Surface modification of carbon electrodes using an argon plasma

In this work, an activated carbon sheet was modified, to improve capacitance and energy density of electric double layer capacitors (EDLCs). Surfaces were treated with plasma for selected times of 1, 5, 10, 20, and 30 min. The plasma source was a DC glow discharge in argon gas. The pressure was 20 Pa and the distance between positive and negative electrodes was 20 mm. DC power was 70 W. The activated carbon sheets were set up so that the sheets were covered with the DC glow discharge. The results showed that plasma treatment led to roughening of the surface of the activated carbon sheets which became more pronounced for increased time. This was attributed to an increased surface area caused by argon plasma etching. For discharge times greater than 10 min, contamination from sputtered PTEE in the chamber appeared to have a smoothing effect and led to a reduction of the measured surface area. Capacitance of the EDLCs cells with the activated carbon sheets after 1 min plasma surface treatment was increased by 2% compared to EDLCs cells with the original activated carbon sheet. The results have shown that the modification by plasma treatment of activated carbon sheets is a suitable technique for EDLCs used in high current applications.