Direct electrodeposition of NiFe-based high-entropy compound on nickel foam for oxygen evolution reaction

Direct electrodeposition of NiFe-based high-entropy compound on nickel foam for oxygen evolution reaction | 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 Direct electrodeposition of NiFe-based high-entropy compound on nickel foam for oxygen evolution reaction Yibin Yang, Jitao Yang, Xinghua Huang, Wang Chen, Yuhao Zhang, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5328722/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Electrochemical water splitting represents a highly promising avenue for sustainable energy conversion and storage, paving the way for a future hydrogen-based society. This approach necessitates the development of durable and cost-effective electrocatalysts for the OER. In this study, we report the as-synthesized NiFe-based high-entropy compound grown on nickel foam via direct electrochemical deposition. Remarkably, electrodeposition onto 1×1 cm 2 nickel foam was optimized by strategically varying critical parameters. Subsequently, the fabricated electrodes underwent evaluation for comprehensive water splitting within the identical flow cell under alkaline conditions. The best-performing sample, NiFe-2:1, required relatively low overpotentials of 232 mV to reach a current density of 10 mA cm -2 for the OER. The NiFe-2:1 hydroxides exhibit high entropy, which optimizes the flat-band potential (E fb ) and carrier concentration (N A ) in high-entropy NiFe-based electrocatalysts. This enhancement facilitates sensitive electron transfer, thereby reducing the kinetic barrier for the OER. Furthermore, this review thoroughly discusses potential degradation mechanisms of active sites and outlines corresponding mitigation strategies. It also offers insights into the discrepancies between research and the design of non-precious metal-based catalysts for the OER, as well as their implementation in practical devices. NiFe-based electrocatalyst high-entropy Mott-Schottky oxygen evolution reaction electrochemical deposition Figures Figure 1 Figure 2 Figure 3 Figure 4 1 Introduction Electrochemical water splitting represents a viable approach for the mass production of hydrogen, which is anticipated to be a promising substitute for fossil fuels in the future. [1-5] The oxygen evolution reaction (OER) represents a critically important phase in electrochemical water splitting. [6-9] The energy conversion efficiency is significantly limited by the anode reaction of the OER, a slow process that involves four proton-coupled electron transfer steps. Among the various strategies for enhancing the efficiency of the OER, the use of electrocatalysts in an alkaline electrolyte is deemed a highly feasible solution. This approach is particularly advantageous due to the potential for utilizing cost-effective, earth-abundant catalysts. These catalysts can serve as effective oxygen electrocatalysts at the anode side. Over the past several decades, significant advancements have been made in the materials utilized to facilitate the OER under alkaline conditions. The first-row transition metals (including Fe, Co, Ni, Cr, Mn etc.) and their compounds (alloy, [10-16] oxides, [17-20] hydroxides, [21-24] oxyhydroxides, [25, 26] carbides, [27-31] sulfides, [1, 3, 32] phosphides, [33-36] selenides [37-39] etc.) have received extensive attention as electrocatalyst for OER. Typically, the variety of transition metal elements present in electrocatalysts is restricted to three or fewer, resulting in a constrained array and diversity of active sites. Among the myriad electrocatalysts, those NiFe-based electrocatalysts demonstrated superior performance in oxygen evolution reactions. [8, 26, 40-45] High-entropy electrocatalysts have recently garnered significant interest within the catalysis community owing to their four principal effects: the high entropy effect, lattice distortion, sluggish diffusion, and cocktail effects. These phenomena collectively have the potential to substantially enhance both the catalytic activity and stability. [11] The transition-metal (oxy)hydroxides synthesized through electrochemical deposition possess an optimal valence state and exhibit an amorphous structure with high entropy. [7, 46-48]These characteristics, along with the presence of multiple active sites inherent to high entropy compounds, enhance the efficacy of the OER catalysis. High-entropy (oxy)hydroxide catalysts are utilized in alkaline OER, demonstrating exceptional catalytic performance characterized by a low overpotential of 244 mV at a current density of 10 mA cm -2 . [7] The high specific surface area exposes numerous active sites for the OER. The high-entropy effect contributes an optimal electronic structure and an efficient synergistic effect, enhancing the activity of electrocatalyst. Additionally, rapid charge and material transport facilitate an accelerated reaction rate. The FeCoNiMnCr@CC materials, characterized by their distinctive electronic structure and stable crystal configuration, necessitated a mere overpotential of 287 mV to achieve a current density of 10 mA cm -2 for OER. This was accompanied by remarkable stability. The superior OER performance of FeCoNiMnCr@CC can be ascribed to the unique synergistic interaction among the highly active transition metals, which is induced by the entropy effect. [49] The activity of the OER has been observed to increase monotonically with the addition of mixing metallic elements in M x S y . [50] The significantly enhanced electrochemical activity of the (CrMnFeCoNi)S x nanoparticles demonstrates the predicted synergistic effect in HEMS, as anticipated by computational models. This effect successfully tailors the electronic structure to optimize interactions between the catalyst and adsorbate, thus improving catalytic performance. Furthermore, the exceptional stability of (CrMnFeCoNi)S x can be attributed to its high-entropy attributes, which confer stability to both its phase and its interface with the carbon substrate. J. Ting et al. [51] demonstrate that hybrid perovskite oxides surpass the performance of single perovskite oxides. The contribution of each metal in the B-site lattices to the activity was explored by doubling its concentration. It was found that increasing the concentration of cobalt was most beneficial; the optimized La(CrMnFeCo 2 Ni)O 3 hybrid perovskite oxide displays a remarkable oxygen evolution reaction overpotential of 325 mV at a current density of 10 mA cm -2 . Therefore, its electronic and ancillary properties are enhanced, thereby augmenting the catalytic efficiency of the OER by modulating the high entropy attributes of the electrocatalyst. Motivated by this concept, we develop a high-entropy compounds electrocatalyst via direct electrochemical deposition. In the