Diffusive charge transport in high-valency redox-active polymer solutions

Redox-active polymers (RAPs) are a promising material for energy storage in flow batteries due their large size preventing detrimental redox material crossover and adjustable molecular chemistry and architecture for optimized performance. There has been a recent effort to understand the physics governing charge diffusion in RAPs and we have used simulations and theory to show how a variety of molecular charge transport mechanisms affect diffusive motion in higher valency RAP solutions with explicit salt by employing a full Coulombic potential. Our coarse-grained model of RAP solutions employs Brownian dynamics for polymer motion and a kinetic Monte Carlo update steps for the charge hopping dynamics. We perform these simulations for single chains and multi-chain systems where we show how a various transport mechanisms interplay, including the intra-polymer transport of charge via self-exchange and polymer segmental motions, as well as hopping due to inter-polymer collisions and translational diffusion of the chains. We also investigated the effect of salt on the radius of gyration and the effect of varying the intra and inter charge hopping rates representative of the Co, Fe, and Ru based RAPs of our experimental counter parts. Additionally, we included a surface in our model to investigate electrode-polymer charge transport.