RESUMO
Doping engineering in nanostructured carbon materials is an effective approach to modify heteroatom species and surface electronic structures. Herein, an advanced electrode material based on a honeycomb-like porous carbon matrix with tunable N-doped configurations is prepared via 4,4'-bipyridine (4,4'-bpy)-assisted pyrolysis of SiO2@ZIF-8 templates and subsequent etching treatment. Interestingly, the amounts of pyridinic-N and graphitic-N can be controlled by rationally varying the content of 4,4'-bpy which acts as the N source in the pyrolysis process. Both experimental results and density functional theory calculations have revealed that synergistically with 3D interconnected porous architecture, pyridinic-N and graphitic-N have different effects on the electrochemical performances in aqueous and ionic liquid gel electrolytes for symmetric supercapacitors. Highly exposed pyridinic-N endows the carbon electrode with a strengthened pseudocapacitance contribution manifested as a high specific capacitance of 436.1 F g-1 and exceptional stability of almost 100% capacitance retention after 5000 cycles at 10 A g-1 in the KOH/polyvinyl alcohol (PVA) electrolyte. By contrast, graphitic-N is propitious for reinforced electrical double-layer capacitance contribution, reflected by a maximum energy density of 125.4 Wh kg-1 in the 1-ethyl-3-methylimidazolium tetrafluoroborate/poly(vinylidene fluoride-co-hexafluoropropylene) (EMIMBF4/PVDF-HFP) electrolyte. This work offers an in-depth insight into the understanding of the energy storage mechanism of N-rich carbon electrodes in different electrolyte media.