An ionic thermoelectric capacitor with continuous power generation for heat harvesting

Ionic conductors emerged as the next-generation thermoelectric (TE) materials mainly due to their high ther-mopower, which is higher than that of the electronic conductors by 1-2 orders in magnitude. However, they cannot be directly used in TE generators (TEGs) because ions cannot transport across the electrodes into the external circuit. Instead, they can be used in ionic TE capacitors (ITECs) to harvest heat. Nevertheless, the ITECs reported in literatures are operated in an intermittent mode, and repeated connection and disconnection to the external load are required. These severely affect their application in practice. Here, we demonstrate the continuous operation of ITECs with the external load always connected. In addition, an equivalent circuit is proposed for the ITECs in the continuous mode, which can account for the TE parameters like the peak voltage and voltage decay time constant. The continuous ITEC can supply comparable power or even higher performance than the control intermittent ITEC, depending on the temperature variation. This work is significant for the practical application of ionic TE materials in heat conversion and the sustainable development of human society.