We investigated the dependence of open-circuit voltage (OCV) on temperature difference, deltaT between hot and cold electrodes for a Br-2/Br--redox thermocell with carbon materials having a large specific surface area (Maxsorb) as electrodes and 3.36 M KBr aqueous electrolyte containing Br-2 and compared it with that for thermocells with Pt electrodes. The rate of change in OCV with deltaT largely changed at a certain value of deltaT (critical deltaT). We assumed that the OCV change with deltaT can be expressed by quadratic or linear equations of deltaT differently in the regions above and below critical deltaT The influence of Br-2 concentration on thermoelectric power IdE/dTl was smaller for Maxsorb electrode cells than for Pt electrode cells, and the IdE/dTl for Maxsorb electrodes was smaller than that for Pt electrodes above the critical deltaT This may be related to differences in the amount of Br-2 adsorption at the reaction sites on the electrode surface. We found hysteresis in the OCV change with deltaT for both electrode systems when deltaT was increased and decreased. The hysteresis appears to depend on cell configuration. 2002 Elsevier Science B.V. All rights reserved.