Unlocking the Key to Photocatalytic Hydrogen Production Using Electronic Mediators for Z-Scheme Water Splitting

A prevalent challenge in particulate photocatalytic water splitting lies in the fact that while numerous photocatalysts exhibit outstanding hydrogen evolution reaction (HER) activity in organic sacrificial reagents, their performance diminishes markedly in a Z-scheme water splitting system using electronic mediators. This underlying reason remains undefined, posing a long-standing issue in photocatalytic water splitting. Herein, we unveiled that the primary reason for the decreased HER activity in electronic mediators is due to the strong adsorption of shuttle ions on cocatalyst surfaces, which inhibits the initial proton reduction and results in a severe backward reaction of the oxidized shuttle ions. To address this, taking typical visible-light-responsive photocatalysts, BaTaO₂N and SrTiO₃:Rh, as examples, we have developed a strategy via selective surface modification of metal cocatalysts (such as Pt, Ru) with chromium oxide species (CrO_x) to prevent the adsorption of shuttle ions. It is demonstrated that the photocatalytic HER activities of BaTaO₂N and SrTiO₃:Rh can be improved by one to two orders of magnitude in diverse shuttle ions. The introduced CrO_x substantially weakens the interaction between the metal cocatalysts and shuttle ions, promotes proton adsorption for the HER reaction, and also suppresses the backward reaction between shuttle ions. Owing to the improved HER activity, the photocatalytic performance of Z-scheme water splitting is significantly enhanced, providing a feasible strategy for constructing efficient Z-scheme systems in heterogeneous photocatalysis.