Facile synthesis of hierarchically ordered Mo2C/Co3Mo3C@C nanosheet heterostructure: A highly durable pH universal electrocatalyst for hydrogen evolution reaction and overall alkaline water splitting

Developing cost-effective, high-efficiency, earth-abundant electrode materials for hydrogen evolution reaction (HER) operating in wide pH range electrolytes is significant for large-scale hydrogen generation. However, the rational design of highly stable electrocatalysts with robust performance remains challenging. Herein, in-situ construction of hierarchically ordered Mo2C/Co3Mo3C nanosheet heterostructure (CMC/MC@C) is achieved by the simple pyrolysis method. The optimized Co1Mo1C/550 catalyst achieves a low HER overpotential of 86, 102, and 323 mV at 10 mA cm-2 current density in 1.0 M KOH, 0.5 M H2SO4, and 0.1 M PBS solutions, respectively, with robust durability over 48 h. Benefiting from the bifunctionality of Co1Mo1C/550, the elec-trocatalyst achieves a current density of 10 mA cm-2 at a low overpotential of 336 mV towards the oxygen evolution reaction (OER) and 1.597 V for overall water splitting in a 1.0 M KOH solution. The exceptional performance of the as-prepared catalyst is primarily attributable to the strong synergistic relationship between Co3Mo3C and Mo2C particles, hierarchically ordered porous carbon nanosheet structure, and superhydrophilic electrode surface, which not only provide rich exposed active sites but also boost the access of electrolytes and the diffusion of H2 bubbles, thereby effectively enhancing the HER and OER performances. This study offers a new approach to the rational design of various transition metal-based carbide electrode materials via the structural optimization strategy for reliable and efficient universal pH catalysts towards HER and overall alkaline water splitting.