Enhanced production of H2 under visible light via co-deposited Pt and Ir species on g-C3N4

Abstract

Graphitic carbon nitride (g-C₃N₄) is a promising metal-free semiconductor photocatalyst for H₂ evolution. In this work, g-C₃N₄ has been modified with IrO₂via a thermal reaction, followed by photochemical deposition of PtO. After co-catalyst loading, g-C₃N₄ had no change in crystal structure, but its dimension within the layers was reduced, together with a blue shift in light absorption and emission. In a methanol aqueous solution under visible light, g-C₃N₄ was nearly not active for H₂ evolution, but modified g-C₃N₄ was quite active. With IrO₂/g-C₃N₄, Pt/g-C₃N₄, and Pt/IrO₂/g-C₃N₄, the rates of H₂ production were measured to be 10.6, 21.4, and 41.2 μmol min⁻¹ g⁻¹, respectively. Moreover, the reaction rate was greatly dependent on co-catalyst loading in modified g-C₃N₄. The Pt/IrO₂/g-C₃N₄ sample was more active than NiS and MoS₂ loaded g-C₃N₄, by factors of approximately 12 and 24, respectively. (Photo)electrochemical measurement revealed that Pt species catalyzed proton reduction, while Ir species catalyzed water oxidation. A plausible mechanism is proposed, involving synergism between PtO-mediated electron transfer and IrO₂-mediated hole transfer.