Controllable thickness carbon sheet under anion and cation co-doping for supercapacitors and capacitive deionization

Doping can construct abundant active adsorption sites to improve the capacitive properties of carbon materials. However, its induced massive formation of sp3 defects, usually uncontrollable, disrupts the carbon lattice π-conjugation system and leads to a decrease of electrical conductivity. In this work, ultrathin carbon nanosheets (Fe–CNB) with controllable thickness were prepared by ice template-modulated natural biopolysaccharide gels, together with the co-doped defects introduced into its lattice selectively, such as Fe, B and N. The boron doping preferentially converts pyrrolic-N into B–N sites with lower adsorption barriers, which further enhances the capacitance of B, N co-doped carbon. Meanwhile, the conductivity of material was modulated via conjugation function between electron-rich N and electron-deficient B to accelerate the charge transfer kinetics. In addition, the iron source will act as an activator and graphite catalyst to enhance the graphitization of the carbon nanosheets while constructing a rich microporous structure on their surface, further improving its specific surface area and conductivity. As a result, Fe–CNB prepared in this work show desirable supercapacitive properties (306 F g−1 at 0.5 A g−1), exhibiting good potential for applications in supercapacitor and capacitive deionization.