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, 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.