Sol–gel deposited Cu2O and CuO thin films for photocatalytic water splitting

Abstract

Cu₂O and CuO are attractive photocatalytic materials for water splitting due to their earth abundance and low cost. In this paper, we report the deposition of Cu₂O and CuO thin films by a sol–gel spin-coating process. Sol–gel deposition has distinctive advantages such as low-cost solution processing and uniform film formation over large areas with a precise stoichiometry and thickness control. Pure-phase Cu₂O and CuO films were obtained by thermal annealing at 500 °C in nitrogen and ambient air, respectively. The films were successfully incorporated as photocathodes in a photoelectrochemical (PEC) cell, achieving photocurrents of −0.28 mA cm⁻² and −0.35 mA cm⁻² (for Cu₂O and CuO, respectively) at 0.05 V vs. a reversible hydrogen electrode (RHE). The Cu₂O photocurrent was enhanced to −0.47 mA cm⁻² upon incorporation of a thin layer of a NiO_x co-catalyst. Preliminary stability studies indicate that CuO may be more stable than Cu₂O as a photocathode for PEC water-splitting.