One-step fabrication of copper sulfide catalysts for HER in natural seawater and their bifunctional properties in freshwater splitting

Natural seawater electrolysis is an efficient technology to produce hydrogen (H2) fuel and protects the environment from pollution. The lack of research on developing a suitable catalyst for hydrogen evolution reaction (HER) impedes generating an H2 sustainable fuel from natural seawater. In this study, copper sulfide (Cu2S) catalysts were successfully fabricated on nickel (Ni) foam with the help of a low-temperature hydrothermal technique by varying the growth temperatures in the range of 60–80 °C. The increase in growth temperatures improved the crystalline nature of the chalcocite Cu2S structure. The Cu2S catalyst fabricated at 80 °C showed a well-defined and improved the morphology with pores and small nanoparticles compared to other catalysts. An X-ray photoelectron spectroscope (XPS) showed the composition, oxidation state, and binding energy of the Cu2S catalysts. The Cu2S catalyst fabricated at 80 °C showed a little overpotential of 445 mV to attain 10 mA/cm2 for HER activity in natural seawater, and possessed higher intrinsic catalytic activity (136.10 mV/dec), electrochemical surface active site (634 cm2), and charge transfer properties (Rct, 4.40 Ω) with better long–term stability (86.7%) compared to other catalysts fabricated at 60 and 70 °C. Etching test of the Cu2S–80 °C catalyst in diluted hydrochloric (HCl) acid revealed no the insoluble precipitate on catalyst surface with a better 77.74% long–term stability. The bifunctional properties (HER and OER) of Cu2S catalysts for overall splitting were also investigated with three- and two-electrode cell configuration. The Cu2S catalyst fabricated at 80 °C exhibited a little overall cell potential of 1.65 V to reach 10 mA/cm2 compared to other Cu2S catalysts in 1 M KOH solution with impressive long-term stability of 99.23% up to 10 h. The Cu2S-80 °C catalyst was suitable for hydrogen production in natural seawater.