Exploring the Role of Inert Conductive Area on Redox-Mediated Processes
Authors: Matteucci Nicholas J. , Mallia Christopher T. , Brushett Fikile R. 
Published: December 2024

To effectively utilize renewable energy resources, extensive exploration and investment has been directed towards advancing electrochemical technologies that enable reliable power delivery, vehicle electrification, and decarbonization of chemical manufacturing. Redox-mediated systems offer a pathway to decouple the electrochemical reactor from the conversion of an “off-electrode” material by introducing an activated mediator, potentially unlocking new processes opportunities.1 Recent literature highlights how this approach may increase capacity in redox flow batteries,2 facilitate difficult-to-perform electrochemical transformations,3 and allow spatial and temporal flexibility in electrochemical operations.4 However, numerous open questions still surround this concept, including how to predict the rates of the “off-electrode” reactions and how to tune design parameters to control and enhance these reactions. In earlier work, we showed mixed-potential theory could be used to understand performance trends observed in experimental studies of redox-mediated flow batteries.5 Intriguingly, the predicted reaction dynamics appear sensitive to the electronic conductivity of both the solid active materials and of the materials in direct contact with those charge-storage materials. Given the ubiquity of carbon-coated solid active materials found in redox-mediated flow batteries (e.g., lithium-ion intercalation materials2,6), interest in the use of redox-mediators to enhance metal-air batteries,7 and the overarching need to further elucidate design principles for redox-mediated electrochemical systems, understanding how conductive materials alter “off-electrode” processes is of interest.

Here, through experiment and modeling, we explore how the incorporation of additional conductive but chemically inert surface area influences redox-mediated reactions between solid active materials and dissolved redox mediators. We pair electrochemical diagnostics with pre- and post-test materials characterization to assess the impact electron-conducting, inert surfaces in contact with the solid active material have on mediated reaction dynamics, extents, and distributions. In parallel, we develop a theoretical framework to aid in the interpretation of specific results and to generalize findings. Ultimately, these activities expand our knowledge of the role that solid-phase conductivity and conductive additives play in redox-mediated processes for energy storage and conversion.

Acknowledgements

N.J.M gratefully acknowledges the NSF Graduate Research Fellowship Program under Grant Number 2141064. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF.

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