(583ei) Photocatalysis Deconstructed: Design of New Photocatalyst for Carbon Dioxide-Water Reduction

Rapid increase in anthropogenic emission of greenhouse gases, mainly carbon dioxide, has been a growing cause for concern. While photocatalytic reduction of carbon dioxide (CO₂) into solar fuels can provide an alternative, lack of insight into energetic pathways governing photocatalysis has impeded study. The current state-of-the-art for designing new catalysts relies on adding expensive metal dopants (like platinum) to enhance the absorption of CO₂ on the catalyst surface. However, these metal dopants also introduce sites for recombination of photogenerated charges. Here, we present a rational design approach where we started with identification of energy levels responsible for reduction of CO₂-water, by measuring the electronic density of states (DOS) of photocatalytically active titanium dioxide (TiO₂) nanoparticles, using Scanning Tunneling Microscopy (STM) and spectroscopy. These desired energy levels were then introduced in nanoparticles using inexpensive dopants or semiconductor nanocrystals, and the designed photocatalysts were used for selective reduction of CO₂ into hydrocarbons, alcohols and aldehydes using simulated solar irradiation. I will summarize the recent efforts in our group on development of new inexpensive photocatalysts with tuned activity (>5%) and selectivity (>70%) for production of solar fuels . I will also present a theoretical model to explain the photophysics governing the multielectron reduction of CO₂-water to specific fuels, and elucidate the role for solar concentrators to enhance the photocatalytic yields. The insights and advances in this artifical photosynthesis process can have important implications for renewable energy and carbon sequestration.