Preparation Of Multi-elements Doped Carbon Materials From Metal-coordination Polymer Precursors And Oxygen Reduction Property Study

Carbon materials have many advantages including low cost,excellent electrical transport properties,chemical stability,highly active surface area,and wide range applications.They have been widely used in energy storage materials and electrical catalytic field.However,pure carbon materials have many defects including highly hydrophobic surface,limited active sites and electrical in nature,which bring many limitations for their application in energy material field.Heteroatom-doping can increase the surface wettability of carbon materials,affect the distribution of charge in carbon materials and form more active sites,which are beneficial for the application of carbon materials in the energy field.Herein,we focused on the metal complexing method,introducing inorganic atoms and metal ions into the polymer precursors at the same time.After carbonization,we prepared three kinds of carbon materials with inorganic atoms and metal ions co-doped,and achieved the control over active sites,element composition and morphology.And it is also confirmed that these factors could affect the oxygen reduction reaction(ORR)activity.This paper including following three parts:(1)Based on the coordination reaction between 1,3,5-tris(4-aminophenyl)benzene and Fe3+,we developed a facile method to design metallosupramolecular polymer precursors of CNS-TAs.After carbonization,the CNSs carbon materials containing Fe and N elements co-doped were obtained,which denoted as CNS-0.6Fe,CNS-0.8Fe and CNS-1.0Fe.The as prepared carbon flakes displayed wrinkled edges,and comprised with active sites of both Fe3C and Fe-Nx.The unique structure is beneficial for the contact between active sites and oxygen molecules during ORR process.CNS-0.8Fe possesses relative higher specific surface area,better developed lamellar structure and higher pyridinic N and Fe-Nx contents than CNS-0.6Fe and CNS-1.0Fe.These three reasons cause that CNS-0.8Fe has the best ORR activity with Eonset and Ehalf-wave of 0.93 and 0.80 V in alkaline system respectively,which were very close to that of the commercial Pt/C.We also confirmed that CNSs catalyze the ORR process in four electron process,and also demonstrate good stability and catalytic selectivity.(2)Based on the design of the molecular structure,we synthesized the monomer of DFC with catechol groups through dehydration condensation reaction between 4,4’-(((perfluoropropane-2,2-diyl)bis(4,1-phenylene))bis(oxy))dianiline and 3,4-dihydroxybenzaldehyde,and synthesized the monomer of TBB with phenylboronic acid groups from dehydration condensation reaction between tris(4-aminophenyl)amine and 4-formylphenylboronic acid.We developed a supramolecular approach to synthesize boronate polymer spheres(BPN)composite with B,N,F elements doping through nucleation-elongation polymerization between monomer DFC and TBB driven by B-N dative bond.We used Fe3+to etch BPN for 6,12 and 18 h,then carbonized at 650℃ to get the B,N,F and Fe elements co-doped CSs carbon materials named as CS6-650,CS12-650 and CS18-650.To evaluate the carbonization temperature on the electrochemical properties of carbon shells,control experiments were performed at pyrolysis temperatures of 550 and 750 ℃,and the prepared samples were denoted as CS12-550 and CS12-750.Among CSs carbon materials,CS12-650 possesses the thinnest carbon layer,high specific surface area,best hollow structure,and also possesses the best ORR activity with Eonset and Ehalf-wave of 0.91 and 0.82 V in alkaline system respectively,which were very close to that of the commercial Pt/C.We found that the F element in the carbon matrix could promote the generation of defect sites,which was beneficial and important for the ORR activity.We also confirmed that CSs belong to four electron process catalyst,and have better stability and catalytic selectivity than Pt/C.(3)We synthesized the monomer of DNC with catechol groups using dehydration condensation reaction from benzene-1,4-diamine and 3,4-dihydroxybenzaldehyde.We developed a supramolecular approach to synthesize boronate polymer spheres(BPN)composite with B,N elements doping through nucleation-elongation polymerization between monomer DNC and TBB driven by B-N dative bond.After introducing Sn4+and Fe3+mixed methanol solution to etch BPN,the metallosupramolecular polymer with hollow structure could be obtained based on Kirkendall effect.After double carbonization at 850℃,the Fe/Sn-CSs carbon materials co-doped with B,N and metal elements can be get,named as Sn-CS,Fe-CS and Fe/Sn-CS.The synergistic effect between Sn4+and Fe3+could improve the etching efficiency towards boronate polymer.The control of hollow structure and carbon layer thickness is realized by this bimetal ions(Sn4+and Fe3+)etching method based on Kirkendall effect.Fe/Sn-CS possesses the thinnest carbon layer,the highest specific surface area,and can be carbonized into carbon shells comprising FeSn2 alloy.The as formed FeSn2 alloy in the carbon matrix possessed characteristics of rich in electrons,excellent conductivity,high chemical activity,easy to combine with oxygen,and a high binding affinity to oxygen molecules,thus leading to a high catalytic activity towards ORR.So the Fe/Sn-CS has good ORR activity with onset potential(Eonset)of 0.94 V and half-wave(Ehalf-wave)of 0.84 V vs.RHE.We also confirmed that Fe/Sn-CSs have high four electron transfer number,and also with good stability and catalytic selectivity.