Rational design of precatalysts and controlled evolution of catalyst-electrolyte interface for efficient hydrogen production

The concept of precatalyst is widely accepted in electrochemical water splitting, but the role of precatalyst activation and the resulted changes of electrolyte composition is often overlooked. Here, we elucidate the impact of potential-dependent changes for both precatalyst and electrolyte using Co₂Mo₃O₈ as a model system. Potential-dependent reconstruction of Co₂Mo₃O₈ precatalyst results in an electrochemically stable Co(OH)₂@Co₂Mo₃O₈ catalyst and additional Mo dissolved as MoO₄^2- into electrolyte. The Co(OH)₂/Co₂Mo₃O₈ interface accelerates the Volmer reaction and negative potentials induced Mo₂O₇^2- (from MoO₄^2-) further enhances proton adsorption and H₂ desorption. Leveraging these insights, the well-designed MoO₄^2-/Mo₂O₇^2- modified Co(OH)₂@Co₂Mo₃O₈ catalyst achieves a Faradaic efficiency of 99.9% and a yield of 1.85 mol h^-1 at -0.4 V versus reversible hydrogen electrode (RHE) for hydrogen generation. Moreover, it maintains stable over one month at approximately 100 mA cm^-2, highlighting its industrial suitability. This work underscores the significance of understanding on precatalyst reconstruction and electrolyte evolution in catalyst design.