Microwave annealing promoted in-situ electrochemical activation of Ni3S2 nanowires for water electrolysis

Abstract

Microwave is widely used to synthesize advanced nanomaterials for energy storage and conversion, whereas its applications remain limited in water electrolysis. Herein, we qualitatively explore the house-hold microwave annealing in atmosphere as chemical-free oxidation pretreatment strategy on Ni3S2 nanowires for hydrogen evolution reaction (HER). The microwave can induce fast surface oxidation to form metal hydroxides on catalyst which promotes in-situ electrochemical activation (ISEA) to improve the catalytic performance. The microwave annealing is superior to traditional oxidation such as chemical oxidation or Ar gas annealing. Thanks to faster reaction kinetics, better conductivity and larger electrochemical surface area, the formed NiOx/Ni3S2 hybrids by ISEA achieve 7-time higher activity and operate well for 12 h compared with pristine catalyst. The NiOx/Ni3S2 hybrids also perform well in acid (0.5 M H2SO4) and neutral (1.0 M phosphate buffer solution) media to realize all-pH water electrolysis. Moreover, the microwave annealing is found to be applicable for other transition metals such as cobalt sulfide to obtain higher HER properties. Therefore, such chemical-free modulation concept in our work might be a general access for many advanced materials in other electrocatalysis fields.