September 25, 2014
Chemistry Department, Carnegie Mellon University
Beyond Water Splitting: Novel Approaches to Solar Fuels
A fundamental approach to storing solar energy is artificial photosynthesis, whereby uphill chemical reactions are driven by light, e.g. the water gas shift reaction, halogen acid splitting, or water splitting. The first part of this lecture endeavors to define a common context for these research topics, particularly by analyzing the thermodynamic boundaries of photosynthesis. Specifically, the generalized efficiency restrictions on both light absorption and energy storage are expounded, the analogous limitations for several individual photosynthetic strategies are stated, several synthetic catalyst architectures are highlighted, the advantages of molecular and macroscopic approaches are discussed, and key figures of merit are presented.
Later, the lecture will highlight the Bernhard groupís progress in the area of photon-driven fuel production focusing on photocatalytic reduction of Zn2+ ions to metallic Zn. Iridium(III) complexes have proven to be effective photocatalysts for such production of Zn fuel, and the optimization of the catalyst as well as the solvent and zinc starting material will be discussed. An organocatalytic approach will also be presented as an alternative to the use of expensive 3rd row transition metal catalysts. The third part of the talk will highlight new work on the photocatalytic de-hydrogenation of alcohols driven by visible light. These efforts strive to use cheap and abundant biomolecules as a source of carbon neutral hydrogen. Finally, the lecture will end by highlighting the Bernhard groupís ongoing work on water oxidation catalysis. New results involving iron and iridium-based catalysts will be presented with emphasis on the elucidation of the water oxidation mechanism which involves complex, concerted electron and proton transfer processes.