1/16 - Faculty Candidate Seminar (inorganic): Yogesh Surendranath, UC Berkeley
University of California, Berkeley
Host: Andrew Bocarsly
Controlling Holes for Efficient Solar-to-Fuels Conversion
The future renewable energy economy will demand new technologies for the storage of solar energy in the form of chemical fuels. This solar-to-fuels conversion may be realized by addressing two key challenges: (1) transducing sunlight into electrical energy and (2) storing it in the energy-dense chemical bonds of hydrogen and oxygen.
Nanocrystal-based photovoltaic cells have the potential to meet the first challenge but suffer from poor efficiencies relative to established silicon technologies. Efficiency gains are impeded, in part, by a lack of general methods for controllably doping the nanocrystal active layer. To address this need, we have developed a simple strategy for doping nanocrystal thin films via outer-sphere charge transfer to organometallic redox buffers. By modulating the Nernst potential of the redox buffer solution, the hole dopant concentration in a model lead selenide nanocrystal thin film can be incrementally and reversibly tuned with precision.
Electrochemical water splitting has the potential to meet the second challenge but the kinetically demanding oxygen evolution half-reaction (OER) imposes significant efficiency losses. We recently reported that electrolysis of aqueous buffered solutions of Co2+ leads to the in-situ formation of a highly active OER catalyst as an amorphous thin film on inert anodes. Detailed XAS, EPR, and electrochemical studies have revealed key aspects of the catalyst’s structure, valency, and mechanism of action at intermediate pH. Together, the data points to CoIII/CoIV mixed-valent cobaltate clusters that engage in a proton-coupled electron transfer preceding a chemical rate-limiting step for O2 evolution. These insights provide a rigorous framework for designing improved OER catalysts.