Plasmonic Enhancement of Photoactivity by Gold Nanoparticles Embedded in Hematite Films

Semiconducting n-type nanostructured hematite (alpha-Fe2O3) is a promising photocatalyst for solar water splitting because of its favorable band gap of 2.2 eV, low cost, and abundance in natute. However, its photoactivity is limited by the poor absorptivity and short hole diffusion length. Surface plasmon resonance (SPR) of metallic (Au, Ag, and Cu) nanostructures is known to concentrate and scatter incident light over a broad wavelength range and holds the promise of enhancing the light absorption cross section of a semiconducting material around the plasmonic structures. Herein we report enhanced photoelectrochemical (PEC) performance of a smooth chemical vapor deposited hematite film embedded with Au nanopartides (NPs). 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. The improved embedded configuration also has the advantage of consistent performance and protection of plasmonic nanostructures from electrochemical corrosion, resulting in long cycles of operation.