Bifunctional high-entropy alloy electrocatalysts for stable overall water splitting at industrial-level current densities

Abstract

High-entropy materials offer a wide range of potential applications in the catalysis domain due to their multi-active site characteristics and cocktail effect. However, the development of bifunctional electrocatalysts with both superior efficiency and excellent stability under both industrial preparation and industrial running conditions remains a significant challenge. Herein, a scalable plasma spraying strategy is developed to fabricate FeCoNiCrMn HEA catalysts with multimetal synergy, enabling robust bifunctional activity for oxygen and hydrogen evolution reactions (OER/HER). The HEA exhibits ultralow overpotentials of 220 mV (OER) and 69 mV (HER) at 10 mA cm⁻², alongside exceptional durability over 1000 h (OER) and 500 h (HER) at 1000 mA cm⁻². In an anion exchange membrane water electrolyzer (AEMWE), the HEA achieves 1000 mA cm⁻² at merely 2.18 V, outperforming commercial Ni mesh (3.40 V) and Raney Ni (3.03 V) electrode systems. Crucially, stable operation for 200 h at 1000 mA cm⁻² under industrial conditions (1 M KOH, 80 °C) demonstrates the viability of scalable HEA catalysts for practical water splitting. This work bridges the gap between lab-scale innovation and industrial electrocatalyst deployment, offering a promising pathway for large-scale hydrogen production.

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1. Introduction

The worldwide energy and environmental issues have made the development of clean energy more urgent than ever before.^1,2 Hydrogen is a new and renewable energy source that is very energetic, nonpolluting, and essential to human development, which is predicted to be one of the cleanest energy sources for the future. Anion Exchange Membrane Water Electrolyzer (AEMWE) is one of the three types of low-temperature (<100 °C) water electrolysis setup and its application is considered a promising energy strategy for large-scale hydrogen production.³ However, the high cost of current water electrolysis technology limits its broader adoption. Thus, developing highly affordable catalysts is essential to reduce the energy consumption of both half–cell reactions, i.e., the HER and OER.^4–7 On the other hand, most catalysts are effective for either the HER or OER,^8,9 and the use of two or more catalysts significantly increases both process complexity and the cost of constructing a complete water electrolyzer.^10,11

Initially, RuO₂, IrO₂, and Pt/C served as the state-of-the-art catalysts for both the OER and HER.^12,13 Nevertheless, their limited availability, inferior stability, and high cost have impeded their widespread commercial application.¹⁴ Recent investigations have identified nonprecious transition metal-based catalysts as promising alternatives to precious metal catalysts, owing to their lower cost and high catalytic activity.¹⁵ For instance, Li et al. fabricated Fe-doped Ni₃S₂ self-supporting electrodes on NFF through self-derivation reactions, which exhibited high catalytic activity in both water and urea electrolysis.¹⁶ Zhong et al. modified NiFe LDH using ion beam irradiation technology and successfully synthesized NiO–NiFe₂O₄ heterostructure catalysts with abundant oxygen vacancies.¹⁷ Huang et al. activated the catalytic activity of MoSe₂ nanosheets by introducing both anion and cation vacancies.¹⁸

Current research primarily focuses on traditional monometallic and binary alloys, along with their (oxy)hydroxide materials and composites. In contrast, the exploration of high-entropy alloys (HEAs) containing five or more metals remains limited. Compared to traditional alloys, HEAs exhibit unique cocktail effects, tunable electronic properties, and superior structural stability.^19–30 Recent work by Zhu et al. revealed that the FeCoNiCuMn high-entropy alloy supported on carbon nanofibers (HEA/CNFs) achieves exceptional bifunctional activity, outperforming both ternary (FeCoNi) and quaternary (FeCoNiCu and FeCoNiMn) alloy systems in both HER and OER metrics.³¹ Hence, exploring non-precious metal based HEAs in water splitting reactions presents a promising research avenue, warranting further investigation. For instance, Yao et al. presented a monolithic nanoporous CuAlNiMoFe electrode featuring a high-entropy CuNiMoFe surface, which exhibits substantial potential as a cost-effective electrocatalyst for hydrogen evolution.³² Hu et al. synthesized FeCoNiMnCr HEA-HEO/CNT heterostructures via solvothermal synthesis and pyrolysis, thereby enhancing the OER catalytic process. This work has made great breakthroughs in OER performance and stability, but the HER and complete water splitting still need to be studied.² Hence, the application of HEAs, especially earth-abundant metal-based HEAs, for water splitting reactions presents a promising avenue for future research.

