Numerical insight into characteristics and performance of zinc-bromine redox flow battery

The modeling study serves as a pivotal approach for elucidating the fundamental reaction mechanisms and prognosticating the operational performance of zinc-bromine flow batteries (ZBFBs). Herein, a time-dependent model for ZBFB is established, integrating redox reaction kinetics, species transport, two-step electron transfer, and bromine complexation/decomplexation processes, to unravel transient electrochemical phenomena during the charge-discharge phase. Parametric analyses reveal that increasing applied current density (20–40 mA/cm²) intensifies overpotential, reducing energy efficiency (η_E) from 73 % to 69.11 %. Electrode porosity (ɛ_ed) profoundly influences concentration polarization and zinc deposition uniformity. Enhancing specific surface area from 10,000 to 20,000 m²/m³ improves reaction kinetics, elevating η_E by 5.8 % through reduced activation losses. While higher electrolyte conductivity (>200 S/m) yields insignificant returns, boosting flow rates from 10 mL/min to 40 mL/min extends discharge duration by 23.67 % by mitigating concentration gradients. Furthermore, halving or doubling the tank volume improves or diminishes η_E by 6.84 % or 15.01 % owing to the changed bromine concentration. The optimized case achieves voltage, coulombic, and energy efficiencies of 88.13 %, 94.25 %, and 83.1 %, representing 5.27 %, 8.08 %, and 13.78 % enhancements over baseline. This work provides a predictive framework for ZBFB design and operation while highlighting trade-offs between efficiency gains and actual techno-economic costs.