Calculating the Proton Transport and Dielectric Properties of Phosphates and Related Materials

Phosphate based systems are cosidered to be promising electrolyte materials for use in fuel cells.  It is know, for example, that liquid phosphoric acid has the highest known intrinsic proton conductivity of any substance.   However, little is known about the microscopic mechanisms of proton conduction is phosphate based systems or about their dielectric properties.  In this talk, I will discuss efforts we have made to elucidate these properties in pure phosphoric acid, phosphoric acid with imidazole (as a model for the types of stabilizers often used in phosphoric acid fuel cells) and in related phosphonic anc phosphinic acid systems for comparison.  The approaches used mostly rely on first-principles molecular dynamics calculations, which are able to treat the bond-breaking and forming events associated with proton transport, however, I will also discuss the performance of several force fields applied to these systems, which also allow us to test finite-size effects (system sizes are, by necessity, small in first-principles molecular dynamics calculations) and effecdts of simulation length (simulation lengths are also, by necessity, short in first-principles molecular dynamics)..   As will be discusssed in the talk, by examining diffusion, kinetics, microscopic mechanisms, and dipole distributions, we have garnered considerable new insights into these ccomplex systems.