The synergistic effect of Ni–NiMo₄N₅ heterointerface construction and Fe-doping enables active and durable alkaline water splitting at industrial current density

Abstract

Alkaline anion-exchange membrane water electrolysis (AEMWE) is hailed as a promising approach to green hydrogen production due to its cost-effectiveness and high compatibility with intermittent renewable electricity, yet its practical implementation is hindered by the lack of active and durable bifunctional water-splitting electrocatalysts. Here, we developed a heterogeneous NiFeMo-based catalyst with abundant metal–metal nitride heterostructures towards efficient and durable water electrolysis. The heterostructure not only leads to a smaller work function (Φ) for accelerating the electron transfer process, but also tailors the adsorption–desorption behavior of intermediates due to the modified electronic states. As a result, the optimal NiFeMo-based catalyst significantly improves the water-splitting performance with an ultra-low overpotential of 68 and 228 mV at 100 mA cm⁻² for alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. When assembled in an AEM water electrolyzer, the catalyst achieves a current density of 500 and 1000 mA cm⁻² at a low voltage of 1.620 and 1.753 V, respectively. More importantly, it can stably operate over 1630 hours at 500 mA cm⁻², demonstrating its superior long-term stability. This work not only affords a high-performance bifunctional electrocatalyst for AEMWE, but also provides a multi-faceted structural regulation strategy to tailor the catalytic properties of heterogeneous electrocatalysts.

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Meiling Xiao

Dr Meiling Xiao is currently a professor at the Changchun Institute of Applied Chemistry (CIAC), Chinese Academy of Sciences (CAS). She received a PhD degree in physical chemistry from CIAC in 2017. After graduation, she worked at the University of Waterloo as a postdoctoral researcher and then joined CIAC in 2021. She was selected for the Special Talent Program B of CAS and the Outstanding Youth Foundation of Jilin Province. Her research interests include single-atom heterogeneous catalysis, fuel cells and water electrolysers. She has published over 40 papers in J. Am. Chem. Soc., Angew. Chem. Int. Ed., Adv. Mater., etc., with over 7300 citations and an H-factor of 37.

Introduction

Hydrogen energy is deemed an attractive alternative to traditional fossil fuels owing to its high energy density (142 MJ kg⁻¹) and pollution-free use.^1–3 To realize the target of carbon neutrality, electrochemical water splitting driven by renewable electricity has become the most promising approach to green hydrogen production.^4,5 Compared with commercially mature alkaline water electrolyzers (AWEs) and proton exchange membrane water electrolyzers (PEMWEs), alkaline anion-exchange membrane water electrolyzers (AEMWEs) offer compelling advantages of high efficiency, cost-effectiveness, and reliability, thus capturing intensive research attention in the hydrogen community.^6,7 However, commercial noble-metal-based electrocatalysts still show sluggish kinetics of both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in alkaline electrolytes, which limits the overall energy efficiency and large-scale application of AEMWEs.^8–11 Meanwhile, these catalysts only function actively in one of the two essential reactions, while remaining inactive for the other, thereby inevitably increasing the complexity of the water electrolysis equipment and resulting in severe cross-contamination between the two electrodes with different components.^12,13 In this regard, it is highly desirable to develop highly active, stable, and cost-effective bifunctional electrocatalysts for the overall water-splitting reaction (OWS).

Addressing the incompatibility between HER and OER catalytically active sites and unfavorable kinetics, tremendous efforts have been focused on the structural regulation of active sites towards optimizing adsorption/desorption behaviors.^14–19 For example, doping a third metal into NiFe layered double hydroxides (NiFe LDHs) has been widely employed to introduce more active sites and change the electronic structure of LDHs as the pristine NiFe LDH possesses outstanding OER activity yet inferior HER activity.^20–22 Due to the more distortions and lattice defects induced by high-valent Mo, the Mo-doped 2D Ni–Fe LDH demonstrated enhanced electrocatalytic activity, with overpotentials of 167 and 220 mV at 10 mA cm⁻² for the HER and OER, respectively.²³ However, the inherently poor conductivity and insufficient bifunctional nature still restrict the water-splitting performance of the LDH.^24–26 Recently, it has become attractive to support single metal atomic sites on conductive supports, which usually include carbides, nitrogen-carbon compounds, and metal-based compounds.^27–29 Nevertheless, the intrinsically linear scaling relationships of single-site catalysts and rigorous synthetic procedures significantly hinder their large-scale application in multi-electron transfer reactions.²⁷ To overcome this obstacle, it is imperative to construct multi-component systems for highly active bifunctional electrocatalysts, such as the common Schottky-contact dominated heterointerface engineering.^30–32 To be specific, spontaneous and continuous electron redistribution occurs through the heterointerface of metals/metalloids and semiconductors, forming electron-rich and electron-deficient components to regulate the HER and OER processes simultaneously for efficient OWS.^33–35 Benefiting from the strong electronic coupling effect between the iron oxide and the nickel at the interface, Ni-γ-Fe₂O₃ required only 1.55 V cell potential to achieve 10 mA cm⁻².³⁴ However, the lattice mismatches of heterostructures, including stretching and shrinking effects, are generally liable to limit the movement of carriers and reduce structural stability.^36,37 Therefore, it is urgent to explore effective regulation strategies to construct active and durable bifunctional electrocatalysts for AEMWE.