Nonetheless, an issue that cannot be overlooked is that most HEA electrocatalysts exhibit high activity only at low current densities (e.g., 10–100 mA cm⁻²) with few hours of stability under laboratory conditions.^33,34 The performance at high current densities (e.g., 500–1000 mA cm⁻²) is critical for commercial applications, but remains largely unexplored.³⁵ Hence, achieving sustained stability of these catalysts under harsh industrial conditions presents another significant challenge. More importantly, most HEA electrodes are prepared under laboratory conditions with only a few square centimeters of working area, which seriously hinder their industrial application. Moreover, the methods to fabricate these HEA catalysts is complicated, resulting in the inability to mass produce them or high cost. Evidently, developing cost-effective, mass-manufactured, and extremely efficient bifunctional HEA electrocatalysts with high stability under industrial conditions is essential for advancing water splitting technology.

In this work, we highlight a non-precious metal high-entropy alloy FeCoNiCrMn on nickel mesh (labeled as FeCoNiCrMn HEA/NM) obtained by the plasma spraying process. Benefiting from the highly mixed configurational entropy and robust adhesion between HEA and NM due to the high temperature thermal spraying process, FeCoNiCrMn HEA/NM demonstrates markedly superior HER and OER performance compared to commercial nickel-based catalysts, such as nickel mesh and Raney nickel mesh, achieving high efficiency and stability of 1000 h at a current density of 1000 mA cm⁻² required for industrial applications both for the OER and HER. Furthermore, the electrocatalyst functions as a bifunctional electrode for AEMWE, exhibiting a low potential of 2.18 V to achieve a current density of 1000 mA cm⁻², an exceptional stability for hundreds of hours under harsh industrial conditions (1 M KOH and 80 °C) and at ultra-high current densities of 1000 mA cm⁻². The outstanding performance of the FeCoNiCrMn HEA/NM stems not only from its multiple active sites, but also from its electrochemical reconstruction during the OER process, leading to the formation of the NiFeCoCrMn high-entropy (oxy)hydroxide, which significantly enhances OER catalytic efficiency.

2. Results and discussion

2.1. Synthesis and characterization of catalysts

Fig. 1a illustrates a schematic diagram of the synthesis route for the preparation of the FeCoNiCrMn HEA electrode, wherein the FeCoNiCrMn powders are anchored on the Ni mesh by the atmospheric plasma spraying technology. At first, the sandblasting process is done to remove the oxide film on the surface of the nickel mesh and increase the surface roughness of the nickel mesh to enhance the bonding force between the spray coating and the substrate. Then, FeCoCrNiMn coating was prepared by the atmospheric plasma spraying process. Specific spraying process parameters are provided in ESI Table S1.† As shown in Fig. S1,† after spraying, the original Ni mesh changes from silver gray to black. The SEM of the Ni mesh is shown in Fig. S2,† the surface is very smooth. The sprayed FeCoNiCrMn HEA was deposited on the nickel mesh with a thickness of about 5 μm. The surface morphologies of FeCoNiCrMn HEA are presented in Fig. 1b and c. The surface becomes rough and the spherical nanoclusters aggregate. In Fig. 1c, the micro-spheres are approximately 200 nm in diameter. The prepared sample exhibits a homogeneous distribution of metal elements, as confirmed by the energy-dispersive X-ray spectroscopy (EDS) data (Table S2 and Fig. S3†). Fig. 1d exhibits the X-ray diffraction (XRD) pattern of FeCoNiCrMn HEA/NM. Except for the three diffraction peaks of Ni at 44.31°, 51.51°, and 75.91°, diffraction peaks were also observed at 43.53°, 50.77°, and 74.71°, which confirm the single face-centered cubic (FCC) phase of the FeCoNiCrMn HEA/NM.³¹ High-resolution TEM (HRTEM) in Fig. 1f reveals lattice fringes of 0.21 nm, corresponding to the {111} crystal planes of the FCC structure.31 Additionally, the corresponding EDS mapping results (Fig. 1g) further confirm the uniform distribution of components, which is in accordance with the SEM-EDS analysis. The computed mixing entropy, ΔS > 1.53R (Table S3†), provides further evidence for the high-entropy nature of the prepared alloy.³⁶

Fig. 1 (a) Preparation process of the FeCoNiCrMn HEA/NM. (b and c) SEM image of the FeCoNiCrMn HEA/NM. (d) XRD patterns of the FeCoNiCrMn HEA/NM. (e) TEM image of the FeCoNiCrMn HEA/NM. (f) HRTEM image of the FeCoNiCrMn HEA/NM. (g) STEM-HAADF image and corresponding EDS mapping images of FeCoNiCrMn HEA/NM.

