Researching On Amorphous MOF-Derived Oxygen Reduction Reaction Catalysts

With the consumption of fossil energy and the increase in energy demand,people have paid great attention to the development and application of renewable energy.The fuel cell is the device that efficiently utilizes electrochemical conversion and storage of renewable energy.Due to its slow kinetics of cathodic oxygen reduction（ORR）,in the practical application,a large amount of precious metal platinum is used as a catalyst to accelerate the reaction.However,the high cost and scarcity of precious metal Pt hinders the large-scale application of fuel cells.The development of inexpensive and efficient non-precious metal ORR catalysts has become urgently needed.Metal-organic framework（MOF）-derived ORR catalysts have gained widespread attention due to their low cost and high catalytic performance.This paper uses an amorphous metal（Co,Fe,Zn）organic framework.A series of non-precious metal ORR catalysts were prepared as precursors,and they were fully characterized and tested.The main research work includes the following three aspects:（1）Research on ORR catalyst based on amorphous Co（Ⅱ）-organic framework（Co-MOF）as precursor.The amorphous form was synthesized by solvothermal method using 3,6-bis（1-imidazolyl）-1,2,4,5-tetrazine（BIMT）as ligand and Co（Ⅱ）as coordination metal ion.Co（Ⅱ）-organic framework（in combination with MOF）,and further pyrolysis of Co/N co-doped non-precious metal ORR catalyst（Co/N-C-800）.We found that after high-temperature pyrolysis of Co-MOF,the surface of the originally smooth microspheres produced a large number of mesopores and bamboo-shaped carbon nanotubes with a diameter of 10 nm.This edge defect structure makes the Co/N-C-800 higher ORR catalytic activity.Co/N-C-800 showed good ORR catalytic performance in both alkaline and acidic media.In alkaline medium,the initial potential（E_o）of Co/N-C-800 is 0.981 V（vs RHE）;in acidic medium,the E_o of Co/N-C-800 is 0.863 V.Its excellent ORR catalytic performance is also attributed to a larger specific surface area(381 m² g^-1)and a higher N content（4.95 at%）.（2）Research on ORR catalyst based on amorphous Fe（Ⅱ）-organic framework（Fe-MOF）as precursor.The amorphous form was synthesized by solvothermal method using 3,6-bis（1-imidazolyl）-1,2,4,5-tetrazine（BIMT）as ligand and Fe（Ⅱ）as coordination metal ion.The Fe（Ⅱ）-organic framework（Fe-MOF）pyrolyzed Fe-based MOF as a precursor to prepare an Fe/S/N co-doped ORR catalyst（Fe/SN-C-800）.During pyrolysis,the spherical Fe-MOF undergoes rupture,melting and recombination to form a porous cellular carbon material.The Fe/SN-C-800 has a honeycomb morphology and Fe/S/N co-doping characteristics,and the Fe/SN-C-800exhibits excellent ORR catalytic performance.In alkaline medium,the initial potential（E_o）,half-wave potential(E_1/2)and limiting current density（J_l）of Fe/SN-C-800 are0.989 V,0.879 V and 5.93 mA cm^-2,respectively.Far better than Pt/C catalyst(E_o=0.964 V,E_1/2=0.829 V,J₁=5.28 mA cm^-2).In acidic media,Fe/SN-C-800 also has good ORR catalytic properties.Its E_o,E_1/2 and J_l are 0.893 V,0.733 V and 5.50 mA cm^-2,respectively,close to the high loading Pt/C catalyst(E_o=0.922 V,E_1/2=0.758V,J₁=5.61 mA cm^-2).At the same time,Fe/SN-C-800 exhibits good stability and anti-poisoning properties in acidity.（3）Research on ORR catalyst based on amorphous Zn（Ⅱ）-organic framework（Zn-MOF）as precursor.The amorphous form was synthesized by solvothermal method using 3,6-bis（4-methyl-1H-imidazolyl）-1,2,4,5-tetrazine（mBIMT）as ligand and Zn（Ⅱ）as coordination metal ion.Amorphous Zn（Ⅱ）-organic framework（Zn-MOF）was synthesized by solvothermal method and the nitrogen-doped carbon material（N/C-900）was prepared by further pyrolysisof Zn-MOF.Due to the low boiling point characteristic of zinc（907^oC）,the precursor Zn-MOF generates a large number of micropores along with the evaporation of Zn（Ⅱ）during pyrolysis,and N₂ isothermal adsorption-desorption of N/C-900 With the test,we found that it has a high specific surface area(961 m² g^-1)and a microporous ratio of 91.7%.In an alkaline medium,E_o,E_1/2 and J_l of N/C-900 are 0.955 V,0.855 V and 7.10 mA cm^-2,respectively,and N/C-900 catalyst also have excellent stability.