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 Co(2)Mo(3)O(8) as a model system. Potential-dependent reconstruction of Co(2)Mo(3)O(8) precatalyst results in an electrochemically stable Co(OH)(2)@Co(2)Mo(3)O(8) catalyst and additional Mo dissolved as MoO(4)(2-) into electrolyte. The Co(OH)(2)/Co(2)Mo(3)O(8) interface accelerates the Volmer reaction and negative potentials induced Mo(2)O(7)(2-) (from MoO(4)(2-)) further enhances proton adsorption and H(2) desorption. Leveraging these insights, the well-designed MoO(4)(2-)/Mo(2)O(7)(2-) modified Co(OH)(2)@Co(2)Mo(3)O(8) 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.