The elemental composition and surface chemical bonding state of FeCoNiMnCr HEA/NM were further investigated using X-ray photoelectron spectroscopy (XPS). The binding energies of Fe⁰ 2p_3/2, Co⁰ 2p_33/2, Ni⁰ 2p_3/2, Mn⁰ 2p_3/2, and Cr⁰ 2p_3/2 were determined to be 710.6, 774.7, 850.3, 641.3, and 576.6 eV, respectively (Fig. S4 a–f†). A comparison of the electron binding energies of the FeCoNiCrMn high-entropy alloy, metal, and metal oxide is shown in Fig. S5.† Due to the differences in metal electronegativity, the electron binding energies of Co and Ni are lower than those in their metallic states, while those of Mn, Fe, and Cr shift to higher energies. This suggests a localized electron transfer from Mn, Cr, and Fe to Ni and Co atoms, further supporting a cooperative electronic interaction between these elements. The rich electronic effects resulting from the coupling of multiple metals in HEAs offer a diverse range of catalytic active sites to gain exceptional electrocatalytic activity.³⁷ Additionally, surface oxidation of the sample led to the appearance of high-valent metals in the XPS spectrum. The Raman spectrum of the pristine FeCoNiCrMn HEA/NM (Fig. S6†) shows no characteristic peaks in the range of 200 to 1000 cm⁻¹, indicating the absence of metal oxides. All results reveal the successful preparation of the HEA.

2.2 Electrocatalytic OER performance of FeCoNiCrMn HEA/NM

The electrocatalytic OER performance of FeCoNiCrMn HEA/NM and commercial Ni mesh catalysts was evaluated through a traditional three-electrode electrochemical system (ESI†). Fig. 2a presents the linear sweep voltammetry (LSV) curves of FeCoNiCrMn HEA and Ni mesh. The catalyst exhibits exceptionally low overpotentials of 1.44, 1.50, and 1.56 V at current densities of 10, 100, and 1000 mA cm⁻², respectively, which are much lower than those of the Ni mesh (1.50, 1.55, and 1.77 V at current densities of 10, 100 and 1000 mA cm⁻², respectively), demonstrating excellent electrochemical properties. These values significantly outperform those of the commercial Ni mesh catalyst (Fig. S7†), indicating the excellent potential for industrial application. Fig. S8† highlights the exceptional OER performance of FeCoNiCrMn HEA/NM, which requires an overpotential of only 270 mV to achieve 100 mA cm⁻² in 1 M KOH—significantly lower than that of commercial RuO₂ (380 mV). This remarkable activity not only surpasses noble-metal benchmarks but also underscores the practical potential of our catalyst as a high-performance, cost-effective alternative. As shown in Fig. 2b, the FeCoNiCrMn HEA has a Tafel slope of 44 mV dec⁻¹, compared to 50 mV dec⁻¹ for the nickel mesh, indicating faster OER kinetics. Electrochemical impedance spectroscopy (EIS) tests were performed to explore the OER reaction kinetics (Fig. 2d). The FeCoNiCrMn HEA shows a significantly smaller semicircular diameter in comparison to Ni mesh (Fig. 2c), suggesting a lower charge transfer resistance (Table S4, ESI†). This implies that FeCoNiCrMn HEA possesses superior electronic conductivity and enhanced surface charge transfer, which effectively accelerates OER reaction kinetics and improves the catalyst's inherent activity.³⁸

Fig. 2 OER electrocatalytic behavior. (a) Polarization curves for FeCoNiCrMn HEA/NM and Ni mesh. (b) Tafel plots based on the polarization curves in (a). (c) Nyquist plots from EIS measurements. (d) Plot showing differences in charging current density. (e) Comparison of η₁₀ and Tafel slope for FeCoNiCrMn HEA/NM against other catalysts reported recently. (f) Stability evaluation of FeCoNiCrMn HEA/NM at 1000 mA cm⁻² for 1000 h.

