Modulating Photoelectrochemical Water-Splitting Activity by Charge-Storage Capacity of Electrocatalysts

Electrocatalysts (ECs) are indispensable for high-efficiency photoelectrochemical (PEC) water splitting, but the underlying mechanism for performance modulation is still not clear. Taking the α-Fe2O3 semiconductor (SC) decorated with the cobalt oxide ECs as the model photoanode system, we demonstrate the opposite changes of PEC water oxidation activities by tuning the charge-storage capacity of ECs. Holes stored in the EC can increase the hole density on the photoanode surface, which can benefit the multihole surface water oxidation reaction, as well as aggravate the SC–EC interfacial charge recombination due to the Coulomb attraction. Both experimental and theoretical data prove that the EC with low hole-storage capacity brings limited interfacial charge recombination, enabling faster hole injection to improve the water oxidation activity. In contrast, the EC with high hole-storage capacity causes severe interfacial charge recombination, hindering the hole injection, thus decreasing the water oxidation activity. As a result, the PEC activity of photoanodes changes nonmonotonically with increasing surface hole density. This study can provide insightful guidance to interface design for solar energy-conversion systems.