Electrocatalytic Properties Of Iron Phthalocyanine (cobalt)/defective Graphene Composites

Due to the unsustainability of traditional fossil energy,clean and sustainable electric energy has attracted worldwide attention.Chemical battery can directly convert chemical energy into electric energy,which has the advantages of safety,cleanliness,and high energy conversion efficiency.Among them,zinc-air battery(ZAB)is regarded as a new generation energy storage and conversion device owing to its small size,environmental friendliness and high theoretical energy density.However,ZABs also suffer from adverse kinetics of oxygen reduction reaction(ORR)at the cathode.Therefore,to realize the large-scale application of ZABs and solve the problem of energy shortage,it is the key to explore new ORR catalyst with low cost,high activity,and high stability.At the same time,the continuous consumption of traditional fossil energy leads to a large amount of carbon dioxide(CO₂)emission,which further aggravates the greenhouse effect.Thus,people attempt to reduce the CO₂ concentration in the atmosphere.Among many CO₂ capture or conversion methods,using clean and sustainable electric energy to carry out CO₂ reduction reaction(CO₂RR),realizes electrochemical conversion of CO₂,which is considered as the most promising method to solve global warming problem.However,due to its inert chemical activity,catalysts are needed to accelerate the CO₂RR.Transition metal phthalocyanines(MPcs)have a typical M-N₄-C structure,due to the unfilled valence d orbitals,which enables them to gain and lose electrons freely.So they are used as active centers in various electrocatalytic reactions.However,the aggregation of MPcs and the unfavorable conductivity of M-N₄ macrocycle lead to low current density of ORR and CO₂RR.The M-N₄-C active sites can be fully exposed by dispersively coupling MPcs on carbon nanomaterials(CNMs),which increases the current density of ORR and CO₂RR but not enhance the intrinsic catalytic activity of materials.In order to improve the intrinsic catalytic activity of transition metal center,the structure and properties of CNMs substrate need to be changed,and then optimize the electronic environment of transition metal center.It is expected that high-density electrons at defective sites can optimize the electronic environment and enhance the intrinsic activity of catalytic reactions.In this paper,DG was prepared by simple doping and removal of nitrogen atoms.MPcs/DG composites as ORR and CO₂RR catalysts were prepared by coupling DG with MPcs at defect sites through?-?stacking.Specific research contents are as follows:(1)Density functional theory(DFT)results prove that the graphene with 585 defects can transfer electron to iron phthalocyanine(Fe Pc),forming an electron-rich region at the active Fe sites.The high-density electrons further lift the d-band orbit of Fe atoms,so that its d-band center is raised from-0.87 eV to-0.57 eV,which is beneficial to the adsorption and reaction of O₂ molecules at the active Fe sites.Based on this,Fe Pc/DG composite was prepared by coupling the single-layer dispersed Fe Pc to DG.Electrochemical performance test results reveal that the initial potential is positively shifted from 0.87 V vs.RHE of Fe Pc to 0.98 V vs.RHE of Fe Pc/DG.In addition,the half-wave potential of Fe Pc/DG is 0.90 V vs.RHE,which is better than 0.86 V vs.RHE of commercial Pt/C catalyst.Furthermore,this catalyst exhibits excellent stability due to the strong chemical and electronic coupling between DG and Fe Pc,which make it difficult for Fe Pc to re-aggregate and then protect active sites from loss in the long-term catalytic reaction.(2)Based on?-?stacking of benzene rings,the CoPc/DG composite was synthesized by direct chemical and electronic coupling between Co metal center and graphene defect site.During the CO₂RR,the CO Faraday efficiency of CoPc/DG is 94%at-1.08 V vs.RHE,while the H₂ Faraday efficiency is only 5%.After 11000 s continuous catalytic reaction,the Faraday efficiency of CO remained at 93%,which indicated that prepared CoPc/DG composite was a CO₂RR catalyst with high activity,selectivity and stability.It is attributed that the direct chemical and electronic coupling between DG and CoPc keep the active sites of Co singe atom centers.