Nanopillar Composite Electrodes for Solar-Driven Water Splitting

Spontaneous noble metal dopant segregation in an oxide lattice can lead to the formation of metallic clusters and extended acicular inclusions. In a thin-film process, the shape and orientation of such noble metal inclusions are governed by the crystal growth direction, giving rise to a composite material with lattice-matched metal nanopillars embedded vertically in an insulating or semiconducting oxide matrix. An interesting application of such composites is in photoelectrochemical cell electrodes, where the metallic nanopillars take on three distinct roles: forming a Schottky junction with the host matrix, providing a low-loss current path from bulk to surface, and creating an efficient electrocatalytic active site on the electrode surface. In particular, we discuss the application of vertically aligned metal–oxide nanopillar composites in photoelectrochemical water-splitting cells used for direct solar-powered hydrogen generation.