Hydrogen-bromine (HBr) fuel cells and electrolyzers consist of a bromine electrode and a hydrogen electrode with a proton-conducting membrane between them. There are two major applications of HBr fuel cells and electrolyzers: electrical energy storage systems (ESSs) and hydrogen production. The HBr system is attractive for energy storage applications because of the high reversibility of both hydrogen and bromine electrodes, which allows a single electrochemical unit to be used in both fuel cell and electrolyzer modes. The hydrogen oxidation catalyst with the highest activity is platinum (or its alloys), and it is used in most hydrogen-oxygen proton exchange membrane (PEM) fuel cells. However, there is continuing effort to find better and lower cost catalysts. In HBr fuel cells and electrolyzers, the membrane does not completely prevent the crossover of bromides or bromine species. Therefore, these species tend to poison the hydrogen electrode catalyst, and thereby reduce the catalyst activity. In this article, the following issues are reviewed: the properties of the bromine electrode and the construction materials, platinum group metals as hydrogen electrode catalysts in hydrogen bromide solutions, the adsorption of bromine species and hydrogen kinetics on the platinum electrode, electrolyzer and fuel cell stacks for the hydrogen bromide system - construction materials, membranes and catalysts, the durability of the HBr fuel cell, and applications of HBr fuel cells and electrolyzers.
- Regenerative fuel cell