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

Here, we have developed an organic photocathode for water reduction to H2, 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 H2 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 H2 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 Zn2+/Zn0 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 H2 from sea water.