Direct conversion of thermal energy to electric energy with thermoelectric generators is an attractive technique to recover low-temperature heat. Thermoelectric generators based on galvanic cells (thermocells) provide promising results with respect to the Seebeck coefficient. In this study, based on the theory of non-equilibrium thermodynamics, we simulated a thermocell with hydrogen gas electrodes and a proton exchange membrane. We calculated a maximum power density of 1461 mW/m(2) and a thermal efficiency of 2% relative to the Carnot efficiency for a cell operating with the same gas composition at both the anode and the cathode, but fully saturated at the anode. We predict a Seebeck coefficient in the range of 0.7-1.8 mV/K, higher than those of classical thermoelectric generators. The thermocell presented here provides promising values regarding the Seebeck coefficient. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.