Design Of Nitrogen Doped Carbon Material And Its Oxygen Reduction Properties

Electrochemical oxygen reduction?ORR?is the core reaction in many energy conversion systems such as fuel cells and metal-air batteries.Low-cost,high-activity and high-stability ORR catalysts are decisive for large-scale applications of these energy systems.Non-metallic catalysts have been one of the research hotspots results from their unique advantages,among them,nitrogen-doped carbon nanomaterials?CN_x?have attracted extensive attention in the field of metal-free ORR catalysts due to their abundant reserves,excellent anti-toxicity and stability.In this paper,zeolitetic imidazolate framework-8?ZIF-8?and graphadiyne?GDY?were used as precursors to design and construct nitrogen-doped nano-carbon materials as high-activity non-metallic carbon-based ORR catalysts by regulating the topology of the carbon matrix.nanosized mesoporous silica powder was impregnated with dicyandiamide?DCD?,which polymerizes into g-C₃N₄ during subsequent thermal treatment.Thus-obtained powder was modified by?3-aminopropyl?triethoxysilane?APTES?,onto which the zeolitic imidazolate framework compound,ZIF-8,was grown from dimethylimidazole and Zn?NO₃?₂·6H₂O.After the high-temperature annealing and the etching of SiO₂,ZIF-8 derived porous nitrogen-doped carbon is prepared.A method of controlled in situ conversion of graphitic N was established,and a monovacancy coupled pyridinic N?MV-c-PN?active site with high ORR activity was successfully designed.X-ray photoelectron spectroscopy?XPS?and ¹³C solid-state nuclear magnetic resonance?ssNMR?characterizations,together with theoretical calculation,confirm the presence of MV-c-PN sites.Thus-obtained HPC material with such MV-c-PN sites exhibits surging ORR activity:a half-wave potential of 0.855 V and a kinetic current density of 19.11 mA·cm^-2 at 0.80 V,which outperform most of the reported metal-free catalysts.Impressively,the maximum power density of the zinc-air battery with MV-c-PN sites is 40.3%higher than that with benchmark Pt/C catalyst.This outstanding activity can be mainly attributed to the intrinsic high-activity of the unique active site.The turnover frequency?TOF?of such MV-c-PN active site is as high as 1.328 e·site^-1·s^-1 at 0.80V,7.26 times that of conventional pyridinic N sites(0.183 e·site^-1·s^-1).coupling of pyridinic N and topological monovacancy defect,which synergistically modulate the charge density of MV-c-PN sites,alter the ORR pathway,and effectively increase the reaction kinetics.Our work clearly highlights the importance of tuning the CN_x active sites,and provides an efficient strategy for developing carbon-based metal-free ORR catalysts with outstanding activity.The graphdiyne derived nitrogen-doped carbon material is prepared by conventional coupling reaction.Protected from light,the copper ions eluted in pyridine solution,catalyzing the polymerization of different ratios of diacetylenylbenzene and triacetylenylbenzene into a carbon network.The reaction product was collected,mixed with dicyandiamide and sintered to obtain nitrogen-doped graphdiyne.A novel nitrogen-doped graphdiyne derived carbon nanostructure ORR catalyst copolymerized with diacetylenylbenzene and triacetylenylbenzene was successfully designed.Through various physical characterizations and electrochemical tests,the effect of different proportions of monomers on the physical properties and ORR performance of the catalysts was discussed.It was found that the defect level and the pyridinic N content of the catalyst were different with different proportions of monomers,acting together to affect the ORR performance.This work discusses the influence of different proportions of monomer on the physical properties and electrochemical activity of graphdiyne,providing an effective design idea and construction strategy for the further development of new graphdiyne derived carbon-based ORR catalysts.