Preparation of heterogeneous NiCo2S4/Ru composite electrode materials and their electrocatalytic properties for hydrogen evolution

Abstract

In order to increase the effective electrochemically active area of electrocatalyst materials and improve their electrocatalytic hydrogen evolution performance, nano-porous Ni–Co alloys were prepared by rapid solidification and dealloying methods. After that, bimetallic sulfides (NiCo₂S₄) were formed in situ by vapor deposition, then Ru and RuS₂ which have excellent intrinsic catalytic activity were adhered to the NiCo₂S₄ surface by a solvothermal method. Meanwhile, the Ru content was regulated to prepare the NiCo₂S₄/Ru electrode which was used to figure out the best component and structure for hydrogen evolution. Research shows that when the Ru content reaches 60% (wt/%), the Ru element formed a three-dimensional network flake structure and covered the NiCo₂S₄ surface. The active area for the reaction (C_dl = 27.6 mF cm⁻²) and electron transfer ability (R_ct = 0.487 Ω cm⁻²) were increased because of the formation of the heterostructure and surface modification. At a current density of 50 mA cm⁻², the NiCo₂S₄/Ru (60%) composite electrode possessed fast HER kinetics with a hydrogen evolution overpotential of 70 mV and a Tafel slope of 76 mV dec⁻¹, whose electrocatalytic properties are much better than those of NiCo₂S₄/RuS₂ with the same Ru content. The NiCo₂S₄/Ru (60%) catalyst exhibited superior stability with a small increase in overpotential of just 10 mV after chronopotentiometry tests for 12 h at 10 mA cm⁻².