as-synthesized high-entropy compounds, the chemical states of + 2 valence and 0 valence exist simultaneously by the XPS analysis, suggesting the NiFe-based compounds is not a simple alloy or hydroxide. Compared to the OER activity of the other, the fabricated NiFe-2:1 demonstrates a higher overpotential, measuring at 232 mV when operating at a current density of 10 mA cm -2 . XPS analysis indicates that the metal elements in the compounds are all in a low-valence state. Moreover, Mott-Schottky analysis elucidate that NiFe-2:1 can also have enormous acceptor concentration, thereby catalyzing oxygen evolution. Overall, the proposed methodology offers an effective, economical, and sustainable strategy for producing high-quality electrocatalysts, suitable for extensive application in electrochemical water-splitting technologies over an extended duration. Experimental Section Chemical Reagents : Fe(NO 3 ) 3 ·9H 2 O, Ni(NO 3 ) 2 ·6H 2 O, and KOH were procured from Aladdin Reagent (Shanghai) Co., Ltd. HCl was obtained from Chuan Dong Co., Ltd. Nickel foams (NFs) were acquired from CeTech Co., Ltd. All chemicals were employed as received, without additional purification. Treatment of NFs : The nickel foams (NFs), possessing appropriate shape and size, underwent ultrasonic cleaning in absolute alcohol for 10 minutes to eliminate potential organic contaminants adhering to their surfaces. Following this, they were dried at 60°C for 2 hours. The dried NFs were then immersed in an HCl solution for 10 minutes to remove metal oxides present on their surfaces. Finally, the treated NFs were extensively rinsed and subsequently stored in deionized water. Electrochemical synthesis of Ni-based high-entropy compound on NFs: A solution containing the requisite metal cations for incorporation into metal substrates was prepared. Table 1 illustrates the varying Ni/Fe ratios present in the solution. Electrodeposition was conducted by applying a constant cathodic current of 10 mA cm -2 for 30 s at 25 ℃. This process took place in a standard three-electrode electrochemical glass cell, utilizing an Ag/AgCl electrode as the reference electrode and a Pt plate with a geometric area of 1×1 cm -2 as the counter electrode. The Ni/Fe electrodes were electrodeposited onto NF. Table 1 The metal ion ratios in the precursor solution. Samples Ni (%) Fe (%) NiFe-3:1 75 25 NiFe-2:1 66.7 33.3 NiFe-1:1 50 50 NiFe-1:2 33.3 66.7 NiFe-1:3 25 75 Materials Characterizations : X-ray diffraction (XRD) data were obtained using an X-ray diffractometer equipped with Cu-kα radiation (λ=1.5418 Å). The measurements were conducted at a scan rate of 5° per minute, covering a 2θ range from 5° to 90°. Scanning electron microscopy (SEM) was carried out using a Nova 400 Nano-SEM. Additionally, X-ray photoelectron spectroscopy (XPS) was performed utilizing a Thermal ESCALAB 250 spectrometer, which featured an Mg kα X-ray source. Electrochemical characterizations : Electrochemical data were acquired using a CHI 660E potentiostat (CH Instruments, Inc., Shanghai) configured with a tri-electrode system in a 1.0 M KOH alkaline solution. A nickel foams (1 cm × 1 cm) grown on the sample served as the working electrode, while a Pt electrode and a saturated Ag/AgCl electrode functioned as the counter electrode and reference electrode, respectively. The electrode potentials were calibrated against a reversible hydrogen electrode (RHE), calculated as E(RHE) = E(Ag/AgCl) + 0.197 V + 0.059 × pH. Polarization curves were derived from cyclic voltammetry scans over a potential range of 0 to 0.7 V (vs. Ag/AgCl) at a scan rate of 5 mV s -1 , with all data adjusted for an 85% iR compensation. It is important to highlight that the current densities were standardized based on the geometric surface area of the working electrode. Electrochemical impedance spectroscopy (EIS) assessments were conducted by administering an alternating current (AC) voltage of 5 mV amplitude at 0.5 V (vs. Ag/AgCl), across a frequency spectrum from 100 kHz to 0.1 Hz. Mott-Schottky measurements were conducted using an AC amplitude of 5 mV and a frequency of 2000 Hz. The range of the applied bias voltage spanned from -1.2 to 0.2 V (vs. Ag/AgCl). Results and discussion The electrocatalysts of Ni-based high-entropy compound were grown on nickel foams (NFs) by a simple direct electrochemical deposition method. The experimental procedures for the synthesized NiFe-based compounds are elaborated in the Experimental Section . Figure 1 a displays the XRD patterns of the synthesized NiFe-based high-entropy compound developed on NFs. The X-ray diffraction peaks, as depicted in Figure 1 a, positioned at 44.5°, 51.9°, and 76.4° correspond to the (111), (200), and (220) planes of the cubic structure (Ni, JCPDS Card no. 87-0712), respectively. These reflections align harmoniously with the established patterns of nickel foam, whose diffraction peaks are attributed to the XRD diffraction peaks of nickel foam. Otherwise, no other positional diffraction peaks were found in the sample. However, the scanning electron microscope (SEM) image could further verified that the samples had been successfully deposited by electrochemical onto nickel foam in Figure 1 b-f, which shows the Ni-based compounds are successful synthesized via direct electrochemical deposition method. The samples in the SEM structure morphology does not show a regular morphology, and thus show no significant peak in the XRD patterns, which indicates this compound forms rather a regular crystal structure than an atomically disordered high-entropy compound. Consequently, the high-entropy compounds were prepared by direct electrochemical deposition method. X-ray photoelectron spectroscopy (XPS) was employed to investigate the effects of non-metallic elements on the surface properties and electronic structure of newly synthesized high-entropy compounds. As shown in Figure 2 a, the XPS survey spectra reveal that the samples exhibit similar spectral profiles. There are the metal element of Ni and Fe in the compound by XPS, suggesting the high-entropy NiFe-based compounds are successful synthesized via direct electrochemical deposition. The high-resolution Ni 2p spectra of NiFe-3:1, shown in Figure 2b, displays three notable peaks. These peaks, with binding energies of 850.48 eV, 855.18 eV, and 861.08 eV, correspond to the Ni(0) 2p 1/2 , Ni(Ⅱ) 2p 1/2 states, and satellite peaks, respectively. This observation is consistent with results from previous studies. Compared to Ni(OH)₂, the peak positions of NiFe-3:1 (850.48 eV and 855.18 eV) in the electrocatalysts are shifted to lower values, indicating that the chemical state of Ni atoms in the electrocatalysts is lower than that of Ni atoms in Ni(OH)₂. As depicted in Figure 2 b, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 850.48 eV, 851.08 eV, 851.58 eV, 851.68 