Effects of Different Sulfidation Temperatures on the Hydrogen Evolution Reaction Performance of Fe-Co-Ni-Mo-Cu High-Entropy Alloys

In this study, FeCoNiMoCu high-entropy alloy thin films were sulfided at different temperatures ranged from 250 °C to 450 °C by chemical vapor deposition, and the resultant sulfided Fe-Co-Ni-Mo-Cu-S alloys were characterized by means of XRD, SEM, XPS and EDS. HER performance tests were carried out in four electrolyte systems, namely 0.5 M H2SO4, 1 M KOH, 1 M KOH + 0.5 M NaCl and 1 M KOH + 1 M Na2S. The results indicated that the as-prepared electrodes exhibited low HER overpotentials in all four electrolytes, with the optimal catalytic performance consistently achieved at a sulfidation temperature of 350 °C. Among the tested systems, the electrode delivered the best HER activity in 0.5 M H2SO4, showing an overpotential of merely 53 mV and a Tafel slope of 86.72 mV dec−1 at a current density of 10 mA·cm−2. In 1.0 M KOH, the overpotential required to reach the same current density was 98 mV with a Tafel slope of 72.43 mV dec−1. For the mixed electrolyte of 1 M KOH and 0.5 M NaCl, the overpotential at 10 mA·cm−2 was 142 mV accompanied by a Tafel slope of 49.51 mV dec−1. In contrast, the 1 M KOH + 1 M Na2S electrolyte yielded an overpotential of 77 mV and a Tafel slope of 84.01 mV dec−1 at the identical current density. HER tests revealed that the sulfidation temperature exerts a significant influence on the formation and distribution of active phases of multi-metal sulfides (e.g., FeSx, CoSx, NiSx, MoS2) on the electrode surface. The electrodes prepared at an appropriate sulfidation temperature exhibit a larger specific surface area and enhanced hydrogen evolution reaction performance for water electrolysis. These findings may provide useful references for other researchers in the design and fabrication of high-entropy alloy-based HER catalysts.