Photocurrent switching effect and visible light activity of electrochemically synthesized bifunctional through oxide via TiO2/CuO composites

Abstract

Photoelectrochemical conversion of solar energy into fuel products such as H₂ or CH₄ is an appealing, but technologically difficult process due to the simultaneous requirements for stability, efficiency and selectivity in the photoelectrode. One approach to design a photoelectrode with suitable properties is by using different materials that can complement each other. In this study, we introduce a novel approach by compositing TiO₂ with CuO via electrodeposition of Cu into through-oxide vias/channels – a design that offers enhanced synergy between the materials. The Cu is then precisely transformed into Cu₂O, CuO, or a mixture, based on annealing temperature, enabling tunable properties and optimized functionality. Unlike in traditional “sandwich” composites, this structuring reduces bulk charge carrier recombination through the formation of a depletion zone between TiO₂ and CuO, allowing both materials to perform distinct functions. As a result, photocurrent switching is achieved by altering the applied potential, which is a functionality not previously demonstrated for photoactive composite materials. Our study also reports evidence of visible light sensitivity in TiO₂/CuO composites when illuminated by a 4100K LED without UV components. Open circuit voltage decay measurements reveal that the improved charge carrier transport is due to the formation of a conductive Cu pathway—a novel finding that opens new possibilities for efficient photoexcitation. Although the charge carrier lifetimes were found to be shorter in TiO₂/CuO electrodes compared to pure TiO₂, we attribute this to the phenomenon of Cu "filling" the TiO₂ channels and decreasing the available surface area, a trade-off that provides crucial insights into material design for future applications.