eV and 852.88 eV, respectively. In a word, the chemical valence of the nickel element increases gradually with the decreasing Ni/Fe ratio, which the Ni atoms in the Ni-based compounds donate electrons transfers from Ni to another element. As depicted in Figure 2 c, the high-resolution Fe 2p spectra of NiFe-3:1 exhibits two peaks. These peaks, with binding energies at 705.88 eV, 712.08 eV and 717.38 eV, correspond to the Fe(0) 2p 1/2 , Fe(Ⅱ) 2p 1/2 states and satellite peaks, respectively. Figure 2 c, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 705.28 eV, 705.48 eV, 705.68 eV, 705.88 eV and 706.08 eV, respectively. In a word, the chemical valence of the nickel element increases gradually with the decreasing Ni/Fe ratio, which the Fe atoms in the Ni-based compounds donate electrons transfers from Fe to another element. The XPS O 1s profiles for NiFe-3:1 can typically be deconvoluted into two prominent peaks at 529.48 eV and 531.88 eV, corresponding to adsorbed oxygen species, such as water molecules and surface hydroxyl groups, respectively ( Figure 2 d). Compared to the O atom peak positions in Ni(OH)₂, the peak positions for O atoms in the Ni-based compound NiFe-3:1 (529.48 eV and 531.88 eV) show a distinct negative shift. This shift indicates that the O atoms in the NiFe-3:1 compound gain more electrons than those in Ni(OH)₂. Figure 2 d, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 529.48 eV, 528.78 eV, 528.68 eV, 528.58 eV and 528.58 eV, respectively. The XPS peaks also exhibits an obvious negative shift with the decreasing Ni/Fe ratio, suggesting the O atoms in the Ni-based compound receive more electrons. Combined with the above Ni and Fe charge transfer cases, we can assume that the charge is transferred from Fe-sites and Ni-sites to O atoms in the Ni-based compounds, and the number of electrons on O atoms in the electrocatalysts is increased, which would affect the adsorption energy and energetic barrier of dissociation of active species for OER. The electrocatalytic performance of Ni-based series compounds was characterized using an electrochemical workstation. The electrocatalytic OER activity of these compounds was investigated in a 1.0 M KOH solution employing a standard three-electrode system. Figure 3 a demonstrates that the electrocatalytic activity of Ni-based series compounds, which are grown on NF, is significantly influenced by the Ni/Fe ratio. Among the synthesized Ni-based compound electrocatalysts, the NiFe-3:1 Ni-based electrocatalyst demonstrates superior oxygen evolution reaction (OER) performance. It achieves a catalytic current density of 10 mA cm-2 with a minimal overpotential of 232 mV, which is 9 mV more efficient than the NiFe-2:1 electrocatalyst, which requires an overpotential of 241 mV. The overpotential of NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 234 mV, 258 mV and 261 mV, respectively ( Figure 3 a). The NiFe-2:1 compound exhibits the lowest overpotential, indicating its superior catalytic activity for the OER. These findings demonstrate that the overpotentials for OER are reduced by optimizing the Ni/Fe ratio in nickel-based compounds. To gain insight into the OER process, the kinetic parameters of the electrocatalytic reaction were determined by analyzing the OER polarization curves, which illustrate the relationship between overpotential and current density ( Figure 3 b). The Tafel slope value of NiFe-2:1 was found to be 56.70 mV dec -1 , which is less than that of NiFe-3:1 (82.16 mV dec-1), NiFe-1:1 (78.17 mV dec -1 ), NiFe-1:2 (75.13 mV dec -1 ) and NiFe-1:3 (76.68 mV dec -1 ). This indicates that NiFe-2:1 exhibits a faster kinetic OER process, leading to an improved OER performance. Electrochemical Impedance Spectroscopy (EIS) is employed to examine the interfacial properties of electrocatalytic materials. The results from EIS indicate that the charge-transfer resistance of the NiFe-2:1 electrocatalyst is comparatively lower than that observed in the pristine NiFe-3:1, NiFe-1:1, NiFe-1:2, and NiFe-1:3 electrocatalysts, as illustrated in Figure 3 c. Additionally, the electrochemical double-layer capacitance (C dl ) exhibits a direct proportionality to the electrochemical active surface area (ECSA). Consequently, the ECSA was estimated by calculating the C dl . This was achieved by recording cyclic voltammetry curves within a potential window devoid of redox reactions ( Figure S 2-6). The NiFe-2:1 had much larger C dl (127 μF cm -2 ) than that of NiFe-3:1 (123 μF cm -2 ), NiFe-1:2 (115 μF cm -2 ) and NiFe-1:3 (111 μF cm -2 , showing more electrocatalytic active sites on the NiFe-2:1 ( Figure 3 d). We also found that NiFe-1:1 has more catalytic active sites, but it can be seen that NiFe-2:1 presents a higher catalytic activity due to its higher essential activity. To elucidate the intrinsic correlation between the augmented electrocatalytic efficacy and the Ni/Fe ratio in catalyzing the oxygen evolution reaction, Mott-Schottky (MS) analysis has been extensively utilized within the field to determine critical operational parameters of semiconductors, specifically the flat-band potential and carrier concentration, as depicted in Figure 4 . Representative MS plots for various compositions of NiFe-based compounds are presented in Figure 4 a. The negative slopes of these plots suggest that the samples are p-type semiconductors. The deviations observed in the slope of the MS plot may be attributed to a variety of factors. The flat-band potential of Ni-based compounds were calculated in Figure 4 b, whose values for the diodes along with the corresponding values of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 1.44 V, 1.45 V, 1.43 V, 1.45 V and 1.45 V, respectively. The flat-band potential of NiFe-3:1 is superior to that of NiFe-3:1 and NiFe-1:1, suggesting the OER kinetics is faster with decreasing the E fb of Ni-based compounds. According to research, an effective catalyst for the OER should exhibit adequate conductivity, a high concentration of oxygen vacancies (acceptor concentration, N A ), and an appropriate flat band potential (E fb ). As shown in Figure 4 c, the acceptor concentration of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 6.39×10 17 cm 3 , 7.71×10 17 cm 3 , 6.53×10 17 cm 3 , 5.52×10 17 cm 3 , and 4.94×10 17 cm 3 , respectively. The acceptor concentration of NiFe-2:1 is superior to that of NiFe-3:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3, showing the acceptor concentration may dominate the catalytic reaction performance of OER. Besides, as described in Figure 4 d, the space-charge depletions (W d ) of were estimated from the data of Figure 4 a. The space-charge depletion of NiFe-2:1 is lower to that of the other samples, suggesting the space-charge depletion of NiFe-2:1 is less affected than that of the other samples, thus showing better