Electric Double-Layer Capacitors from Activated Carbon Derived from Black Liquor

Black liquor derived from a hardwood tree was activated by potassium hydroxide, and the performance as electric double-layer capacitors in a non-aqueous electrolyte of activated carbons with high surface area was presented in this work. The effects of preparation parameters on the char yield, Brunauer−Emmett−Teller (BET) surface area, pore structure, and capacitance of the resulting products were investigated. The results show that the char yield and capacitance decrease with the increase of the carbonization temperature (600−900 °C). Nitrogen adsorption isotherms of activated carbons indicate that they were mainly micropores. The BET surface area increases slowly with the increase of the activation temperature, reaching the maximum value of 3089.2 m 2 g −1 at 900 °C, 3 times larger than a commercial activated carbon from charcoal (943.5 m 2 g −1 ). Capacitance is found to be approximately proportional to the BET surface area, and the maximum capacitance of 41.4 F g −1 was developed. In addition, the results obtained in this study confirm that capacitance of activated carbons from black liquor depends upon not only the surface area but also the pore size.