Hydrogen transport in superionic system Rb3H(SeO4)2: a revised cooperative migration mechanism

TL;DR

This study uses density functional theory to revise the understanding of hydrogen transport in Rb3H(SeO4)2, highlighting the importance of lattice dynamics and oxygen displacements in enabling low-energy proton conduction.

Contribution

It introduces a revised cooperative migration mechanism emphasizing lattice oxygen displacements, contrasting with the traditional Grotthuss model.

Findings

Lattice dynamics are crucial for proton migration.

Oxygen displacements facilitate low activation energy.

Proton transport involves interactions with XO4 groups.

Abstract

We performed density functional studies of electronic properties and mechanisms of hydrogen transport in Rb3H(SeO4)2 crystal which represents technologically promising class M3H(XO4)2 of proton conductors (M=Rb,Cs, NH4; X=S,Se). The electronic structure calculations show a decisive role of lattice dynamics in the process of proton migration. In the obtained revised mechanism of proton transport, the strong displacements of the vertex oxygens play a key role in the establishing the continuous hydrogen transport and in the achieving low activation energies of proton conduction which is in contrast to the standard two-stage Grotthuss mechanism of proton transport. Consequently, any realistic model description of proton transport should inevitably involve the interactions with the sublattice of the XO4 groups.