Optical and Electrochemical Characterization of Aqueous Organic Redox Flow Batteries

Abstract

As our world transitions to renewable energy generation, a host of technical challenges remain unaddressed to economically integrate these intermittent sources into our electricity grids. Aqueous organic redox flow batteries (AORFB) presented a promisingly inexpensive electrochemical energy storage solution to this end. However, many challenges remain in advancing this nascent technology, particularly pertaining to the interactions between dissolved organic species themselves, and interfaces with various electrochemical reactor elements. In this thesis, I demonstrate how optical techniques, including absorption spectroscopy and fluorescence microscopy, and electrochemical methods can be used to illuminate the intertwining physics of AORFBs. Chapter 1 serves as a historical introduction to the AORFB topic. In Chapters 2 and 3, I describe how in-line UV-Vis spectrophotometry can be used to actively observe electrolyte imbalances and active species interactions; this insight then leads to opportunities for electrolyte engineering and enhanced voltage characterization, enabling extended AORFB performance and performance predictions respectively. In Chapter 4, I use a suite of electrochemical, physical, and chemical characterization techniques to evaluate a variety of woven carbon cloth electrodes, which stand as promising dual-length scale reactors for electrochemical systems. In Chapters 5 and 6, I develop a fluorescence microscopy technique as a direct method for observing the reaction-advection-diffusion properties of AORFB electrolytes in porous electrodes. This technique is used for both idealized electrode geometries that are coupled with computational multiphysics simulations, and high performance commercial materials. The culmination of this thesis will present unique insights into and propose future opportunities for AORFBs that could enable this technology to flourish in a renewable grid.