Abstract: Water electrolysis efficiency has long been constrained by the high energy barrier of the four-electron reaction in the oxygen evolution reaction (OER). Gradient composition design can effectively improve OER performance by optimizing electronic structure and stress distribution. The dealloying method for controlling the selective dissolution of metals can simultaneously achieve gradient composition construction, three-dimensional porous surface structure, and integrated self-supporting electrodes with catalytic layers/current collectors. Compared to other methods, the anti-passivation properties and wide electrochemical window of chloride molten salts, combined with rapid atomic diffusion kinetics and sintering effect at high temperatures, effectively promote the dissolution of active metals and structural stability of the retained elements in alloy components. Here, selective dissolution of Fe in the FeNi36 alloy was successfully achieved through anodization in LiCl-KCl molten salts, resulting in a three-dimensional porous Fe_xNi electrode with a surface-to-bulk gradient (Fe ∼ 20 at.% → 30 at.%). The dealloying process is primarily influenced by temperature, exhibiting a phase transition from FeNi36 → Ni3Fe (450 °C) → Ni (550/650 °C). Fe dissolves preferentially at grain boundaries, while the surface diffusion of Ni atoms drives the restructuring of the three-dimensional porous network. At 450 °C, the dealloying sample forms discrete FeOOH phases due to local Fe enrichment (> 30 at.%), leading to the lowest OER activity. Whereas at 550-650 °C, Fe content remains below 25 at.%, forming highly active Ni_1-xFe_xOOH phases. The optimal sample (650 °C, 30 min) exhibits both a high electrochemical active area (11.71 mF cm^-2) and an overpotential of 223 mV at 10 mA cm^-2 in 1 M KOH, with a Tafel slope of 35.3 mV dec^-1. Grain boundary corrosion channels contribute to stress alleviation and promote bubble desorption, ensuring the operational stability of the electrode for at least 120 h. This work provides a scalable gradient-controlled paradigm for the development of efficient and stable OER catalysts.

Key words: Oer catalysts, Molten salt electrolysis, Dealloying, Porous electrode, Fe-Ni alloy