| dc.description.abstract | A low-cost and efficient electrical energy storage system is needed to implement intermittent renewable energy sources such as solar and wind while maintaining grid reliability, and could also reduce the use of inefficient peak-load electrical generating units through peak shaving and load leveling. Batteries have proper energy and power densities for these applications. A flow battery is advantageous to a secondary battery because the reactants are stored externally and the electrodes are inert, allowing the power and energy densities to be separated and increasing durability and lifetime by eliminating physical and structural changes to the electrode surface. The hydrogen-bromine (H2-Br2) system is advantageous to other redox chemistries due to its fast kinetics, the high solubility of bromine in aqueous hydrobromic acid, the low cost of the electrolyte, and the ability to avoid water electrolysis. It is disadvantaged by the high cost of suitable electrodes and membranes, possible poisoning of the platinum catalyst at the hydrogen electrode by bromide, and the corrosiveness of aqueous HBr/Br2 solution. The effects of bromine concentration (0.7 M to 2 M), flow field design (serpentine or interdigitated), temperature (23 °C to 45 °C), hydrogen pressure (1 to 5 psig), flow rates, membrane thickness and bromine electrode materials on a hydrogen-bromine flow battery are presented. The cell consists of compressed graphite powder flow field blocks treated with polymer sealant, Nafion membrane, stainless steel current collectors and end plates, SGL 35BC with platinum catalyst as the hydrogen electrode, and plain Toray 090 with platinum or graphite catalysts as the bromine electrode. A potentiostat/gavalnostat by Arbin Instruments was used to set the voltage and measure the steady state current. A H2-Br2 flow battery using platinum as the catalyst for both sides is molecular transport limited, with decreases in performance at lower temperatures, lower aqueous HBr/Br2 flow rates, and when using serpentine rather than interdigitated flow field channels. The decreased performance at higher membrane thickness also demonstrates ionic transport limitations. While platinum at the bromine electrode increases the performance for both charge and discharge, no metal catalyst is needed as graphite is active for both bromine reduction and evolution. | |
