A Study of Anthraquinone Structural Changes for Aqueous Redox Flow Ballery Materials

Abstract

The transition away from fossil-fuel-based electricity production is critical for cutting the emissions of climate change causing carbon dioxide emissions. Renewable energy sources, including solar and wind energy, are now cost-competitive with fossil fuels. This has generated serious interest in energy storage technologies to help manage the intermittency of these energy sources. Redox flow batteries provide a promising technology for providing grid-scale energy storage. Chapter 1 describes the current state of renewable energy and energy storage in electricity generation. The design and current state of redox flow batteries are discussed. Chapter 2 details the synthesis and characterization of a new anthraquinone, 2,6-D2PEAQ. A novel method of installing branched side chains to improve the aqueous solubility of anthraquinones is presented. Cell studies demonstrating a daily capacity fade of .02%/day are described. Chapter 3 describes the properties of the anthraquinone BEAQ, which forms a gel in aqueous solutions rather than the high-concentration homogenous solutions seen from similarly structured anthraquinones. The characterization of the gel is described. A potential application in gel batteries is presented. Chapter 4 uses a simpler single branched-chain substituted anthraquinone (2-2PEAQ) to study the decomposition and potential regeneration of highly-soluble anthraquinones. The synthesis and characterization of 2-2PEAQ are discussed and cell testing to give a fade rate of .05%/day is presented. The capacity fade was decreased to .01%/day through the use of electrochemical regeneration strategies in the cell. Finally, the effect of the substitution position of an ether-linked side chain on the anthraquinone is explored by comparing the performance of 2-2PEAQ to the isomer 1-2PEAQ in cell testing and through post-cycling analysis Chapter 5 describes chemical characterization studies of four commercial anthraquinones, including cyclic voltammetry, thermal decomposition, and solubility measurements. The limitations that would need to be overcome to make these anthraquinones good candidates for further study are described.