Ru@Ni3S2 nanorod arrays as highly efficient electrocatalysts for the alkaline hydrogen evolution reaction

Abstract

Water splitting by electricity is believed to be a promising approach to obtain high-purity H₂ on a large scale. Highly efficient electrocatalysts are of great importance for the electrocatalytic hydrogen evolution reaction (HER). Herein, we designed a highly efficient electrocatalyst (Ru@Ni₃S₂) for the HER by immersing Ni₃S₂ nanorod arrays into a RuCl₃ aqueous solution. The obtained Ru@Ni₃S₂ with an increased electrochemical surface area and a decreased charge-transfer resistance demonstrates an enhanced electrocatalytic performance toward the HER in alkaline media, suggested by an overpotential of −19.8 mV to achieve a current density of 10 mA cm⁻² and a Tafel slope of 33.2 mV dec⁻¹. Both the in situ formed Ru nanoparticles and the adsorbed Ru³⁺ ions are responsible for the electrocatalytic hydrogen evolution reaction. Density functional theory (DFT) calculations reveal that the enhanced electrocatalytic HER activity of Ru@Ni₃S₂ compared with pure Ru can be ascribed to the lowered water dissociation energy barrier as well as the more favorable adsorption energy for the H intermediate (H*). During the long-term stability test, the adsorbed Ru³⁺ on the Ni₃S₂ nanorods would be converted to Ru(OH)₃, leading to attenuated electrocatalytic activity. This drawback can be overcome by further surface modification with polyaniline (PANI). The obtained PANI–Ru@Ni₃S₂ exhibits a comparable catalytic HER activity to Ru@Ni₃S₂ but an extraordinary stability with continuous electrolysis at a current density of 20 mA cm⁻² for 35 hours. Our design strategy here for synthesizing the Ru@Ni₃S₂ hybrid and effectively improving the stability of Ru-based catalysts could be extended to develop other noble metal/transition metal sulfides for practical water electrolysis and other applications.