Electrochemical Performance of Dual-layer Carbon Electrodes for Aqueous Redox Flow Batteries

Recognizing the urgent need for further cost reduction to drive broad adoption of redox flow batteries, it is critical to improve the reactor performance. Improved performance leads to higher efficiency, potential for a decrease of the stack size, and reduced capital cost. As one of the main contributors to reactor internal resistance, porous electrodes with properly designed structures and optimized physicochemical properties offer a pathway to reduced voltage losses, including kinetic and concentration overpotentials. Recently, carbon cloth electrodes were explored in flow battery applications owing to their bimodal pore size distributions, which opens a potential opportunity for improved mass transport behavior. Although the unique woven structure of cloth provides flexibility in the electrode design, finding an optimal trade-off between abundant electrolyte penetration pathways and a high active surface area is still challenging. In the present study, we investigate a duallayer electrode configuration to meet the requirements of high active surface area and low mass transport resistance. 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, and a carbon paper sub-layer was placed near the membrane to provide a high density of reaction sites. Overall, the results show that the proposed strategy is an effective way to achieve high electrochemical performance and low pressure drop. It can be regarded as a promising approach for boosting system efficiency.