performance at the applied voltage. Our research indicates that by modulating the ratio of nickel (Ni) to iron (Fe) atoms within the compound, we optimized the acceptor concentration, thereby enhancing the OER catalytic performance. Adjusting the Ni/Fe ratio in the electrocatalyst allows for effective control over the carrier concentration, which in turn influences the electronic structural entropy of the system. It is clear that the electronic structural entropy of the electrocatalyst plays a crucial role in determining the catalytic efficiency of the OER. The high-entropy strategy is instrumental in augmenting both the activity and the structural stability of the OER catalysts. Conclusions In conclusion, we have successfully demonstrated the utilization of Ni-based high-entropy as an exceptional electrode material. Our study introduces a novel approach to improving the kinetics of the OER in NiFe-2:1. The fabricated NiFe-2:1 exhibits a higher overpotential compared to the other, measuring 232 mV at an operating current density of 10 mA cm -2 during the OER activity. XPS analysis indicates that the metal elements in the compounds are all in a low-valence state. Moreover, Mott-Schottky analysis elucidate that NiFe-2:1 can also have enormous acceptor concentration, thereby catalyzing oxygen evolution. This innovative concept of electron-regulated electrocatalysis could furnish substantial insights for catalyst design, not only for OER but also for other applications. Declarations Conflicts of interest There are no conflicts to declare. Author Contribution All authors reviewed the manuscript. Acknowledgement Jitao Yang, Xinghua Huang, Wang Chen, Yuhao Zhang, Xiaowen Zhang, Lijuan Dong and Zhihao Duan gave professional writing services for Abstract, Introduction, Experimental Section, Results and discussion, Conclusions, SI, and Cover letter, respectively. Mingzhu Wu and Ying Li gave professional revising for paper; Yibin Yang gave professional materials and design. Data Availability Data is provided within the manuscript or supplementary information files. References S. Chandrasekaran, L. Yao, L. Deng, C. Bowen, Y. Zhang, S. Chen, Z. Lin, F. Peng, P. Zhang, Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond, Chem. Soc. Rev., 48 (2019) 4178–4280. M. Chatenet, B.G. Pollet, D.R. Dekel, F. Dionigi, J. Deseure, P. Millet, R.D. Braatz, M.Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn, H. 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Chen, Electrodeposition of (hydro)oxides for an oxygen evolution electrode, Chem. Sci., 11 (2020) 10614–10625. R. Zhang, Z. Xu, Z. Du, Y. Wan, S. Yuan, F. Zeng, J. Xu, Z. Meng, X. Hu, H. Tian, Electrodeposition of self-supported high-entropy spinel oxides for stable oxygen evolution, Inorg. Chem., 62 (2023) 19052–19059. M. Cui, C. Yang, B. Li, Q. Dong, M. Wu, S. Hwang, H. Xie, X. Wang, G. Wang, L. Hu, High-entropy metal sulfide nanoparticles promise high‐performance oxygen evolution reaction, Adv. Energy Mater., 11 (2020) 2002887. T.X. Nguyen, Y.C. Liao, C.C. Lin, Y.H. Su, J.M. Ting, Advanced high entropy perovskite oxide electrocatalyst for oxygen evolution reaction, Adv. Funct. Mater., 31 (2021) 2101632. Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5328722","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":382977056,"identity":"6288f428-fdd1-48b7-af4b-d633006b25b0","order_by":0,"name":"Yibin 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01:23:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5328722/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5328722/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":71202697,"identity":"f47d597c-6d32-41cc-ae11-f33be13a3e7e","added_by":"auto","created_at":"2024-12-12 06:33:27","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":347822,"visible":true,"origin":"","legend":"\u003cp\u003eSynthetic process and material characterizations of Ni-based high-entropy compound. a) XRD patterns of Ni-based high-entropy compound, b)-f) SEM images of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2, NiFe-1:3, respectively.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/26bc5d19c12bf1e32bff00fe.png"},{"id":71202386,"identity":"a3e911e0-abc9-480b-b875-c27ee0567122","added_by":"auto","created_at":"2024-12-12 06:25:27","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":388004,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectra of a) survey, b) Ni 2p, c) Fe 2p and d) O 1s in Ni-based high-entropy compound, respectively.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/e74680263b3b15f82ac5a94a.png"},{"id":71202385,"identity":"fe0ab221-f14c-4223-aa94-8180a690d8e5","added_by":"auto","created_at":"2024-12-12 06:25:27","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":367352,"visible":true,"origin":"","legend":"\u003cp\u003eOER activity of Ni-based high-entropy compound in alkaline media. a) \u003cem\u003ei\u003c/em\u003eR-corrected CVs. b) Tafel plots. c) EIS and d) C\u003csub\u003edl\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/b638b00ba05e7f19d260353c.png"},{"id":71202384,"identity":"88dcb83d-4e85-4fe3-a967-038cc59cf216","added_by":"auto","created_at":"2024-12-12 06:25:27","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":312440,"visible":true,"origin":"","legend":"\u003cp\u003ea) Mott-Schottky form Ni-based high-entropy compound. The plots are recorded at 2 kHz. For the bias voltage polarity used with these diode structures, a positive slope indicates p-type behavior. The data of flat band potentials b), carrier concentration c) and depleted layer width d) from a).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/01277d2db0b2abb0e3eb9a6c.png"},{"id":79364245,"identity":"f21477c2-0458-4be6-b44f-00ac988093db","added_by":"auto","created_at":"2025-03-27 13:01:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2006785,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/35b790fc-9c15-4d11-b060-f89b081b447a.pdf"},{"id":71202388,"identity":"95d775c1-87fa-48c3-9e58-185ef2741fe1","added_by":"auto","created_at":"2024-12-12 06:25:27","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1019364,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-5328722/v1/170425bd8c2c7569d7f254eb.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Direct electrodeposition of NiFe-based high-entropy compound on nickel foam for oxygen evolution reaction","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eElectrochemical water splitting represents a viable approach for the mass production of hydrogen, which is anticipated to be a promising substitute for fossil fuels in the future. [1-5] The oxygen evolution reaction (OER) represents a critically important phase in electrochemical water splitting. [6-9]\u0026nbsp;The energy conversion efficiency is significantly limited by the anode reaction of the OER, a slow process that involves four proton-coupled electron transfer steps. Among the various strategies for enhancing the efficiency of the OER, the use of electrocatalysts in an alkaline electrolyte is deemed a highly feasible solution. This approach is particularly advantageous due to the potential for utilizing cost-effective, earth-abundant catalysts. These catalysts can serve as effective oxygen electrocatalysts at the anode side.