Influence of electrode materials on open-circuit voltage profiles with a temperature difference for a thermocell using a Br2/Br−-redox reaction

We investigated the dependence of open-circuit voltage (OCV) on temperature difference, δT, between hot and cold electrodes for a Br2/Br−-redox thermocell with carbon materials having a large specific surface area (Maxsorb) as electrodes and 3.36 M KBr aqueous electrolyte containing Br2 and compared it with that for thermocells with Pt electrodes. The rate of change in OCV with δT largely changed at a certain value of δT (critical δT). We assumed that the OCV change with δT can be expressed by quadratic or linear equations of δT differently in the regions above and below critical δT. The influence of Br2 concentration on thermoelectric power dE/dT was smaller for Maxsorb electrode cells than for Pt electrode cells, and the dE/dT for Maxsorb electrodes was smaller than that for Pt electrodes above the critical δT. This may be related to differences in the amount of Br2 adsorption at the reaction sites on the electrode surface. We found hysteresis in the OCV change with δT for both electrode systems when δT was increased and decreased. The hysteresis appears to depend on cell configuration.