Preparation of Porous Carbon from Buckwheat Husk and its Electrochemical Properties

To reduce environmental pollution and recycle biomass waste, high value-added activated carbon (AC) for supercapacitors was prepared from buckwheat husk with KOH as the activating agent. The relationship between the amount of KOH and the porosity of the ACs was studied. Thermogravimetric analysis (TG), X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and N2 adsorption were used to characterize the morphology and structure of the materials. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) were also employed to analyze the electrochemical performance of the electrodes and supercapacitors based on the ACs in 0.5 M Na2SO4. The results show that AC prepared with a KOH/char ratio of 5:1 possesses a high specific surface area of 2347 m2 g-1 and a suitable pore size distribution, with micropores distributed mainly in the range from 1 to 2 nm, mesopores between 2 to 4 nm, and an average pore diameter of 2.1 nm. A utilization rate of specific surface area up to 63% is obtained. At a current density of 1 A g-1, a specific capacitance of 295 F g-1 is achieved. At a power density of 500 W kg-1, the supercapacitor based on the prepared AC has a high energy density of 12.3 Wh kg-1. Even if the power density is increased by a factor of 30, the energy density retention rate still reaches 70.5%. After 3000 charge-discharge cycles, the specific capacitance retention rate remains at 98.5%. This study developed a high value-added utilization approach for large amounts of buckwheat husks worldwide that are difficult to dispose of.