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 mu W 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.

Automated summary

This study demonstrates a unique device that achieves high value-added conversion of low-grade heat by introducing redox-active organic compounds onto the surface of N-doped hollow carbon nanofibers. The device shows high specific capacitance and outstanding rate capability, as well as high energy density and maximum power density. The thermally chargeable proton capacitors exhibit a surprisingly high Seebeck coefficient and power factor, achieving a satisfying open-circuit voltage.