Controllable adjustment of oxygen contents in activated carbons and oxygen effect on electrochemical performances in supercapacitors

In this work, oxygen-doped activated carbons (ACs) are derived from glucose by hydrothermal synthesis (HTS) and a two-step consecutive activation/treatment. The first KOH activation leads to the formation of well-developed hierarchical porous structure. The second H₂O-steam treatment controls the fraction of oxygen contents ranging from 3.35 to 10.43 at% by regulating the treatment time and temperature. We propose a reaction for the oxygen reduction during the H₂O-steam treatment, of which the resultant reaction rate increases with the increase of the treatment temperature. The nominal activation energy for the reaction is 18.79 kJ/mol. The symmetric supercapacitors with the ACs of the highest oxygen content exhibit the best electrochemical performances of an optimum specific capacitance of 240.49 F/g in the electrolyte of 1 M H₂SO₄. However, the symmetric supercapacitors with the ACs of the lowest oxygen content exhibit the best electrochemical performances of an optimum specific capacitance of 171.81 F/g in the organic electrolyte of 1 M Et4BF4 in AN.