Performance Evaluation of a Regenerative Hydrogen-Bromine Fuel Cell

Intermittent renewable energy sources like wind and solar require energy storage to be fully exploited. The H2-Br2 flow battery has been identified as a great candidate for this application because of its high energy conversion efficiency and power density capability. To evaluate the performance of this system a fuel cell with a membrane electrode assembly made of a Nafion 212 membrane and electrodes with 0.55 mg Pt/cm2 loading was tested at 22°C under the H2-H2, H2-O2, H2-Br2 modes to compare the performance between these systems. The exchange current density of the Br−/Br2 reactions on platinum was found to be about a quarter of that of the hydrogen reactions on the same substrate (0.3 mA/cm2 Pt versus 1.2 mA/cm2 Pt). Peak power density during discharge was 0.30 W/cm2 at a voltage efficiency of 70% for the H2-Br2 mode versus 0.17 W/cm2 at 40% for the H2-O2 mode under similar conditions. The performance of the H2-Br2 fuel cell is determined mainly by the ohmic and mass transport resistances in the cell, which could be improved by using higher reactant concentrations, higher operating temperatures, more conductive membranes, and electrode and cell designs that enhance transport.