Improving the Stability and Efficiency of CuO Photocathodes for Solar Hydrogen Production through Modification with Iron

Cupric oxide (CuO) is considered as a promising photocathode material for photo(electro)chemical water splitting because of its suitable band gap, low cost related to copper earth abundancy, and straightforward fabrication. The main challenge for the development of practical CuO-based photocathodes for solar hydrogen evolution is to enhance its stability against photocorrosion. In this work, stable and efficient CuO photocathodes have been developed by using a simple and cost-effective methodology. CuO films, composed of nanowires and prepared by chemical oxidation of electrodeposited Cu, develop relatively high photocurrents in 1 M NaOH. However, this photocurrent appears to be partly associated with photocorrosion of CuO. It is significant though that, even unprotected, a faradaic efficiency for hydrogen evolution of ∼45% is attained. The incorporation of iron through an impregnation method, followed by a high-temperature thermal treatment for promoting the external phase transition of the nanowires from CuO to ternary copper iron oxide, was found to provide an improved stability at the expense of photocurrent, which decreases to about one-third of its initial value. In contrast, a faradaic efficiency for hydrogen evolution of ∼100% is achieved even in the absence of co-catalysts, which is ascribable to the favorable band positions of CuO and the iron copper ternary oxide in the core–shell structure of the nanowires.Authors are grateful to MINECO of Spain for the financial support through project MAT2015-71727-R (FONDOS FEDER). A.C. wants to acknowledge the University of Alicante for a predoctoral grant (FPU-UA)