(Invited) Nitride Plasmonics for Enhanced Electrochemical Oxidation

Abstract

Refractory nitride plasmonics offer the potential to realize enhanced light interactions for energy harvesting and photo-driven chemistry with materials systems that are thermally rugged, inexpensive, and potentially catalytic. Here, we have embedded commercial and in-house synthesized titanium nitride (TiN) nanoparticles into matrixes of titanium dioxide (TiO2) and compared their ability to enhance electrochemical oxidation reactions to that of conventional gold (Au) nanoparticles. Although the photon-to-carrier conversion efficiencies were low (~10-4 %), the reaction rates were enhanced by a factor of 4 in the visible and near-infrared for Au and TiN, respectively, compared to a pure TiO2 control. The spectral dependence of reaction rate enhancement followed the nanoparticle extinction spectra and a linear power-dependence identifies a photo-excited carrier mechanism (i.e., decaying plasmons excite carriers which participate in chemistry rather than heating of the system). Lastly, photo-induced transients of the electrochemical signal are found to be consistent with the band structures of these heterosystems. Specifically, the TiN/TiO2 system, which has little or no Schottky barrier, exhibits a bias-dependent photoelectrochemical response rate while the Au/TiO2 system, which naturally forms a Schottky barrier that immediately separates charged carriers, exhibits a near-instantaneous response.