Three-dimensional porous CoNiO2@reduced graphene oxide nanosheet arrays/nickel foam as a highly efficient bifunctional electrocatalyst for overall water splitting

Abstract

It is crucial to develop high-performance and cost-effective bifunctional electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) toward overall water splitting. Herein, a unique heterostructure of reduced graphene oxide (rGO) and CoNiO2 nanosheets directly grown on nickel foam (NF) were successfully fabricated and applied as a kind of highly efficient bifunctional electrocatalyst. The optimum CoNiO2@rGO/NF electrode exhibits excellent electrocatalytic OER performance with an overpotential of only 272 mV to drive a current density of 100 mA·cm−2, and HER performance with an overpotential of 126 mV to achieve a current density of 10 mA·cm−2. Meanwhile, the electrodes also display outstanding long-term stability for OER and HER with negligible activity and morphology degradation after at least 40 h testing. Furthermore, when employed as both cathode and anode for overall water splitting, CoNiO2@rGO/NF electrode only requires 1.56 V at 10 mA·cm−2 and operates stably for over 40 h, which is among the best performing Co-based and Ni-based non-precious metal electrocatalysts. Detailed characterizations reveal that the extraordinary electrocatalytic performance should be attributed to the synergistic effect of the unique heterostructure of CoNiO2 nanosheets and rGO for increasing the electrode conductivity and integrity, ultrasmall primary particle size for providing larger electrode/electrolyte contact area and abundant active sites, and three-dimensional (3D) conductive networks for facilitating the electrochemical reaction.