Optimization of preparation of lignite-based activated carbon for high-performance supercapacitors with response surface methodology

Coal-based activated carbon (CBAC) is prepared from lignite as raw material by the potassium-catalyzed steam activation method. The effect of various process variables like activation temperature, activation time, immer-sion time and the mass ratio of activator to coal on the electrochemical performance are optimized according to the Box-Behnken design and analyzed using response surface methodology (RSM). The optimization synthesis of CBAC is determined by the conditions of the activation temperature of 758.0 degrees C, the immersion time of 23.9 h, the activation time of 1.9 h, the mass ratio of activator to coal as 5.1:1. The optimal product (CBAC-2) obtain by the above procedure displays a high specific surface area (2380.4 m2 g-1) and a large pore volume (1.1 cm3 g-1). The supercapacitor of CBAC-2 presents a high specific capacitance of 374.1 F g-1 at 1 A g-1 and excellent ca-pacity retention of 93.3 % after 10,000 cycles at 10 A g-1 in 6 M KOH aqueous electrolyte. Therefore, the developed RSM is accurate and precise for regulating the pore size distribution of CBAC. The optimal synthesis of supercapacitor electrodes with the extract from lignite can expand our horizons for utilising low-rank coal.

Automated summary

In this study, coal-based activated carbon (CBAC) was prepared from lignite and its synthesis process was optimized using response surface methodology. The optimal conditions resulted in a product with high specific surface area and large pore volume, and the CBAC-based supercapacitor exhibited high specific capacitance and excellent capacity retention at high current density.