Hydrogen Production on Ag-Pd/TiO2 Bimetallic Catalysts: Is there a Combined Effect of Surface Plasmon Resonance with Schottky Mechanism on the Photo-Catalytic Activity?

Despite many observations that plasmonics can enhance photocatalytic reactions, their relative role in the overall reaction rate is not thoroughly investigated. Here we report that silver nanoparticles contribution in the reaction rate by its plasmonic effect is negligible when compared to that of Pd (Schottky effect). To conduct the study a series of Ag−Pd/TiO2 catalysts have been prepared, characterized and tested for H2 production from water in the presence of an organic sacrificial agent. Pd was chosen as a standard high work function metal needed for the Schottky junction to pump away electrons from the conduction band of the semiconductor and Ag (whose work function is ca. 1 eV lower than that of Pd) for its high plasmonic resonance response at the edge of the bandgap of TiO2. While H2 production rates showed linear dependency on plasmonic response of Ag in the Pd−Ag series, the system performed less than that of pure Pd. In other words, the plasmonic contribution of Ag in the Ag−Pd/TiO2 catalyst for hydrogen production, while confirmed using different excitation energies, is small. Therefore, the “possible” synergistic effect of plasmonic (in the case of Ag) and Schottky-mechanism (in the case of Pd) is minor when compared to that of Schottky-effect alone.