Method development for the analysis of electrochemical and transport processes in redox flow batteries at practical operating conditions

Abstract

The focus of this thesis is the development and assessment of techniques for the analysis of electrochemical and transport processes in redox flow batteries (RFBs) at moderate to high active species concentrations under direct current conditions. RFBs hold promise as an energy-intensive storage technology suitable for supporting the integration of intermittent renewable energy sources into the grid, but further improvements in technical performance and reductions in system cost are needed for broad deployment. At their core, all thesis projects are aimed at enabling the development of system descriptors that correlate material properties (e.g., viscosity, conductivity), cell geometry (e.g., flow field design), and operating parameters (e.g., flow rate, current density) to system performance metrics, such as cycle efficiencies and area-specific resistance.

More specifically, the investigation is divided into three primary projects: the development and assessment of a research-scale flow cell; measurements of mass-transfer coefficients; and integration of a polarization model into a standalone application useful for assessing system performance. The differential flow cell is engineered leveraging validation material from industrial collaborators. Not only is the performance is consistent with that of a ten-fold larger cell, but its smaller modular design enables rapid assessment of new chemistries and cell components with minimal materials requirements. Mass-transfer coefficients are then measured using this cell with a well-behaved redox active electrolyte (RAE), in which glucose is added in various amounts to modify the system viscosity with minimal changes to other properties.

The results or methodology developed could be extended other similar RAE systems either as preliminary estimates of mass-transfer performance or as a protocol for carefully evaluating the impact of new system parameters on mass-transfer. Finally, results of this mass-transfer analysis are incorporated into a simple flexible stack model, which can be used to estimate system performance as a function of key materials properties with limited empiricism.