EFRI-RESTOR: Thermochemical Routes to Efficient and Rapid Production of Solar Fuels

The objective of this project is to transform and expand the nation's renewable energy storage capacity using a thermochemical approach for converting the energy of photons into chemical bonds. The approach relies on the capacity of selected nonstoichiometric metal oxides, specifically cerium oxide (ceria), to store and release oxygen in response to changes in temperature, where the thermal cycling is induced by exposure to solar radiation. The resulting stoichiometry changes can be directly utilized for fuel production when coupled with the introduction of appropriate reactant gases. Such fuel, in turn, can be used for electricity generation on demand, employing either conventional combustion or fuel cells. The PIs will build on recent breakthroughs in the understanding of thermochemical cycling behavior of nonstoichiometric oxides and expand the effort so as to (a) attain targeted thermodynamic and kinetic characteristics and (b) demonstrate technical feasibility in a prototype reactor, designed and optimized on the basis of validated models and measured material properties. Critical to the materials success is enhancing reaction kinetics and tuning the thermodynamics of the redox reactions so as to enable operation at temperatures compatible with reactor construction materials and solar concentrating optics under atmospheres conducive to high heat recovery. Both objectives will be pursued through the introduction of transition metal dopants and other substitutional cations into the host oxide, modifications which can further enhance solar absorptance. Beyond the manipulation of the fundamental materials properties, porous materials with engineered architectures will be employed to enhance thermochemical cycling characteristics, by, for example, providing high surface area for rapid reaction kinetics, ensuring minimal resistance to gas flow, and providing tunable solar absorption properties. A hierarchy of thermal and solar-thermal reactor models with increasing complexity will be employed to achieve the transition from benchtop experiments to a working prototype operated under concentrated solar radiation. A thermochemical approach to solar energy storage has the potential for large-scale implementation and hence broad impact because the method employs relatively earth-abundant materials, and the efficiency can be extremely high. Beyond the advancement of a technically feasible approach, the proposal provides a multi-disciplinary and international environment for the education and training of the next generation of energy scientists and technologists.

The FY 2010 EFRI-RESTOR Topic that supports this project was sponsored by the US National Science Foundation (NSF) Directorates for Engineering (ENG), Mathematical and Physical Sciences (MPS) and Social, Behavioral and Economic Sciences (SBE), and Computer & Information Science and Engineering in collaboration with the US Department of Energy (DOE).