Enhanced Photoelectrocatalytic Reduction of Oxygen Using Au@TiO₂ Plasmonic Film

Novel Au@TiO₂ plasmonic films were fabricated by individually placing Au nanoparticles into TiO₂ nanocavity arrays through a sputtering and dewetting process. These discrete Au nanoparticles in TiO₂ nanocavities showed strong visible-light absorption due to the plasmonic resonance. Photoelectrochemical studies demonstrated that the developed Au@TiO₂ plasmonic films exhibited significantly enhanced catalytic activities toward oxygen reduction reactions with an onset potential of 0.92 V (vs reversible hydrogen electrode), electron transfer number of 3.94, and limiting current density of 5.2 mA cm^-2. A superior ORR activity of 310 mA mg^-1 is achieved using low Au loading mass. The isolated Au nanoparticle size remarkably affected the catalytic activities of Au@TiO₂, and TiO₂ coated with 5 nm Au (Au₅@TiO₂) exhibited the best catalytic function to reduce oxygen. The plasmon-enhanced reductive activity is attributed to the surface plasmonic resonance of isolated Au nanoparticles in TiO₂ nanocavities and suppressed electron recombination. This work provides comprehensive understanding of a novel plasmonic system using isolated noble metals into nanostructured semiconductor films as a potential alternative catalyst for oxygen reduction reaction.