Decoupling heat and ion transport with supercapacitor-mediation in cold-source-free thermogalvanic cells

Thermogalvanic cells represent a pivotal technology for the direct conversion of low-grade thermal energy into electricity. However, constrained by the strong coupling between heat and ion transport within the redox mediators, conventional approaches rely on introducing a cold source to disrupt this coupling and enhance cell output, making efficient and sustainable operation dependent on an external cold supply. In the absence of forced cooling, the temperature difference (ΔT) and the output current of the cell exhibit a mutual limitation, resulting in a low relative Carnot efficiency (η _r  < 3%) or low output power density (P _max < 0.5 W m ^− 2 ). Here, we report a cold-source-free thermogalvanic cell that decouples heat and ion transport in the redox medium. This design, for the first time, utilizes supercapacitor-mediated redox reactions within the thermogalvanic cell. It achieves thermal isolation through the spatial separation of the hot and cold electrodes and establishes a high-speed ionic transport highway via the supercapacitor unit. This device, operating without forced cooling with a heat source at 70°C, realizes a temperature difference ΔT > 40 K between the two electrodes and enables unrestricted ion transport. The cell achieves a high output power density of 3.52 W m ^− 2 and a maximum relative Carnot efficiency of 7.3%, which are the highest reported value without an external cold source and the η _r value exceeds the predicted commercialization threshold of 5%. This novel thermogalvanic cell design promises the ultimate utilization and commercialization of low-grade thermal energy.