Anodizing Construction Of Porphyrin MOFs For Electrocatalytic Reduction Of Carbon Dioxide

With the rapid development of society and economy,people’s demand for energy continues to increase,and the excessive development and use of traditional fossil fuels has resulted in a large amount of carbon dioxide（CO₂）emissions.The greenhouse effect is an important cause of global warming.Achieving CO₂conversion and fixation can not only alleviate the greenhouse effect,but also store it as a carbon source,save energy and help achieve carbon neutrality.Electrochemical catalytic reduction of CO₂（CO₂RR）can realize electron exchange of CO₂ molecules at lower voltages and activate stable CO₂ molecules,and it is also an effective conversion technology that is being widely studied.Therefore,it is an effective way to use electricity generated from clean renewable energy to drive CO₂RR,so as to reduce the CO₂ content in the atmosphere and realize its resource utilization.The key to CO₂RR is the development of efficient and highly selective catalysts.So far,researchers have developed a variety of CO₂RR catalysts.Among them,metal-organic frameworks（MOFs）are considered to be one of the most potential CO₂RR catalysts due to their long-range ordered crystal structures,a large number of metal active sites,specific surface areas,and regularly ordered pore structures.Porphyrin has a macrocyclic conjugated structure formed by 18πelectrons,which is beneficial to its electron transport.The central metal can be used as the active site of CO₂RR.The central metal and the junction coordination metal can form a bimetallic catalytic synergistic effect.Introduced into MOFs as organic ligands,it is expected to further enhance their electrocatalytic efficiency.The porphyrin-based MOFs currently is used as CO₂RR catalysts mainly useing tetraphenylcarboxyporphyrin（TCPP）as the organic ligand and metal junction,but most TCPP-based MOFs are unstable in basicity,which limits their application in CO₂RR.Tetrapyridyl porphyrin（H₂TPy P）is chemically basic and can exist stably in the CO₂RR system,and the M-N-C structure formed after its coordination with metals can also serve as the CO₂RR active site.The new method of electrochemical in-situ growth of porphyrin MOFs developed by our research group can directly grow TCPP-based MOFs thin films on conductive substrates,which solves the key problems of weak bonding between catalysts and substrates and poor electron transport performance,showing excellent performance.electrochemical performance.But so far,H₂TPy P-based MOFs have not been synthesized by electrochemical in situ growth method.Based on the above investigations,the electrochemical anodic oxidation method was developed for in situ preparation of regular and porous H₂TPy P-based porphyrin MOFs.The material has good alkali stability,and its use in CO₂RR shows good catalytic performance.Specifically,the following research contents were carried out:1.In order to controllably grow tetrapyridyl porphyrin MOFs thin films on conductive substrates,a Cu metal layer was first electrochemically deposited on the substrate as a sacrificial layer,and Cu was oxidized to form Cu²⁺by electrochemical anodic oxidation.Cu²⁺coordinated with the pyridyl group of porphyrin to form MOFs in situ.The thickness of the Cu deposition layer,the growth time and the oxidation voltage of the film can be adjusted to realize the adjustment of the thickness of the film and the stacking pore size.This in situ growth method improves the stability and electron transport properties of MOFs and it is expected to improve their electrocatalytic performance.Spectral characterization proves that the porphyrin is successfully coordinated with the metal junction.The acid-base stability experiment proves that the MOFs can exist stably under the alkaline condition of p H 7-14.The EIS impedance results prove that the MOFs prepared in situ by anodization method Compared with the drop-coated film,the film has lower charge transfer resistance,indicating better electrical conductivity.Comparing the CO₂RR performance of the porphyrin MOFs with the CO₂RR performance of the material obtained by mixing porphyrin and copper ions by mechanical stirring,it is found that the pyridine N carried by the porphyrin is coordinated with the metal to be the catalytic active center.2.The electrochemical anodic oxidation method has good universality.In this chapter,tetrapyridyl porphyrin（MTPy P）with different metal active centers was used as the organic ligand of MOFs,and good MOFs films were prepared by changing the reaction conditions.The introduction of metal in the center of porphyrin increases the concentration of catalytically active sites.And the introduction of different transition metals（Fe,Co,Ni,Cu）in the porphyrin center can introduce a second catalytic active center to achieve bimetallic synergistic catalysis and improve the catalytic efficiency.When it was applied to electrocatalytic CO₂RR,it was found that the catalytic performance of metalloporphyrin MOFs was improved,of which Cu-Co TPy P MOFs had the greatest improvement（FE=92%）.Finally,the differences in the catalytic performance of porphyrin MOFs with different central metals were investigated,and it was observed that the catalytic performance increased with the increase of the reaction kinetics of the materials.