Design And Preparation Of Metal-Organic Framework/Conducting Polymer Composite Nanofilms For Electrocatalytic Reduction Of Carbon Dioxide

Since the third industrial revolution,the consumption of conventional fossil energy by industry,construction,and transportation has rapidly increased.The consumption of large amounts of fossil energy not only leads to a dramatic depletion of conventional energy stocks but also has unpredictable negative consequences for the global environment,most notably due to unrestricted carbon dioxide（CO₂）emissions.Therefore,CO₂ reduction projects such as"carbon peaking"and"carbon neutral"have become the goal of all countries in the world,and electrocatalysis is considered one of the most promising CO₂ reduction technologies from the viewpoint of industrial application feasibility.This is because electrocatalytic CO₂ reduction（CO₂RR）has the advantages of high catalytic efficiency,simple installation,mild and controllable reaction conditions,and the ability to be used in conjunction with solar/wind energy and other clean energy sources,which further enhances the application prospects of CO₂RR.Metal-organic framework（MOF）,a newly emerging highly crystalline porous material in the last two decades,has a designable internal pore structure,large specific surface area,and pre-tailorable physicochemical properties.In CO₂RR,the homogeneity of MOF metal centers facilitates the high selectivity of the characteristic reduction products.However,at the same time,we note that the inherent limitations of MOF materials,such as their poor electrical conductivity and low catalytic site utilization,can seriously limit the broad application of MOF in practice.Therefore,the use of customized MOF-based composites is one of the effective strategies to solve this problem and improve the electrocatalytic efficiency of MOF in CO₂RR.Based on this,this thesis combines the current research results of MOF-based CO₂RR electrocatalysts.It develops MOF-polymer thin film materials with high selectivity and high conductivity to achieve the results of high catalytic efficiency for CO₂.The analytical characterization,reduction performance evaluation,and electrocatalytic mechanism of MOF-polymer materials have confirmed the rationality and effectiveness of the above strategies and methods,thus providing a new idea and basis for the design and preparation of MOF-based composites for electrocatalytic CO₂ reduction.The research of this thesis mainly includes the following.（1）Preparation of ZIF-8@PPy composite nanofilm electrocatalysts.ZIF-8 nanofilms were prepared by a layer-by-layer self-assembly method,and then MOF-polymer composites were obtained on ZIF-8 nanofilms by in situ electrochemical polymerization of pyrrole monomers.By adjusting the polymerization conditions,the charge transfer was greatly promoted,which in turn improved the effective utilization of catalytic active sites to obtain efficient and selective CO₂RR.polypyrrole chains were precisely wrapped around the ZIF-8 nanocrystals in a synergistic manner to provide a continuous electron conduction channel.Furthermore,DFT calculations showed that the grafting of polypyrrole shifted the sp2 C atomic site of ZIF-8 to the adjacent sp² C atomic site of grafted polypyrrole,promoting the formation of*COOH and ultimately leading to the increase of CO₂RR activity.（2）Preparation of polymer-MOF composite nanofilms containing different functional groups.A series of ZIF-8@Polymer composite nanofilm electrocatalysts were synthesized by the electropolymerization of monomer molecules with different functional groups,which electrochemically polymerized conducting polymer chains in situ into surface-mounted ZIF-8nanofilms by a programmed layer-by-layer assembly（Lb L）technique.By introducing polymers containing different H-bonding functional groups into the MOF,the enabled conducting polymer network can facilitate rapid charge transfer to catalytic sites and capture immobilized reaction intermediates,ultimately enabling the effective utilization of the catalytically active sites of the composite to obtain efficient and selective CO₂RR.we selected three conducting polymers to precisely wrap around the ZIF-8 nanocrystals in a synergistic manner.The conducting polymer network provides a continuous electron conduction channel.This provides some inspiration for the design and construction of MOF-based CO₂ conversion electrocatalysts.（3）ZIF-L@PCA composites with restricted domain polymerization effect were prepared.Rapid charge transport and improved catalytic active site accessibility were achieved by synthesizing poly（caffeic acid）（PCA）confined to the nanopores of ZIF-L films.By immersing the obtained ZIF-L films in a solution containing CA monomer to fully diffuse the CA monomer into the MOF pores,followed by in situ electrochemical polymerization,the obtained ZIF-L@PCA can form a continuous conductive network within the MOF pores.Compared with the conventional ZIF-L,the selectivity of ZIF-L@PCA for CO was 71%at-1.1 V.This study highlights the importance of in situ electrochemical polymerization in MOF to obtain a continuous conductive network in CO₂ electroreduction performance and provides more opportunities for the application of MOF electrocatalysts.