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 [(H(4)dphbpy)Ir-III(Cp*)Cl]Cl (Ir-PO3H2 ; H-4 dphbpy=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.