• Energy Research

Interdigitated flow field and serpentine flow field are widely adopted in redox flow batteries, but their superiority cannot be determined independently of the operating conditions, electrode properties, and electrolyte properties. Matching the flow field to the operating conditions can effectively improve the efficiency of flow cells. To this end, the present study proposes a model-based optimization method to promote the system energy efficiency of flow cells by combining the interdigitated and serpentine flow channels and considering the heterogeneous distribution of reactants. The fluid dynamic model, electrochemical model, and genetic algorithm are integrated into an optimization framework in the present study to obtain the novel interdigitated-serpentine flow field. Simulative results show that compared to the interdigitated or serpentine flow field, the optimized interdigitated-serpentine flow field yields increments in the system energy efficiency ranging from 2% to 20% under varying operation conditions.

Interdigitated flow field and serpentine flow field are widely adopted in redox flow batteries, but their superiority cannot be determined independently of the operating conditions, electrode properties, and electrolyte properties. Matching the flow field to the operating conditions can effectively improve the efficiency of flow cells. To this end, the present study proposes a model-based optimization method to promote the system energy efficiency of flow cells by combining the interdigitated and serpentine flow channels and considering the heterogeneous distribution of reactants. The fluid dynamic model, electrochemical model, and genetic algorithm are integrated into an optimization framework in the present study to obtain the novel interdigitated-serpentine flow field. Simulative results show that compared to the interdigitated or serpentine flow field, the optimized interdigitated-serpentine flow field yields increments in the system energy efficiency ranging from 2% to 20% under varying operation conditions.

Abstract Recognizing the importance of the cost to the wider adoption of redox flow batteries, it is critical to achieve the higher utilization of electrolytes and thus reduce the required electrolyte volume. Although the effects of the applied current on the battery performance were extensively explored in previous studies, few of them investigated how to dynamically optimize the applied current with varying state-of-charge conditions during the (dis-)charging process. A variable current strategy is proposed in the present study to dynamically vary the applied current density according to the real-time state-of-charge conditions in a vanadium redox flow battery system. Both simulations and experiments are conducted to confirm the feasibility and practicality of the proposed strategy. The results show that the concentration overpotentials and ohmic losses can be reduced at relatively large or low state-of-charge conditions under the proposed strategy, leading to a more than 10% increment in the effective energy capacity at the required power density, compared to the constant current strategy. In addition, the strategy is further improved by incorporating the variable flowrate, which is shown to further enhance the performance of the battery system.

Abstract Recognizing the importance of the cost to the wider adoption of redox flow batteries, it is critical to achieve the higher utilization of electrolytes and thus reduce the required electrolyte volume. Although the effects of the applied current on the battery performance were extensively explored in previous studies, few of them investigated how to dynamically optimize the applied current with varying state-of-charge conditions during the (dis-)charging process. A variable current strategy is proposed in the present study to dynamically vary the applied current density according to the real-time state-of-charge conditions in a vanadium redox flow battery system. Both simulations and experiments are conducted to confirm the feasibility and practicality of the proposed strategy. The results show that the concentration overpotentials and ohmic losses can be reduced at relatively large or low state-of-charge conditions under the proposed strategy, leading to a more than 10% increment in the effective energy capacity at the required power density, compared to the constant current strategy. In addition, the strategy is further improved by incorporating the variable flowrate, which is shown to further enhance the performance of the battery system.

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.

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.