Enhanced Photothermal Reduction of Gaseous CO2 over Silicon Photonic Crystal Supported Ruthenium at Ambient Temperature

Solar-driven CO2 hydrogenation can provide a renewable source of fuels and reduce greenhouse gas emissions if operated at industrial scales. Herein we investigate the photomethanation (light-driven Sabatier reaction) rates over Ru films sputtered onto silica opal (Ru/SiO2) and inverted silicon opal photonic crystal (Ru/i-Si-o) supports at ambient temperature under solar-simulated radiation as a function of incident light intensity. Photomethanation rates over both the Ru/SiO2 and Ru/i-Si-o catalysts increase significantly with increasing light intensity, and rates as large as 2.8 mmol g(-1) h(-1) are achieved over the Ru/i-Si-o catalyst. Furthermore, the quantum efficiency of the photomethanation reaction is almost three times larger when measured over the Ru/i-Si-o catalyst as compared to the Ru/SiO2 catalyst. The large photomethanation rates over the Ru/i-Si-o catalyst are attributed to its exceptional light-harvesting properties. Moreover, we perform DFT analysis to investigate the potential role of photo-induced charges on the Ru surface. The results from the simulation indicate that charged Ru surfaces can destabilize adsorbed CO2 molecules and adsorb and dissociate H-2 such that it can readily react with CO2, thereby accelerating the Sabatier reaction.