High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Batteries

Abstract

Aqueous organic redox flow batteries (AORFBs) have emerged as potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources. With the goal of cost-effective, safe, and scalable stationary long duration energy storage systems, AORFBs could eclipse Li-ion batteries due to their inherent non-flammability, lack of materials scarcity fluctuations, and intrinsic decoupling of energy and power capacities. In this thesis, I describe the development and use of a high-throughput setup for experimental electrochemical cycling of flow batteries. Consistent with battery modelling predictions, we observe that redox-active organic molecules that demonstrate decay mechanisms with reaction orders larger than one can display temporal capacity fade rates that depend on the employed battery cycling protocol. Elevated temperature battery cycling is used to demonstrate Arrhenius-like behaviour in the temporal capacity fade rates of multiple AORFB electrolytes, permitting extrapolation to lower operating temperatures. Assessment of the suitability of ferri-/ferrocyanide as an electroactive species for long-term utilization in AORFBs reveals how apparent capacity fade rates can be engineered by the initial system setup. Finally, an open source software package is developed to simulate the effects of chemical degradation mechanisms and electrochemical cycling protocols on the evolution of cell capacity in a cycled flow battery. By accelerating the screening process of candidate molecules for AORFBs and ensuring rigorous assessment of battery performance, the techniques described in this thesis are expected to more rapidly advance good candidates for long lifetime RFB designs, capable of enabling massive penetration of intermittent renewable energy.