Untangling Thermal and Nonthermal Effects in Plasmonic Photocatalysis

Presenter: Xueqian (Lucy) Li, Ph.D. candidate Jie Liu, advisor

Plasmonic photocatalysis exploits the strong light-matter interactions of small metal nanoparticles and offers a sustainable route for the synthesis of fuels such as hydrocarbons and ammonia (NH3) from light. Illumination of tailored plasmonic photocatalysts or traditionally thermal catalysts with intrinsic plasmonic properties leads to several photo-physical effects including: (1) generation of hot carriers, (2) photothermal heating, and (3) local enhancement of the electric field. Demonstrations of the excitation of localized surface plasmon resonances in plasmonic photocatalysis have shown enhanced reaction rates and improved product selectivity at reduced temperatures which alleviates several problems found in thermally-driven processes. While the injection of hot carriers from the metal nanoparticles is usually proposed as the dominant mechanism, the contribution of plasmon-induced heating must not be neglected. To understand the underlying mechanism in these plasmon-driven processes, the intertwined thermal and nonthermal effects from light must be untangled.  This dissertation summarizes our efforts in establishing theoretical and experimental techniques to accurately distinguish between thermal and nonthermal contributions. The intrinsic plasmonic and catalytic properties of supported rhodium (Rh) and ruthenium (Ru) catalysts are investigated in two model reactions of plasmonic photocatalysis: carbon dioxide (CO2) hydrogenation and NH3 synthesis.