Insight into the origin of the limited activity and stability of p-Cu2O films in photoelectrochemical proton reduction

The origin of instability of p-Cu2O films deposited on a platinized Si substrate when used as photocathode in photoelectrochemical water splitting, was studied in the absence or presence of a protective layer of RuO2. When applied at +0.3 V vs. RHE and at pH 7, p-Cu2O films were found to show a slightly more stable performance as compared to photoelectrochemical measurements reported in the literature at 0 V vs. RHE and under acidic conditions. In addition, the stability and the photocurrent induced by the Cu2O films were significantly improved when H2O2 was added to the electrolyte, which is explained by efficient scavenging of electrons, yielding oxygen and water as confirmed by gas chromatography (GC). Also, other electron acceptors improved the photocatalytic performance of the p-Cu2O films, demonstrating that the transfer of photo-excited electrons to protons adsorbed on the surface is the rate determining step in p-Cu2O based photo-electrochemical water splitting. We confirmed that deposition of RuO2 improves the stability of the films, but to the expense of a decrease in photocurrent density. The results provided in this study rationalize the attachment of an effective H2 evolution catalyst as a means to significantly improve the stability of p-Cu2O electrodes