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

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. [ABSTRACT FROM AUTHOR]