\u003c/p\u003e\n\u003cp\u003eOver the past several decades, significant advancements have been made in the materials utilized to facilitate the OER under alkaline conditions. The first-row transition metals (including Fe, Co, Ni, Cr, Mn etc.) and their compounds (alloy, [10-16] oxides, [17-20] hydroxides, [21-24] oxyhydroxides, [25, 26] carbides, [27-31] sulfides, [1, 3, 32] phosphides, [33-36] selenides [37-39] etc.) have received extensive attention as electrocatalyst for OER. Typically, the variety of transition metal elements present in electrocatalysts is restricted to three or fewer, resulting in a constrained array and diversity of active sites. Among the myriad electrocatalysts, those NiFe-based electrocatalysts demonstrated superior performance in oxygen evolution reactions. [8, 26, 40-45] High-entropy electrocatalysts have recently garnered significant interest within the catalysis community owing to their four principal effects: the high entropy effect, lattice distortion, sluggish diffusion, and cocktail effects. These phenomena collectively have the potential to substantially enhance both the catalytic activity and stability.\u0026nbsp;[11]\u0026nbsp;The transition-metal (oxy)hydroxides synthesized through electrochemical deposition possess an optimal valence state and exhibit an amorphous structure with high entropy.\u0026nbsp;[7, 46-48]These characteristics, along with the presence of multiple active sites inherent to high entropy compounds, enhance the efficacy of the OER catalysis. High-entropy (oxy)hydroxide catalysts are utilized in alkaline OER, demonstrating exceptional catalytic performance characterized by a low overpotential of 244 mV at a current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e.\u0026nbsp;[7]\u0026nbsp;The high specific surface area exposes numerous active sites for the OER. The high-entropy effect contributes an optimal electronic structure and an efficient synergistic effect, enhancing the activity of electrocatalyst. Additionally, rapid charge and material transport facilitate an accelerated reaction rate. The FeCoNiMnCr@CC materials, characterized by their distinctive electronic structure and stable crystal configuration, necessitated a mere overpotential of 287 mV to achieve a current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e for OER. This was accompanied by remarkable stability. The superior OER performance of FeCoNiMnCr@CC can be ascribed to the unique synergistic interaction among the highly active transition metals, which is induced by the entropy effect.\u0026nbsp;[49] The activity of the OER has been observed to increase monotonically with the addition of mixing metallic elements in M\u003csub\u003ex\u003c/sub\u003eS\u003csub\u003ey\u003c/sub\u003e.\u0026nbsp;[50] The significantly enhanced electrochemical activity of the (CrMnFeCoNi)S\u003csub\u003ex\u003c/sub\u003e nanoparticles demonstrates the predicted synergistic effect in HEMS, as anticipated by computational models. This effect successfully tailors the electronic structure to optimize interactions between the catalyst and adsorbate, thus improving catalytic performance. Furthermore, the exceptional stability of (CrMnFeCoNi)S\u003csub\u003ex\u003c/sub\u003e can be attributed to its high-entropy attributes, which confer stability to both its phase and its interface with the carbon substrate. J. Ting et al.\u0026nbsp;[51]\u0026nbsp;demonstrate that hybrid perovskite oxides surpass the performance of single perovskite oxides. The contribution of each metal in the B-site lattices to the activity was explored by doubling its concentration. It was found that increasing the concentration of cobalt was most beneficial; the optimized La(CrMnFeCo\u003csub\u003e2\u003c/sub\u003eNi)O\u003csub\u003e3\u003c/sub\u003e hybrid perovskite oxide displays a remarkable oxygen evolution reaction overpotential of 325 mV at a current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e. Therefore, its electronic and ancillary properties are enhanced, thereby augmenting the catalytic efficiency of the OER by modulating the high entropy attributes of the electrocatalyst.\u003c/p\u003e\n\u003cp\u003eMotivated by this concept, we develop a high-entropy compounds electrocatalyst via direct electrochemical deposition. In the as-synthesized high-entropy compounds, the chemical states of + 2 valence and 0 valence exist simultaneously by the XPS analysis, suggesting the NiFe-based compounds is not a simple alloy or hydroxide. Compared to the OER activity of the other, the fabricated NiFe-2:1 demonstrates a higher overpotential, measuring at 232 mV when operating at a current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e. XPS analysis indicates that the metal elements in the compounds are all in a low-valence state. Moreover, Mott-Schottky analysis elucidate that NiFe-2:1 can also have enormous acceptor concentration, thereby catalyzing oxygen evolution. Overall, the proposed methodology offers an effective, economical, and sustainable strategy for producing high-quality electrocatalysts, suitable for extensive application in electrochemical water-splitting technologies over an extended duration.\u003c/p\u003e"},{"header":"Experimental Section","content":"\u003cp\u003e\u003cstrong\u003eChemical Reagents\u003c/strong\u003e: Fe(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e\u0026middot;9H\u003csub\u003e2\u003c/sub\u003eO, Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026middot;6H\u003csub\u003e2\u003c/sub\u003eO, and KOH were procured from Aladdin Reagent (Shanghai) Co., Ltd. HCl was obtained from Chuan Dong Co., Ltd. Nickel foams (NFs) were acquired from CeTech Co., Ltd. All chemicals were employed as received, without additional purification.\u003cbr\u003e\u003cstrong\u003eTreatment of NFs\u003c/strong\u003e: The nickel foams (NFs), possessing appropriate shape and size, underwent ultrasonic cleaning in absolute alcohol for 10 minutes to eliminate potential organic contaminants adhering to their surfaces. Following this, they were dried at 60\u0026deg;C for 2 hours. The dried NFs were then immersed in an HCl solution for 10 minutes to remove metal oxides present on their surfaces. Finally, the treated NFs were extensively rinsed and subsequently stored in deionized water.