Overall Water Splitting under Visible Light through a Two‐Step Photoexcitation between TaON and WO₃ in the Presence of an Iodate–Iodide Shuttle Redox Mediator

Abstract

A two-step, photocatalytic water splitting system consisting of Pt-loaded TaON (a H(2) evolution photocatalyst), Pt-loaded WO(3) (an O(2) evolution photocatalyst), and an iodate-iodide (IO(3)(-)/I(-)) shuttle redox mediator is investigated under visible light irradiation. Photocatalytic oxidation of water to O(2) and reduction of IO(3)(-) to I(-) proceeded with good selectivity over the Pt-WO(3) photocatalyst, even in the presence of a considerable amount of I(-) anions in the solution. The key difference between the adsorption properties of IO(3)(-) and I(-) anions on WO(3) strongly suggested that the photoexcited electrons could react efficiently with IO(3)(-) adsorbed on WO(3), whereas the photogenerated holes selectively reacted with water molecules owing to the low adsorptivity of I(-) on WO(3). Photocatalytic H(2) evolution on Pt-TaON proceeded efficiently, accompanied by I(-) oxidation to IO(3)(-) due to a substantial amount of adsorption of I(-) anions on the surface, whereas H(2) evolution was significantly inhibited by the competitive adsorption of IO(3)(-), which consumes photoexcited electrons. It was also found that WO(3) photocatalysts loaded with platinum oxide (PtO) showed a much higher activity for O(2) evolution in the presence of the electron acceptor IO(3)(-), compared to those loaded with Pt metal. Overall water splitting at a steady rate was demonstrated using a combination of Pt-TaON and Pt(PtO)-WO(3) in an aqueous NaI solution with neutral or weakly acidic pH values, where the concentration of NaI significantly affected the efficiency.

Mimicking Natural Photosynthesis: Solar to Renewable H2 Fuel Synthesis by Z-Scheme Water Splitting Systems

“… 58 Overall water splitting was achieved when PtO x /WO 3 was combined and stably produced the stoichiometric H 2 and O 2 for 60 h at the pH of 5.3, reaching 0.5% of AQY at 420 nm. 59 …”

“…The reaction was carried out in aqueous solution (250 mL) containing NaIO 3 (2 mM). Reproduced with permission from ref ( 59 ). Copyright 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.…”

Metal oxynitrides as emerging materials with photocatalytic and electronic properties

“…35,36 This oxynitride is an important visible active photocatalyst for water splitting. 37 Efficient reduction and oxidation of water has been achieved in two steps, 40,41 and more recently in one step by using ZrO 2 as a co-catalyst. This requires that the minimum of the conduction band and the maximum of the valence band of the photocatalyst would be lower and higher than the oxidationreduction potential of H + /H 2 and O 2 /H 2 O respectively.…”

Ni(OH)2 loaded on TaON for enhancing photocatalytic water splitting activity under visible light irradiation

“…On account of a narrow band gap and favorable band gap position, TaON has been extensively studied for hydrogen production in the presence of a sacrificial reagent (e.g. methanol) as well as for the overall water splitting reaction under Z scheme under visible light irradiation [14]. However, to achieve high photocatalytic * Corresponding author.…”