An Oxysulfide Photocatalyst Evolving Hydrogen with an Apparent Quantum Efficiency of 30 % under Visible Light

Photocatalytic water splitting is a simple means of converting solar energy into storable hydrogen energy. Narrow-band gap oxysulfide photocatalysts have attracted much attention in this regard owing to the significant visible-light absorption and relatively high stability of these compounds. However, existing materials suffer from low efficiencies due to difficulties in synthesizing these oxysulfides with suitable degrees of crystallinity and particle sizes, and in constructing effective reaction sites. The present work demonstrates the production of a Gd₂ Ti₂ O₅ S₂ (λ<650 nm) photocatalyst capable of efficiently driving photocatalytic reactions. Single-crystalline, plate-like Gd₂ Ti₂ O₅ S₂ particles with atomically ordered surfaces were synthesized by flux and chemical etching methods. Ultrafine Pt-IrO₂ cocatalyst particles that promoted hydrogen (H₂ ) and oxygen (O₂ ) evolution reactions were subsequently loaded on the Gd₂ Ti₂ O₅ S₂ while ensuring an intimate contact by employing a microwave-heating technique. The optimized Gd₂ Ti₂ O₅ S₂ was found to evolve H₂ from an aqueous methanol solution with a remarkable apparent quantum efficiency of 30 % at 420 nm. This material was also stable during O₂ evolution in the presence of a sacrificial reagent. The results presented herein demonstrates a highly efficient narrow-band gap oxysulfide photocatalyst with potential applications in practical solar hydrogen production.