Improved Stability of Atomic Layer Deposited Amorphous TiO(2) Photoelectrode Coatings by Thermally Induced Oxygen Defects

[Image: see text] Amorphous titanium dioxide (a-TiO(2)) combined with an electrocatalyst has shown to be a promising coating for stabilizing traditional semiconductor materials used in artificial photosynthesis for efficient photoelectrochemical solar-to-fuel energy conversion. In this study we report a detailed analysis of two methods of modifying an undoped thin film of atomic layer deposited (ALD) a-TiO(2) without an electrocatalyst to affect its performance in water splitting reaction as a protective photoelectrode coating. The methods are high-temperature annealing in ultrahigh vacuum and atomic hydrogen exposure. A key feature in both methods is that they preserve the amorphous structure of the film. Special attention is paid to the changes in the molecular and electronic structure of a-TiO(2) induced by these treatments. On the basis of the photoelectrochemical results, the a-TiO(2) is susceptible to photocorrosion but significant improvement in stability is achieved after heat treatment in vacuum at temperatures above 500 °C. On the other hand, the hydrogen treatment does not increase the stability despite the ostensibly similar reduction of a-TiO(2). The surface analysis allows us to interpret the improved stability to the thermally induced formation of O(–) species within a-TiO(2) that are essentially electronic defects in the anionic framework.