Thermochemistry of Redox Active Oxides and its Relevance to Solar Fuel Production
Friday, September 13, 2019 at 3:00pm to 4:00pm
Laboratories around the world are pursuing a variety of promising strategies for converting solar energy into a reliable energy source for on-demand utilization. We describe here a thermochemical approach for achieving this goal using concentrated solar heat as the energy source and redox active non-stoichiometric oxides as the reaction medium. Specifically, upon exposure to high temperatures and/or inert gas, the oxide undergoes reduction (without change in crystalline phase) to release oxygen. Upon exposure to H2O (or CO2), the oxide is reoxidized, releasing H2 (or CO). We compare the thermochemical fuel production behavior of a variety of oxides, including those of the fluorite structure-type (ceria and its derivatives) and those of the perovskite structure-type (La1-xSrxMnO3). A shared characteristic of the most promising materials is that bulk oxygen diffusion (chemical diffusion) is fast such that fuel production rates are limited either by surface reaction kinetics or, at high temperatures, gas flow rates due to attainment of quasi-equilibrium. We develop an analytical model to treat the behavior under gas-phase limited behavior and explore the implications on macroscopic fuel production rates.
Sossina M. Haile
Walter P. Murphy Professor of Materials Science and Engineering;
Professor of Applied Physics; Affiliated Professor of Chemistry