Investigation of interfacial charge transfer in CuxO@TiO2 heterojunction nanowire arrays towards highly efficient solar water splitting

Abstract

We investigated the interfacial charge transfer driven by the buried p-n junctions in CuxO@TiO2 nanowires for solar water splitting. The interfacial p-n junctions in the nanowire are constructed by a novel integrating in situ oxidation and thermal annealing method. The interfacial heterojunctions accelerate the transfer of photogenerated charge carriers and provide thickness controllable protective layer for CuxO nanowires suffering from photocorrsion. The optimized CuxO@TiO2 photocathode achieves a remarkable photocurrent density of -2.43 mA•cm−2 at 0 V versus a reversible hydrogen electrode (RHE), which is approximately two times of the bare CuxO photocathode (-1.12 mA•cm−2 at 0 V vs RHE). And the heterojunction photocathode displays a durable cathodic current with a slight decay of 9.3% over 3 h under continuous illumination. The effects of interfacial p-n junctions in CuxO@TiO2 nanowires in improving photogenerated charge carrier transfer were further disclosed by X-ray absorption spectroscopy (XAS) analysis and density functional theory (DFT) calculation. This work might afford a promising insight in understanding the mechanism of interfacial charge transfer towards designing highly efficient photoelectrodes for solar water splitting.