Design and Performance of a Hierarchical Porous FeCoNiCuV High-Entropy Alloy as an Efficient Oxygen Evolution Catalyst for Water Electrolysis

Catalysts with hierarchical porous structures spanning from the microscale to the macroscale can significantly enhance charge-transfer efficiency and active site exposure during the oxygen evolution reaction (OER). Herein, a hierarchical porous electrocatalyst was fabricated by chemically dealloying a phase-separated FeCoNiCuV high-entropy alloy (HEA). Benefiting from the phase-separated microstructure of the FeCoNiCuV HEA, selective etching generated an interconnected multiscale porous network. The dealloyed surface exhibited a hierarchical pore structure with pore sizes of approximately 30–50 μm, 3–5 μm, and 60–80 nm, increasing the electrochemical surface area (ECSA) significantly from 9.4 cm2 to 21.5 cm2 (more than doubling). Electrochemical tests conducted in 1.0 M KOH electrolyte demonstrated that the electrocatalyst exhibited excellent OER performance, with an overpotential of 296.4 mV @10 mA/cm2 and a Tafel slope of 52.2 mV/dec. The ECSA and electrochemical impedance analysis results revealed that the enhancement in catalytic activity originated from both the increased electrochemical surface area and the accelerated charge transfer rate. Furthermore, the catalyst remained stably operational under a constant current of 200 mA/cm2 for 300 h of chronopotentiometry (CP), with negligible performance degradation. These results indicate that the hierarchical porous structure plays a crucial role in enhancing catalytic activity and long-term stability, providing a promising strategy for the development of efficient and durable water oxidation electrocatalysts.