Preparation By Pyrolysis-free Method And Research Of Their Performance Of COP-based Oxygen Reduction Electrocatalysts

In recent years,transition metal-based MOFs/COFs single-atom catalysts have been found to have excellent performance beyond that of noble metals,but traditional preparation methods often involve high-temperature pyrolysis.There are many uncertainties in the high temperature process:It is easy to appear metal clusters;The configuration of catalyst is indefinite and the morphology is difficult to manipulation,etc.;These problems bring difficulties to the in-depth understanding of the catalytic mechanism.Exploring non-pyrolysis methods to synthesize catalysts with well-defined structures is of great significance for the catalytic mechanism research and the preparation of numerous catalysts.Therefore,in this paper the preparation and activity of COP-based oxygen reduction catalysts were studied by non-pyrolysis methods,and their application in batteries was tested.The main research results and innovations are as follows:（1）Preparation of well-defined COP-based three-dimensional structured oxygen reduction catalysts.A well-defined iron polyphthalocyanine（pFePc）macrocyclic compound was synthesized by a low-temperature microwave method,and three-dimensional hierarchical porous nitrogen-doped graphene（3D NG）was constructed as a support.The pFePc and3D NG were co-sonicated and composited in a high-pressure hydrothermal kettle to form 3D NG@pFePc,which is a product of pFePc supported on the surface of 3D NG.The physical characterization of the catalyst shows that the morphology is porous on the surface,with many mesopores and macropores.XRD,XPS,Fe K-edge XAF and other tests show that the Fe element in the catalyst 3D NG@pFePc is Fe-N₄ coordination,and there is no metal clusters or metal oxides.In 0.1 M HCl O₄ electrolyte,3D NG@pFePc exhibits good oxygen reduction catalytic activity similar with non-noble metal catalysts partially obtained by pyrolysis.It has an E_onset and E_1/2 of 0.88 V（vs.RHE）and 0.74 V（vs.RHE）,respectively,and the electrochemical specific area of up to 667 m²g^-1,which is much higher than that of the two-dimensional nitrogen-doped graphite-supported iron polyphthalocyanine 2D NG@pFePc,the half-wave potential is only 0.69 V,and the electrochemical specific area is 241.5 m²·g^-1.3D NG@pFePc and 2D NG@pFePc were loaded into hydrogen-oxygen fuel cells,respectively,where the power density of 3D NG@pFePc was 30 mW·cm^-2 higher than that of 2D NG@pFePc.（2）Preparation of Conjugated Layered MOF/COP Efficient Bifunctional Catalysts.FeNi nanosheet（NS）bimetallic MOF material were synthesized by stirring at room temperature,and the FeNi-NS and COP Fe were combined into a lamellar MOF/COP material by utilizing theπ-πinteraction between layers,and added XC-72 increases the conductivity and dispersibility of the material and enhances its electrocatalytic performance.After a series of characterizations,the morphology of the catalysts shows that the FeNi-NS@COP Fe material is coated with XC-72 microspheres.The structure of the catalyst is analyzed by XRD,Raman and XPS.Metal clusters and metal oxides were found to be absent from the catalyst.In alkaline electrolyte,the catalyst FeNi-NS@COP Fe-XC72 exhibits excellent two-way catalytic performance with a half-wave potential is 0.9 V,which is higher than that of the 20 wt%Pt/C catalyst.The potential is 1.65 V when current density is up to 10 m A·cm^-2,which has comparable oxygen evolution performance to commercial Ir O₂.Further,it was applied to rechargeable zinc-air batteries with a power density of115 mW·cm^-2.