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical synthesis of Ni-based high-entropy compound on NFs:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA solution containing the requisite metal cations for incorporation into metal substrates was prepared. \u003cstrong\u003eTable 1\u003c/strong\u003e illustrates the varying Ni/Fe ratios present in the solution. Electrodeposition was conducted by applying a constant cathodic current of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e for 30 s at 25 ℃. This process took place in a standard three-electrode electrochemical glass cell, utilizing an Ag/AgCl electrode as the reference electrode and a Pt plate with a geometric area of 1\u0026times;1 cm\u003csup\u003e-2\u003c/sup\u003e as the counter electrode. The Ni/Fe electrodes were electrodeposited onto NF.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u0026nbsp;\u003c/strong\u003eThe metal ion ratios in the precursor solution.\u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eSamples\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNi (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eFe (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNiFe-3:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNiFe-2:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e66.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e33.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNiFe-1:1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNiFe-1:2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e33.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e66.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 33.3333%;\"\u003e\n \u003cp\u003eNiFe-1:3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 33.3333%;\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials Characterizations\u003c/strong\u003e: X-ray diffraction (XRD) data were obtained using an X-ray diffractometer equipped with Cu-k\u0026alpha; radiation (\u0026lambda;=1.5418 \u0026Aring;). The measurements were conducted at a scan rate of 5\u0026deg; per minute, covering a 2\u0026theta; range from 5\u0026deg; to 90\u0026deg;. Scanning electron microscopy (SEM) was carried out using a Nova 400 Nano-SEM. Additionally, X-ray photoelectron spectroscopy (XPS) was performed utilizing a Thermal ESCALAB 250 spectrometer, which featured an Mg k\u0026alpha; X-ray source.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrochemical characterizations\u003c/strong\u003e: Electrochemical data were acquired using a CHI 660E potentiostat (CH Instruments, Inc., Shanghai) configured with a tri-electrode system in a 1.0 M KOH alkaline solution. A nickel foams (1 cm \u0026times; 1 cm) grown on the sample served as the working electrode, while a Pt electrode and a saturated Ag/AgCl electrode functioned as the counter electrode and reference electrode, respectively. The electrode potentials were calibrated against a reversible hydrogen electrode (RHE), calculated as E(RHE) = E(Ag/AgCl) + 0.197 V + 0.059 \u0026times; pH. Polarization curves were derived from cyclic voltammetry scans over a potential range of 0 to 0.7 V (vs. Ag/AgCl) at a scan rate of 5 mV s\u003csup\u003e-1\u003c/sup\u003e, with all data adjusted for an 85% iR compensation. It is important to highlight that the current densities were standardized based on the geometric surface area of the working electrode. Electrochemical impedance spectroscopy (EIS) assessments were conducted by administering an alternating current (AC) voltage of 5 mV amplitude at 0.5 V (vs. Ag/AgCl), across a frequency spectrum from 100 kHz to 0.1 Hz. Mott-Schottky measurements were conducted using an AC amplitude of 5 mV and a frequency of 2000 Hz. The range of the applied bias voltage spanned from -1.2 to 0.2 V (vs. Ag/AgCl).\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eThe electrocatalysts of Ni-based high-entropy compound were grown on nickel foams (NFs) by a simple direct electrochemical deposition method. The experimental procedures for the synthesized NiFe-based compounds are elaborated in the \u003cstrong\u003eExperimental Section\u003c/strong\u003e. \u003cstrong\u003eFigure 1\u003c/strong\u003ea displays the XRD patterns of the synthesized NiFe-based high-entropy compound developed on NFs. The X-ray diffraction peaks, as depicted in \u003cstrong\u003eFigure 1\u003c/strong\u003ea, positioned at 44.5\u0026deg;, 51.9\u0026deg;, and 76.4\u0026deg; correspond to the (111), (200), and (220) planes of the cubic structure (Ni, JCPDS Card no. 87-0712), respectively. These reflections align harmoniously with the established patterns of nickel foam, whose diffraction peaks are attributed to the XRD diffraction peaks of nickel foam. Otherwise, no other positional diffraction peaks were found in the sample. However, the scanning electron microscope (SEM) image could further verified that the samples had been successfully deposited by electrochemical onto nickel foam in \u003cstrong\u003eFigure 1\u003c/strong\u003eb-f, which shows the Ni-based compounds are successful synthesized via direct electrochemical deposition method. The samples in the SEM structure morphology does not show a regular morphology, and thus show no significant peak in the XRD patterns, which indicates this compound forms rather a regular crystal structure than an atomically disordered high-entropy compound. Consequently, the high-entropy compounds were prepared by direct electrochemical deposition method.\u003c/p\u003e\n\u003cp\u003eX-ray photoelectron spectroscopy (XPS) was employed to investigate the effects of non-metallic elements on the surface properties and electronic structure of newly synthesized high-entropy compounds. As shown in \u003cstrong\u003eFigure 2\u003c/strong\u003ea, the XPS survey spectra reveal that the samples exhibit similar spectral profiles.\u0026nbsp;There are the metal element of Ni and Fe in the compound by XPS, suggesting the high-entropy NiFe-based compounds are successful synthesized via direct electrochemical deposition. The high-resolution Ni 2p spectra of NiFe-3:1, shown in Figure 2b, displays three notable peaks. These peaks, with binding energies of 850.48 eV, 855.18 eV, and 861.08 eV, correspond to the Ni(0) 2p\u003csub\u003e1/2\u003c/sub\u003e, Ni(Ⅱ) 2p\u003csub\u003e1/2\u003c/sub\u003e states, and satellite peaks, respectively. This observation is consistent with results from previous studies. Compared to Ni(OH)₂, the peak positions of NiFe-3:1 (850.48 eV and 855.18 eV) in the electrocatalysts are shifted to lower values, indicating that the chemical state of Ni atoms in the electrocatalysts is lower than that of Ni atoms in Ni(OH)₂.