Coordination Modification Of N-containing Porous Organic Polymers And Their Catalytic Properties

Porous organic polymers own the benefits of high specific surface area,tunable pore size structure and stable backbone,bearing the promising electrode materials.Currently,most porous organic polymers are unable to anchor the active substances,which hinders their further development.Construction of N-containing porous organic polymers is expected to enhance their ability to coordinate metals as well as their electrical conductivity,thus enhancing their intrinsic catalytic activity.This topic focuses on the preparation of 2D/3D N-containing porous organic polymers together with their derivatives and explores their electrocatalytic properties.The main contents are as follows.（1）2D N-containing covalent organic framework and thier electrocatalytic oxygen evolution performance.Two AA-stacked and well-crystallized 2D covalent organic frameworks,COF-1 and COF-2,were synthesized by the Schiff base reaction of D_2h-symmetric tetra-formaldehyde 3,3’,5,5’-tetra-formyl-4,4’-dihydroxybiphenyl（TFBD）as a tetra-connected building block and two tetraamines,tetra-（4-aminophenyl）ethylene（ETTA）and tetra-（4-aminobiphenyl）ethylene（ETTBA）,which are also tetra-connected building blocks,respectively.COF-2(641 m²·g^-1)has a larger specific surface area compared to COF-1(615 m²·g^-1),and the diamond-shaped heteroporous pore size of COF-2（0.86 nm and 1.48 nm）is larger than that of COF-1（0.68 nm and 1.27 nm）;Introducing Fe,Co,and Ni metal ions into the material skeleton with the aid of post-modification has yielded six electrode materials（MCOFs）.Benefit from the large specific surface area of COF-2 and the large number of Fe-NO coordination catalytic active sites in the COF-2-Fe,it exhibited excellent oxygen evolution reaction（OER）catalytic activity with an overpotential of 282 m V@10 m A·cm^-2.（2）2D N-containing covalent organic framework-derived Fe single atoms and their electrocatalytic oxygen reduction properties.The above prepared 2D MCOF was used as a precursor for the high-temperature pyrolysis to construct Fe single atoms with Fe-N-C active centers（Fe SAC）.Powder X-ray diffraction and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy showed that Fe SAC was distributed in the form of single atoms.Due to the high content of pyridine N in Fe SAC and the strong affinity of pyridine N to oxygen atoms,it is beneficial to improve the electrocatalytic oxygen reduction activity.The Fe SAC exhibited a half-wave potential(E_1/2)of 0.897 V in an alkaline environment,outperforming the commercial Pt/C catalysts.Fe SAC was also evaluated in the practical device（zinc-air battery）,showing higher peak power density of 117.3 m W/cm² than the control battery.（3）3D N-containing porous organic polymers and their electrocatalytic oxygen evolution performance.An iron-based porous organic polymer（Fe₂-POP）was synthesized using ferrous chloride,2,6-diformyl-4-methylphenol dioxime（H₃DFMP）and tetrakis（4-boronic acid phenyl）methane（TBPM）through a one-step coordination and boronic acid esterification dehydration polymerization reaction.Fe₂-POP is an iron-based porous organic polymer with a binuclear ferrous Fe₂-POP has a high specific surface area(510 m²·g^-1)and uniform pore size（0.6～0.8 nm）.Due to the binuclear ferrous active center in the structure of Fe₂-POP,the binuclear can accelerate the electron transport and charge transfer in the oxygen evolution reaction compared with the mononuclear.As expected,the Fe₂-POP overpotential is only 258m V@10 m A·cm^-2.