The Synthesis Of Metal Porphyrin Complex Crystal Material And Its Electrocatalytic Performance

The large consumption of traditional non-renewable energy and the rapid growth of CO₂ emissions have led to energy crisis and global warming..Therefore,the development of economic and environmentally friendly carbon neutralization strategy is of vital importance to human society.Among them,CO₂ electroreduction technology and fuel cell?H₂/O₂?are very promising in the development of green energy.However,the main limiting factors is that it is difficult to complete the reduction reaction of CO₂ or O₂ in cathode,which involves multiple electron transfers and the reaction kinetics is slow.Therefore,the design and development of efficient,stable and low-cost electrocatalysts for the electroreduction of CO₂ and O₂ is the current research hotspot.In order to further promote the development of this field,it is important to establish and understand the relationship between material structure and catalytic performance for the development of efficient catalysts.Metalloporphyrin complexes have great attraction for basic research because of their clear crystal structure and open metal active sites.When electrochemistry is coupled in situ or ex situ to spectroscopic measurement,metalloporphyrin complexes usually show clear homogeneous and/or heterogeneous electrochemistry traces at the catalytic site.The measurement results can be used to reveal the internal mechanism of the reaction,and infer the deep mechanism and insights of related catalytic active substances,so as to quantitatively evaluate and comprehensively understand the thermodynamic and kinetic parameters controlling the whole catalytic cycle.In addition,the tunable properties and electronic properties of metalloporphyrin complexes enable people to achieve strict catalytic control through structural modification of synthetic chemistry,and overcome the limitations of research diagnosis through catalyst reengineering strategy,so as to minimize or eliminate by-products,and maximize the purity/Faraday efficiency?FE?or selectivity of the final product.Finally,a variety of catalysts with high activity,high selectivity and high durability were obtained.In this paper,the electrocatalytic properties of metalloporphyrin complexes were studied as the main line,and the following research contents are carried out:?1?Three stable complexes of Ni porphyrin?Ni-TPYP,Ni-TPYP-1 and Ni-TPP?were synthesized by controlling the number of catalytic sites.For the first time,the real catalytic sites of CO₂ reduction reaction?CO₂RR?were identified by the crystalline supramolecular complex model system,and the catalytic activity of pyridine containing materials was determined structurally.With the decrease of the number of active pyridine groups in the compounds,the properties of CO₂RR decreased gradually,mainly showing the decrease of the highest FE_CO?99.8%,83.7%and 25.6%,respectively?.Crystallography,experiments and DTF calculations show that the high activity of CO₂RR is more likely to originate from uncoordinated pyridine nitrogen than the electrocatalytic inert metal nickel at the porphyrin center.This work provides an important research case for the identification of electrocatalytic activity of reactants in CO₂RR through the system with clear molecular structure.?2?Compared with the CO in the previous chapter,the more advanced products of CO₂ electroreduction often have greater economic value.We used solvothermal method to synthesize two copper metalloporphyrin complexes crystals?Cu-TPP and Cu-TPYP?by replacing the substituents on porphyrin ring.Both of them can be used as catalysts to reduce CO₂ to gaseous carbon products such as CO,CH₄ and C₂H₄.Among them,Cu-TPYP has higher Faraday efficiency in reducing CO₂ to advanced gas products,that is,the sum of FE_CH4 and FE_C2H4 of Cu-TPYP is greater than that of Cu-TPP at the same potential.In addition,the sum of FE_CH4 and FE_C2H4 of Cu-TPYP at–1 V can reach more than 90%,and the high catalytic efficiency can be maintained for 12 hours.Studies have shown that the pyridine modified on porphyrin can adjust the electronic structure of the complex framework,enhance the intramolecular multi-electron transfer of the catalyst itself and improve the performance of electrocatalytic CO₂ reduction.This novel strategy provides a new idea for the design and construction of crystalline complex CO₂ electroreduction catalyst.?3?In view of the good performance of the above porphyrin complexes in electrocatalytic CO₂ reduction and the relationship between the catalyst structure and catalytic performance in the first two chapters,we hope to further explore the performance and application of porphyrin complexes in more electrocatalytic systems.Three cobalt porphyrin complexes?Co-TPP,Co-TCPP and Co-TAPP?were synthesized by introducing different substituent groups to study the effect of ligand modification on the electrocatalytic reduction of O₂.Electrochemical test results show that compared with Co-TPP?TPP=phenylporphyrin?,Co-TCPP?TCPP=carboxyphenylporphyrin?has corrected initial potential?Eonset=0.46 V vs.Ag/Ag Cl?,half wave potential(E_1/2=0.29 V vs.Ag/Ag Cl)and maximum limiting current(|J_L|=4.58 m A cm^-2).However,the electrocatalytic performance of CO-TAPP?TAPP=aminophenyl porphyrin?is worse than that of CO-TPP.These results indicate that the electron-donating group can promote the oxidation of the central metal or the whole complex,thus weakening the catalytic performance of the cobalt porphyrin complex for O₂ reduction,while the electron-withdrawing group can reduce the electron cloud density of the central metal and the porphyrin ring,thus better stabilizing the low valence metal ions and promoting the reduction reaction.