Photo-Chlorine Production with Hydrothermally Grown and Vacuum-Annealed Nanocrystalline Rutile

Photo-generated high-energy surface states can help to produce chlorine in aqueous environments. Here, aligned rutile (TiO2) nanocrystal arrays are grown onto fluorine-doped tin oxide (FTO) substrates and activated either by hydrothermal Sr/Ba surface doping and/or by vacuum-annealing. With vacuum-annealing, highly photoactive films are obtained with photocurrents of typically 8 mA cm(-2) at 1.0 V vs. SCE in 1 M KCl (LED illumination with lambda = 385 nm and approx. 100 mW cm(-2)). Photoelectrochemical chlorine production is demonstrated at proof-of-concept scale in 4 M NaCl and suggested to be linked mainly to the production of Ti(III) surface species by vacuum-annealing, as detected by post-catalysis XPS, rather than to Sr/Ba doping at the rutile surface. The vacuum-annealing treatment is proposed to beneficially affect (i) bulk semiconductor TiO2 nanocrystal properties and electron harvesting, (ii) surface TiO2 reactivity towards chloride adsorption and oxidation, and (iii) FTO substrate performance.

Automated summary

Photo-generated high-energy surface states can assist in the production of chlorine in aqueous environments. Aligned rutile nanocrystal arrays grown on fluorine-doped tin oxide substrates and activated by hydrothermal Sr/Ba surface doping and/or vacuum-annealing exhibit highly photoactive properties, leading to efficient photoelectrochemical chlorine production. Vacuum-annealing is suggested to enhance semiconductor TiO2 nanocrystal properties, surface reactivity, and substrate performance.