Sulfur–nitrogen co-doped graphene supported cobalt–nickel sulfide rGO@SN-CoNi2S4 as highly efficient bifunctional catalysts for hydrogen/oxygen evolution reactions

Designing highly active and stable electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a challenge for energy conversion and storage technology. In this work, a S and N co-doped graphene supported cobalt–nickel sulfide composite catalyst (rGO@SN-CoNi2S4) was synthesized simply via a one-step hydrothermal method. The as-synthesized CoNi2S4 particles grew in a mosaic manner inside GO lamellae and were encapsulated with graphene. As a bifunctional catalyst, the rGO@SN-CoNi2S4 exhibits excellent electrocatalytic performance under alkaline conditions, which only required the overpotential of 142.6 mV (vs. RHE) and 310 mV (vs. RHE) to deliver a current density of 10 mA·cm−2 for HER and OER, respectively. The good hydrophilicity of the rGO@SN, the pure phase of bimetallic structure, and the chemical coupling/interaction between the CoNi2S4 and the rGO@SN are attributable to be the possible reasons responsible for the higher HER and OER catalytic activities. Additionally, the rGO@SN-CoNi2S4 also shows a great potential for serving as an excellent cathode and anode electrolyzer during the water splitting process.