Electrochemical active surface area (ECSA) is a key parameter to assess catalysts. The electrochemical double layer capacitance (C_dl), determined by the double layer capacitance method, is proportional to ECSA. Fig. 3d and S9 (ESI†) show that the C_dl of FeCoNiCrMn HEA is 22.72 mF cm⁻².³⁹ Notably, the C_dl of FeCoNiCrMn HEA is higher than that of Ni mesh, presumably owing to the increased number of exposed active sites from its high-entropy structure.⁴⁰

As a further point, the η₁₀ and Tafel slope of FeCoNiCrMn HEA were compared with those of several high-entropy alloy (HEA) catalysts reported in the literature. It was found that FeCoNiCrMn HEA outperforms many recently reported high-entropy catalysts under identical conditions (Fig. 2f, Table S5 and ESI†).

The durability of electrocatalysts is crucial for assessing their practical feasibility, particularly while operating at high current densities in practical applications, where durability is essential. To evaluate the stability of FeCoNiCrMn HEA electrodes in water electrolysis, the voltage–time (V–t) curves of the electrodes were measured at a high current density by using the chronoamperometry (CP) method. As shown in Fig. 2f, after continuous operation for 1000 hours at a constant industry-level high current density of 1000 mA cm⁻², FeCoNiCrMn HEA retains over 98% of its initial catalytic activity, fully demonstrating its excellent long-term stability.

To further investigate the OER mechanism of the prepared catalyst, we conducted Raman, XRD, SEM, HRTEM, and XPS analyses on the post-stability-test samples. The Raman spectrum displayed two newly formed peaks at 478 cm⁻¹ (δ (Ni^III–O)) and 560 cm⁻¹ (ν (Ni^III–O)) (Fig. S10†), corresponding to the bending and stretching vibration modes of Ni–O bonds in γ-NiOOH.⁴¹ The results indicate that after stability testing, the surface of FeCoNiCrMn HEA underwent reconstruction into highly active γ-NiFeCoCrMnOOH.⁴² As shown in Fig. 3a, the diffraction peak signal corresponding to the original FeCoNiCrMn HEA almost entirely disappeared. Broad diffraction peaks were observed at approximately 37° and 66° corresponding to the {102} and {110} crystal planes of γ-NiOOH (PDF#06-0075), respectively.⁴³ These observations align with the Raman results. The SEM image (Fig. 3b) reveals that the reconstructed catalyst exhibits small nanoparticle clusters forming on the surface, which can be the metal hydroxides or oxyhydroxides due to the electrochemical reconstruction.⁴⁴ The EDS analysis (Fig. S11†) reveals that Fe, Co, Ni, Cr, and Mn remain uniformly distributed across the catalyst surface after long-term testing. Notably, the oxygen content increases to 51.5% (Table S6†), which is primarily ascribed to the formation of surface oxyhydroxide species and the oxygen-rich environment during extended electrochemical operation. Among the metallic elements, a modest reduction in Co content was observed, potentially due to partial dissolution under harsh alkaline conditions.^45,46 These results collectively demonstrate the excellent compositional homogeneity and structural stability of the FeCoNiCrMn HEA catalyst under prolonged industrial-relevant electrochemical conditions. The spacing between adjacent lattice fringes in the HRTEM image (Fig. 3c) is 0.14 nm, corresponding to the {110} crystal plane of γ-NiOOH.⁴³ This observation is consistent with previous XRD and Raman results and confirms the formation of the γ-NiFeCoCrMnOOH phase.

Fig. 3 Structural analysis of the FeCoNiCrMn HEA/NM catalyst after 1000 hours of testing. (a) XRD pattern of the FeCoNiCrMn HEA/NM catalyst after 1000 h. (b) SEM image after the stability test. (c) HRTEM image. (d–i) XPS spectra of Fe 2p (d), Co 2p (e), Ni 2p (f), Cr 2p (g), Mn 2p (h) and O 1s (i) before and after the stability test.

