Preparation Of CMPs Electrocatalysts Containing N-S Diatoms And ORR Properties

Noble metal Pt is widely considered as cathode catalyst of high active components in fuel cells,but its high cost and limited natural resources have become the main bottleneck restricting the commercialization of fuel cells.In order to solve this problem,a lot of research work has been focused on the development of non-noble metal catalysts for fuel cells.Among them,heteroatom doped carbon material catalysts have developed rapidly.Conjugated microporous polymers（CMPs）have uniqueπ-πconjugated structure,large specific surface area and good pore structure.More importantly,CMPs have the advantages of adjustable structure and composition that natural carbon materials do not possess.The preparation methods of CMPs are various,and they can maintain excellent pore properties after carbonization,CMPs are ideal precursors of porous carbon materials.Therefore,based on the unique physical and chemical properties of CMPs,seven kinds of CMPs were synthesized by Sonogashira-Hagihara reaction using suitable alkynyl aromatic compounds and halogenated aromatic compounds as monomers.A series of heteroatom-doped carbon-based catalysts based on conjugated microporous polymers were synthesized by physically doping CMPs with ionic liquids as sources of nitrogen and sulfur atoms,and their electrochemical catalytic properties were systematically investigated.The main contents of this paper are as follows:（1）Using Pd（0）/CuI as catalyst,two conjugated microporous polymers were synthesized by self-polymerization of 1,3,5-triethynylbenzene and copolymerization of 1,3,5-triethynylbenzene and 1,4-diethylbenzene via typical Sonogashira-Hagihara reaction,namely 1,3,5-triethynylbenzene self-polymerization microporous polymer（CMPs-1）and 1,3,5-1,4-copolymerized microporous polymer（CMPs-2）.Four heteroatom-doped carbon-based catalysts based on conjugated microporous polymers,C-CMPs-1NP、C-CMPs-2、C-CMPs-3NP and C-CMPs-4,were prepared by using ionic liquids as the source of nitrogen and sulphur,and then carbonized with CMPs-1and CMPs-2 as precursors.The chemical structure and surface chemical composition of heteroatom-doped carbon-based catalysts based on conjugated microporous polymers were characterized by advanced analytical methods such as SEM,elemental analysis,Raman spectroscopy,XPS and XRD.The morphology,thermal stability and pore properties of heteroatom-doped carbon-based catalysts based on conjugated microporous polymers were characterized by means of SEM,TEM and BET.The results showed that the presence of N promoted the graphitization of carbon materials and induced the formation of more stable aromatic groups（graphite-N,pyridine-N）.The doping of sulfur and nitrogen atoms can provided the large number of defects,and the double doping of S and N atoms can formed a synergistic effect to further improve the oxygen reduction activity.The conjugated microporous polymers had unique pore structure,the specific surface area and micropore volume of C-CMPs-1NP catalyst reached 937.6 m² g^-1 and 0.396 cm³ g^-11 respectively.C-CMPs-1NP catalyst exhibited excellent oxygen reduction reaction（ORR）activity in alkaline medium during oxygen reduction test,the half-wave potential reached 0.82V,initial potential was 0.95 V（vs.RHE）,and diffusion limit current density was 4.2mA cm^-2.Anti-methanol poisoning experiments showed that the cyclic voltammetry（CV）curve had almost no ORR polarization curve drift after the addition of 3 M methanol,and the methanol tolerance was much higher than that of commercial 20wt%Pt/C.（2）Three macrocyclic conjugated microporous polymers were synthesized by Sonogashira-Hagihara reaction of 1,3,5-triacetylenebenzene with 1,4-diiodobenzene,4,4’-diiodobiphenyland4,4’’-diiodoterphenylrespectively.Subsequently,carbon-based catalysts（C-CMPs-1INP,C-CMPs-2INP and C-CMPs-3INP）doped by sulfur-nitrogen double-doped macrocyclic conjugated microporous polymers were prepared by high temperature carbonization modified by ionic liquids.The morphology,thermal stability and pore properties of carbon-based catalysts doped with macrocyclic conjugated microporous polymers were characterized by means of SEM,TEM and BET.The results showed that the three polymer samples had large specific surface area and abundant pore structure.It was found that the shorter the monomer chain length,the better the ORR performance of the conjugated microporous polymer.ORR measurements based on macrocyclic conjugated microporous polymer doped carbon-based catalysts in 0.1 M KOH solution showed that C-CMPs-1INP had excellent ORR catalytic activity and good stability.The specific surface area of C-CMPs-1INP catalyst reached 592.6 m² g^-1,and the micropore volume reached 0.221 cm³ g^-1.C-CMPs-1INP exhibited excellent redox activity in alkaline medium:half-wave potential was 0.81 V and initial potential was0.92 V（vs.RHE）,and diffusion limit current density was 3.8 mA cm^-2.In addition,the anti-methanol interference ability of the sample was far superior to that of the commercial Pt/C catalyst.