Cupric oxide nanowire photocathodes stabilized by modification with aluminum

Abstract The use of sunlight for photoelectrochemically splitting water into hydrogen and oxygen has aroused great interest in the last decades. Photocathode materials based on cupric oxide (CuO) are promising for large-scale, widespread photoelectrochemical water splitting due to the high Earth-abundance of copper, suitable band gap, and favorable band alignment for hydrogen generation. The main challenge for the development of practical CuO photocathodes is to enhance stability against photocorrosion, together with increasing the efficiency of solar hydrogen evolution. In this work, stable CuO nanowire photocathodes are synthetized in a straightforward and scalable way by electrodeposition followed by chemical oxidation and thermal treatment. Subsequently, the electrodes are modified with aluminum following two different strategies: (i) adsorption of aluminum from an Al acetylacetonate solution or (ii) drop-casting of a solution containing Al nitrate. In both cases, a thermal treatment is applied after Al addition. The stability of CuO nanowires (measured as the percent of the initial photocurrent retained after 20 min of continuous illumination at −0.4 V vs. Ag/AgCl) is enhanced from 2% up to 80%. The amount of aluminum needed to modify cupric oxide is very low in both strategies, indicating that Al operates at the surface level. Admittedly, these modifications improve stability at the expense of photocurrent. To palliate this, the addition of co-catalysts should be addressed in the future.