Motivated by the previously mentioned approaches, here we report the design and synthesis of an Fe atom-doped Ni–NiMo₄N₅ heterostructure catalyst for alkaline overall water splitting. The as-developed NiFeMo-based catalyst exhibited excellent catalytic activity for the HER (68 mV@100 mA cm⁻²) and OER (228 mV@100 mA cm⁻²), superior to commercial Pt/C (101 mV@100 mA cm⁻²) and RuO₂ (325 mV@100 mA cm⁻²), respectively. Additionally, an outstanding two-electrode electrolyzer was subsequently fabricated by using the heterointerface structured NiFeMo catalyst as both the cathode and the anode, where a current density of 100 mA cm⁻² is achieved at a record low voltage of 1.603 V, for overall alkaline splitting at 25 °C. More impressively, the assembled AEM electrolyzer can achieve an industrial current density of 500 mA cm⁻² at a low cell voltage of 1.638 V and maintain excellent durability over 1630 h. Combining multiple material characterization techniques with in situ Raman spectroscopy, we reveal that the Fe-doped Ni–NiMo₄N₅ heterostructure possesses lower metal valences and a smaller work function (Φ), and accelerates surface reconstruction from Ni(OH)₂/NiO to active NiOOH, thus favoring the electron transfer reactions towards boosted HER and OER performance. This work opens a new avenue for designing active and durable bifunctional electrocatalysts for AEMWE.

Results and discussion

A ternary NiFeMo-based rod-like catalyst supported on porous nickel foam was prepared by the facile two-step method of hydrothermal and pyrolysis, as shown in Fig. S1.† Initially, the optimal doping amount of Fe was explored (Fig. S2†). Subsequently, three kinds of NiFeMo-based catalysts with different interfacial structures and metal valences were constructed by regulating the pyrolysis atmosphere, including NH₃, Ar, and air, which were denoted as NiFeMo–NH₃, NiFeMo-Ar, and NiFeMo-Air, respectively. The iron-free NiMo-based catalyst was prepared with heat treatment under NH₃ for a comparative study (NiMo–NH₃). The scanning electron microscopy (SEM) images showed that large amounts of nanorods were uniformly and vertically grown on the surface of the Ni foam (Fig. S3–S6†). We further analyzed the content of metals by inductively coupled plasma-mass spectrometry (ICP-MS). As shown in Table S1,† the mole ratios of Ni and Mo of the four catalysts were close, while the content of Fe was as low as 1.29 wt%, indicating that Fe might be atomically doped into the NiMo species.

