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

Abstract

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 λ = 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.

TiO2 nanocrystal rods on titanium microwires: growth, vacuum annealing, and photoelectrochemical oxygen evolution

“…5B, which showed three strong peaks all correlating to rutile, as expected for the nanorods based on previous work. 12 Further evidence for the presence of rutile nanocrystal rods comes from transmission electron microscopy data, as seen in Fig. 6.…”

“…The wires were then further annealed at 550 1C in a vacuum environment (Speedivac Edwards High Vacuum Pump ED50, Crawley, England) for 4 hours in order to dope the material with oxygen vacancies and to enhance the photoelectrochemical properties, as shown in previous work. 12 The effect of vacuum annealing on performance is substantial and further improvements are likely with further optimisation of the annealing temperature and time, but this was outside of the scope of this work. Fig.…”

“…Previous work on similar TiO 2 nanocrystal rod systems grown on FTO substrate has proven the effectiveness of a vacuum annealing post treatment to greatly enhance the photoelectrochemical activity of the TiO 2 due to the effective doping of oxygen vacancies. 12 All microwires used in this study have therefore been annealed in vacuo as a final step in the synthesis (see Experimental). Fig.…”

“…Of particular note was the increased selectivity towards chloride ion oxidation resulting in the chlorine evolution reaction occurring simultaneously to the oxygen evolution reaction at the photo-anode. 12 The same TiO 2 nanocrystal rod array system was used in a heterojunction, where the TiO 2 nanocrystals were coated with NiO using atomic layer deposition (ALD), yielding significantly increased photoelectrochemical performance. 13 Here, TiO 2 nanocrystal rods are grown directly onto pre-passivated titanium microwire substrates.…”

Chemical Solution Deposition of Single‐Phase BiFeO3 Thin Films on Transparent Substrates

“…In applications such as solar active devices and photochemical cells, the system often requires transparent electrodes to enable light to activate the film via the back interface. [ 13 ] In these instances, the BiFeO 3 thin film needs to be produced on industry‐standard transparent substrates such as fluorine doped tin oxide (FTO) or indium doped tin oxide (ITO) coated glass. Deposition of a BiFeO 3 thin film on readily available, transparent and conductive FTO glass is a preferable choice for a wide range of applications.…”