| Oxygen reduction reaction（ORR）is the core process of many green energy devices that determines the efficiency of energy conversion,such as Zn-air battery and proton exchange membrane fuel cell.The slow kinetic of ORR requires precious metal catalyst of Pt-based to accelerate reaction process,which restrict the large-scale application of these energy conversion devices.Therefore,it is of great importance to develop non precious metal materials to replace commercial Pt-based precious metal catalysts.Transition metal coordinated by nitrogen doped carbon materials,referred to as M-N-C（M:Fe,Co,Mn,Zn,Cu,etc.）,are considered to be the most promising non precious metal ORR electrocatalysts,which have been widely studied.However,the precise construction of active sites in M-N-C catalyst still remains challenges,inhibiting the improvement of the activity and stability of catalytst.In this thesis,a general method of synthesizing M-N-C was developed via a synchronous complexation-polymerization strategy,in which nitrogen-containing ligand was coordinated with specific transition metal ions and diamino aromatic compound was simultaneously polymerized by the metal ion as initiator;by the following pyrolysis in a molten Na Cl bath,M-N-C was finally synthesized.The key influencing factors of this method were also systematically investigated on the derived M-N-C mophorlogy and the configuration of oxygen reduction active sites,including the molar ratio of complexing ligand and polymerizing monomer,the kinds of ligands for transition metal ions and monomers for polymerization.And the activity and stability of the prepared M-N-C ORR catalysts were evaluated under different p H value.The main achievements are as follows:（1）Flexible synthesis of M-N-C oxygen reduction catalyst by complexation-polymerization method.M-N-C catalyst was successfully prepared by using nitrogen-containing compound 2,4,6-tri（2-pyridin）-1,3,5-triazine（TPTZ）as transition metal ligand and diaminoaromatic compound 1,8-naphthalenediamine（DAN）as polymer monomer,which demonstrated the universality of synchronous complexation–polymerization method.The influence of different heat treatment temperature and thermal treatment medium on Fe-N-C catalyst was revealed.Attributed to the vast kinds of ligands,metal ions and polymerizing monomers,this strategy provides a flexible platform of synthesizing advanced M-N-C catalysts,and also provides a reference for the synthesis of other catalysts.（2）The key influence of the molar ratio of complexing ligand and polymerizing monomer on the M-N-C catalyst syntheized by complexation-polymerization method.Results showed that the molar ratio of TPTZ to DAN significantly affected the active sites,carbon structure and ORR performance of corresponding Fe-N-C catalyst.And the Fe-N-C prepared by TPTZ and DAN with the molar ratio of 1:1 shows excellent ORR performance,whose initial half-wave potential is 0.90 V in 0.1 M KOH and 0.80 V in 0.5 M H2SO4,respectively.The highest power density obtained by the prepared proton exchange membrane fuel cell and Zn-air battery using the catalyst are 640 m W cm-2 and 192 m W cm-2,respectively,demonstrating the potential of the catalyst for practical application.（3）The key influence of the kinds of ligands for transition metal ions and monomers for polymerization on the M-N-C catalyst syntheized by complexation-polymerization method.Results showed that the defects of carbon structure,specific surface areas and the content of N and metal Fe of Fe-N-C catalysts synthesized by different polymering monomers（benzidine,m-phenylenediamine,2,6-diaminopyridine and 4,6-diaminopyrimidine）are various,which further affects the oxygen reduction activity of Fe-N-C catalysts.The half-wave potential of Fe-N-C catalyst prepared by TPTZ and 4,6-diamaminopyrimidine reached 0.89 V,confirming the feasibility of synchronous complexation-polymerization strategy,and provided a new direction for further optimization of Fe-N-C catalyst. |
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