Branched TiO2/Si nanostructures for enhanced photoelectrochemical water splitting

We report a successful fabrication of hierarchical three-dimensionally branched TiO2/Si nanowire arrays and their application as the photoelectrochemical electrode for solar water splitting. The branched TiO2/Si nanowire arrays improved the photoelectrochemical (PEC) performance compared to TiO2 thin film-coated Si nanowire arrays because of the substantially increased surface area for electrochemical reactions and enhanced charge transfer kinetics. Wavelength-dependent photocurrent response of the branched nanowire array indicates a strong response in the ultraviolet region (<400 nm), while a negligible photocurrent is observed under visible illumination, primarily caused by the high overpotential loss of n-Si photoanode and energy band configuration of the TiO2/Si heterojunction. The working mechanism based on recombination at this heterogeneous n-n junction is proposed. This study provides insights on the fundamental understanding and potential optimizations of nanoscale hierarchical 3D structured devices for renewable energy applications. Published by Elsevier Ltd.