Photocatalytic Overall Water Splitting under Visible Light Using ATaO₂N (A = Ca, Sr, Ba) and WO₃ in a IO₃⁻/I⁻ Shuttle Redox Mediated System

Abstract

Three mixed tantalum oxynitrides, ATaO 2 N (A = Ca, Sr, Ba), prepared by heating amorphous A 2 Ta 2 O 7 under NH 3, are applied in a two-step photoexcitation water-splitting system as a photocatalyst for H 2 evolution. Platinum-loaded CaTaO 2 N and BaTaO 2 N are demonstrated to be active for H 2 evolution in the presence of methanol or I − as an electron donor, whereas SrTaO 2 N is unable to produce H 2 stably in the presence of I − due to self-oxidative decomposition accompanied by N 2 production. The combination of Pt−CaTaO 2 N or Pt−BaTaO 2 N with Pt−WO 3 achieves overall water splitting under visible irradiation. Pt−BaTaO 2 N is also demonstrated to be photoactive at wavelengths up to 660 nm, representing the first example of an overall water-splitting system in which visible light at wavelengths longer than 600 nm is effectively utilized for H 2 evolution.