Preparation And Electrocatalytic Properties Of ZIFs Derived Porous Carbon Materials

At present,due to the severe environmental problems caused by the use of fossil fuels such as coal and oil,the development of clean energy has been promoted to a large extent.Metal-organic framework（MOFs）derived carbon materials have rich and adjustable composition and porous structure,as well as simple physical and chemical properties that can be adjusted.These advantages make them promising for energy storage systems（supercapacitors,regenerative fuel cells,etc.）and catalysts in the energy or chemical industry.Among the developed electrocatalysts,commercial Pt/C based electrocatalysts have higher performance,but there are still some problems such as high cost and rare materials.As an alternative catalyst for precious metals,MOFs derived carbon materials can reduce the cost and improve the electrocatalytic performance at the same time.The main research contents are as follows:（1）In this thesis,ZIF-67,ZIF-8 and ZIF-9 were used as precursors to prepare in-situ nitrogen-doped Co and Zn-based derived carbon materials by self-sacrificial template method,and the effects of different carbonization temperatures on their composition and morphology were explored.These materials well retain the advantages of the precursors,but also make up for the poor conductivity of ZIF precursors.Under the condition of no introduction of exogenous substances,the carbonized samples have not only rich pore structure and high N content,but also excellent electrical conductivity at the optimum temperature.Co-ZIF pyrolysis at 700℃ had the largest specific surface area（370.753 cm²/g）and micropore volume（0.126 cm³/g）,while Zn-ZIF pyrolysis at 1000℃ had a specific surface area of 1373.886cm²/g and a micropore volume of 0.489 cm³/g.（2）The test results of oxygen reduction reaction（ORR）show that different carbonization temperatures and metal centers have a great influence on the electrocatalytic performance.Co-based ZIF derived carbon has abundant Co-N active sites,the ZIF-67 catalyst prepared at800℃ showed strong methanol tolerance and long-time stability（89%of the original current density after 50000 s）,which is far more than commercial Pt/C,and has great commercial value.However,the electrocatalytic activity of Zn-based ZIF derived carbon needs to be improved,and the post-doping of co-pyrolysis with exogenous substances should be considered.（3）Three different exogenous substances,ZIF-67,glucose and melamine,were introduced to modify the one-step co-carbonization of Zn-based ZIF to prepare the composite material,and the changes of its morphology and structural characteristics were studied in detail,and used as an electrocatalyst for reoxidation and reduction reactions in fuel cells.It is worth noting that the electrocatalytic performance of porous carbon materials with the addition of exogenous substances is far better than that of single-phase ZIF-derived carbon materials,which further enhances the stability and electrical conductivity of single-phase ZIFs-derived carbon.Among them,the ZIF-67 co-carbonization composite showed a half-wave potential of E_1/2=0.821 V,which was almost identical with the commercial 20%Pt/C.Compared with the single-phase Zn-based ZIF-derived carbon material,the half-wave potential increased by 69m V,and no"poisoning"phenomenon occurred after methanol was added.Compared with other carbon-based catalysts,ZIFs carbon-based nanomaterials have great advantages in morphology control,high porosity and easy functionalization with other heteroatoms.