Data for Electrochemical Performance and Mass Transfer Properties of Dual Electrode Assemblies for Aqueous Redox Flow Batteries

Recognizing the urgent need for further cost reduction to drive wider adoption of redox flow batteries, it is critical to improve the reactor performance, which is a key approach to reducing the stack size and the high capital cost. As one of the main contributors to reactor internal resistance, porous electrodes with properly designed structure and optimized physio-chemical 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, which opens a potential opportunity for improved mass transport behavior. The woven structure of cloth provides flexibility in the electrode designs through variation of the weave pattern, but finding a suitable trade-off between the electrolyte penetration pathways and abundant active surface area is still a challenge. In the present study, we investigate a dual-layer electrode configuration to simultaneously meet the requirements of high active surface area, low mass transfer resistance, and low-pressure drop. A carbon cloth was placed close to the flow plate to serve as an electrolyte distributor to ensure efficient mass transport in a lateral flow-through configuration, while a carbon paper sub-layer was placed near the membrane to provide a high density of reaction sites. Two types of carbon cloth with different weave patterns and fiber bundle dimensions were investigated in combination with the carbon paper. Electrochemical measurements were conducted in a symmetric vanadium flow battery setup to decouple the electrochemical losses and provide an in-depth understanding of the performance gain. Quantitative analysis of contributions from each type of polarization was conducted using both V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox couples. The Lattice Boltzmann Method was adopted based on the 3-D reconstructed electrode structure to provide insights into the electrolyte distribution and the electrolyte velocity profile within the dual-layer electrode assembly. Besides, we found that a single-layer carbon cloth electrode imprinted its woven pattern on the ion exchange membrane after battery assembly due to the unevenness of the surface. The sub-layer of carbon paper served as a protective layer to avoid excessive stretching and mechanical failure of the membrane and the resulting increase of crossover-induced capacity decay. Overall, the results showed that the investigated strategy effectively achieves high electrochemical performance and a low pressure drop. It can be regarded as a promising approach for high system efficiency while maintaining long-term stability in a flow-through configuration.