Chemistry Department Seminar

Solid oxide fuel cells (SOFCs) are an energy user's dream: an efficient, combustion-less, virtually pollution-free power source, and promising enough for both stationary and mobile applications. Identifying the best electrolyte material is imperative for the development of next generation SOFCs. Doped ceria is recognized as one of the most promising solid electrolyte materials for the operation of SOFCs in the intermediate temperature range. We have developed an innovative simulation approach comprising a blend of first-principles calculations and kinetic lattice Monte Carlo (KLMC) modeling to predict the optimal composition of doped ceria that exhibits maximum ionic conductivity, a critical aspect involved in designing the finest electrolyte materials. The KLMC model uses the database of activation energies for defect migration in ceria and aliovalently doped ceria calculated within the framework of density functional theory (DFT+U). Results pertaining to the activated vacancy mechanism, favorable oxygen vacancy formation sites and preferred vacancy migration pathways in these materials will be elaborated. Since the first-principles calculations revealed significant vacancy-vacancy repulsion, we have conducted KLMC simulations with and without a repulsive interaction between the charged species. Details of KLMC model will be elucidated and the rationale behind the calculated maximum in ionic conductivity as a function of dopant concentration using two separate models will be discussed. Overall, due to its fundamental nature and reasonable agreement with experiment, this model demonstrates the possibility that it can be used as a design tool to predict novel ceria based electrolyte materials. Briefly, results of first-principles based electronic structure calculations depicting the interaction of hydrogen and water with (0001) surface of americium will be presented.