Effect of conductive substrate on the photoelectrochemical properties of Cu2O film electrodes for methyl viologen reduction

Abstract

Cuprous oxide (Cu2O) is a candidate for low-cost p-type semiconductor oxides for photoelectrochemical solar energy conversion. The Cu2O crystalline films electrodeposited on conductive substrates have been extensively studied as photocathodes because of their moderate photoelectrochemical performance, but their incident photon-to-current conversion efficiency (IPCE) was still limited because of the incompatibility between minority carrier diffusion length and light absorption depth in planar structures. One of the strategies to solve this issue is to decrease the thickness of the Cu2O films with keeping the loading amount. Herein, we used a sintered titanium microfiber felt as a three-dimensional macroporous scaffold for Cu2O crystalline thin films because it exhibits a large surface area compared with the conventional flat substrate. The effect of the Cu2O film thickness on the photocathode properties was investigated using methyl viologen as an acceptor of the photoexcited electrons. The Cu2O thin films deposited on Ti microfibers were superior to that of the Cu2O films deposited on dense planar substrates such as fluorine-doped tin oxide (FTO)-coated glass and titanium sheets. It was revealed that the large Cu2O–electrolyte and Cu2O–substrate interfaces resulted in the enhancement of IPCE for the photoelectrochemical cathodic reaction.