Along-flow-path gradient flow field enabling uniform distributions of reactants for redox flow batteries

Designing flow fields that can lead to uniform distributions of reactants at a minimum pump work is critical to enhancing the performance of redox flow batteries. This paper reports on an improved design of conventional serpentine flow fields, in which the channel depth is linearly reduced from the inlet to the outlet, speeding up the flow speed along the flow path and enhancing the under-rid convection downstream toward the outlet. Three-dimensional numerical simulations reveal that the optimized gradient at 25% (the channel-depth ratio between the outlet and inlet) can lead to the highest pump-based voltage efficiency. Experimental validations demonstrate that the application of the optimized flow field to a vanadium redox flow battery leads to significant improvements in both energy efficiency and electrolyte utilization, which is 5.0% and 27.7%, respectively, higher than that with the conventional serpentine flow field at a relatively high current density and low flow rate (400 mA cm−2, 12 mL min−1 cm−2). The effectiveness of the flow field design in boosting the uniform reactant distribution provides a feasible approach for scaling up high-performance redox flow batteries.