High-resolution transmission electron microscopy (HRTEM) was used to examine the composition and heterointerfaces (Fig. 1a and S7–S9†). Obviously, there existed two sets of lattice distances of 0.245 nm and 0.207 nm in the NiFeMo–NH₃ sample, which were indexed to the (100) facet of NiMo₄N₅ and the (111) facet of Ni, respectively, implying the successful construction of a heterointerfacial structure. Consistent with the HRTEM observation, the selected area electron diffraction (SAED) (Fig. 1b) further presented apparent diffraction rings that could be assigned to the (310) and (411) facets of Ni₃Mo₃N, the (101) facets of NiMo₄N₅, and the (111) facets of Ni. Compared with the theoretical lattice distances of Ni and NiMo nitrides, their lattice distances slightly increased after Fe incorporation without obvious lattice distortion, implying that Fe was doped into the lattice. This hypothesis was further confirmed by energy dispersive spectroscopy mapping (EDS mapping) analysis (Fig. 1c), revealing the uniform distribution of Fe onto the whole NiFeMo–NH₃. The iron-free NiMo–NH₃ catalyst displayed a similar metallic Ni–NiMo nitride heterointerfacial structure (Fig. S7†). The above results indicate that ammonia treatment facilitates the formation of a metal–metal nitride heterointerfacial structure. Meanwhile, the sample treated under the Ar atmosphere exhibited lattice distances of 0.268 nm and 0.185 nm, which were indexed to the (1̄31) facet of NiMoO₄ and the (242) facet of MoNi, respectively, illustrating the presence of MoNi alloy (Ni)–NiMoO₄ heterogeneous interface structures. By contrast, only the NiMoO₄ phase was observed in the NiFeMo-Air catalyst. The interplanar spacings of the crystalline phases of the above Fe-doped samples differed slightly from the standard value, possibly originating from Fe doping or replacement (Fig. S8 and S9†).

Fig. 1 Morphological and structural characterization. (a) High-resolution transmission electron microscopy (HRTEM), the corresponding FFT diagrams (b and d), and lattice spacing diagrams (c and e). (f) Selected area electron diffraction image (SAED) and (g) corresponding EDS images of NiFeMo–NH₃.

To investigate the chemical composition and electronic structures of the catalysts, X-ray diffraction (XRD), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS) measurements were performed. In line with the TEM observation, typical peaks corresponding to Ni (JCPDS#04-0850) and metal nitrides could be clearly discerned in the XRD patterns of NiMo–NH₃ and NiFeMo–NH₃, further demonstrating the successful construction of metal–metal nitride heterogeneous interfaces (Fig. 2a and b). Notably, there were no visible Fe-containing species in the pattern of NiFeMo–NH₃, possibly due to the atomic incorporation of Fe into the crystal lattice. By contrast, NiFeMo-Ar displayed dominant peaks of NiMoO₄ (JCPDS#86-0361) and minor peaks corresponding to metal phase Ni (JCPDS#45-1027) and MoNi (JCPDS#48-1745). Meanwhile for the NiFeMo-Air sample, only characteristic peaks assignable to NiMoO₄ were present. These findings reveal the successful regulation of the hetero-interfacial structure by heat treatment in different thermal atmospheres. The hetero-interfacial structure would lead to distinctive physiochemical properties, such as work function (Φ), for desirable catalytic performance, which was further verified by ultraviolet photoelectron spectroscopy (UPS) analysis. The calculated Φ values were 5.01, 5.12, and 5.38 eV for NiFeMo–NH₃, NiFeMo-Ar, and NiFeMo-Air, respectively (Fig. 2b). Notably, compared with NiFeMo-Air (single metal oxide) and single metal (nickel, Φ = 4.6 eV), the Φ values of heterostructures can be regulated by inducing two-phase charge redistribution, which, in turn, optimizes the intermediate adsorption processes.^38,39 Additionally, smaller Φ values imply a smaller energy barrier of electron transfer from the surface of electrocatalysts to reactants and intermediates.^40,41 As shown in Fig. S10,† Bader charge analysis displayed a significant electron transfer of 4.12e from Ni to NiMo₄N₅, much greater than that of Ni–NiMoO₄ (3.31e). The result indicates that the Ni–NiMo₄N₅ heterostructure can enable a much faster electron transfer to regulate the electronic structure, thereby optimizing the adsorption energy of intermediates. Therefore, the construction of metal–metal nitride heterojunctions is expected to improve the performance of electrocatalytic water splitting.

Fig. 2 (a) XRD pattern of the catalysts along with the standard PDF cards for Ni, NiMo₄N₅, and NiMoO₄. (b) UPS spectra of the prepared NiFeMo-based catalysts and (c) the schematic diagram of the Ni–NiMo₄N₅ heterostructure of the NiFeMo–NH₃ catalyst. XPS spectra of (d) Ni, (e) Fe, and (f) Mo for the catalysts.

