Photoelectrochemical Transients for Chlorine/Hypochlorite Formation at “Roll-On” Nano-WO₃ Film Electrodes

Abstract

Commercial nano-WO 3 (10−100 nm average particle size) is dispersed in nhexanol and applied to tin-doped indium oxide (ITO) substrates in a simple "roll-on" process. As-deposited and annealed (500 °C) films are compared and shown to be photoactive for the formation of hypochlorite in neutral aqueous NaCl (e.g., seawater). Annealing at 500 °C in air improves photocurrents most likely due to improved interparticle charge transport (e.g., removal of hydration or n-hexanol surface layers). In phototransients (interpreted here in the limiting case of a weakly associated nanoparticle aggregate as opposed to the limiting case of a single-crystal semiconductor), evidence for the presence of both holes (as O(-I), fast moving) and electrons (as W(V), slow moving) is obtained in particular in as-deposited films. Bipotentiostat experiments reveal the presence of chlorine as a reaction intermediate close to the photoanode when immersed in 3 M NaCl. A "molecular conduit" effect with adsorbed Co(II/III) sepulchrate is observed to significantly enhance the photocurrents at as-deposited electrodes (but not at annealed electrodes).

Photoanodes on titanium substrates: one-step deposited BiVO4 versus two-step nano-V2O5 films impregnated with Bi3+

“…The band gap can be estimated as 2.52 eV (see red line), which is close to the values reported previously [10,11,13,17]. In contrast, tetragonal zircon type BiVO4 has been reported to exhibit a wider less beneficial band gap (2.9 eV) [18].…”

“…This mixture was then used as the precursor for deposition of BiVO4 films. The deposition was carried out by employing a drawing roller (hard rubber lino printing roller) [13]. The precursor solution was distributed evenly onto the ITO substrate (ca.…”

Nanostructured Tungsten Trioxide Thin Films Synthesized for Photoelectrocatalytic Water Oxidation: A review

“…[94] As for the elucidation of charge-transfer processes in nanostructured WO 3 , the recent developments are mainly based on the synthesis of multilayer thin films such as TiO 2 /WO 3 /Pt, [86] Ag/AgCl/plate-WO 3 , [95] Mo-BiVO 4 /WO 3 , [87] WO 3 /Fe 2 O 3 /WO 3 , and Fe 2 O 3 /WO 3 /Fe 2 O 3 . In addition, heterojunction structures can also offer enhanced separation of photogenerated charge carriers as previously reported for WO 3 /BiVO 4 , [67] Bi 2 S 3 /WO 3 , [89] graphene oxide-WO 3 , [88] and multiple (WO 3 -Pt)/TiO 2 . [91] Figures 23 and 24 show the summary of photoelectrochemical tandem cells for different photocatalysts.…”

“…Ahmed et al explained the photocurrent process in detail using as-deposited and annealed commercial nano-WO 3 on ITO-coated glass as electrode substrate immersed in 3 m NaCl. [88] Once a photostationary state is reached, the photogenerated holes will react with chloride leading to a net anodic photocurrent with electrons reaching the underlying ITO electrode surface. Thus, the photocurrent is affected by the presence of ions in the solution.…”

Synthesis and characterization of tungstite (WO3·H2O) nanoleaves and nanoribbons

“…A simple heat-treatment of tungstite (WO 3 .H 2 O) allows for the phase transformation to tungsten oxide (WO 3 ), an important class of n-type semiconductors with a tunable band gap of 2.5-2.8 eV [16]. Moreover, its high chemical stability, low production costs and non-toxicity have recently generated significant interests for a wide variety of applications in microelectronics and optoelectronics [17][18], super-hydrophilic thin films [15], dye-sensitized solar cells [19], colloidal quantum dot LEDs [20], photocatalysis [21] and photoelectrocatalysis [22], water splitting photocatalyst as main catalyst [23][24][25][26][27][28][29][30][31][32][33][34]. Environmental applications can also benefit from WO 3 as a visible light photocatalyst to generate OH radicals for bacteria destruction [35] and photocatalytic reduction of CO 2 into hydrocarbon fuels [36].…”