Jiawei Gu,Hongfei Wang,Sha Li,Muhammad Sohail Riaz,Jiqiang Ning,Xiong Pu,Yong Hu
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 SiO 2 @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) (EMIMBF 4 /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.
Carbon nanosheets with layer-stacked porous structures and surface functionalized groups are beneficial for efficient ion storage in supercapacitor electrode materials, but achieving high cost-effectiveness and controllable surface groups remains a significant challenge. Herein, the biomass-derived chitosan and sodium alginate are selected as raw materials for self-assembly reaction with phytic acid as a cross-linking agent. The protonated chitosan and sodium alginate form a cross-linked network structure through hydrogen bonding and electrostatic adsorption, which is subsequently carbonized and activated to synthesize porous graphitic carbon nanosheets (PNPCN-X). PNPCN-X realizes an efficient distribution of porous and graphitic structures. It's noteworthy that phytic acid facilitates the fixation of N atoms, and various N configurations can be adjusted by altering the content of phytic acid. Optimized PNPCN-1.5 exhibits a high content of structurally stable pyridinic-N and graphitic-N configurations, which are confirmed to serve as active sites substantially augmenting the ion adsorption capacity through Density Functional Theory (DFT) calculations. Benefiting from its exceptional physicochemical properties, PNPCN-1.5 achieves 322 F g −1 as electrode materials in the three-electrode system, while the symmetrical supercapacitor assembled with EMIMBF 4 electrolyte attains 56.29 W h kg −1 . Furthermore, various kinetic analyses extensively elucidate its capacitance distribution characteristics and ion diffusion rates.
The catalytic oxidation of alcohols is an important transformation in the chemical industry. Carbon materials with a large surface area and N doping show great promise as metal-free catalysts for the reaction. In this study, a rich N-containing covalent triazine framework polymerized by cyanuric chloride and p-phenylenediamine was used to synthesize N-doped porous carbon with the assistance of a pore-forming agent—NaCl. First, the mass ratio of the polymer/NaCl was optimized to 1:9. Then, the influence of the pyrolysis temperatures (700–1000 °C) on the materials was studied in detail. It was found that the carbon materials were gradually exfoliated by molten salt at high temperatures. XRD and Raman characterizations showed them with a certain graphitization. The optimal doped carbon CNN-1-9-900 achieved the highest surface area of 199.03 m2g−1with the largest pore volume of 0.29 cm3g−1. Furthermore, it had a high N content of 9.9 at% with the highest relative proportion of pyridinic/graphitic N. Due to the synergistic effect between the surface area and pyridinic/graphitic N, CNN-1-9-900 showed the best performance for benzyl alcohol oxidation with TBHP at moderate conditions, and the process also worked for its derivatives.
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