Photoenhanced Water Electrolysis in Separate O(2) and H(2) Cells Using Pseudocapacitive Electrodes

[Image: see text] Water electrolysis has received much attention in recent years as a means of sustainable H(2) production. However, many challenges remain in obtaining high-purity H(2) and making large-scale production cost-effective. This study provides a strategy for integrating a two-cell water electrolysis system with solar energy storage. In our proposed system, CuO-Cu(OH)(2)/Cu(2)O was used as a redox mediator between oxygen and hydrogen evolution components. The system not only overcame the gas-mixing issue but also showed high gas generation performance. The redox reaction (charge/discharge) of CuO-Cu(OH)(2)/Cu(2)O led to a significant increase (51%) in the initial rate of H(2) production from 111.7 μmol h(–1) cm(–2) in the dark to 168.9 μmol h(–1) cm(–2) under solar irradiation. The effects of light on the redox reaction of CuO-Cu(OH)(2)/Cu(2)O during water electrolysis were investigated by in situ X-ray absorption and photoemission spectroscopy. These results suggest that surface oxygen vacancies are created under irradiation and play an important role in increased capacitance and gas generation. These findings provide a new path to direct storage of abundant solar energy and low-cost sustainable hydrogen production.