Abstract
Both Pd and Au metal particles are used in photocatalytic hydrogen generation. Yet while both act as electron sink only gold is poised to respond to visible light due to its plasmonic response. In order to quantitatively gauge their relative contribution into the reaction, the photocatalytic H-2 production, from Au/TiO2 and Pd/TiO2 catalysts was studied under UV and UV-Vis light. While under UV light excitation, a weak dependence on the work function of the metal is observed, under UV-Vis light, Au is found to be twice more active than Pd. Under identical UV-Vis light irradiation, the turn over frequency calculated from XPS at.% is found to be 2.8 and 1.8 s(-1) for Au and Pd, respectively. The effect is far more pronounced when the rates are normalized to the number of particles of each metal. Both the semiconductor TiO2 (UV light) and the plasmonic metal (visible light) need to be excited for the enhancement to occur; visible light alone causes a negligible reaction rate. Photocurrent measurements further confirmed the difference in the photocatalytic activity under UV and UV-Vis light excitation. Moreover, because of the presence of Au particles responding to visible light the reaction rate is enhanced due to "light penetration depth" effect.