| The fuel cell has the advantages of high efficiency,no environmental pollution,and wide range of reactant resources,and it has become a hotspot energy conversion device for research today.However,due to the limitation of the kinetics,the oxygen reduction reaction（ORR）of the fuel cell’s cathode is slow,which limits the popularization and application of fuel cell.Therefore,it is very important to study the cathode catalysts that accelerate the oxygen reduction reaction.In nature,under the catalytic action of biological enzymes,the ORR involved in cellular respiration can be efficiently performed.The core structural unit of the catalytic ORR enzyme is the metalloporphyrin,so the metalloporphyrin has become the core structural unit of the bionic ORR catalyst.The metal porphyrin with a metal-N4 structure has good thermal stability and chemical stability,and it has a good 4-electron selectivity in the ORR reaction.In addition,the electron transport chain is an important guarantee for the continuous and efficient enzyme-catalyzed 4-electron ORR in vivo.The reduced graphene is simple in preparation,which has good conductivity and large specific surface area,and is favorable for the conduction of electrons and the exposure of active sites.Graphene oxide contains a variety of oxygen-containing functional groups,good water solubility,so it can be complexed with different kinds of porphyrins,and is easily reduced to reduced graphene oxide.In this dissertation,graphene oxide（GO）and porphyrin were used for compounding.After the completion of the compounding,reduction was performed to improve the electron transfer ability of the complex and the catalytic performance of ORR was investigated.The type of interaction between porphyrin and graphene is a key factor affecting the uniform distribution of the active site of the catalyst.On the one hand,non-covalent bonds are achieved using electrostatic interactions.By using the electrostatic attraction between negatively charged graphene oxide and positively charged pyridyl cobalt porphyrins,we adjusted the reaction system and the optimum pH values of the two,thereby regulating the interaction between the two,and seeking for optimal condition of non-covalent bonds.The optimal conditions for compounding are to use a layer of PtCl42-with electrostatic interaction to obtain a compound.A series of characterizations such as UV-visible absorption spectrum and Zeta potential,show that the three non-covalent bonds are achieved through electrostatic attraction.After the high temperature pyrolysis,a composite catalyst prepared.Characterizations of the composites were Co-Pt alloys and Co-N structures by XRD,HRTEM and elemental mapping.XPS measurements performed to prove that the electrons on Pt were transferred to Co and N,its electrons are shifted to change the electronic structure,thereby promoting ORR activity.The mechanism of oxygen reduction explored by rotating disk electrode and the rotating ring disk electrode,and found that the initial potential was increased by 20 mV from Pt/C.The ORR reaction mechanism calculated by calculating the number of transferred electrons.It is a 4-electron transfer process,and the yield of intermediate product H2O2 is low.Compared with other samples,we attribute its high performance to the synergistic effect between CoPt alloy and CoN.The electrochemical active area tested and found to have a higher electrochemical area and the catalyst stability was better than Pt/C.On the other hand,porphyrin-graphene complexes were achieved using covalent bonds.The carboxylated graphene oxide is rich in carboxylic acid oxygen-containing functional groups,and the tetraaminophenyl metalloporphyrin contains four anilino groups,and a stable amide bond formed by using a covalent bond between a carboxylic acid functional group and an anilino group to covalently bonded graphene oxide-metal porphyrin complexes.The physical properties of the obtained complexes characterized by SEM and TEM,and the presence of amide bonds characterized by Fourier transform infrared spectroscopy.After high-temperature calcination,we found that the rGO’-FeTAPP-800 ORR had the best performance.The number of electrons transferred by the K-L equation was 3.42,and the starting potential was-0.01 V（vs.Hg/HgO）,indicating its ORR process include two-electron process and four-electron process coexist,and the proportion of four electrons is 71%.The stability test of the four-electron process shows that the catalyst is superior to Pt/C stability and methanol resistance. |
