Optimization of electrode characteristics for the Br2/H2 redox flow cell

The Br2/H2 redox flow cell shows promise as a high-power, low-cost energy storage device. The effect of various aspects of material selection, processing, and assembly of electrodes on the operation, performance, and efficiency of the system is determined. In particular, (+) electrode thickness, cell compression, hydrogen pressure, and (−) electrode architecture are investigated. Increasing hydrogen pressure and depositing the (−) catalyst layer on the membrane instead of on the carbon paper backing layers have a large positive impact on performance, enabling a limiting current density above 2 A cm−2 and a peak power density of 1.4 W cm−2. Maximum energy efficiency of 79 % is achieved. In addition, the root cause of limiting-current behavior in this system is elucidated, where it is found that Br− reversibly adsorbs at the Pt (−) electrode for potentials exceeding a critical value, and the extent of Br− coverage is potential-dependent. This phenomenon limits maximum cell current density and must be addressed in system modeling and design. These findings are expected to lower system cost and enable higher efficiency.