Morphological Properties and Electrochemical Performance for Compressed Carbon-fiber Electrodes in Redox Flow Batteries

Abstract

Improving reactor performance of redox flow batteries is critical to reduce capital cost, and one of the main contributions to the internal resistance is generated by the electrodes, which also impact the pressure drop of the stack. Porous electrodes with optimized microstructure and physiochemical properties play a key role in enhancing electrochemical and fluid dynamic performance. Electrode compression significantly impacts morphology and battery behavior, but the relationship between microstructure and performance remains unclear. In the present study, three representative, commercially available, carbon-fiber electrodes (i.e., paper, felt, and cloth) with distinct microstructures were investigated, and a comprehensive study was conducted to compare morphology, hydraulic permeability, mechanical behavior, electrochemical performance in a lab-scale vanadium redox flow battery at compression ratios of 0-50%. The 3D electrode morphology was characterized through X-ray computed tomography and the extracted microstructure parameters (e.g., surface area and tortuosity) were compared with corresponding electrochemically determined parameters. The optimal trade-off between fluid dynamics and electrochemical performance occurred at the compression ratios of 30%, 20%, and 20% for the felt, paper, and cloth, respectively. Owing to the bi-modal porosity of the woven microstructure, the cloth showed a better trade-off between the electrochemical performance and pressure drop than the other electrodes.