Comparative Study with Phenol and Furfural Resin-Based Active Carbon for High Density Electric Double Layer Capacitor

Abstract

Electric double layer capacitor (EDLC) has been attracted much attention as one of the most promising high power and durable energy storage devices. However, low energy density is the major drawback, therefore, the optimization of specific surface area, nanoscale and mesoscale pore volume should be necessary to improve electrostatic capacity and reliability. In this study, we carburized thermosetting resin-based particles (phenol resin and furfural resin, 10 µm in diameter) in N2 atmosphere in three hour (temperature rising rate 1ºC /min) at 400 ºC or 600ºC. Then, we treated carburized particle by three kinds of methods, KOH activation (KOH: samples = 4: 1 in weight ratio), CO2 activation or a combination of KOH and CO2 activation (KOH+CO2 activation). All activation methods were performed for 30 minutes at 800ºC or 850ºC (temperature rising rate 10ºC /min). Also, some samples were treated in the acid solution (Sulfuric acid: nitric acid = 3:1 in volume ratio) for 30 minutes at 60 ºC before KOH activation. Specific surface area/pore size distribution measurement was performed by N2 adsorption method. Elemental analysis was done by using to determine CHNO fraction. We prepared coin shaped carbon electrode (12 mm in diameter, from 8:1:1 mixture of active carbon, carbon black, and PTFE), and investigated the electrostatic characteristics of the capacitors in 6M KOH to elucidate the relationship between characteristic structure properties and electrochemical. We obtained large specific surface area as 1253 m2/g and 1240 m2/g in phenol resin by KOH activation and KOH+CO2 activation, respectively, however, did 515 m2/g by CO2 activation. The mesopore volume to total pore volume ratio of (12.8 %) KOH+CO2 activation method is larger than KOH activated method (11.5 %), suggesting that CO2 activation after the KOH activation increase pore size. Electrostatic capacity was 125 F/g and 158 F/g KOH activation and KOH+CO2 activation, respectively, though specific surface area is almost the same with both cases. This same trend was also seen with furfural resin. Electrostatic capacity was 163 F/g with phenol resin and 119 F/g with furfural resin at 20mA/g. The specific capacity became three times, from 45 F/g to 153 F/g by introducing acid-treatment before KOH activation with furfural resin. Oxygen contents by elemental analysis also became three times. The results suggested that active carbon surface having an oxygen containing functional groups enhance capacitor performances.