The possible electronic modulation effect originating from the hetero-interfacial structure was further unveiled through X-ray photoelectron spectroscopy (XPS). For the high-resolution Ni 2p XPS of the four catalysts (Fig. 2d), the two peaks at 852.40 and 869.65 eV attributed to the Ni 2p_3/2 and 2p_1/2 of Ni⁰ species were only detected in the NH₃-treated samples. The peaks with binding energies of 857.07 and 874.78 eV ascribed to the Ni³⁺ peaks were merely observed in NiFeMo-Ar and NiFeMo-Air, but absent in the spectra of NH₃-treated samples, indicating that the metal–metal nitride heterostructure can induce lower valence metal sites by electronic interaction. The XPS spectrum of Fe 2p (Fig. 2e) could be deconvoluted into three main peaks with binding energies of 704.9, 709, and 712 eV assigned to Fe⁰, Fe²⁺, and Fe³⁺, respectively, and the corresponding satellite peaks.⁴² Similarly, it was worth noting that the Ni–NiMo nitride heterostructure had a higher proportion of low valence Fe (Fig. S11†). In the Mo 3d XPS spectrum (Fig. 2f), the peaks located at 228.4 and 231.4 eV were ascribed to Mo²⁺, which was only found in NiFeMo–NH₃,^3,43 implying the electronic modulation effect of the Fe dopant. Apart from the Mo²⁺ species, Mo³⁺ and Mo⁴⁺ were also found in both NiFeMo–NH₃ and NiMo–NH₃, with dominant peaks at 229.1 and 232.4 eV and minor peaks centered at 229.9 and 233.1 eV. Meanwhile, NiFeMo-Ar and NiFeMo-Air only identified Mo⁶⁺ peaks, demonstrating that the construction of a Ni–NiMo nitride hetero-interfacial structure and Fe-doping successfully promoted the form of low valence Mo species. According to the analysis of XPS results, the Fe-doped Ni–NiMo nitride catalysts can induce the formation of low valence metal sites, indicating that they have a higher electron density for upshifting the d band center, in compliance with the decreased work function values.^44,45 Due to the regulated electronic structure, we expect enhanced water-splitting performance for the well-designed NiFeMo–NH₃ catalyst.

We evaluated the HER and OER activity of the as-prepared catalysts in 1 M KOH electrolyte at room temperature (25 °C). As displayed in Fig. 3a–c and S12,† NiFeMo–NH₃ and NiMo–NH₃ possessed excellent HER activity with low overpotentials (η) at 100 and 500 mA cm⁻² (η₁₀₀ = 68 mV and η₅₀₀ = 169 mV; η₁₀₀ = 69 mV and η₅₀₀ = 165 mV, respectively), which were superior to those of NiFeMo-Ar (η₁₀₀ = 321 mV) and NiFeMo-Air (η₁₀₀ = 351 mV). In addition, the Tafel slopes are plotted in Fig. 3c to study the hydrogen evolution reaction kinetics. The Tafel slopes of NiMo–NH₃, NiFeMo–NH₃, NiFeMo-Ar, and NiFeMo-Air were determined to be 43.8, 46.9, 97.1, and 113.6 mV dec⁻¹, respectively. Compared to the metal–metal oxide heterostructure and metal oxides, the Tafel slope of the NH₃-treated samples clearly decreased, manifesting the conversion of the reaction mechanism from Volmer-Heyrovsky to desirable Volmer-Tafel. This suggests that the Ni–NiMo nitride heterostructures are conducive to promoting water dissociation to create H₃O⁺ and tremendously accelerating the process of H* recombining directly into H₂.

Fig. 3 Comparison of HER and OER performance in 1 M KOH electrolytes. (a) HER polarization curves of different catalysts, (b) comparison of overpotentials (at 10, 100, and 500 mA cm⁻²), and (c) Tafel plots obtained from the polarization curves; (d) OER reverse-scan polarization curves, (e) comparison of overpotentials (at 100 and 250 mA cm⁻²), and (f) corresponding Tafel plots. (g) Chronopotentiometric curves of NiFeMo–NH₃ at 100 mA cm⁻² as the cathode and anode, respectively.

