Redox flow battery design for enhanced reactant distribution

Abstract

As the world is forced to move away from fossil fuels, it is becoming increasingly apparent that the pathway to a sustainable future is to avail of renewable energy sources. Improved energy storage technologies are thus required to harness these sources, due to their intermittent and unpredictable nature. One of the leading technologies for large-scale, long-duration energy storage is the redox flow battery, which demonstrates high customisability and a long working life. However, limiting factors preventing the wider utilisation of flow batteries include their low energy and power densities. These factors can be improved by changing cell design to enhance mass transport and reduce concentration losses during charging and discharging. Research has suggested that this can be achieved by moving away from the traditional “filter press” design, detailed by NASA in the 1980s, moving instead towards alternative cell topologies. In this thesis, the impact of cell design on reactant distribution is thoroughly examined using a combination of experimental evaluation and coupled electrochemical/computational fluid dynamics modelling.  Fused-deposition-modelling 3D-printing has been used to develop a platform facilitating the production of fully customisable laboratory-scale flow cells. Printing parameters have been refined, reducing void formation, and resulting in more robust test cells. To obtain statistically significant data from experiments that compare cell geometries, refinements to existing flow battery testing protocols have been made. Key shortcomings in these protocols have been identified yielding recommendations that detail the importance of replicate testing, the calibration of fluidics, and the proper processing and handling of electrode and membrane materials. The development of a 3D full-cell transient model is detailed and improved parameters have been implemented. The model has been validated against experimental results and subsequently used to evaluate several cell designs through simulation of charge-discharge cycling and polarisation curve analysis. The efficacy of different performance metrics found in literature are discussed along with modelling limitations and proposed future developments. The approaches developed in this thesis provide potential improvements to the processes of flow battery cell design, manufacture, testing and simulation.

Thesis is embargoed until 31 July 2025.