Preparation of lignin-based carbon aerogel under hypersaline template and its electrochemical applications

ObjectiveThe porous carbon aerogel was prepared by hydrothermal reactions of industrial lignin, formaldehyde and salt undercarbonization process. The structure, physicochemical and electrochemical properties were tested to explore its possible applications in supercapacitor electrode materials.

MethodAlkali-lignin (2 g) was mixed with three different salts (ZnCl₂, NaCl and Na₂CO₃) following the addition of 1.5 mL of formaldehyde. The mixture was stirred into a thick paste and transferred to the reactor. The temperature was raised to 160 ℃ for 2 hours to produce a series of lignin carbon aerogel (LCA) precursors. In a tube furnace filled with nitrogen, the temperature was raised to 900 ℃ at a rate of 3 ℃/min, and the temperature was kept warm for 3 hours for carbonization. Then the product was washed and cooled to obtain LCA. The structure and physicochemical properties of carbon aerogel were characterized by specific surface area (SSA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). After being grounded, the carbon aerogel was made into supercapacitor electrodes. Electrochemical energy storage was characterized by cyclic voltammetry, cyclic charge-discharge test and open-circuit impedance test.

ResultThe maximum specific surface area of LCA prepared with ZnCl₂ as template was 711 m²/g. The gelatinous structure observed under SEM and XRD results revealed that the bulk of LCA was composed of amorphous carbon. Furthermore, at a current density of 0.2 A/g, the specific capacitance reached 124 F/g, however, increasing the current density up to 10 A/g, the specific capacitance remained 60 F/g, with a capacitance retention rate of about 48%, which had the best multiplier performance.

ConclusionFinally, LCA was directly prepared by hydrothermal and carbonization process under hypersaline condition with cheap industrial lignin as raw material. LCA dominated by amorphous carbon can be prepared under ZnCl₂ salt template. It has high specific surface area and excellent electrochemical performance, which can be used as an electrode material for supercapacitor. This method has the advantages such as environmental friendliness, simple operation and low cost with possible industrial applications.