Electrochemical performance and mass transfer properties of dual electrode assemblies for aqueous vanadium redox flow batteries

Recognizing the urgent need of further cost reduction to drive wider adoption of redox flow batteries, it is critical to improve the reactor performance, which has been regarded as a key approach to reduce the high capital cost. Porous electrodes with properly designed structure and optimized physiochemical properties offer pathways for reduced voltage losses, including kinetic and concentration overpotentials. Recently, carbon cloth electrodes have been explored in flow battery applications owing to their bimodal pore size distributions. Although the unique woven structure of cloth provides flexibilities in electrode designs, it is still a barrier to strike a trade-off between the electrolyte penetration pathways and abundant active surface area. This study investigates a dual-layer electrode design combining carbon cloth and carbon paper to achieve high performance in a flow-through vanadium redox flow battery. The carbon cloth, placed adjacent to the flow plate, acts as an electrolyte distributor, while the carbon paper sub-layer near the membrane provides dense reactive sites. Electrochemical testing in a symmetric cell setup using both V 2+ /V 3+ and VO 2+ /VO 2 + redox couples was conducted to isolate polarization losses. Additionally, 3D-reconstructed electrode structures were analyzed using the Lattice Boltzmann Method to reveal electrolyte flow distribution and velocity profiles. The dual-layer strategy demonstrated improved electrochemical performance, lower mass transfer resistance, reduced pressure drop, and enhanced membrane durability. It can be regarded as a promising approach for high system efficiency while maintaining cycling stability in a flow-through configuration. • A dual-layer electrode assembly combines carbon cloth and carbon paper. • Quantitative analysis of electrochemical polarizations is performed using vanadium symmetrical cells. • Local electrolyte velocity profiles in dual-layer electrodes are simulated through Lattice-Boltzmann method. • 3D electrode morphology and fiber orientations are mapped using X-ray computed tomography and structure tensors. • The impact of electrode imprints on membrane morphology is investigated.