Increase of porosity by combining semi-carbonization and KOH activation of formaldehyde resins to prepare high surface area carbons for supercapacitor applications

A series of porous carbon samples were prepared by combining a semi-carbonization process of acidic polymerized phenol-formaldehyde resins and a following chemical activation with KOH used in different ratios to increase specific surface area, micropore content and pore sizes of the carbons which is favourable for supercapacitor applications. Samples were characterized by nitrogen physisorption, powder X-ray diffraction, Raman spectroscopy and scanning electron microscopy. The results show that the amount of KOH, combined with the semi-carbonization step had a remarkable effect on the specific surface area (up to S-BET: 3595 m(2) g(-1) and S-DFT: 2551 m(2) g(-1)), pore volume (0.60-2.62 cm(3) g(-1)) and pore sizes (up to 3.5 nm). The carbons were tested as electrode materials for electrochemical double layer capacitors (EDLC) in a two electrode setup with tetraethylammonium tetrafluoroborate in acetonitrile as electrolyte. The prepared carbon material with the largest surface area, pore volume and pore sizes exhibits a high specific capacitance of 145.1 F g(-1) at a current density of 1 A g(-1). With a high specific energy of 31 W h kg(-1) at a power density of 33028 W kg(-1) and a short time relaxation constant of 0.29 s, the carbon showed high power capability as an EDLC electrode material. (C) 2017 Elsevier B.V. All rights reserved.