Revealing the mechanism of oxygen-containing functional groups on the capacitive behavior of activated carbon

O-doping is important to regulate the electrochemical behavior of activated carbon (AC) used in supercapacitors. However, the clear mechanism and relationship of O-doping on the capacitance behavior of AC seem contradictory and remain undisclosed. This is because when O-doping is carried out, it often causes changes in the physical and chemical properties such as defect state, structure, and specific surface area of AC. The superposition of these factors on capacitance behavior complicates the research problem. Here, a low-temperature oxidation method was adopted to achieve doping of different forms of O-functional groups on the AC with minimal effect on its structure and specific surface area. It can be found that the effect of O-doping on the double-layer capacitance of AC is relatively small, but positively correlated with the pseudocapacitance. This is because the functional groups C-O and COOH by O-doping can not only improve the wettability between the electrolyte and AC, but also combine with cations in the electrolyte to enhance the pseudo capacitance. The influence mechanism of O-doping on the capacitance behavior of AC has been verified in different electrode systems and aqueous electrolytes. This study provides theoretical support for rational O-doping to enhance the electrochemical performance of AC.