Diffusive Charge Transport in High-Valency Redox-Active Polymer Solutions*

Redox-active polymers (RAPs) are a promising material for redox-flow batteries which are durable, scalable, and can quickly charge and discharge. However, redox material crossover can diminish capacity and lifetime of redox flow batteries. A strategy to mitigate this crossover uses porous membranes to separate RAP-based anolytes and catholytes by size exclusion. The performance of these batteries is related to charge transport mechanisms in these RAP solutions leading to an interest in understanding its fundamental physics.

Building on previous simulation and theory of charge transport mechanisms in monovalent RAPs with implicit salt, we now extend our model to consider higher valency RAP solutions. We use a coarse-grained approach where we combine Brownian dynamics simulations with a kinetic Monte Carlo update step to capture charge hopping behavior. We perform simulations for single- and multi-chain systems, varying the intra- and inter-chain charge hopping rates to study the interplay between self-exchange rates and salt concentration on the mechanisms of diffusive charge transport in these higher valency RAPs. Using this model, we can understand how polymer conformations impact charge transport in high valency redox active polymers to design RAPs on a molecular level to improve performance and durability of redox flow batteries.