Plasmon resonance-enhanced photoelectrodes and photocatalysts

Abstract

Growing interest in composite plasmonic-metal/semiconductor photocatalysts is motivated by the ability of plasmonic nanostructures to capture light, most particularly at their resonance frequencies at which they exhibit high absorption and scattering cross-sections. In the cases when plasmon resonance frequency overlaps absorption spectrum of the semiconductor, large electric field enhancement near the surface of the metal nanostructure leads to increased charge carrier generation in the nearby semiconductor (plasmonic near-field effect). Another, largely evoked, kind of interaction is the spectral sensitization of a semiconductor to longer wavelengths absorbed only by the plasmonic nanostructure. In such a process, hot electrons generated in the metal nanostructure via the decay of optically excited plasmons are transferred over the Schottky barrier to the nearby semiconductor resulting in extra band-gap photoactivity. Several examples pertaining to each of these interactions will be discussed. While interest in composite plasmonic-metal/semiconductor photocatalysts is relatively recent, there has been substantial earlier work on plasmon-mediated photoelectrochemistry on a typical plasmonic metal-silver. It is shown that roughening of the silver electrode surface leads, for example, to largely enhanced cathodic CO2 reduction photocurrents observed under illumination with UV-visible wavelengths that coincide with plasmon resonance frequencies in silver.