Although Fe-Ni combination performs well in transition metal-based oxygen evolution reaction (OER) electrocatalysts, there are lack of clear and general regulations mechanism to fully play the synergistic catalytic effect. Here, we made the utmost of the interaction of Fe–Ni heteroatomic pair to obtain a highly active Fe-Ni(oxy)hydroxide catalytic layer on iron foam (IF) and nickel foam (NF) by in-situ electrochemical deposition and rapid surface reconstruction, which only required 327 and 351 mV overpotential to provide a large current of 1,000 mA·cm⁻², respectively. The results confirm that the moderate Ni-rich heteroatomic bonding (Ni–O–Fe–O–Ni) formed by adjusting the Ni/Fe ratio on the catalyst surface is important to offer predominant OER performance. Fe is a key component that enhances OER activity of Ni(O)OH, but Fe-rich structural surface formed by Fe–O–Ni–O–Fe bonding is not ideal. Finally, the remarkable oxygen evolution performance of the prepared Ni₂Fe(O)OH/IF and FeNi₂(O)OH/NF can be chalked up to the optimized electronic structure of Fe–Ni heteroatomic bonding, the efficient gas spillover, the fast electron transport, and nanosheet clusters morphology. In summary, our work suggests a comprehensive regulation mechanism for the construction of efficient Fe-Ni(oxy)hydroxide catalytic layer on inexpensive, stable, and self-supporting metallic material surface.

The effective electron and interface/structural coupling for heterostructure electrocatalyst is the key to regulating the intrinsic activity and stability for oxygen evolution reaction (OER). Herein, a facile strategy is developed to fabricate well-dispersed zero-dimensional (0D) metallic Co₉S₈ nanoparticles on two-dimensional (2D) FeS nanosheets, forming FeS-Co₉S₈ Schottky heterostructures with abundant heterointerfaces as OER electrocatalyst. The strong electronic coupling between FeS and Co₉S₈ expedites electrons flow from Fe atoms in FeS nanosheets to Co atoms in tetrahedron sites (Co_Td), thereby leading to the structural integrity of the heterostructure and the constant exposure of active sites. Operando Raman spectroscopy also indicates the Co sites in the FeS-Co₉S₈ Schottky heterostructure are OER active sites. Therefore, FeS-Co₉S₈ heterostructure supported by iron foam (FeS-Co₉S₈/IF) shows the remarkable activity and durability, achieving an industrial-level 500 mA·cm⁻² current density at an overpotential of only 332 mV and maintaining for 100 h. This work demonstrates that constructing Schottky heterostructure interface with strong coupling effect may be a good strategy for excellent catalytic performances.

Iron plays a crucial role in improving the oxygen evolution reaction (OER) activity of hydroxide materials. Increasing the number of iron active sites at the solid–liquid interface is beneficial to enhancing the OER performance of catalysts but still challenging. Here, by systematic exploring the activity trends of M(OH)_x and Cu-M(OH)_x (M = Mn, Cu, Ni, Fe, and Co), we discover that the Cu doping can promote the deposition of Fe active sites on metal hydroxide and Cu-Co(OH)₂ shows the most favorable iron adsorption capacity. When loaded on a conductive substrate (cobalt foam (CF), the M-Cu-Co(OH)₂/CF (Co(OH)₂ prepared by molten salt method) exhibits an attractive low overpotential of 337 mV at 1,000 mA·cm⁻². Using in anion exchange membrane (AEM) water electrolyzer, the single cell with M-Cu-Co (OH)₂/CF as anode catalyst performs a stable cell voltage of 2.02 V to reach 1,000 mA·cm⁻² over 24 h, indicating a great application potential for actual electrolytic water. Therefore, the promoted adsorption of copper on iron provides a new perspective for further enhancing the OER activity of other metal hydroxides.

The development of high-efficiency electrocatalysts for overall water splitting under large current density is significant and challenging. Herein, a high-performing Fe-doped MoNi alloy catalyst (M-H-MoNiFe-50) abundant with flower-like nanorods assemblies has been prepared by high-pressure microwave reaction and hydrogen reduction. Firstly, Fe doped NiMoO₄ precursor (M-MoNiFe-50) was synthesized by microwave fast heating, ensuring the robustness of nanorods, which owns larger area and improved catalytic activity than that by conventional hydrothermal method. Secondly, M-MoNiFe-50 was reduced in H₂/Ar to fabricate Fe-incorporated MoNi₄ alloys (M-H-MoNiFe-50), greatly enhancing the conductivity and facilitating hydrogen/oxygen spillover. The final M-H-MoNiFe-50 exhibits remarkable activity for alkaline/acidic hydrogen evolution reaction and oxygen evolution reaction with low overpotential of 208 (alkaline), 254 (acid) and 347 mV at 1,000 mA·cm⁻². Moreover, an alkaline water electrolyzer is established using M-H-MoNiFe-50 as anode and cathode, generating a current density of 100 mA·cm⁻² at 1.58 V with encouraging durability of 50 h at 1,000 mA·cm⁻². The extraordinary water splitting performance can be chalked up to the large surface area, favorable charge transfer, modified electron distribution, intrinsic robustness as well as an efficient gas spillover of M-H-MoNiFe-50. The final electrocatalyst has great prospects for practical application and confirms the significance of Fe doping, microwave method and spillover effect for catalytic performance improvement.