Interfacial and Dimensional Effects of Pd Co-Catalyst for Efficient Photocatalytic Hydrogen Generation

Metal nanocrystal is widely used as cocatalyst to facilitate semiconductor-based photocatalytic conversion from water to hydrogen. While incredible developments are achieved to design the primary semiconductor photocatalysts, a few efforts are devoted to revealing the effect of shape, size, and surface structure of a metal cocatalyst. Herein, taking Pd as a model cocatalyst, the roles of cocatalyst are systematically studied by combining it with a commercial TiO₂ (P25) photocatalyst. The success relies on a seed-mediated-approach for the fine integration of Pd nanocubes or nanooctahedra on the P25 surface. Both theoretical and experimental results demonstrate the advantage of Pd nanocubes over nanooctahedra in boosting photoactivity of TiO₂ nanocrystals. The superiority arises from the appropriate interfacial Schottky barrier between TiO₂ and Pd nanocubes and proper atomic H adsorption free energy of the {100} facets for accelerating interfacial charge separation and surface redox reaction, respectively. The activity could be further improved by selective removal of surface ligands of the nanocube. This work not only gives an insight into the effects of geometrical characteristics, such as the surface structure of a metal cocatalyst, in finely tuning the photoactivity of TiO₂-Pd composites but also provides an extendable strategy to investigate similar photocatalytic manners of other metal or even compound cocatalysts.