Preparation Of Phthalocyanine-Based Two-Dimensional MOF And COF With High Conductivity For Electroreduction Of CO₂

Electrocatalytic conversion of CO₂ into value-added products is an effective way to solve the problem of excessive temperature rise and to alleviate energy crisis.Nevertheless,the catalytic process still encounters a series of challenges,such as poor selectivity and low energetic efficiency.Thus,it is of great significance to design and synthesize electrocatalysts for efficient CO₂ electroreduction reaction.Metal-organic frameworks（MOFs）and covalent organic frameworks（COFs）,as typically crystalline porous framework materials,possess definite adjustable chemical compisitons and pore structures,highly dispersed active sites and strong ability of CO₂ enrichment.MOFs and COFs have found extensive applications in the field of catalysis.However,the majority of MOFs and COFs have poor electrical conductivity,which make it difficult for the transfer of electrons to active sites.During electrocatalysis,these catalysts usually exhibit low current density,which thus impede their applications.In view of this,we synthesized two cases of intrinsically conductive crystalline porous frameworks and investigated their performance in electroreduction of CO₂.The contents of this dissertation includes the following parts:（1）2,3,9,10,16,17,23,24-octaaminophthalocyaninato nickel（II）（Ni Pc-（NH₂）₈）with18-electrons macrocyclic conjugation structure was chosen as the organic ligands to assemble with nickel chloride hexahydrate under solvothermal condition to give the crystalline porous two-dimensional（2D）MOF,Ni Pc-Ni（NH）₄.Due to the high overlap of d-πconjugation orbitals,Ni Pc-Ni（NH）₄ showed fast electron transfer ability.In comparison with the traditional 2D MOF electrocatalysts,Ni Pc-Ni（NH）₄ exhibited excellent catalytic performance towards electroreduction of CO₂ to CO with a Faradaic efficiency of 96.4%at-0.7 V vs.RHE and a CO current density of 24.8 m A cm^-2 at-1.1V vs.RHE.To investigate the catalytic active sites of Ni Pc-Ni（NH）₄,we synthesized a typical conductive 2D MOF Ni₃（HITP）₂,which contained the same Ni（NH）₄ nodes with that of Ni Pc-Ni（NH）₄.Based on the results of series of control experiments,Ni-N₄ units of the phthalocyanine ring are suggested to be the catalytic active sites.In addition,theoretical calculations together with the analysis result of noncovalent-interaction（NCI）and atomic force further verified the above proposal.（2）We further synthesized a crystalline porous 2D COF termed as Ni Pc-COF by the condensation reaction of 2,3,9,10,16,17,23,24-octaaminophthalocyaninato nickel（II）and2,7-bis（1,1-dimethylethyl）-4,5,9,10-pyrenetetrone.The obtained Ni Pc-COF possessed full in-planeπ-conjugation,and thus showed intrinsically high conductivity.The results of CO₂ electroreduction experiments revealed that Ni Pc-COF has high CO₂ reactivity and can efficiently catalyze the reduction of CO₂ to CO within the investigated potential range,with a Faraday efficiency over 93%.Compared with the previously reported COF electrocatalysts,the results showed that the optimal CO selectivity（99.1%）and partial current density of Ni Pc-COF were much higher than the traditional COF materials.Moreover,the long-term catalytic operation indicated that Ni Pc-COF had good stability over 10 h,which highlighted the advantage of the robust 2D framework linked by pyrazine units.The theoretical calculations further proved the high catalytic performance of Ni Pc-COF.The above work is helpful for the development and applications of conductive framework materials for electrocatalytic reduction of CO₂,and provides new scientific insights for the design of efficient electrocatalysts in the future.