Abstract
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.
Highlights
The ubiquitous availability of water and sunlight on Earth makes hydrogen gas an excellent fuel candidate for a clean and sustainable energy cycle, provided that the hydrogen fuel is obtained in a sustainable solar-powered process
The PEC response of the Ir nanopillar–Ir:SrTiO3 composite electrodes is in a sense a lucky case, because Ir doping
O2 eh eh matches the deep Fermi level position of Rh:SrTiO3, which means that no Schottky-type space–charge regions form
Summary
The ubiquitous availability of water and sunlight on Earth makes hydrogen gas an excellent fuel candidate for a clean and sustainable energy cycle, provided that the hydrogen fuel is obtained in a sustainable solar-powered process. Among the various options for harvesting and storing solar energy in the form of hydrogen, photoelectrochemical (PEC) water splitting, illustrated, is the most direct method, where the splitting of water and the evolution of either hydrogen or oxygen gas occur on the surface a semiconductor photoelectrode, which is essentially a simplified solar cell placed in water. In terms of band structure, an oxygen evolution photoelectrode consisting of an n-type semiconductor, such as S rTiO3, exhibits an upward band bending in the space–charge layer that forms at the water interface. This internal field drives the photogenerated holes to the electrode surface where oxygen gas is produced in an electrocatalytic water oxidation reaction. Once a photon is absorbed and an electron–hole pair is formed, only a i
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