Carbon nanodot modified N, O-doped porous carbon for solid-state supercapacitor: A comparative study with carbon nanotube and graphene oxide

Highlights: • Nanocarbons can improve the pore structure and heteroatom doping of polyacrylonitrile-derived carbon materials. • The carbon composites showed enhanced electrochemical performance. • Carbon nanodots are superior to carbon nanotubes and graphene oxide. • The enhanced mechanism of electrochemical performance was clarified. -- Abstract: Herein, a series of nanocarbons, including carbon nanodots (CD), carbon nanotubes (CNT) and graphene oxide (GO), modified N, O doped hierarchical porous carbons (NOHPC) were prepared by carbonization using the silica nanospheres and ZnCl₂ as templates. The N, O doping content, N, O species and the ratio of micro/mesopore pore structures of NOHPC can be effectively improved by the modification of nanocarbons in organic precursor of polyacrylonitrile. The as-prepared CD modified NOHPC (CD/NOHPC) showed superior capacitance performance than that of CNT (CNT/NOHPC) and GO (GO/NOHPC), and the CD/NOHPC exhibited a high specific capacitance of 343.6 F g⁻¹ at a current density of 1 Ag⁻¹ and an excellent rate capability (304.7 F g⁻¹ at 50 Ag⁻¹ and 88.7% capacitance retention). The symmetric supercapacitor of CD/NOHPC delivered an energy density of 10.3 Wh kg⁻¹ (0.31 mWh cm⁻³) at a power density of 489 W kg⁻¹ (14.7 mW cm⁻³), a capacitance retention of 109% after 20000 galvanostatic charge/discharge cycles in H₂SO₄/PVA solid-state electrolyte. The systematic study clarified that CD can be utilized for the regulation and improvement of the internal structure of traditional porous carbon materials, resulting in better electrochemical energy storage than that of CNT and GO.