ZIFs Derived Hierarchically Porous Carbon Materials And Their Electrocatalytic Properties

As a new type of energy power device with high efficiency,energy conservation,environmental protection and sustainability,fuel cell has attracted wide attention.However,the further development of fuel cell is limited by the sluggish kinetic process of cathode reaction.Precious metal,such as Pt catalyst is a commercial catalyst for efficient cathodic oxygen reduction（ORR）process,but precious metal is still limited by the development of fuel cell due to its high cost,scarce reserves and poor stability.Therefore,it’s pressing to develop a low-cost and stable non-precious metal catalysts for ORR process.Recently,carbon-based catalysts doped with heteroatoms,especially transition metal atoms,have attracted much attention.Its special catalytic site,metal-nitrogen（M-N₄）,has been shown to have catalytic activity no less than that of Pt-based catalysts.Based on ZIFs,polyaniline-pyrrole and other common organic precursors,this paper prepared three kinds of Co and N co-doped carbon materials by in-situ doping strategy,studied the physical and chemical characteristics of the materials such as morphology,structure and composition,and characterized the electrochemical performance of the catalyst,as follows:1.The Co and N co-doped multistage porous nanofibers（Co-N-PCNF）were prepared by electrospinning technology and in situ synthesis of Co,Zn Bimetallic ZIFs,and the structure,composition and electrochemical properties of the material were charactered.The results show that a large number of nano-sized Co particles are exist in Co-N-PCNF-025,which promotes the formation of graphite structure;Besides,Co and N elements from Co-N-PCNF-025 were form the Co-N_xstructure.The electrochemical measurements results show the ORR activity of Co-N-PCNF-025 is close to that of the Pt/C catalyst.According to the calculation of K-L curve,the oxygen reduction reaction of Co-N-PCNF-025 is mainly an efficient 4-electron process.2.The Co and N co-doped hollow nanospheres（Co-N-HNCS）were prepared by in-suit doping and surface modification and the structure,composition and electrochemical properties of the material were charactered.The results show that the metal element in Co-N-HNCS exbihits well dispersion without obvious aggregation.In addition,Co and N elements from Co-N-HNCS-033 were form the Co-N_x site.The electrochemical measurements results show the ORR activity of Co-N-HNCS-033 is close to that of the Pt/C catalyst.According to the calculation of K-L curve,the oxygen reduction reaction of Co-N-HNCS-033 is mainly an efficient 4-electron process.3.On the basis of 2,Co and N co-doped hierarchical porous hollow carbon spheres（Co-N-HPHNCS）were prepared by KOH chemical activation treatment,and analyzed the relation between the application amount of KOH and the ORR activity of samples.The results show that the specific surface area of Co-N-HPHNCS-033_2:1 up to 445.3 m² g^-1;In addition,Co-N-HPHNCS-033_2:1 still retains certain elements of Co and N,which form the structure of Co-N_x.The electrochemical measurements results show the ORR activity of Co-N-HPHNCS-033_2:1 be superior to Co-N-HNCS-033 and close to that of the Pt/C catalyst.According to the calculation of K-L curve,the oxygen reduction reaction of Co-N-PCNF-025 is mainly an efficient 4-electron process.