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

Three mixed tantalum oxynitrides, ATaO(2)N (A = Ca, Sr, Ba), prepared by heating amorphous A(2)Ta(2)O(7) under NH3, are applied in a two-step photoexcitation water-splitting system as a photocatalyst for H-2 evolution. Platinum-loaded CaTaO2N and BaTaO2N are demonstrated to be active for H-2 evolution in the presence of methanol or I- as an electron donor, whereas SrTaO2N 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-CaTaO2N or Pt-BaTaO2N with Pt-WO3 achieves overall water splitting under visible irradiation. Pt-BaTaO2N 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.