CuO photoelectrodes synthesized by the sol–gel method for water splitting

CuO is an attractive photocatalytic material for water splitting due to its high earth abundance and low cost. In this paper, we report the deposition of CuO thin films by sol–gel dip-coating process. Sol deposition has attractive advantages including low-cost solution processing and uniform film formation over large areas with a fairly good control of the film stoichiometry and thickness. Pure CuO phase was obtained for calcination temperatures higher than 360 °C in air. The CuO photocurrents for hydrogen evolution depend on the crystallinity and the microstructure of the film. Values of −0.94 mA cm⁻² at pH = 8 and 0 V vs. RHE were achieved for CuO photoelectrodes annealed at 400 °C under air. More interestingly, the stability of the photoelectrode was enhanced upon the sol–gel deposition of a TiO₂ protective layer. In this all sol–gel CuO/TiO₂ photocathode, a photocurrent of −0.5 mA cm⁻² is achieved at pH = 7 and 0 V vs. RHE with a stability of ~100% over 600 s.