(605b) Defect Structure for Proton Transport in a Triflic Acid Monohydrate Solid

Polymer electrolyte membranes (PEMs) of current fuel cell designs require substantial hydration for satisfactory proton conductivity, and thus impose penalties of low operating temperatures and stringent water management. A membrane exhibiting good proton conductivity with minimal amount of water, tightly bound to a stable host polymer, would be a technological breakthrough. Trifluoromethane sulfonic acid monohydrate solid is a suitable model system for investigation of proton transport in minimally hydrated sulfonic acid based PEMs. Ab-initio molecular dynamics calculations have identified a defect that suggests a specific proton transport mechanism: the formation of an H5O2+ ion and the reorganization of neighboring sulfonate groups to accommodate a proton, which shuttles between the oxygen atoms of these anionic sites. The energy of formation of this defect is about the same as the activation energy for proton transport in minimally hydrated Nafion®. These results are consistent with current theory and experiment on the chemical state of H+(aq) in bulk aqueous solutions, which are briefly reviewed.