Interface Manipulation to Improve Plasmon-Coupled Photoelectrochemical Water Splitting on α-Fe₂ O₃ Photoanodes

The plasmon resonance effect of metal nanoparticles (NPs) offers a promising route to improve the solar energy conversion efficiency of semiconductors. In this study, it is revealed that hot electrons generated by the plasmon resonance effect of Au NPs tend to inject into the surface states instead of the conduction band of Fe₂ O₃ photoanodes, and then severe surface recombination occurs. Such an electron-transfer process seems to be independent of external applied potentials, but is sensitive to metal-semiconductor interface properties. Passivating the surface states of Fe₂ O₃ with a noncatalytic Al₂ O₃ layer can construct an effective resonant energy-transfer interface between Ti-doped Fe₂ O₃ (Ti-Fe₂ O₃ ) and Au NPs. In such a Ti-Fe₂ O₃ /Al₂ O₃ /Au electrode configuration, the enhanced photoelectrochemical (PEC) water-splitting performance can be attributed to the following two factors: 1) in the non-light-responsive wavelength range of Au NPs, both the relaxing Fermi pinning effect of the Al₂ O₃ passivation layer and the higher work function of Au enlarge band bending; thus promoting the charge separation; and 2) in the light-responsive wavelength range of Au NPs, the effective resonant energy transfer contributes to light harvesting and conversion. The interface manipulation proposed herein may provide a new route to design efficient plasmonic PEC devices for energy conversion.