Zachary Gossage1 Noah Schorr1 E. Montoto1 Arneet Rajput1 Michael Counihan1 Joaquin Rodriguez-Lopez1

1, University of Illinois at Urbana Champaign, Urbana, Illinois, United States

Highly-soluble redox-active polymers (RAPs) and colloids (RACs) [1] are a new class of materials in the form of fluid dispersions that support a new concept in size-exclusion flow batteries. Because RAPs and RACs rely on intra-particle charge transfer to yield quantitative charge accessibility and high rate, understanding the intrinsic properties of these particles, as opposed to them in the bulk fluids, is of great interest to understand their limitations and to identify design opportunities. In this talk, I will present on the of RAPs and RACs through a spectrum of powerful electrochemical techniques, ranging from spectroelectrochemical approaches to single-particle analysis.

In a first application, I will describe how nano-resolved scanning electrochemical microscopy (SECM) and its combination with Raman spectroscopy has helped us understand the mechanisms of individual electrochemical entities.[2] These experiments provide us with unprecedented versatility to identify kinetic bottlenecks, such as charge trapping, and to determine the maximum current densities attainable in flow devices. Our data indicate that RACs undergo some conditioning upon electrolysis, and that their charge transport is sensitive to state-of-charge (SoC).

In a second application, I will describe how new redox mediation electrocatalysis using each redox-active pendant in RAPs as an electron transfer agent can be exploited to solve pervasive problems with passivating interfaces in complex chemistries, such as those involved in Li-air batteries. Here, investigations of charge transfer and of transient titration of reaction intermediates using SECM is paving the way to understanding how to leverage the properties of polymers to solve rate-limiting interfacial processes.

The insightful use of analytical approaches allows us to understand charge transfer, and the conditions that lead to effective storage or to failure. We expect that our methods will be extendable to other energy storage systems of interest to the community.

[1] Burgess, M.; Moore, J.S.; Rodríguez-López, J. Redox Active Polymers as Soluble Nanomaterials for Energy Storage. Acc. Chem. Res. 2016, 49, 2649-2657.
[2] Gossage, Z.T.; Hernandez-Burgos, K.; Moore, J.S.; Rodríguez-López, J. Impact of Charge Transport Dynamics and Conditioning on Cycling Efficiency within Single Redox-Active Colloids. ChemElectroChem, 2018, 5, 3006-3013.