Interfacial engineering of a bifunctional electrocatalyst with outstanding catalytic performance, high intrinsic activity and solar-to-hydrogen conversion efficiency†

Carbides are commonly regarded as efficient hydrogen evolution reaction (HER) catalysts, but their poor oxygen evolution reaction (OER) catalytic activities seriously limit their practical application in overall water splitting. Herein, embedded nanosheets and plates of cobalt oxy carbide (Co–O–C/CPs) were successfully synthesized as an efficient bifunctional electrocatalyst using a solvent-free combustion process. To contribute to the clarification of catalytic particle composition during electrochemical reactions, we thoroughly characterized the Co–O–C/CPs using HR-TEM, which revealed that the filled nanoplates, with a cobalt oxide shell and cobalt carbide core, were wrapped with carbon. During electrochemical reactions, the filled nanoplates changed to an amorphous state owing to the decomposition of the crystalline material. After amorphization, the Co–O–C/CPs maintained the shape of the parent compound and exhibited a higher electrochemically active surface area (ECSA) and thereby demonstrated enhanced HER (115 mV) and OER (240 mV) performances at 10 mA cm⁻². When applying the Co–O–C/CPs as both the cathode and anode, a lower cell voltage of 1.60 V was required at 10 mA cm⁻² than that for the benchmark catalyst IrO₂/Pt/C/NF (1.63 V) with great stability in alkaline solution. This work provides a feasible strategy to fabricate cobalt oxy carbides and explores their possibility as bifunctional catalysts for water splitting.