\u0026nbsp;As depicted in \u003cstrong\u003eFigure 2\u003c/strong\u003eb, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 850.48 eV, 851.08 eV, 851.58 eV, 851.68 eV and 852.88 eV, respectively. In a word, the chemical valence of the nickel element increases gradually with the decreasing Ni/Fe ratio, which the Ni atoms in the Ni-based compounds donate electrons transfers from Ni to another element. As depicted in \u003cstrong\u003eFigure 2\u003c/strong\u003ec, the high-resolution Fe 2p spectra of NiFe-3:1 exhibits two peaks. These peaks, with binding energies at 705.88 eV, 712.08 eV and 717.38 eV, correspond to the Fe(0) 2p\u003csub\u003e1/2\u003c/sub\u003e, Fe(Ⅱ) 2p\u003csub\u003e1/2\u003c/sub\u003e states and satellite peaks, respectively. \u003cstrong\u003eFigure 2\u003c/strong\u003ec, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 705.28 eV, 705.48 eV, 705.68 eV, 705.88 eV and 706.08 eV, respectively. In a word, the chemical valence of the nickel element increases gradually with the decreasing Ni/Fe ratio, which the Fe atoms in the Ni-based compounds donate electrons transfers from Fe to another element. The XPS O 1s profiles for NiFe-3:1 can typically be deconvoluted into two prominent peaks at 529.48 eV and 531.88 eV, corresponding to adsorbed oxygen species, such as water molecules and surface hydroxyl groups, respectively (\u003cstrong\u003eFigure 2\u003c/strong\u003ed). Compared to the O atom peak positions in Ni(OH)₂, the peak positions for O atoms in the Ni-based compound NiFe-3:1 (529.48 eV and 531.88 eV) show a distinct negative shift. This shift indicates that the O atoms in the NiFe-3:1 compound gain more electrons than those in Ni(OH)₂. \u003cstrong\u003eFigure 2\u003c/strong\u003ed, with the decreasing Ni/Fe ratio, the peaks position of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 529.48 eV, 528.78 eV, 528.68 eV, 528.58 eV and 528.58 eV, respectively. The XPS peaks also exhibits an obvious negative shift with the decreasing Ni/Fe ratio, suggesting the O atoms in the Ni-based compound receive more electrons. Combined with the above Ni and Fe charge transfer cases, we can assume that the charge is transferred from Fe-sites and Ni-sites to O atoms in the Ni-based compounds, and the number of electrons on O atoms in the electrocatalysts is increased, which would affect the adsorption energy and energetic barrier of dissociation of active species for OER.\u003c/p\u003e\n\u003cp\u003eThe electrocatalytic performance of Ni-based series compounds was characterized using an electrochemical workstation. The electrocatalytic OER activity of these compounds was investigated in a 1.0 M KOH solution employing a standard three-electrode system. \u003cstrong\u003eFigure 3\u003c/strong\u003ea demonstrates that the electrocatalytic activity of Ni-based series compounds, which are grown on NF, is significantly influenced by the Ni/Fe ratio. Among the synthesized Ni-based compound electrocatalysts, the NiFe-3:1 Ni-based electrocatalyst demonstrates superior oxygen evolution reaction (OER) performance. It achieves a catalytic current density of 10 mA cm-2 with a minimal overpotential of 232 mV, which is 9 mV more efficient than the NiFe-2:1 electrocatalyst, which requires an overpotential of 241 mV. The overpotential of NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 234 mV, 258 mV and 261 mV, respectively (\u003cstrong\u003eFigure 3\u003c/strong\u003ea). The NiFe-2:1 compound exhibits the lowest overpotential, indicating its superior catalytic activity for the OER. These findings demonstrate that the overpotentials for OER are reduced by optimizing the Ni/Fe ratio in nickel-based compounds.\u003c/p\u003e\n\u003cp\u003eTo gain insight into the OER process, the kinetic parameters of the electrocatalytic reaction were determined by analyzing the OER polarization curves, which illustrate the relationship between overpotential and current density (\u003cstrong\u003eFigure 3\u003c/strong\u003eb).\u0026nbsp;The Tafel slope value of NiFe-2:1 was found to be 56.70 mV dec\u003csup\u003e-1\u003c/sup\u003e, which is less than that of NiFe-3:1 (82.16 mV dec-1), NiFe-1:1 (78.17 mV dec\u003csup\u003e-1\u003c/sup\u003e), NiFe-1:2 (75.13 mV dec\u003csup\u003e-1\u003c/sup\u003e) and NiFe-1:3 (76.68 mV dec\u003csup\u003e-1\u003c/sup\u003e). This indicates that NiFe-2:1 exhibits a faster kinetic OER process, leading to an improved OER performance. Electrochemical Impedance Spectroscopy (EIS) is employed to examine the interfacial properties of electrocatalytic materials. The results from EIS indicate that the charge-transfer resistance of the NiFe-2:1 electrocatalyst is comparatively lower than that observed in the pristine NiFe-3:1, NiFe-1:1, NiFe-1:2, and NiFe-1:3 electrocatalysts, as illustrated in \u003cstrong\u003eFigure 3\u003c/strong\u003ec. Additionally, the electrochemical double-layer capacitance (C\u003csub\u003edl\u003c/sub\u003e) exhibits a direct proportionality to the electrochemical active surface area (ECSA). Consequently, the ECSA was estimated by calculating the C\u003csub\u003edl\u003c/sub\u003e. This was achieved by recording cyclic voltammetry curves within a potential window devoid of redox reactions (\u003cstrong\u003eFigure S\u003c/strong\u003e2-6). The NiFe-2:1 had much larger C\u003csub\u003edl\u003c/sub\u003e (127 \u0026mu;F cm\u003csup\u003e-2\u003c/sup\u003e) than that of NiFe-3:1 (123 \u0026mu;F cm\u003csup\u003e-2\u003c/sup\u003e), NiFe-1:2 (115 \u0026mu;F cm\u003csup\u003e-2\u003c/sup\u003e) and NiFe-1:3 (111 \u0026mu;F cm\u003csup\u003e-2\u003c/sup\u003e, showing more electrocatalytic active sites on the NiFe-2:1 (\u003cstrong\u003eFigure 3\u003c/strong\u003ed). We also found that NiFe-1:1 has more catalytic active sites, but it can be seen that NiFe-2:1 presents a higher catalytic activity due to its higher essential activity.\u003c/p\u003e\n\u003cp\u003eTo elucidate the intrinsic correlation between the augmented electrocatalytic efficacy and the Ni/Fe ratio in catalyzing the oxygen evolution reaction, Mott-Schottky (MS) analysis has been extensively utilized within the field to determine critical operational parameters of semiconductors, specifically the flat-band potential and carrier concentration, as depicted in \u003cstrong\u003eFigure 4\u003c/strong\u003e. Representative MS plots for various compositions of NiFe-based compounds are presented in \u003cstrong\u003eFigure 4\u003c/strong\u003ea. The negative slopes of these plots suggest that the samples are p-type semiconductors. The deviations observed in the slope of the MS plot may be attributed to a variety of factors. The flat-band potential of Ni-based compounds were calculated in\u003cstrong\u003e\u0026nbsp;Figure 4\u003c/strong\u003eb, whose values for the diodes along with the corresponding values of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 1.44 V, 1.45 V, 1.43 V, 1.45 V and 1.45 V, respectively. The flat-band potential of NiFe-3:1 is superior to that of NiFe-3:1 and NiFe-1:1, suggesting the OER kinetics is faster with decreasing the E\u003csub\u003efb\u003c/sub\u003e of Ni-based compounds. According to research, an effective catalyst for the OER should