Understanding the Mechanisms of Proton Transport in Hydrogen Bonded Media from First-Principle Molecular Dynamics

Proton transport in aqueous and non-aqueous hydrogen-bonded media has long been an area of intense study due to its fundamental importance in emerging energy technologies such as hydrogen fuel cells and in biological problems such as proton pumping.  Our understanding of proton transport phenomena is based on the concept structural diffusion of a topological defect in the hydrogen bond network originally proposed by C. J. T. von Grotthuss in 1806.  Within this picture, long-range proton transport is driven by specific structural rearrangements in the local hydrogen bonding environment, however, pinning down the specific microscopic mechanisms in different media remains an immense challenge that has an immediate impact on the problem of designing novel materials for enhancing the proton transport process.  In this talk, I will show how first-principles molecular dynamics has contributed to our understanding of proton transport phenomena in a variety of systems including aqueous acidic and basic solutions, acid hydrate crystals, and phosphate based materials including pure phosphoric acid and its mixtures with heterocycles.  It will be shown that proton transport in aqueous systems relies largely on local fluctuations in the hydrogen bond network while phosphate systems, by contrast, transport protons along extended, polarized chains in a manner much closer to the original picture suggested by von Grotthuss.