Preparation And Electrochemical Properties Of Transition Metal/nitrogen Doped Porous Carbon

Heteroatoms doped porous carbon materials have the advantages of improved surface activity,good electrical conductivity,high chemical stability,adjustable pore structure and high specific surface,the applications of them in catalysts and supercapacitors electrode materials have received widespread attention.Seeking simple,easy,low-cost and controllable methods to prepare heteroatoms doped porous carbon materials with high catalytic activity,high specific surface area and abundant pore structure has become one of the important research contents in this field.In order to simplify the process of preparing nitrogen-doped porous carbon,reduce the consumption of resources and improve rate performance,milk powder was acted as carbon and milk powder,N-doped hierarchical porous carbon?NHPC-1?was obtained by pyrolysis of milk powder at 700°C for 1 h in n NaCl/Na₂CO₃ molten salt in air atmosphere.NHPC-1 not only had a high specific surface area and an abundant hierarchical porous structure,but also the N element is successfully doped in the carbon structure.In a symmetrical two-electrode system of 6 M KOH,the specific capacitance of NHPC-1 electrode reached 360.2 F?g^-1 at 0.25 A?g^-1 and kept 258.6 F?g^-1 even at 20 A?g^-1,indicating high specific capacitance and good rate performance.In 1 M Na₂SO₄,the assembled supercapacitor showed a high energy density of 33.0 Wh?kg^-1 at 0.25 A?g^-1and maintained a high energy density of 22.3 Wh?kg^-1 at 20 A?g^-1.NHPC-1 electrodes showed good cycle stability in both electrolytes.As an oxygen reduction reaction?ORR?catalyst,NHPC-1 displayed a half-wave potential of 0.75 V vs.RHE and a limiting current density of 4.7 mA?cm^-2,which exhibited a performance close to that of Pt/C?20 wt?4??catalyst.In order to further improve the activity of carbon-based catalysts for ORR catalytic activity,citric acid and ammonium chloride were served as carbon and nitrogen sources,respectively.Fe₂O₃ was acted as template and iron source.A in situ templates etching method was used to prepare three-dimensional interconnected Fe-N doped hierarchical porous carbon materials?Fe-NHPC-8?after carbonization at 800°C and pickling.Fe-NHPC-8 possessed a large specific surface area of 1643.6 m²?g^-11 and an abundant hierarchical porous structure.Fe and N elements were uniformly distributed in the carbon structure of Fe-NHPC-8,and Fe-N bond was formed.When as an ORR catalyst in 0.1 M KOH,it showed a positive half-wave potential?0.85 V vs.RHE?,excellent durability and a low H₂O₂ yield which are superior to those of Pt/C?20 wt?4??catalyst in 0.1 M KOH.This was attributed to the formed Fe-N_x active sites in the carbon structure and the hierarchical pore structure with high specific surface area.In a three-electrode system with6 M KOH,Fe-NHPC-8 displayed a high specific capacitance of 378.6 F?g^-1 at 0.5 A?g^-1and excellent rate performance of 276.6 F?g^-1 at 20 A?g^-1.This study used another strategy of initiating gelatin crosslinking using salts solution to prepare the Fe-N doped aligned porous carbon active material.Low-cost food-grade gelatin was served as a carbon and nitrogen source.FeCl₃ was used as the Fe source.The gel induced by CaCl₂ solution was pyrolyzed at 900°C to obtain a long-range oriented carbon material with a hierarchical porous structure?Fe-NAHPC-900??And Fe-N doped short-range aligned honeycomb hierarchical porous carbon?Fe-NHHPC-900?was obtained at 900°C heating treatment of a gel induced by a mixed solution of CaCl₂ and NaCl.Both of them exhibited a large specific surface area with an abundant aligned and hierarchical porous structure.And Fe and N elements were uniformly distributed in the carbon structure in the form of Fe-N bonds.For ORR catalysts,in addition to excellent durability in 0.1 M KOH electrolyte,Fe-NHHPC-900 and Fe-NAHPC-900 possessed excellent ORR performance with positive half-wave potential of 0.86 and 0.85 V vs.RHE,superior to Pt/C?20 wt?4??catalysts.This is attributed to the formed Fe-N_x active sites and aligned porous structures in the carbon structure.In a three-electrode system of 6 M KOH,Fe-NHHPC-900 also showed a high specific capacitance of 328.5 F?g^-1 at 0.5 A?g^-1and excellent rate performance of 76.9?4?from 0.5 to 20 A?g^-1.This work proved that the unique aligned porous structure can effectively optimize catalyst activity and improve supercapacitor performance.In order to reduce or avoid agglomeration or aggregation of Mn metal atoms during the preparation of a Mn-N doped porous carbon catalyst,MnCl₂ was selected as Mn source,based on the principle of combining Ca Cl₂ with gelatin to form a aligned porous structure,Mn-N doped aligned hierarchical porous carbon catalyst?Mn-NAHPC-900?was prepared under 900°C through inorganic metal salt sublimation gas doping strategy.Mn-NAHPC-900 displayed a large specific surface area of 1177.8 m²?g^-1 with an aligned hierarchical porous carbon structure.XPS and XAFs results showed that Mn metal atoms coordinated with N atom to form Mn-N_x active sites in the carbon structure.Notably,Mn-NAHPC-900 as an ORR catalyst,it had excellent catalytic ORR performance with a positive half-wave potential of 0.86 V vs.RHE,small Tafel slope of 56.1 mV?dec^-1,number of reaction electrons very close to 4 and excellent durability,which were superior to Pt/C?20 wt?4??catalysts in 0.1 M KOH.Meanwhile,it displayed enhanced ORR catalytic performance and outstanding stability in an 0.1 M HClO₄ as well.