Exploring the Structure-Function-Performance Relationship of Carbon Electrodes Toward Rational Design of High-Performance Redox Flow Cells

Abstract

Redox flow batteries (RFBs) are a promising grid-scale energy storage technology for the integration of intermittent renewable sources, such as wind and solar, into the electrical grid due to their modularity, flexible design, and cost-effectiveness in long-duration storage [1]. Unlike traditional batteries, for RFBs, electrolytes are stored in external tanks and are circulated through the flow cell. In the flow cell, electrical energy is stored via the electrochemical reactions of the redox active species dissolved in liquid electrolytes. While this new archetype provides unique benefits, the flow-assisted nature of RFBs presents many challenging issues, including but not limited to significant transport losses due to the poor electrode and cell design, and the related low power density [2-3]. It can be hypothesized that many of these challenges are primarily related to the concept of electrolyte utilization [4]. In this regard, porous electrode is the key component, which is responsible for multiple critical functions including delivery of liquid electrolytes as well as facilitating ion/charge transfer and providing sites for electrochemical reactions [4]. Despite its importance, the required fundamental knowledge on how to systematically design effective electrodes specifically tailored for RFB applications has not received much attention [5].In this talk, the recent efforts on establishing the structure-function-performance linkages for commercially available carbon electrodes will be presented. The results of the experiments utilizing an electrochemical protocol that combines symmetric flow cell cycling with electrochemical impedance spectroscopy (EIS) and polarization curve (PC) measurements will be discussed. The impedance data is fitted into a mathematical model, and key physicochemical properties of carbon electrodes and the correlated performance losses are quantified. Additionally, we will share our perspective on manufacturing high-performance carbon electrodes using a high-throughput screening platform.