The Study Of Bimetallic Coordination Metal-organic Framework Derived Electrocatalysts Preparation And Their Oxygen Reduction Performance

Platinum catalyst with high-efficiency catalytic performance acts as a cathodic catalyst of oxygen reduction reaction?ORR?in proton exchange membrane fuel cell?PEMFC?,however,its high price,rare reservation and poor stability restrict its industrial application.Metal organic framework?MOF?is a kind of new material,which is composed of metal ions and organic ligands by coordination bonds via self-assembly.MOF has the advantage of controllable structures,high specific surface area and channel adjustable,which makes this material becoming an ideal candidate for ORR catalysis.But it still has some drawbacks,such as low electrical conductivity and monometal catalytic activity.In this work,two-coordination metals?Fe/Co?doped MOF was synthesized by hydrothermal method.The following carbonization and etch by acid promotes higher catalytic ability for ORR.Electrostatic spinning was used to fabricate porous carbon fibers using the MOF derivated material,building up fiber-type network to improve electrical conductivity,thereby enhancing the performance of ORR.The details of research results are illustrated as follows:Fe/Co doped MOF was prepared by hydrothermal synthesis as the precursor of catalyst.And then it was carbonated and etched by hydrochloric acid to obtain the M-Ta catalyst?T represents the carbonization temperature?.Its physical performance,like material'structures,and pore structures,were investigated in different carbonization temperatures.Meanwhile,the relationship between material structures and ORR performance was also studied.As increase of carbonization temperature,the graphitization degree of M-Ta raised gradually,while the specific surface areas of M-Ta decreased.M-800a showed well ORR performance with a starting voltage in 1.06 V,maximum current density of 3.82 mA cm^-2,Tafel slope in 114 mV dec^-1,respectively.Meanwhile,its reaction electron number was 3.94,which was fitted for four electrons catalytic process.It proved that Fe/Co doped MOF derived catalysts materials exhibited good catalytic kinetic behavior when the carbonization temperate was 800oC.Since nanoscale MOF materials exhibit higher stability in materials'structure,this work focuses on the tuning of nanoscale MOF's particle size via hydrothermal synthesis with reaction solvent in different ratio.Meanwhile,the physical performance under various carbonization temperatures,such as materials'structure,specific surface area and pore structure,and the relationship between materials'structure and ORR performance were studied.Fe/Co doped MOF with 300 nm particle size was successfully synthesized and N-Ta catalyst was prepared by following carbonization and etch process.With the increase of carbonization temperature,the graphitization degree gradually increased,while the specific surface suffers from a fluctuation with a slight increase at first,it reached 630.02 m² g^-11 at 700oC.N-800a showed outstanding ORR performance with starting voltage at 1.10 V,maximum current density of 5.88 mA cm^-2,Tafel slope in 84 mV dec^-1,respectively.Its reaction electron number was 3.98,which was fitted for four electrons catalytic process.It illustrated that Fe/Co doped MOF derived catalysts material had good catalytic kinetic behavior when the carbonization temperate was 800oC,and its ORR activity and kinetic behavior were better than those of micro-scale Fe/Co doped MOF.Fe/Co doped MOF fiber network was fabricated by the composition of Fe/Co doped MOF and polyacrylonitrile?PAN?using electrostatic spinning process.Carbonization and acid etching processed were conducted to form a fiber-type ORR catalyst,which was named as S_xCNF-Ta?x represents doping ratio for MOF material?.These studies showed the effect of carbonization temperature and doping ratios of structure,specific surface areas,pore structures,and the degrees of graphitization.Meanwhile,the relationship between structures and ORR performances was also studied.It showed that the nano Fe/Co doped MOF fiber catalyst was successfully synthesized,and its ORR performance was the best both micro-scale and nano-scale Fe/Co doped MOF derived catalysts.S_1.5CNF-800a's starting voltage,limiting current density and Tafel slope were 1.17 V,5.68 mA cm^-22 and 129 mV dec^-1,respectively.Its reaction electron number with four electronic catalytic process.