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 TiO 2 surfaces to produce Au nanoparticles with an average size tunable in the 3–200 nm range. Such Au-decorated TiO 2 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 TiO 2 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.