Author: ["Linas Vilčiauskas","Mark E. Tuckerman","Gabriel Bester","Stephen J. Paddison","Klaus-Dieter Kreuer"]
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Abstract
Neat liquid phosphoric acid (H3PO4) has the highest intrinsic proton conductivity of any known substance and is a useful model for understanding proton transport in other phosphate-based systems in biology and clean energy technologies. Here, we present an ab initio molecular dynamics study that reveals, for the first time, the microscopic mechanism of this high proton conductivity. Anomalously fast proton transport in hydrogen-bonded systems involves a structural diffusion mechanism in which intramolecular proton transfer is driven by specific hydrogen bond rearrangements in the surrounding environment. Aqueous media transport excess charge defects through local hydrogen bond rearrangements that drive individual proton transfer reactions. In contrast, strong, polarizable hydrogen bonds in phosphoric acid produce coupled proton motion and a pronounced protic dielectric response of the medium, leading to the formation of extended, polarized hydrogen-bonded chains. The interplay between these chains and a frustrated hydrogen-bond network gives rise to the high proton conductivity. Proton transport in phosphate-based systems is important in biology and clean energy technologies, and phosphoric acid, being the best known intrinsic proton conductor, represents an important model. Ab initio molecular dynamics simulations now reveal that the interplay between extended, polarized, hydrogen-bonded chains and a frustrated hydrogen-bond network gives rise to the high conductivity in liquid phosphoric acid. Cite this article
Vilčiauskas, L., Tuckerman, M., Bester, G. et al. The mechanism of proton conduction in phosphoric acid. Nature Chem 4, 461–466 (2012). https://doi.org/10.1038/nchem.1329 