We report here a fully contained electrolyzer that drives the CO2 reduction reaction (CO2RR) with thermoelectric generators instead of a potentiostat. The thermoelectric generators generate the electricity required to drive electrolysis when the temperature difference between the two faces is at least 40 oC. We show that the temperature gradients that could exist at a geothermal plant are sufficient to drive the reduction of gaseous CO2 into CO in an electrochemical flow cell, creating an opportunity to use waste heat to help decarbonization and clean fuels production. We also show how the electrolyzer system may be relevant to the future colonization of Mars, where there are large temperature differentials and an atmosphere rich in CO2.