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 WO3 photoanode modified with the iridium complex [(H4dphbpy)IrIII(Cp*)Cl]Cl (Ir‐PO3H2; H4dphbpy=2,2′‐bipyridine‐4,4′‐bisphosphonic acid, Cp*=pentamethylcyclopentadiene (WO3+Ir‐PO3H2)‐ for PEC water oxidation. When Ir‐PO3H2 is anchored to a WO3 electrode, the photoanode shows a significant improvement in both photocurrent and faradaic efficiency compared to the bare WO3 photoanode. Under simulated sunlight illumination (AM 1.5G, 100 mW cm−2) with an applied bias of 1.23 V (vs. reversible hydrogen electrode), the photoanode exhibits a photocurrent of 1.16 mA cm−2 in acidic conditions, which is double that of the bare WO3 photoanode. 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. Ir‐PO3H2, as a water‐oxidation catalyst, can accelerate the surface charge transfer through rapid surface kinetics.