Efficient microwave absorber and supercapacitors derived from puffed-rice-based biomass carbon: Effects of activating temperature.

Biomass-based carbon is gaining increasing attention because it presents a promising prospect for economic growth and social sustainable development. Moreover, it is an excellent medium for application in electromagnetic and electronic devices. Here, puffed-rice-based carbon is obtained at various activating temperatures, and when the hollow bulges on the carbon disappear, the morphology of the carbon changes into sheet-like structures. The R-800 sample displays the highest I/I value and demonstrates the best performance when used as both a microwave absorber and an electrode material. The minimum reflection loss (RL) and bandwidth for RL < -10 dB of the R-800 sample reach -72.1 dB and 13.2 GHz, respectively, and the bandwidth for RL < -20 dB is as large as 7.0 GHz, illustrating the widest bandwidth among the five carbon specimens. The multiple reflection effects and scattering, good impedance matching, and interfacial polarization synergistically enhance the microwave absorption performances of the sample. At 1 A g, the specific capacitance of the R-800 sample reaches 117.2 F g and the capacitance retention remains at 85.3%. Moreover, a hybrid supercapacitor R-800//R-800 demonstrates an outstanding energy density of 15.23 Wh kg, power density of 5739.43 W kg, and high cycle stability (94.5% after 5000 cycles). This functionalized biomass carbon provides a promising media for constructing a bridge between sustainable development and biomass materials.