The XPS results before and after the stability test are presented in Fig. 3d–i. In the Fe 2p spectrum (Fig. 3d), the Fe³⁺/Fe⁰ ratio increases from 0.6 : 1 in the original FeCoNiCrMn HEA to 2.6 : 1 after the stability test. The metallic Fe peak diminishes, and the Fe³⁺ peak becomes dominant. Similar trends are observed in the high-resolution XPS spectra of Mn 2p and Cr 2p (Fig. 3g–h). In the high-resolution Co 2p XPS spectrum of NiFeCoCrMnOOH (Fig. 3e), two new peaks emerge at 780.7 and 795.8 eV, corresponding to the Co³⁺ 2p_3/2 and 2p_1/2 absorption peaks, which are absent in the original FeCoNiCrMn HEA. In the Ni 2p XPS spectrum (Fig. 3f), the peak corresponding to the original metallic Ni disappears, with only the high-valent Ni³⁺ remaining. In the O 1s XPS spectrum, the peaks at 530.1, 531.2, and 532.6 eV correspond to lattice oxygen (M–O) in the oxide lattice, hydroxyl groups (M–OH)⁴⁷ (attributed to lattice OH species in the hydroxide or (oxy)hydroxide), and oxygen from surface-adsorbed water (H₂O),¹⁷ respectively. Compared with the original FeCoNiCrMn HEA sample, the M–OH peak in the post-stability test sample is significantly more prominent, confirming the transformation of FeCoNiCrMn HEA into NiFeCoCrMnOOH after the electrochemical reconstruction process. As for the disappearance of Ni⁰ and Co⁰, while Cr⁰, Mn⁰, and Fe⁰ are still partially retained, this phenomenon can be attributed to the different redox potentials and oxidation behaviors of the constituent elements. Ni and Co are more prone to surface oxidation and transformation into high-valent oxyhydroxide phases (e.g., Ni³⁺, Co³⁺) under the strong anodic conditions used for the OER, especially in alkaline media. Their high redox flexibility allows them to more readily participate in dynamic surface reconstruction processes, forming highly active oxyhydroxide species during prolonged operation.^48–50 In contrast, Fe, Cr, and Mn tend to exhibit more complex or slower oxidation kinetics, and a fraction of the metallic core species can persist even after long-term electrochemical operation. This behavior has also been observed in other high-entropy or multimetallic electrocatalyst systems, where the surface undergoes partial reconstruction without full oxidation of the metallic core.³³

Clearly, the chemical environment of all elements underwent significant changes throughout the long-term stability testing. The original metal centers or M²⁺ species in FeCoNiCrMn are effectively oxidized to higher valence states (M³⁺). This could be because the metal sites tend to interact with hydroxyl groups in the KOH electrolyte under the influence of potential pulses, leading to the reconstruction of multi-metal co-(oxy)hydroxides on the surface, effectively improving the OER catalytic activity.⁵¹ Moreover, the above results are consistent with the valence distribution of NiMOOH (M = Co, Fe, Cr, Mn) reported in the literature.^52,53 These demonstrate that the FeCoNiCrMn HEA underwent an electrochemical reconstruction during the OER, resulting in the synthesis of NiFeCoCrMn high-entropy (oxy)hydroxides with enhanced OER catalytic efficiency.

2.3 Electrocatalytic HER performance of FeCoNiCrMn

In the HER test, commercial pure nickel mesh was similarly used for comparison to evaluate the performance of the prepared samples. Fig. 4a shows HER polarization curves of FeCoNiCrMn HEA/NM and Ni mesh. FeCoNiCrMn HEA/NM exhibits an extremely low overpotential of 69 mV at a current density of 10 mA cm⁻², outperforming the Ni mesh (237 mV) (Fig. S12†). Moreover, it only needs 425 mV to reach a current density of 1000 mA cm⁻², demonstrating its potential for practical use. In addition, a comparison of the HER polarization curves of X and Pt/C is given in Fig. S13.† The comparison clearly demonstrates that our HEA catalyst exhibits a competitive performance, with an overpotential (69 mV) close to that of Pt/C (49 mV) at 10 mA cm⁻², while offering superior durability and cost-effectiveness. The Tafel slope of FeCoNiCrMn HEA is 83 mV dec⁻¹, lower than the 117 mV dec⁻¹ of Ni mesh (Fig. 4b). Consequently, FeCoNiCrMn HEA shows faster HER kinetics.

Fig. 4 HER performance of FeCoNiCrMn HEA/NM in 1 M KOH electrolyte. (a) polarization curves. (b) Tafel plots from (a). (c) Charging current density difference plot. (d) EIS Nyquist plots. (e) Stability test of FeCoNiCrMn HEA at 1000 mA cm⁻² for 500 h.

C _dl is determined using cyclic voltammetry (CV) cycling, and the results are presented in Fig. 4c. Additionally, EIS is employed to investigate the electron transfer process, with corresponding results presented in Fig. 4d and Table S6.† The R_ct of the FeCoNiCrMn HEA catalyst is substantially lower than that of the pure Ni mesh electrode, suggesting faster electron transfer and enhanced HER performance.

