Redox-mediation, or redox-targeting, is an emerging approach for electrochemical energy storage and conversion, offering a pathway to decouple the electrochemical flow cell from the redox reaction of interest. In this technology concept, soluble redox-active mediators are employed to shuttle charge between the electrodes of electrochemical flow cells and “off-electrode” active materials residing within external vessels. Proof-of-principle demonstrations in literature suggest that this configuration can increase the energy density of flow batteries, accelerate the transformation of electrochemically-sluggish reactions, and unlock new modes of operation for electroprocesses. However, the intricate coupling of the electrochemical and thermochemical reactors involving multiple active species limits our understanding of the underlying system dynamics, hindering assessment of technical and economic potential of proposed redox-mediated devices. To address this challenge, we have developed a qualitatively-validated model framework to aid in predicting the behavior of redox-mediated systems. This approach incorporates physics-based constitutive equations and mixed potential theory to describe the transient mass and charge dynamics in the flow cell and tank, for both the dissolved mediators and off-electrode materials of interest.
In this presentation, we will focus on how these models offer insights into the performance of redox-mediated flow batteries (RMFBs) that incorporate solid active materials, highlighting new design and operation strategies. Through dimensional analysis and broad parametric sweeps, we identified a critical dimensionless scaling relationship that connects RMFB capacity utilization to physical and operating variables. Orthogonally, we have explored the impact material properties and design choices (e.g., particle size, porosity, and packing) have on overall system power and efficiency. Together, these analyses provide guidance into holistically integrating solid active materials, reactor architectures, and operational strategies to balance energy and power tradeoffs for RMFBs.
