Surface Passivation Effect of Ferrihydrite with Hole-Storage Ability in Water Oxidation on BiVO<sub>4</sub> Photoanode
Heng Yin, Dongfeng Li, Xiuli Wang, Can Li
Abstract
Ferrihydrite (Fh) is an effective surface modifier for enhancing photoelectrochemical (PEC) performance of photoanode, while the exact role of Fh, serving as cocatalyst, hole-storage layer, or passivation layer, is still in debate due to the lack of direct dynamic evidences. In this work, the role of Fh in water oxidation on Fh/BiVO4 photoanode has been investigated using various time-resolved spectroscopic techniques. With the modification of Fh, both density and lifetime of long-lived holes in Fh/BiVO4 increased by a factor of ∼2.4 than those of bare BiVO4 revealed by transient absorption spectroscopy, demonstrating the retardation of electron/hole recombination of BiVO4 by Fh. This retardation should result from the passivation effect of surface defects in BiVO4 by Fh. More importantly, 40 times increase in photoinduced absorption amplitude of Fh/BiVO4 relative to that of BiVO4 illustrates transfer of holes from BiVO4 to Fh, and the transferred holes accumulate in Fh with lifetimes above 10 s, demonstrating directly that Fh has hole-storage ability. The dynamic evidences illustrate that the main roles of Fh in PEC water oxidation on Fh/BiVO4 serve as a passivation layer with hole-storage ability.