Enhanced Interfacial Charge Transfer on a Tungsten Trioxide Photoanode with Immobilized Molecular Iridium Catalyst

The rational design of active photoanodes for photoelectrochemical (PEC) water splitting is crucial for future applications in sustainable energy conversion. A combination of catalysts with photoelectrodes is generally required to improve surface kinetics and suppress surface recombination. In this study, we present an iridium complex (Ir-PO3H2) modified WO3 photoanode (WO3+Ir-PO3H2) for PEC water oxidation. When the Ir-based molecular catalyst (Ir-PO3H2) is anchored to a WO3 electrode, the photoanode shows a significant improvement both in photocurrent and faradaic efficiency compared to bare WO3. Under simulated sunlight illumination (AM 1.5G, 100 m Wcm−2) with an applied bias of 1.23 V vs. RHE, the photoanode exhibits a photocurrent of 1.16 mA cm−2 in acidic conditions, which is double that of bare WO3. The faradaic efficiency is promoted from 56% to 95%. Kinetic studies reveal that Ir-PO3H2 exhibits a different interfacial charge transfer mechanism on the WO3 photoanode for PEC water oxidation compared to iridium oxide (IrOx). Ir-PO3H2, as a water oxidation catalyst, can accelerate the surface charge transfer through rapid surface kinetics.