Self-Supported Porous High-Entropy Phosphide Film Electrodes for Hydrogen Evolution in Diverse Electrolytes

A self-supported porous FeCoNiCuMo high-entropy alloy phosphide (HEAP) film electrode was prepared by brush coating followed by CVD phosphidation. XRD analysis identified the crystalline phases of the film electrodes. XPS was used to analyze the surface chemical states. Their surface features were observed by SEM, while EDS mapping resolved the spatial distribution of the constituent elements. Hydrogen evolution measurements on the HEAP electrodes were conducted in a three-electrode configuration. Four electrolytes were used: 1 M KOH, 0.5 M H2SO4, 1 M KOH + 1 M Na2S, and 1 M KOH + 1 M NaCl. Phosphidation temperature had a pronounced effect on catalytic activity. Among the electrodes examined, HEAP-550 showed the best overall performance. It required overpotentials of 63, 59, 60, and 57 mV to deliver 10 mA·cm−2 in the four electrolytes, respectively. Electrochemical impedance spectroscopy distinguished the electrodes in terms of charge-transfer resistance. The Cdl values derived from cyclic voltammetry reflected differences in electrochemically accessible surface area across the three phosphidation temperatures. HEAP-550 exhibited relatively low charge-transfer resistance together with a large ECSA. These characteristics are consistent with its superior HER activity. Furthermore, the HEAP-550 electrode demonstrated excellent long-term stability, maintaining stable operation at a current density of 100 mA cm−2 for 24 h in all four electrolytes. This work provides a novel strategy for designing self-supported porous high-entropy phosphide film electrodes by integrating multicomponent alloy design with CVD phosphidation, offering new insights into the regulation of synergistic catalytic sites for efficient HER. The developed self-supported HEAP electrode holds great potential for practical applications in efficient water electrolysis and sustainable hydrogen production.