Strain-Engineered Heterointerfaces of Bimetallic Sulfides for the Alkaline Hydrogen Evolution Reaction

Efficient non-noble-metal catalysts are vital for the alkaline hydrogen evolution reaction (HER), where slow H2O dissociation at the cathode markedly surges the overpotential in water splitting. Herein, we developed Cu2S nanorod arrays on Cu foam (CF) under wet-chemical conditions, which were further subjected to electrodeposition as a function of time (30, 60, and 90 s) to create heterointerfaces of urchin-like CoS-Cu2S/CF structures. These nanorod arrays/urchin interfaces demonstrated elongated strain (∼5.83%) at CoS/Cu2S surfaces. When these catalysts were assessed for HER in 1 M KOH, CoS-Cu2S-60/CF delivered a low overpotential of 232 mV at 10 mA·cm–2 with a Tafel slope of 113 mV·dec–1. The CoS-Cu2S-60/CF overpotential (232 mV) was lower by 283 and 146 mV than those of CF (515 mV) and Cu2S/CF (378 mV), respectively. After the post-HER studies, the overpotential at 10 mA·cm–2 was decreased to 138 mV, and potentiostatic stability revealed an increase in current densities, because of the elongated strain of 5.89%. Post-structural and chemical analyses revealed the presence of Cu2+ states from the in situ formed CuO-Cu2S interfaces. This phenomenon promotes strong Jahn–Teller distortion, and the eg bonds thus elongated, contributing to increased strains and effectively absorbing protons, thereby accelerating H2 production.