Reducing the cost of redox flow batteries (RFBs) is critical to achieving broad commercial deployment of largescale energy storage systems. This can be addressed in a variety of ways, such as reducing component costs or
improving electrode design. The aim of this work is to better understand the relationship between electrode
microstructure and performance. Four different commercially available carbon electrodes were examined – two
cloths and two papers (from AvCarb® and Freudenberg Performance Materials) – and a comprehensive study of
the different pore-scale and mass-transport processes is presented to elucidate their effect on the overall cell
performance. Electrochemical measurements were carried out in a non-aqueous organic flow-through RFB with
these different electrodes, using two supporting solvents (propylene carbonate and acetonitrile) and at a variety
of flow rates. Electrode samples were scanned using X-ray computed tomography, and a customised segmentation technique was employed to extract several microstructural parameters. A pore network model was used to
calculate the pressure drops and permeabilities, which were found to be within 1.26 × 10− 11 and 1.65 × 10− 11
m2 for the papers and between 8.61 × 10− 11 and 10.6 × 10− 11 m2 for the cloths. A one-dimensional model was
developed and fit to polarisation measurements to obtain mass-transfer coefficients, km, which were found to be
between 1.01 × 10− 6 and 5.97 × 10− 4 m s
− 1 with a subsequent discussion on Reynolds and Sherwood number
correlations. This work suggests that, for these fibrous materials, permeability correlates best with electrochemical cell performance. Consequently, the carbon cloths with the highest permeability and highest masstransfer coefficients, displayed better performances.