Photoelectrochemical Oxidation Enhanced by Nitride Plasmonics

Refractory nitride plasmonics offer the potential to realize enhanced light-matter 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 (NPs) into matrices of titanium dioxide (TiO2) and compared their ability to enhance electrochemical oxidation reactions to that of conventional gold (Au) NPs. Although the photon-to-carrier conversion efficiencies were low (similar to 10(-4)%), the reaction rates were enhanced by a factor of 4 in the visible and near-infrared (IR) regions for both Au and TiN compared to a pure TiO2 control, with TiN showing an order of magnitude improvement over Au in the near-IR region. The spectral dependence of reaction rate enhancement followed the NP extinction spectra, and a linear power dependence identifies a photoexcited carrier mechanism (i.e., decaying plasmons excite carriers that participate in chemistry rather than heating of the system). Last, photoinduced transients of the electrochemical signal are consistent with interfacial defect charging in these heterosystems. Specifically, the TiN/TiO2 system, which has no Schottky barriers, exhibits a bias-dependent and transient photoelectrochemical response, whereas the Au/TiO2 system, which naturally forms a Schottky barrier that immediately separates charged carriers, exhibits a near-instantaneous response.