Simple descriptors for proton-conducting perovskites from density functional theory

A series of (pseudo) cubic perovskites, ABO(3), have been investigated using density functional theory calculations. The structures have been optimized and thermodynamic properties and activation energies for the relevant steps of the hydrogen/proton diffusion mechanism have been calculated using the nudged elastic band path technique. We find a strong correlation between the O-H binding energy for hydrogen/proton uptake in perovskites and the energy barriers involved in the observed Grotthuss-type diffusion process. We demonstrate the possibility of estimating diffusion rates based on O-H binding energy and temperature only, without determining transition states and vibrational frequencies. We determine the binding energy providing the optimal tradeoff between occupation and diffusion rate at a given temperature, and finally we show how these correlations can be used to suggest candidate materials with improved kinetic properties for potential application as hydrogen permeable membranes and proton-conducting electrolytes.