Integrating surface functionalization and redox additives to improve surface reactivity for high performance supercapacitors

The charge storage in porous carbon is mainly from the ions adsorption on the carbon electrode. Meanwhile, the functional groups and incorporations of redox additives on porous carbon have been reported for improving the capacity of carbon electrode through redox reactions. Here, commercially available porous carbon materials have been successfully modified, increasing surface reactivity in particular of ethylenediamine (EDA), by a facile but efficient solvothermal method. It is revealed that the EDA-functionalized porous carbon at 140 °C exhibits the best electrochemical performance and surface properties (surface wetting angle is 45° and the content of nitrogen is 3.26%). Moreover, redox additives such as p-phenylenediamine (PPD) and hydroquinone (HQ) can be linked to the amino groups (-NH2/–NH–) of EDA-functionalized porous carbon by hydrogen bonding, which can further increase the surface reactivity by redox reaction. As a result, the energy densities of samples in 6 M KOH and 1 M H2SO4 are as high as 8.3 Wh kg−1 and 8.8 Wh kg−1at 250 W kg−1, which are 3.6 and 3.2 times higher than those of pristine porous carbon, respectively. Other electrochemical performances such as cycling stability, coulomb efficiency are also largely improved. This integration of surface functionalization and redox additives is an effective strategy for remarkably improving the performance of carbon-based supercapacitors. [Display omitted] •Carbon surface functionalization is realized by solvothermal method.•Amino groups from ethylenediamine exhibits excellent surface reactivity.•p-phenylenediamine and hydroquinone serves as redox additives in alkaline and acidic electrolyte, respectively.•Redox additives and functional groups make integrating pseudocapacitive effect.