The durability of the electrode is also critical. The HER stability of FeCoNiCrMn HEA/NM was evaluated by a chronopotentiometry test. Fig. 4e shows that the overpotential remained nearly constant at 1000 mA cm⁻² for 500 hours, indicating that the FeCoNiCrMn HEA/NM electrode exhibits excellent durability during the HER process. Notably, the decrease in overpotential may result from the prolonged CP test, which facilitates the reduction of the surface oxide layer under cathodic conditions, thereby exposing more active sites and enhancing metal site utilization.^54,55

Furthermore, the SEM and XRD results after 500 hours stability test reveal no significant morphological or structural alterations in the electrode (Fig. S14 and S15†). The corresponding EDS results are provided in the ESI (Fig. S16 and Table S9†). To deeply clarify the HER electrocatalytic performance of the FeCoNiCrMn HEA/NM catalyst, a comparison of the performance and stability of diverse alkaline HER catalysts is listed in Table S7.† Obviously, this work exhibits more remarkable HER electrocatalytic activity than those recently reported for high-entropy electrocatalysts under the same conditions. More importantly, the FeCoNiCrMn HEA/NM electrode fabricated in this study is suitable for production in a large scale, offering significant industrial application potential.

2.4 Overall water-splitting performance

Because of the remarkable HER and OER catalytic performance, FeCoNiCrMn HEA/NM served as both the anode and cathode for overall water splitting in the AEMWE device (FeCoNiCrMn HEA/NM ‖ FeCoNiCrMn HEA/NM). The schematic diagram and digital photos of the AEMWE system are shown in Fig. 5a and S13 (ESI†). The AEMWE is equipped with a heating and circulation system and operates at 80 °C with a 1 M KOH solution flow rate of 26 mL min⁻¹.⁵⁶Fig. 5b shows that the cell voltage required for the FeCoNiCrMn HEA/NM ‖ FeCoNiCrMn HEA/NM to reach 1000 mA cm⁻² is 2.18 V, significantly lower than the 3.4 V of the nickel mesh ‖ nickel mesh AEMWE and the Raney nickel ‖ Raney nickel AEMWE. After using the FeCoNiCrMn HEA/NM electrolyzer, the power consumption decreased by approximately 35.9%. Notably, the catalytic activity is significantly enhanced at high temperatures, with the cell voltage at 1000 mA cm⁻² decreasing from 2.18 V at 25 °C to 2.04 V at 80 °C. This improvement can be attributed to the accelerated reaction kinetics and enhanced ionic conductivity in the alkaline electrolyte at high temperatures. Additionally, a comparison of the polarization curves for all three samples at 80 °C has been included in the ESI (Fig. S14†). Furthermore, after operating at a high current density of 1000 mA cm⁻² and elevated temperature (80 °C) for 200 h (Fig. 5c), the cell voltage increased from 2.06 to 2.18 V. This corresponds to a retention of over 94% of the initial catalytic activity, clearly demonstrating the excellent durability and structural robustness of the FeCoNiCrMn HEA catalyst under industrially relevant conditions.

Fig. 5 Performance of overall water-splitting. (a) Schematic representation of the AEM electrolyzer. (b) Polarization curve. (c) Chronopotentiometry curve for the AEM electrolyzer using the FeCoNiCrMn HEA/NM catalyst operated at 1000 mA cm⁻² and 80 °C.

3. Conclusion

In summary, the FeCoNiCrMn HEA/NM is prepared by an atmospheric plasma spraying technology and exhibits outstanding electrocatalytic activity for both the HER (with an overpotential of 69 mV at 10 mA cm⁻²) and OER (with an overpotential of 270 mV at 100 mA cm⁻²). The results show the localized electron transfer from Cr, Fe and Mn to Co and Ni atoms, which regulated the electronic structure of FeCoNiCrMn HEA/NM. For the OER, the enhanced catalytic activity results from the formation of multi-component NiFeCoCrMn high-entropy (oxy)hydroxides through surface reconstruction during the electrochemical test. For the HER, the abundant active sites are crucial to its exceptional activity. In practical applications, for the AEMWE assembled with FeCoNiCrMn HEA/NM both as the anode and cathode, a lower voltage of 2.18 V is required to achieve an industrial high current density of 1000 mA cm⁻², with a highly stable performance maintained for 200 hours without clear deterioration. The bifunctional FeCoNiCrMn HEA/NM catalyst demonstrates the high activity and stability under industrial conditions and provides a general strategy for preparing self-supporting HEA catalysts. Moreover, it offers a promising route for the commercialization of AEMWEs for sustainable hydrogen production.

Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the ESI.† Additional data related to this paper may be requested from the author.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

The authors thank the National Natural Science Foundation of China (11875207and 12275199) for financial support. We also thank the Core Facility of Wuhan University for supporting.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta02103k

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