Copyright © 2020 American Chemical Society. Photocatalytic splitting of aqueous NH3 into H2 and N2 on semiconductor powders is an important reaction toward on-site production of H2 from NH3, a promising hydrogen carrier for sustainable energy society. Earlier reports revealed that TiO2 loaded with Pt nanoparticles (Pt/TiO2) is the most effective catalyst for this reaction. Herein, we report that TiO2 loaded with homogeneously mixed bimetallic alloy nanoparticles containing 90 mol % Pt and 10 mol % Au (Pt0.9Au0.1/TiO2) promotes photocatalytic NH3 splitting very efficiently. Electrochemical analysis indicates that Au alloying to Pt lowers the height of Schottky barrier created at the metal/TiO2 interface. This promotes efficient transfer of conduction band electrons on TiO2 to metal particles. This results in enhanced separation of the photogenerated charges, thus promoting efficient NH3 splitting.