Thermally Chargeable Proton Capacitor Based on Redox‐Active Effect for Energy Storage and Low‐Grade Heat Conversion

Thermal energy is abundantly available in our daily life and industrial production, and especially, low‐grade heat is often regarded as a byproduct. Collecting and utilizing this ignored energy by low‐cost and simple technologies may become a smart countermeasure to relieve the energy crisis. Here, a unique device has been demonstrated to achieve high value‐added conversion of low‐grade heat by introducing redox‐active organic alizarin (AZ) onto N‐doped hollow carbon nanofibers (N–HCNF) surface. As‐prepared N–HCNF/AZ can deliver a high specific capacitance of 514.3 F g −1 (at 1 A g −1 ) and an outstanding rate capability of 60.3% even at 50 A g −1 . Meanwhile, the assembled symmetric proton capacitor can deliver a high energy density of 28.0 Wh kg −1 at 350.0 W kg −1 and a maximum power density of 35.0 kW kg −1 at 17.0 Wh kg −1 . Significantly, the thermally chargeable proton capacitors can attain a surprisingly high Seebeck coefficient of 15.3 mV K –1 and a power factor of 6.02 µW g –1 . Taking advantage of such high performance, a satisfying open‐circuit voltage of 481.0 mV with a temperature difference of 54 K is achieved. This research provides new insights into construction of high value‐added energy systems requiring high electrochemical performances.