Thermoelectric conversion is a direct conversion of thermal energy to electricity, triggered by the Seebeck effect. Typically, the configuration of a thermoelectric device and the absorptivity of both electrodes exhibit symmetrical optical characteristics between the hot and cold ends, and these factors usually are not expected to affect the direction of the thermal gradient. Here, we first demonstrate the ability to reverse the direction of thermal flow across a thermoelectric element by adjusting the absorptivity of electrodes at both ends in an environment with uniform thermal radiation. For example, when the metamaterial or fullerene electrodes were attached to one end a p-type thermoelectric element, they generated output voltages of 19.0 and -4.0 V, respectively, in an environment with uniform thermal radiation at 364 K. Using this insight, we demonstrated power generation on a