Composition-Dependent Catalytic Activities of Noble-Metal-Free NiS/Ni3S4 for Hydrogen Evolution Reaction

The development of efficient noble-metal-free hydrogen evolution catalysts is quite appealing with the aim of providing cost-competitive hydrogen. Herein, nickel sulfides (NiS x ) with tunable NiS/Ni3S4 molar ratios were synthesized via a simple hydrothermal method. Detailed electrochemical studies under neutral conditions indicated that the electrocatalytic property of NiS x catalysts was determined by the composition. Notably, the NiS x sample with the NiS/Ni3S4 molar ratio of 1.0 exhibited the lowest overpotential and charge-transfer resistance. As analyzed from the Tafel plots, the rate-determining step of NiS x catalysts for hydrogen generation was the Volmer step, in which the proton adsorption played a key role. Theoretical calculation revealed that NiS and Ni3S4 exhibited the metallic behaviors with different work functions. Consequently, the NiS x sample with the NiS/Ni3S4 molar ratio of 1.0 owned the most adsorbed protons, which led to the highest electrocatalytic property. Meanwhile, NiS x was demonstrated to be efficient cocatalysts to promote photocatalytic hydrogen generation. NiS x /CdS with the NiS/Ni3S4 molar ratio of 1.0 showed the best photocatalytic activity with the apparent quantum efficiency of 56.5% at 420 nm. This result was in good agreement with the electrocatalytic activities of NiS x samples, indicating the intrinsic property for efficient hydrogen generation.