To examine the bifunctional performance of the four catalysts, we further conducted OER performance tests under the same conditions (Fig. 3d–f and S13†). NiFeMo–NH₃ exhibited excellent OER activity with low overpotentials (η₁₀₀ = 228 mV), outperforming NiMo–NH₃ (η₁₀₀ = 305 mV), NiFeMo-Ar (η₁₀₀ = 281 mV), and NiFeMo-Air (η₁₀₀ = 262 mV). In sharp contrast with the similar HER activity observed for NiMo–NH₃ and NiFeMo–NH₃, Fe doping can significantly improve the OER activity by lowering the overpotential by 77 mV at 100 mA cm⁻². In addition, the initial oxidation peak corresponding to Ni(II)/Ni(III) negatively shifted for the NH₃-treated catalysts, indicating that the NH₃-induced metal/metal nitride heterogeneous interfaces can significantly accelerate the transformation process to NiFeOOH, thus promoting the expression of OER activity. The accelerated OER kinetics on NiFeMo–NH₃ was further confirmed by the lowest Tafel slope of 37.4 mV dec⁻¹. Since long-term stability is crucial for the application of HER and OER electrocatalysts, we evaluated the stability by testing NiFeMo–NH₃ at 100 mA cm⁻². The NiFeMo–NH₃ catalyst as a cathode showed outstanding stability with almost no overpotential change for 94.5 h. Even under harsh OER conditions, the NiFeMo–NH₃ catalyst can operate stably for 94.5 h (Fig. 3h). The excellent stability can be attributed to the following factors: (1) the interfacial charge redistribution at the heterogeneous interface facilitated rapid electron transfer under high current density conditions; (2) the self-supporting nanorod structure improved hydrophilicity and gasiphobicity, effectively mitigating structural instability induced by bubble accumulation at high current densities. Moreover, the Nyquist diagrams (R_ct) revealed that the charge transfer resistance of the Ni–NiMo nitride catalysts was greatly reduced to contribute to enhanced mass transfer (Fig. S14†). The double-layer capacitance (C_dl) calculation results showed that the Fe-doped Ni–NiMo nitride heterostructure exhibited excellent specific activities for both the HER and the OER (Fig. S15–S17†). Above all, the synergistic effect between the electron redistribution at the heterointerfaces and Fe doping not only exposes the catalytically active sites but also enhances the intrinsic activity.

In situ Raman spectroscopy was employed to investigate the dynamic surface reconstruction process (Fig. 4a and b, Fig. S18 and S19†). For the hydrogen evolution process, the Raman peaks of NiFeMo–NH₃ and NiFeMo-Ar had almost no change with the variation of potential, revealing their excellent structural stability. Then, during the oxygen evolution process, the NH₃-treated samples exhibited two prominent broad peaks in the ranges of 450–480 cm⁻¹ and 500–550 cm⁻¹, which could be deconvoluted into the Ni^II–O bond in Ni(OH)₂ centered at 457 cm⁻¹ and NiO at 528 cm⁻¹, respectively. Both of them showed a slow phase transition before 1.42 V. As the potential was increased to 1.42 V, the peaks located at 475 and 550 cm⁻¹ emerged, which were assigned to the E_g(Ni^III-O) bending vibration and A_1g(Ni^III-O) stretching vibration mode, confirming the phase transition to form NiOOH.^46,47 In contrast, the phase transition process to NiOOH in NiFeMo-Ar and NiFeMo-Air began to occur at 1.44 V. These results demonstrate that the Ni–NiMo nitride hetero-interfacial structures can accelerate the phase transition from Ni(OH)₂/NiO to NiOOH, which was consistent with the LSV results of the OER process. Notably, no Fe-related phases were found, further implying that Fe may function as a dopant to transform into Ni(Fe)OOH, thereby enhancing intrinsic OER catalytic activity.

Fig. 4 In situ Raman spectral measurements at different potentials (from OCV to 1.52 V vs. RHE) in 1 mol L⁻¹ KOH electrolyte with (a) NiFeMo–NH₃ and (b) NiFeMo–Ar as the anode. Material characterization to explore the HER and OER active sites. XPS of (c) Ni 2p and (d) Mo 3d of NiFeMo–NH₃ after 10 000 cycles of ADT tests for the HER and OER in comparison with initial states.

