and technology plan (2024LQRD0012) and by projects of Administration for State Market Supervision Administration (No.2024MK114) and by Central Government-Guided Special Fund for Local Science and Technology Development in Sichuan Province (2024ZYD0302). We acknowledge Key Laboratory of Vehicle Fuel Quality Safety and Risk Assessment, State Administration for Market Regulation. The characterization results were supported by Beijing Zhongkebaice Technology Service. Ltd (www.zkbaice.cn), especially thank Zelin Yang. (www.zkbaice.cn)\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eY. Zhai, X. Ren, B. Wang, S. (Frank) Liu, High‐Entropy Catalyst\u0026mdash;A Novel Platform for Electrochemical Water Splitting, Adv Funct Materials 32 (2022) 2207536. https://doi.org/10.1002/adfm.202207536.\u003c/li\u003e\n\u003cli\u003eM. Yang, C.H. Zhang, N.W. Li, D. Luan, L. Yu, X.W. (David) Lou, Design and Synthesis of Hollow Nanostructures for Electrochemical Water Splitting, Advanced Science 9 (2022) 2105135. https://doi.org/10.1002/advs.202105135.\u003c/li\u003e\n\u003cli\u003eF. Zeng, C. Mebrahtu, L. Liao, A.K. Beine, R. 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Wu, High-Entropy Approach vs. Traditional Doping Strategy for Layered Oxide Cathodes in Alkali-Metal-Ion Batteries: A Comparative Study, Energy Storage Materials 79 (2025) 104295. https://doi.org/10.1016/j.ensm.2025.104295.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Ni-based electrocatalyst, cerium and sulfur co-doping, oxygen vacancies, surface reconstruction, oxygen evolution reaction, alkaline water electrolysis","lastPublishedDoi":"10.21203/rs.3.rs-9258813/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9258813/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eRational regulation of surface reconstruction and defect chemistry is crucial for developing high-performance non-noble-metal electrocatalysts toward the oxygen evolution reaction (OER). Herein, a Ce- and S-co-induced oxygen-vacancy strategy is developed to construct an ultrathin NiCeS nanosheet array grown in situ on nickel foam (NiCeS/NF) via a molten-salt route. Structural analyses reveal that NiCeS/NF features a multiphase Ni\u0026ndash;Ce\u0026ndash;S framework composed of sulfide, oxysulfide, and sulfate species, together with abundant heterointerfaces and defect-rich surface environments. Spectroscopic studies demonstrate that the synergistic coupling of Ce and S effectively redistributes the local electronic structure of Ni sites, enriches oxygen-deficient species, and accelerates electrochemical surface reconstruction into the active oxyhydroxide phase. Benefiting from the integrated structural and electronic modulation, NiCeS/NF exhibits outstanding OER performance in alkaline media, delivering a low overpotential of 187 mV at 10 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, a small Tafel slope of 44.1 mV dec\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and robust durability at 1000 mA cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for \u0026asymp;\u0026thinsp;400 h. This work provides an effective defect/interfacial engineering strategy for promoting alkaline water oxidation and offers insight into the cooperative role of rare-earth and sulfur species in reconstructive electrocatalysis.\u003c/p\u003e","manuscriptTitle":"Ce and S Co-Induced Oxygen Vacancies for Enhanced Alkaline Water Electrolysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-07 19:15:31","doi":"10.21203/rs.3.rs-9258813/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-26T11:11:06+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-22T20:33:39+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-11T07:04:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-10T06:14:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-10T01:17:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"167624716162794091887122131658083746421","date":"2026-04-04T01:38:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"122832069497765688448353049715690593409","date":"2026-04-03T19:33:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-03T03:53:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"277544319841051607067780747406072505628","date":"2026-04-02T05:50:43+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"70277985349017238832925685930520257937","date":"2026-04-02T04:00:40+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"145862608731069182733925014159158343512","date":"2026-04-02T00:59:09+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"166544840890672905520386016695971096119","date":"2026-04-01T23:56:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"320919382212691333405475220311723121210","date":"2026-04-01T22:21:48+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-01T19:20:24+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-01T05:22:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-01T05:21:21+00:00","index":"","fulltext":""},{"type":"submitted","content":"Ionics","date":"2026-03-29T12:30:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"ionics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Ionics](https://www.springer.com/journal/11581) ","snPcode":"11581","submissionUrl":"https://mc.manuscriptcentral.com/ionics","title":"Ionics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0fda95c3-17b2-4d59-9369-0912ad965893","owner":[],"postedDate":"April 7th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[],"tags":[],"updatedAt":"2026-04-26T11:23:39+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-07 19:15:31","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9258813","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9258813","identity":"rs-9258813","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}