The Preparation And Electrochemical Properties Of The Materials Based On MOF

With the serious destoryment of human beings'living environment,the concept of green and environment protection is becoming popular among people all over the world.As a type of new energy,proton exchange membrane fuel cell?PEMFC?gets the favor of people,but unfortunately the commercial Pt/C catalyst used in PEMFC is so expensive that it has impeded the development of PEMFC.So it is very urgent for us to develop a new kind of non-noble metal catalysts.As one kind of porous materials,metal-organic frameworks?MOFs?have carbon source,metal source and tunable structure.The abundance in microporous and mesoporous structure endows MOFs the potential to catalyze oxygen reduction reaction?ORR?.However,the porous materials derived from pure MOFs have limited ORR catalytic activities which are far from with commercial Pt/C,they can't satisfy the actual demand.Hence,we need to modify the properties of MOFs for the purpose of getting ORR catalysts with improved activities.This article selected Co-MOF?ZIF-67?as the precursor and improved the material's ORR catalytic activity by two different ways,one was doping with the second metal,the other was combining with graphene.The main research methods and conclusions are just as follows:1)We used Co-MOF as carbon source and the first metal source and adopted the method of doping the material with the second metal?M=Fe?Ni?Cu?Zn?in order to enhance the material's catalytic activity.This method was easy to operate at room temperature,both transmission electron microscopy?TEM?and X-ray photoelectron spectroscopy?XPS?indicated that the second metal was doping with Co successfully.Besides,N element was evenly dispersed and M/Co-N-Cstructure was formed.Moreover,the metal nanoparticles were closely wrapped by a few layer of graphite carbon and the spatial confinement could suppress the dissolution and aggregation of metal nanoparticles,which was advantageous for the electron transmission during the reaction and important for ORR catalytic activity.The electrochemical performance of M/Co-N-C showed that Ni/Co-NC had the best ORR catalytic activity in both alkaline and neutral conditions.At a rotation rate of 1600 rpm,the onset potential and limited current density of Ni/Co-NC were higher than that of Pt/C.Ni/Co-NC catalyst had a desired four-electron process.Furthermore,Ni/Co-NC had better stability and methanol tolerance than Pt/C.All in all,the results demonstrated that Ni/Co-NC was an excellent cathode catalyst.2)The 2-Methylimidazole aqueous solution is electropositive and the graphene oxide?GO?aqueous solution is electronegative.We utilized this phenomenon to combined 2-Methylimidazole with GO by electrostatic attraction.Meanwhile,cobalt acetate combined with 2-Methylimidazole through coordination bond and formed Co-MOF structure.So repeatedly,we loaded Co-MOF on the surface of GO layer by layer.Scanning electron microscope?SEM?,TEM and XPS revealed that Co-MOF combined with GO successfully and we got GO/Co-MOFcompound structure.We investigated the optimum carbonization temperature of GO/Co-MOF and found that the sample carbonized at 600?had the best ORR catalytic activity.At the optimum carbonization temperature,we also studied the influence of the number of self-assembly processes on the sample's ORR catalytic ability.The LSV indicated that the sample had the best ORR catalytic activity when the number arrived 6.At a rotation rate of 1600 rpm,the onset potential and limited current density of the catalyst was 0.09 V?vs.Hg/HgO?,5.5 mA cm^-2,respectively,which was comparable to that of commercial Pt/C catalyst.In addition,the catalyst had better stability and methanol tolerance than Pt/C.Sothis materialas-synthesized had good catalytic activity as one of ORR catalysts.