Dewetted Au Nanoparticles on TiO2 Surfaces: Evidence of a Size-Independent Plasmonic Photoelectrochemical Response

We induce solid-state dewetting of thin Au films (nominal thickness of 0.5–10 nm) on flat TiO2 surfaces to produce Au nanoparticles with an average size tunable in the 3–200 nm range. Such Au-decorated TiO2 surfaces enable plasmonic photoelectrochemical water splitting under visible light illumination (450–750 nm), with a photon-to-current conversion efficiency that reaches a maximum for TiO2 surfaces decorated with ∼30 nm sized Au particles. Optical measurements show, as expected, a red shift of the plasmon resonance with the increasing Au nanoparticle size. More interestingly, the photocurrent is found to peak for every photoanode at ∼600 nm regardless of the Au nanoparticle size, i.e., the wavelength of maximum photocurrent is size-independent. Such a remarkable observation can be ascribed to a hot electron injection cutoff effect, i.e., can be explained in terms of the interband versus intraband transition scenario.