exhibit adequate conductivity, a high concentration of oxygen vacancies (acceptor concentration, N\u003csub\u003eA\u003c/sub\u003e), and an appropriate flat band potential (E\u003csub\u003efb\u003c/sub\u003e). As shown in \u003cstrong\u003eFigure 4\u003c/strong\u003ec, the acceptor concentration of NiFe-3:1, NiFe-2:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3 are 6.39\u0026times;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, 7.71\u0026times;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, 6.53\u0026times;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, 5.52\u0026times;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, and 4.94\u0026times;10\u003csup\u003e17\u003c/sup\u003e cm\u003csup\u003e3\u003c/sup\u003e, respectively. The acceptor concentration of NiFe-2:1 is superior to that of NiFe-3:1, NiFe-1:1, NiFe-1:2 and NiFe-1:3, showing the acceptor concentration may dominate the catalytic reaction performance of OER. Besides, as described in \u003cstrong\u003eFigure 4\u003c/strong\u003ed, the space-charge depletions (W\u003csub\u003ed\u003c/sub\u003e) of were estimated from the data of \u003cstrong\u003eFigure 4\u003c/strong\u003ea. The space-charge depletion of NiFe-2:1 is lower to that of the other samples, suggesting the space-charge depletion of NiFe-2:1 is less affected than that of the other samples, thus showing better performance at the applied voltage.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOur research indicates that by modulating the ratio of nickel (Ni) to iron (Fe) atoms within the compound, we optimized the acceptor concentration, thereby enhancing the OER catalytic performance. Adjusting the Ni/Fe ratio in the electrocatalyst allows for effective control over the carrier concentration, which in turn influences the electronic structural entropy of the system. It is clear that the electronic structural entropy of the electrocatalyst plays a crucial role in determining the catalytic efficiency of the OER. The high-entropy strategy is instrumental in augmenting both the activity and the structural stability of the OER catalysts.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn conclusion, we have successfully demonstrated the utilization of Ni-based high-entropy as an exceptional electrode material. Our study introduces a novel approach to improving the kinetics of the OER in NiFe-2:1. The fabricated NiFe-2:1 exhibits a higher overpotential compared to the other, measuring 232 mV at an operating current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e during the OER activity. XPS analysis indicates that the metal elements in the compounds are all in a low-valence state. Moreover, Mott-Schottky analysis elucidate that NiFe-2:1 can also have enormous acceptor concentration, thereby catalyzing oxygen evolution. This innovative concept of electron-regulated electrocatalysis could furnish substantial insights for catalyst design, not only for OER but also for other applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflicts of interest\u003c/h2\u003e \u003cp\u003eThere are no conflicts to declare.\u003c/p\u003e \u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eJitao Yang, Xinghua Huang, Wang Chen, Yuhao Zhang, Xiaowen Zhang, Lijuan Dong and Zhihao Duan gave professional writing services for Abstract, Introduction, Experimental Section, Results and discussion, Conclusions, SI, and Cover letter, respectively. Mingzhu Wu and Ying Li gave professional revising for paper; Yibin Yang gave professional materials and design.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData is provided within the manuscript or supplementary information files.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eS. Chandrasekaran, L. Yao, L. Deng, C. Bowen, Y. Zhang, S. Chen, Z. Lin, F. Peng, P. Zhang, Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond, Chem. Soc. Rev., 48 (2019) 4178\u0026ndash;4280.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eM. Chatenet, B.G. Pollet, D.R. Dekel, F. Dionigi, J. Deseure, P. Millet, R.D. Braatz, M.Z. Bazant, M. Eikerling, I. Staffell, P. Balcombe, Y. Shao-Horn, H. Schafer, Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments, Chem. Soc. 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Mater., 31 (2021) 2101632.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"NiFe-based electrocatalyst, high-entropy, Mott-Schottky, oxygen evolution reaction, electrochemical deposition","lastPublishedDoi":"10.21203/rs.3.rs-5328722/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5328722/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eElectrochemical water splitting represents a highly promising avenue for sustainable energy conversion and storage, paving the way for a future hydrogen-based society. This approach necessitates the development of durable and cost-effective electrocatalysts for the OER. In this study, we report the as-synthesized NiFe-based high-entropy compound grown on nickel foam via direct electrochemical deposition. Remarkably, electrodeposition onto 1×1 cm\u003csup\u003e2\u003c/sup\u003e nickel foam was optimized by strategically varying critical parameters. Subsequently, the fabricated electrodes underwent evaluation for comprehensive water splitting within the identical flow cell under alkaline conditions. The best-performing sample, NiFe-2:1, required relatively low overpotentials of 232 mV to reach a current density of 10 mA cm\u003csup\u003e-2\u003c/sup\u003e for the OER. The NiFe-2:1 hydroxides exhibit high entropy, which optimizes the flat-band potential (E\u003csub\u003efb\u003c/sub\u003e) and carrier concentration (N\u003csub\u003eA\u003c/sub\u003e) in high-entropy NiFe-based electrocatalysts. This enhancement facilitates sensitive electron transfer, thereby reducing the kinetic barrier for the OER. Furthermore, this review thoroughly discusses potential degradation mechanisms of active sites and outlines corresponding mitigation strategies. It also offers insights into the discrepancies between research and the design of non-precious metal-based catalysts for the OER, as well as their implementation in practical devices.\u003c/p\u003e","manuscriptTitle":"Direct electrodeposition of NiFe-based high-entropy compound on nickel foam for oxygen evolution reaction","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-12 06:25:22","doi":"10.21203/rs.3.rs-5328722/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"6a1952da-9dc6-4f4f-96ec-6fa0451489ae","owner":[],"postedDate":"December 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-03-27T12:53:45+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-12 06:25:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5328722","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5328722","identity":"rs-5328722","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}