Improved water splitting efficiency of Au-NP-loaded Ga 2 O 3 thin films in the visible region under strong coupling conditions.

We fabricate a novel photoanode consisting of TiO 2 /Au nanoparticles (Au-NPs)/Ga 2 O 3 /TiN/Au-film (TAGA), efficiently increasing light absorption and electron transfer from Au-NPs to Ga 2 O 3 under modal strong coupling. A TiN thin layer deposited on an Au film enables stable high-temperature deposition of Ga 2 O 3 onto the reflective Au film mirror. Modal strong coupling is observed when the resonance wavelength of the Ga 2 O 3 /TiN/Au-film Fabry-Pérot cavity overlaps with the plasmon resonance wavelength of Au-NPs partially inlaid in a thin TiO 2 layer. Under strong coupling conditions, the light absorption and photoelectrochemical conversion efficiency in the visible region increased more than in the samples without coupling. In this structure, the TiO 2 layer partially inlaying Au-NPs plays a vital role in effectively enhancing the coupling strength. We accomplish water splitting at zero bias potential by taking advantage of the intrinsically negative conduction band potential of Ga 2 O 3 .