Development of Organic Molecules for Aqueous Redox Flow Battery

Abstract

The cost of renewable energy sources such as solar and wind has dropped significantly such that the main barrier for a wider adoption is intermittency. The unsynchronized power supply from renewables and the power demand from human activity limit the reliance on renewables. Energy storage is the key enabler in accelerating the integration of renewables. Aqueous organic redox flow battery (AORFB) offers a potential cost-effective solution to the energy storage. AORFB works by storing liquid electrolyte outside out the electrochemical conversion stack, decoupling battery power and capacity. Redox-active organic molecules are used as electrolyte in the battery. Properties of organic molecules such as solubility, reduction potential, and stability are tunable through structural modification. Chapter 2 examines the optical properties of anthraquinone-disulfonic acid (AQDS) flow battery system, and correlates its molecular complexation with electrochemical performance. UV-Vis spectroscopy is demonstrated as a powerful tool to study the quinone chemistry in redox flow battery systems. By incorporating AQDS complexation, a more accurate modelling of battery voltage is achieved. In addition, the mechanistic investigation of the degradation of anthraquinone-based flow battery is presented by using 2,6-dihydroxyanthraquinone (DHAQ) in alkaline solution as a model system. Through high-resolution LC-MS, NMR, and synthesis validation, the DHAQ degradation mechanism and the proposed remedy are discussed. This chapter demonstrates that how anthraquinones degrade in alkaline solution during electrochemical cycling, and paves the path for the rational design of next generation redox-active organic molecules. Chapter 3 introduces 2,5-dihydroxybenzoquinone (DHBQ) as a new candidate negolyte molecule for alkaline redox flow battery. The stability, kinetics, cycling performance, and capacity retention are all characterized. Various synthetic strategies to improve the stability of DHBQ are also discussed. The structural modification demonstrates that organic molecules can be tuned with different functional groups to improve the battery performance. Chapter 4 explores the idea of using a fused quinone as both the posolyte and negolyte material. The electrochemical behavior of fused quinones will be presented and the degradation mechanism will be discussed. Adsorbed and solid batteries with fused quinone are demonstrated. Chapter 5 presents the synthesis of volatile, thermally stable, and reactive coinage metal 5,5-bicyclic amidinates for chemical vapor deposition (CVD). X-ray structures of the gold, silver and copper amidinates will be presented together with thermalgravimetric analysis. Metallic films with low to none carbon content are obtained through CVD of the silver and gold amidinates. This chapter demonstrates the development of these CVD precursors and offers the opportunity for synthesizing other stable metal precursors which are previously inaccessible with other ligands.