Two-Dimensional Perovskite Oxynitride K2LaTa2O6N with an H+/K+ Exchangeability in Aqueous Solution Forming a Stable Photocatalyst for Visible-Light H2 Evolution

Undoped layered oxynitrides have not been considered as promising H-2-evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K2LaTa2O6N, as an exceptional example of a water-tolerant photocatalyst for H-2 evolution under visible light. The material underwent in-situ H+/K+ exchange in aqueous solution while keeping its visible-light-absorption capability. Protonated K2LaTa2O6N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H-2 evolution in the presence of I- as an electron donor and under visible light; the activity was six times higher than Pt/ZrO2/TaON, one of the best-performing oxynitride photocatalysts for H-2 evolution. Overall water splitting was also achieved using the Ir-loaded, protonated K2LaTa2O6N in combination with Cs-modified Pt/WO3 as an O-2 evolution photocatalyst in the presence of an I-3(-)/I- shuttle redox couple.