Hydrogen Dynamics in Superprotonic CsHSO4

TL;DR

This study uses first-principles molecular dynamics to analyze proton transport mechanisms in CsHSO4, revealing the roles of Grotthus mechanism, hydrogen-bond network reorganization, and SO4 tetrahedra dynamics in proton diffusion.

Contribution

It provides a detailed first-principles analysis of proton dynamics in CsHSO4, highlighting the interplay of chemical bonds, hydrogen bonds, and tetrahedral reorientations in proton conduction.

Findings

Grotthus mechanism dominates proton transport

Hydrogen-bond network reorganizes via angular hops

SO4 tetrahedra dynamics influence diffusion pathways

Abstract

We present a detailed study of proton dynamics in the hydrogen-bonded superprotonic conductor CsHSO4 from first-principles molecular dynamics simulations, isolating the subtle interplay between the dynamics of the O--H chemical bonds, the O...H hydrogen bonds, and the SO4 tetrahedra in promoting proton diffusion. We find that the Grotthus mechanism of proton transport is primarily responsible for the dynamics of the chemical bonds, whereas the reorganization of the hydrogen-bond network is dominated by rapid angular hops in concert with small reorientations of the SO4 tetrahedra. Frequent proton jumping across the O--H...O complex is countered by a high rate of jump reversal, which we show is connected to the dynamics of the SO4 tetrahedra, resulting in a diminished CsHSO4/CsDSO4 isotope effect. We also find evidence of multiple timescales for SO4 reorientation events, leading to distinct diffusion mechanisms along the different crystal lattice directions. Finally, we employ graph-theoretic techniques to characterize the topology of the hydrogen-bond network and demonstrate a clear relationship between certain connectivity configurations and the likelihood for diffusive jump events.