Green synthesis of N-doped porous carbon/carbon dot composites as metal-free catalytic electrode materials for iodide-mediated quasi-solid flexible supercapacitors

Abstract

P-Nitroaniline has been adopted as a versatile precursor for the selective preparation of N-doped porous carbon (PC) and carbon dots (CDs) with rich N functionalities. Furthermore, the CDs are anchored on PC to yield PC-CDs composites with the assistance of ultrasonication. Due to the catalytic effect of the pyridinic- and pyrrolic-N sites within the CDs as well as the high specific surface area and conductivity of PC, the optimized PC-CDs-1.5% composite (containing 1.5% CDs) could substantially promote the redox reaction of the acidic KI electrolyte. Therefore, the PC-CDs-1.5%-based supercapacitor demonstrated high specific capacitance (C_s, 1783 F g⁻¹ at 1 A g⁻¹), good rate capability (800 F g⁻¹ at 6 A g⁻¹) and excellent cycling stability (84.7% C_s retention upon 10 000 charge–discharge cycles). Moreover, when employed as the electrode in a flexible supercapacitor, the PC-CDs-1.5% composite also exhibits good capacitive performance in the PVA-H₂SO₄-KI gel electrolyte, and a high energy density (E_cell) of 13.85 W h kg⁻¹ at a power density (P_cell) of 97.00 W kg⁻¹ is also delivered. In addition, the flexible device shows good electrochemical cycling stability and the C_s of the flexible device could be well maintained under bending and twisting deformations.