Direct Hydrogen Evolution from Saline Water Reduction at Neutral pH using Organic Photocathodes

Here, we have developed an organic photocathode for water reduction to H 2 , delivering more than 1 mA cm −2 at 0 V versus RHE and above 3 mA cm −2 at −0.5 V versus RHE with moderate stability under neutral pH conditions. The initial competitive reduction of water to H 2 and ZnO to metallic Zn is responsible for the dynamic behaviour of both photocurrent and Faradaic efficiency of the device, which reaches 100 % Faradaic efficiency after 90 min operation. In any case, outstanding stable H 2 flow of approximately 2 μmol h −1 is measured over 1 h at 0 V versus RHE and at neutral pH, after equilibrium between the Zn 2+ /Zn 0 concentration in the AZO film is reached. This achievement opens new avenues for the development of allsolution‐processed organic photoelectrochemical cells for the solar generation of H 2 from sea water.