Molecular aspects of the Eu³⁺/Eu²⁺ redox reaction at the interface between a molten salt and a metallic electrode

Abstract

We perform molecular dynamics simulations of a system consisting of Eu³⁺ and Eu²⁺ species dissolved in a high-temperature KCl electrolyte between two metallic electrodes. The interaction potential includes ion polarisation effects, and a constant electric potential is maintained within the electrodes by allowing the atomic charges to fluctuate in response to the environment. This setup allows us to study the electrochemical Eu³⁺/Eu²⁺ reaction in the framework of Marcus theory. Numerous studies have pointed to the highly structured nature of ionic liquids and molten salts close to solid surfaces which is not accounted for in the conventional mean-field description of this interface that underpins the theories of electrochemical reaction rates. Here we examine the influence on the kinetics of the charge-transfer event of the electrical potential across the electrode–electrolyte interface and on the effect of the presence of charged surface on the coordination structure and energetics of the ions in the region important for the charge-transfer event.

Keywords:

• molecular dynamics
• Marcus theory
• electron transfer
• molten salt
• pyroprocessing

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1 The parameters governing the europium interactions were set equal to the equivalent terbium parameters in [9]. The differences between the parameter sets used for different materials are related to the crystallographic radius of the cation. Octahedrally coordinated Tb³⁺ and Eu³⁺ have very similar radii (106.3 and 108.7 pm, respectively).