Morphology-controlled In2O3 nanostructures enhance the performance of photoelectrochemical water oxidation

Abstract

Nanotower- and nanowall-like indium oxide structures were grown directly on fluorine-doped tin oxide (FTO)/In₂O₃ seeded substrates and pristine FTO substrates, respectively, by a straightforward solvothermal method. The tower-like nanostructures are proposed to form via a self-assembly process on the In₂O₃ seeds. The wall-like nanostructures are proposed to form via epitaxial growth from the exposed edges of SnO₂ crystals of the FTO substrate. The nanotowers and nanowalls are composed of highly crystalline and ordered nanocrystals with preferred orientations in the [111] and [110] directions, respectively. The two structures display remarkably different activities when used as photoanodes in solar light-driven water splitting. X-ray photoelectron spectroscopy results suggest an increased density of hydroxyl groups in the nanowalls, which results in a decrease of the work function and a concomitant shift in the onset potential of the photocurrent in the linear sweep voltammograms, which is further confirmed by Mott–Schottky and flat-band potential measurements, indicating the importance of hydroxyl content in determining the photoelectrochemical properties of the films. Morphology-controlled, nanostructured transparent conducting oxide electrodes of the kind described in this paper are envisioned to provide valuable platforms for supporting catalysts and co-catalysts that are intentionally tailored for efficient light-assisted oxidation of water and reduction of carbon dioxide.