CoP nanosheets in-situ grown on N-doped graphene as an efficient and stable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions

It is urgent to develop highly efficient and stable non-precious electrocatalysts for electrochemical water splitting due to the rapidly increasing energy demands. In this study, we synthesize a hybrid electrocatalyst constructed by cobalt phosphide nanosheets in-situ grown on few-layered nitrogen-doped graphene nanosheets (CoP@NG) via a facile hydrothermal reaction and subsequent phosphorization process. Due to its unique nanoarchitecture, as a bifunctional electrocatalyst, the CoP@NG electrocatalyst exhibits outstanding electrocatalytic performance for hydrogen and oxygen evolution reactions. In acidic (or alkaline) electrolyte, it delivers very low onset potential of -87 (or -114) mV (vs RHE) and very low Tafel slope of 63.8 (or 59.6) mV dec(-1); it also exhibits excellent performance for oxygen evolution reaction (OER) with a very low onset potential of 1.48 V (vs RHE), a small Tafel slope of 63.8 mV dec(-1) and overpotential of 354 mV (vs RHE) at 10 mA cm(-2); moreover, it shows long-term stability for HER (in both acidic and alkaline medium) and OER. The highly conductive, flexible few-layered N-doped graphene nanosheets can not only facilitate the electron transfer and mechanical and chemical stability, but also prevent the aggregation of CoP nanosheets and cause many more reactive sites. This work provides new insights into the structural design and synthesis of low-cost transition-metal phosphides as non-precious electrocatalysts towards water splitting. (C) 2019 Elsevier Ltd. All rights reserved.