In-situ electrochemical fabrication of CuO/Cu2O photocathode for high-performance photo-assisted Mg/seawater battery

Photo-assisted Mg/seawater batteries (PAMSBs) are attractive power source for marine equipment due to the advantage of simultaneous generation of electricity and hydrogen from seawater. Nonetheless, the serious photo-corrosion of photocathodes results in dissatisfactory battery performance, which substantially hinder their practical applications. Herein, we design a CuO/Cu2O heterostructure as the photocathode of PAMSBs via a facile in-situ electrochemical strategy, successfully enhance the photo-stability of bare Cu2O. During half-cell photoelectrochemical water splitting, the newly-developed CuO/Cu2O photocathode reveals a photo-current density about 2.2 ​mA ​cm−2 at 0 ​V (vs. RHE) and enables nearly 100% retention of the initial photocurrent density after 2h long-term operation, more than 10 times stable than the bare Cu2O photocathode. A PAMSB with a CuO/Cu2O photocathode achieves a maximum power density up to 22.67 ​mW ​cm−2 and a hydrogen yield rate up to 1.18 ​mL ​cm−2 min−1, much higher than those obtained with a bare Cu2O photocathode. This study offers a simple and convenient electrochemical strategy for in-situ fabrication of CuO/Cu2O heterojunction photocathodes, and also demonstrate the feasibility of PAMSBs as a power source and a hydrogen generator, which lays foundation for its future marine application.