Polarity and surface area are two important factors in determining electrochemical performance and are here studied systematically using carbon fiber cloths (CFCs) as electrodes. The CFC polarity is enhanced by plasma treatment that creates polar groups, such as carbonyl and quinone. Carbon nanotubes (CNTs) are sp2 bonded structures and are coated onto CFCs to extend hexagonal lattices (i.e., surface area widening). Experiments indicate that the specific capacitance (Cs) of electrodes made from as-purchased and heat-treated CFCs is 0.3 and 5.75 F g−1 in the acidic electrolyte; this value increases to 18.9 F g−1 as CFCs are coated with CNTs. Oxygenated CFCs give Cs = 30.3 F g−1 with 83% retention over 3000 charge–discharge cycles, indicative of polarity dominated Cs improvement.
