Surface Enhanced Visible Light Photocurrent and Switching Behavior of Metal Oxide Semiconductor Electrodes Modified with Plasmonic Nanoparticles

Abstract

Hematite (α-Fe2O3) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in nature. Surface plasmon-enhanced light absorption for photoelectrochemical water splitting at α-Fe2O3thin film electrode modified with Au nanoparticles (NPs) or nanorods (NRs) is described. About 3 times higher light absorption and photocurrent enhancement are obtained from thin hematite films containing Au NPs than with pristine hematite films. The plasmonic enhancement increases with the amount of Au NPs for the same thickness of hematite. Thickness-dependent study of photoactivity indicates a higher enhancement in hematite thin films compared to thicker films due to reduced charge transport distance and optimal local field enhancement effect. Such enhancement can be obtained by self-assembling Au NRs onto a hematite thin film electrode using electrostatic force between their positively charged cetyltrimethylammonium bromide (CTAB) layer and negatively charged hematite surface functionalized with poly(4-styrenesulfonate). The photoelectrochemical reaction of the plasmon active substrate for water oxidation reaction is performed and compared at various hematite layer thicknesses. When the α-Fe2O3 electrode is biased at a small potential +0.2 V (vs Ag/AgCl), the photocurrent of water oxidation is reduced because of increased recombination of holes and electrons at the surface of the Au NRs. When the bias potential is increased to +0.5 V (vs Ag/AgCl), a plasmon enhancement of the photoelectrochemical reaction of water oxidation at wavelengths near the plasmon resonance condition is observed at the α-Fe2O3 thin film electrodes accompanying a dramatic increase in the background current. The significant increase in photocurrent in the region of surface plasmon absorption is attributed to the enhanced visible light absorption of α-Fe2O3 in the presence of the plasmon active Au NPs and NRs.