Solar-Driven Water Oxidation and Decoupled Hydrogen Production Mediated by an Electron-Coupled-Proton Buffer

[Image: see text] Solar-to-hydrogen photoelectrochemical cells (PECs) have been proposed as a means of converting sunlight into H(2) fuel. However, in traditional PECs, the oxygen evolution reaction and the hydrogen evolution reaction are coupled, and so the rate of both of these is limited by the photocurrents that can be generated from the solar flux. This in turn leads to slow rates of gas evolution that favor crossover of H(2) into the O(2) stream and vice versa, even through ostensibly impermeable membranes such as Nafion. Herein, we show that the use of the electron-coupled-proton buffer (ECPB) H(3)PMo(12)O(40) allows solar-driven O(2) evolution from water to proceed at rates of over 1 mA cm(–2) on WO(3) photoanodes without the need for any additional electrochemical bias. No H(2) is produced in the PEC, and instead H(3)PMo(12)O(40) is reduced to H(5)PMo(12)O(40). If the reduced ECPB is subjected to a separate electrochemical reoxidation, then H(2) is produced with full overall Faradaic efficiency.