Co1-xS/N-doped graphene foam composite as efficient bifunctional electrocatalysts for the evolution reaction of oxygen and hydrogen

Abstract

As an environment-friendly and sustainable energy conversion technology, water electrolysis is strongly dependent on the efficiency and cost of the electrocatalysts. Herein, nanosheet-constructed cobalt sulfide microspheres incorporated with nitrogen-doped graphene foam (Co1-xS/NGF), a highly efficient bifunctional electrocatalyst for overall water splitting, was obtained by controlled two-step synthesis. The nitrogen-doped graphene foam (NGF) underlying the Co1-xS microspheres provides an electrically conducting support for the catalysts, contributes small size and homogeneous distribution of the in-situ grown Co1-xS microspheres, and affords abundant active sites for fast and sufficient transport of mass and electrons and, therefore, highly enhanced catalytic activity through the strong synergistic effect of Co1-xS microspheres and the NGF substrate. In 1 M KOH, the Co1-xS/NGF hybrid catalyst exhibits remarkable OER and HER catalytic performance, with overpotentials of 233.6 mV for the OER and 163.7 mV for the HER at 10 mA cm−2, and the corresponding Tafel slopes of 138 and 95 mV dec−1, respectively. The hybrid material of Co1-xS/NGF even exhibits a lower overpotential (η20) to reach 20 mA cm−2 towards OER than that of RuO2, and its performance matches the best cobalt sulfide bifunctional electrocatalysts reported to date. Besides, the Co1-xS/NGF is highly stable for long-term water electrolysis in the 1 M KOH. These findings support that the current Co1-xS/NGF is a competitive candidate of transition metal-based catalysts for cost-efficient and large-scale overall water electrolysis in the alkaline environment.