Preparation of porous carbons by hydrothermal carbonization and KOH activation of lignite and their performance for electric double layer capacitor

- Shengli lignite via hydrothermal carbonization pre-treatment to prepared PCs.
- The SSA of PCs is higher than the AC directly derived from lignite.
- The PCs electrode exhibits high specific capacitance of 295 F g−1.
- The PCs electrode shows excellent rate performance and superior cycling stability.

A series of porous carbons (PCs) were obtained from Shengli lignite (SL) via hydrothermal carbonization (HTC) pre-treatment and followed by chemical activation with KOH. The effects of preparation parameters including HTC temperature, KOH-hydrochar ratio and activation temperature on pore structure and the electrochemical performances of PCs were investigated in details. The PCs are mainly micropores structure according to the N2 adsorption-desorption isotherms test and the highest specific surface area (SSA) is up to 3162 m2 g−1. The SSA and total pore volume of PCs with HTC pre-treatment are larger than that without HTC treatment. The electrochemical performances of the symmetric electric double layer capacitor (EDLC) fabricated from these PC electrodes were tested by galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy. All the PCs as electrode for EDLC exhibit ideal capacitive behaviors in 6 M KOH electrolyte. The specific capacitance of 200-HTC-800-3 can reach as high as 295 F g−1 at the current density of 40 mA g−1 and still retained 210 F g−1 at the current density of 10 A g−1. It also shows excellent electrochemical cycle performance that after 15000 cycles the specific capacitance value almost not decay. The processes used to produce the PCs can reduce the energy consumption compared to the traditional carbonization-activation method.