Assessing the stability of binary copper oxide photocathodes and augmenting CuO water reduction performance: Comprehensive experimental and theoretical study

Abstract

Using photocathodes such as Cu2O and CuO is an effective strategy for direct hydrogen production in photoelectrochemical (PEC) water splitting. The theoretical photocurrent densities of Cu2O and CuO are ∼14.7 and ∼35 mA cm−2, respectively, suggesting the superiority of CuO over Cu2O. However, the foremost drawback is the poor stability in aqueous solution under illumination. From this perspective, the PEC performance of CuO and Cu2O is compared via experimental and theoretical approaches. In this case, CuO outperformed Cu2O in terms of both PEC performance and stability, and the density functional theory (DFT) studies also evidently showed the same. Further, the AlOx and RuO2 were also loaded over CuO, and the CuO/AlOx/RuO2 delivered a photocurrent density of ∼2 mA cm−2 (@ +0.3 VRHE). The free energy plot shows the lower energy barrier of CuO/AlOx/RuO2 than CuO/AlOx and CuO, and it is present near and left side of the standard volcano plot, which further gives evidence for higher hydrogen evolution reaction (HER) performance.