(709a) Multicomponent Transport Models for Non-Electroneutral Solid Electrolytes

The most popular multicomponent transport models used by chemical engineers are based in the theory of ‘irreversible thermodynamics’, which combines the theory of equilibrium with continuum dynamics to produce an entropy balance equation that guides the formulation of transport constitutive laws. Our group has put significant effort into the development of consistent transport theories to describe concentrated electrolytes of various types, including ionically conductive liquids, ionomer membranes, and even solid ion conductors like glasses or ceramics. In the past we have extended multicomponent transport theory to account for excluded-volume effects, which arise from the thermodynamics of material volume, and have developed transport constitutive laws applicable to domains containing space charges.

When modeling materials in which mass or charge transfer occurs in more than one spatial dimension, the addition of a local thermodynamic state equation for volume makes standard multicomponent models based on Onsager–Stefan–Maxwell theory underspecified. To achieve closure it is necessary to introduce a momentum balance alongside the other transport governing equations. This raises a number of fundamental physical questions about how to handle the potential interactions between mechanical and electrochemical transport.

This talk will address the formulation of multicomponent, multiphysics transport models applicable to ion-conductive solids in which simultaneous mass, heat, charge, and momentum transfer occurs. We will touch on a number of thermodynamic measurements that may be needed to characterize elastic solid electrolytes for accurate modeling, as well as describing how the laws governing diffusion can be modified to include the effects of stress and strain. A number of practical examples will be discussed to illustrate the signatures of electrochemical/mechanical coupling. We will show that the high-frequency impedance of ionically conductive materials is controlled in part by mechanical forces, and discuss the Gibbs–Donnan effect, in which charge separation leads to a pressure gradient that can drive flow.