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 talk 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, the advantages of molecular and macroscopic approaches are discussed, and key figures of merit are presented. Later, the lecture will highlight the Bernhard group’s 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. Finally, the lecture will end by highlighting the Bernhard group’s 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.

Solar fuels: Thermodynamics, candidates, tactics, and figures of merit

249th National Meeting (2015)

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