The effect of felt compression on the performance and pressure drop of all-vanadium redox flow batteries

- The effect of carbon felt compression on electrochemical performance and pressure drop has been studied.
- X-ray computed tomography has been used to study the felt microstructures under compression.
- Increased compression leads to an increase in electrochemical performance for values of compression studied (0-75%).
- The fibre surface area to fibre volume ratio was seen to remain constant for the values of felt compression studied.

The compression of carbon felt electrodes for redox flow batteries leads to changes in the electrochemical performance and has a large effect on the pressure drop of electrolyte flow through the system. In this investigation, the authors have characterised the electrochemical performance of all-vanadium redox flow batteries by studying the effect of compression on the contact resistance, polarisation behaviour and efficiency. Contact resistance was seen to reduce from ca. 2.0 Ω cm2 to 1.2 Ω cm2 and an energy efficiency of 85% was obtained from a felt compressed to 75%. Moreover, X-ray computed tomography (CT) has been employed to study the microstructure of felt electrodes at compressions up to 70%, showing a linear decrease in porosity and a constant fibre surface area-to-volume ratio. The pressure drop was modelled using computational fluid dynamics and employing the 3D structure of the felts obtained from CT, revealing that a 60% increase in compression related to a 44.5% increase in pressure drop.