To gain a deeper insight into the real catalytic active sites for the extraordinary HER and OER activity, we further studied its chemical state during and after HER and OER tests. In the high-resolution XPS spectra (Fig. 4c and d), the proportion of Ni²⁺ and Mo²⁺ in the NH₃-treated catalysts increased obviously after the HER test, indicating that Ni²⁺ and Mo²⁺ were the main active sites for the HER (Fig. S20†). Moreover, peaks of Mo⁶⁺ also arose remarkably, due to the oxidation of Mo to MoO₄²⁻.⁴⁸ After the OER test, the proportion of high-valent Ni³⁺, Mo⁶⁺, and Fe³⁺ improved significantly, corresponding to the transformation into Ni(Fe)OOH and oxidation of Mo under the anode potential. For NiMo–NH₃, the changes after the test were almost consistent with those of the NiFeMo–NH₃ catalyst. However, the NiFeMo-Ar and NiFeMo-Air catalysts displayed almost unchanged valence after the HER and OER tests, possibly due to their high-valent oxidized state (Fig. S21–S23†). In addition, the catalyst structures remained unchanged after 10 000 cycles of ADT tests (Fig. S24†).

The excellent HER and OER activities of NiFeMo–NH₃ inspired us to investigate the bifunctional performance for overall water-splitting. We carried out an overall water-splitting test through a two-electrode system using NiFeMo–NH₃ as both the anode and cathode. As shown in Fig. 5a and b, NiFeMo–NH₃ required a cell voltage of just 1.603 V to achieve a current density of 100 mA cm⁻² in 1M KOH, which was superior to the noble metal benchmarks and the majority of electrocatalysts reported previously.^49–66 Motivated by the outstanding performance, an AEM electrolyzer using NiFeMo–NH₃ as a bifunctional electrode was assembled to examine practical application capability. The overall water-splitting electrolyzer was then tested in a flowing 1M KOH solution at different temperatures ranging from 50 to 80 °C. As displayed in Fig. 5c–e, the assembled AEM electrolyzer can reach a high current density of 2.125 A cm⁻² at a low cell voltage of 2 V at 80 °C, outperforming most AEM electrolyzers. Notably, the cell voltage required to deliver a large current density of 1 A cm⁻² was as low as 1.753 V at 80 °C.^67–74 Remarkably, the electrolyzer was able to operate stably at a large current density of 500 mA cm⁻² over 1630 h with a slight attenuation of less than 5%, demonstrating its excellent long-term stability and industrial application potential.

Fig. 5 Overall water-splitting performance and stability test of NiFeMo–NH₃ conducted in 1.0 M KOH. (a) Polarization curve for overall water splitting with the NiFeMo–NH₃ electrode as both the anode and cathode at a scan rate of 5 mV s⁻¹. (b) Comparison of the required cell voltage at 100 mA cm⁻². (c) Polarization curves measured for AEMWE based on NiFeMo–NH₃ as both the anode and cathode at different temperatures. (d) Comparison of the required cell voltage for 1 A cm⁻² of the assembled AEM electrolyzer with reported AEMWEs. (e) Long-term stability test of the assembled AEMWE at a current density of 0.5 A cm⁻² at 60 °C.

Conclusions

In summary, we developed a unique heterointerface-doping strategy to synthesize an Fe-doped Ni–NiMo nitride heterostructure (NiFeMo–NH₃) towards enhanced bifunctional catalytic properties for AEMWE. The electron-rich Ni–NiMo nitride heterostructure ensured a smaller work function (Φ) through interfacial electronic interaction to reduce the electron transfer barrier and accelerate mass transfer. Besides, the Ni–NiMo nitride heterostructure can accelerate the phase transition from Ni(OH)₂/NiO to active Ni(Fe)OOH, with Fe doping synergically promoting OER kinetics. As a result, the construction of the Ni–NiMo heterostructure significantly reduced the overpotential of the HER by 253 mV at 100 mA cm⁻² compared with the Ni–NiMoO₄ heterostructure, and the Fe doping effect led to an OER overpotential reduction of 77 mV at 100 mA cm⁻², thus improving the bifunctional performance. The superior bifunctional performance endowed the assembled AEM electrolytic cell with a large current density of 2.125 A cm⁻² at 2 V cell voltage. More importantly, the assembled water-splitting electrolyzer was able to robustly operate over 1630 h at a current density of 500 mA cm⁻² with a low decay rate of 46.6 μV h⁻¹, surpassing most literature reports. These results confirm the huge potential of the developed NiFeMo–NH₃ catalyst for practical application in AEMWE.

Data availability

The data that support the findings of this study are available within the article and its ESI files.† All other relevant data supporting the findings of this study are available from the corresponding authors upon request. Source data are provided with this paper.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (22279129) and Jilin Province Science and Technology Development Program (20230201154GX, 20230101367JC).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5ta00038f

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