Controllable Fabrication Of Porphyrin Based Organic Electrocatalyst For Oxygen Reduction Reaction

With the continuous development of economy,the shortage of fossil energy and environmental pollution have become serious problem in current society.In order to solve these problems,researchers have explored various new types of energy,fuel cell have attracted widespread attention,due to its high energy conversion efficiency and environmental friendly property.The catalytic efficiency of cathode of the fuel cell is a key factor influencing the performance of fuel cell and restricting its entry into the market.Because the catalytic efficiency of cathode catalyst is much lower than that of the anode catalyst,researches on efficient catalyst for cathodic oxygen reduction reaction?ORR?have become a hotspot in recent years^[1-3].At present,the best cathode catalyst is platinum-based materials,but platinum is limited,expensive,and easily poisoned.Therefore,the researches focus on searching for efficient and economic non-noble metal catalysts,such as carbon-based materials,transition metal chalcogenides and organometallic compounds,among which porphyrin-based macrocyclic organic compounds have attracted much attention,due to their unique macrocyclic structure and excellent catalytic performance.The chemical properties of porphyrins are stable.In addition,the properties of porphyrin-based electrocatalysts can be improved by modifying the molecular structure of porphyrin and changing the central metal,as well as further compounding with other materials.The reported porphyrin-based electrocatalysts in literature are maily fabricated by carbonization of porphyrins to improve their electrocatalytic performance.However,in this process,the structure of porphyrins is damaged.In this paper,we successfully synthesized porphyrin metal coordination polymers,and further combining them with multi-walled carbon nanotubes.Electrocatalytic test indicated that the porphyrin-based organic hybrid materials showed excellent ORR performance.The content of this paper contains the following two sections:1.Preparation of TPyP-Co@MWCNTs single metal composite for oxygen reduction reaction.The main experimental methods used in this paper is hydrothermal method,using TPyP to react with the salts in Co and producing corresponding porphyrin coordination.In addition,in order to improve the conductivity,during the synthesis process,the multi-walled carbon nanotubes were introduced,and its combination with ultrasonic disrupter to make ultrasonic dispersion of raw materials.Finally,the core-shell structure of porphyrin carbon nanotube was obtained,and the generation of composite materials also was proved through a series of characterization.Then,the electrocatalytic performance in ORR of material was tested,and the test results were the following:the electric potential for oxygen reduction of the optimal samples is-0.180 V?vs.Ag/AgCl,hereinafter the same?,the half wave voltage is-0.176 V.When limited current reached 5.1mA/cm²,equivalent to Pt/C,the electron transfer number is 4,its stability and the performance of anti-methanol interference is better than that of Pt/C catalyst.2.Preparation of FeTPyP-M@MWCNT bimetallic composite for oxygen reduction reaction.The composite nanomaterial of bimetallic porphyrin complexes with carbon tubes was prepared,and the electrocatalytic oxygen reduction performance was tested.The porphyrin was selected as FeTPyP,and the metal salt was Co,Ni,Fe,and the synthesis method was solvothermal method.The results were as follows:through such characterization methods as X-ray diffraction,Fourier transform infrared spectroscopy,Raman spectroscopy,High Resolution Transmission Electron Microscopy,the formation of bimetallic coordination polymerization was proved.The results of performance test show that the performance of oxygen reduction reaction is the best when the nitrogen in the center ring of porphyrin has coordination with Fe,and the coordination metal of pyridine nitrogen is Co among such three metals as Fe,Ni and Co,which indicates that the coordination metal of peripheral pyridine nitrogen affects the catalytic performance of the materials,and the synergism among metals is also a factor that cannot be ignored.The oxygen reduction electric potential of the optimal material is-0.195 V,ORR peak potential is-0.100 V,the half-wave electric potential is-0.193V,the limited current is 5.2 mA/cm²,and the number of transferred electrons is between 3.7³.9.After a current drop of 10000 s to 85.5%of the initial current.This data is superior to that of the Pt/C material and the material has good anti-methanol toxicity.