| With the development of globalization,the traditional energy and environmental protection are facing with great challenges,so seeking renewable,clean and efficient new energy is the most important problem of the sustainable development of the world economy.Oxygen molecule could be directly reduced to water,which can convert chemical energy into electricity in a fuel cell system,so the fuel cell as an environmentally friendly new clean energy has become a main research field in the recent years.Oxygen reduction reaction(ORR)on the cathodic electrode of same type of fuel cells is one of the key points for the energy conversion efficiency.Futhermore,use and select of catalysts of the cathodic reaction may directly affect the efficient of ORR.Platinum and its alloys was found to be the most effective catalyst used today,but the shortage and high price of this rare metal resource restricted its possibility of wide applications.Therefore,in recent decades,study and devalopment of economic and effective catalysts,such as non-platinum metals and metal oxides,inorganic and organometallic complexes,as the replaced materials for patinum catalysts have become hot key issues in the field of fuel cells.The structure of corrole molecular is similar to that of porphyrin but also has significant differences.Corrole and porphyrin are both conjugated macrocycles which are connected by four pyrroles.However,these pyrroles are connected with different ways in corrole and porphyrin.The pyrroles in the porphyrin molecule are linked by four methylenes,which result that the porphyrin core has two N-H groups,and leading to formation of porphyrin dianions when the N-H groups deprotonated.There are only three methylenes in corrole's molecular and two of the four pyrroles are linked directly through a single C-C bond.So there are three N-H groups in the core of corrole.The loss of three N-H protons can generate a corrole trianion.Thus,corroles can complex metal ions with higher oxidation states to form metallocomplexes with different oxidation states.Like porphyrin,variety of substituents can be introduced onto the meso and ?-pyrrole positions of the corrole to tune its electronic and steric structure and to synthesize new corroles having unique properties.In addition,metallocorroles can coordinate different axial ligands to form five or six-coordinate complexes,and further to preparation of dineuclear andmultineuclear complexes which have two or more central metal ions.Since Dr.Kadish and co-workers reported that corrole complexes can be used as effective catalysts for ORR,the study and the application of corrole catalysts have attracted more and more attentions.However,the publications on corrole catalyst for ORR are still rare.Therefore,to design and synthesize metallocorroles with novel structures,examine their electrochemical and electrocatalytic properties may have important academic significance and application values.In addition,graphene has attracted more and more attention as catalyst and catalyst carrier for ORR in recent years becuase it possesses ultra-thin two-dimensional structure and excellent electrical performance.However,there have no reports up to date on functionalization of corroles with graphene in order to increase its catalytic properties.This is addressed in this dissertation.On basis of synthesis of the metallocorrole,a novel organicinorganic hybrid material was prepared by functionalizing the corrole with graphe oxide,and the electrocatalytic properties of the material for ORR was then examined,which could provide an initial treoretical basis and experimental foundation on developping efficient catalysts for ORR in fuel cells.This dissertation mainly includes six charpts.The first Chapter mainly introduced the general synthetic methods,properties and applications of corroles,as well as the research progress of the catalysts for ORR and the graphene used as the catalyst for oxygen reduction.In Chapter 2,four novel A3 type free-based corroles containing strong electron-withdrawing halogen substituents were synthesized in a mixed water and methynol solvent,via the reaction between pyrrole and substituted benzaldehyde to give bilanes which were oxidized using p-chloranil to generate the expected products.Then,the corresponding cobalt corroles with triphenylphosphine axial ligand were synthesized by reaction of the free-based corroles,cobalt acetate and triphenylphosphine.The synthesized compounds are represented as(Ar)3CorCo(PPh)3,where Cor is a trianion of the corrole and Ar is a 2-ClPh,2,6-diClPh or 2,6-diFPh on each of the three meso-positions of the corrole macrocycle.The cobalt corroles were characterized by UV-Vis,1H-NMR and mass spectrometry.The molecular structures of these compounds were examined by X-ray analysis.In Chapter 3,the redox properties of cobalt corroles were examined in nonaqueous media by cyclic voltammetry and the electron transfer mechanism was proposed.The catalytic activity of these compounds for ORR was studied in 1.0 MHClO4 by rotating disk electrode and rotating ring-disk electrod.The results show that the type and position of the substituents have important influence on the spectral and electrochemical properties of the corroles.The cobalt corroles having sterically hindered substituents can be used as the selective catalysts for 2e-reduction of O2 to mainly give H2O2 as the product in acid media.In Chapter 4,dipyrromethane was firstly prepared by reaction of pyrrole and p-tolualdehyde in water-methanol system,and then reacts with p-nitrobenzaldehyde using modified Lindsey method in which a acid was used as catalyst to generate bilanes.After being oxidized by p-chloranil,the bilanes was used to react with cobalt salt resulting an A2 B type cobalt corrole complexe.The cobalt derivative was represented as(NH2Ph)(CH3Ph)2CorCo(PPh3),where Cor is a trianion of the corrole macrocycle,and characterized by UV-vis,1H NMR and mass spectrometry.In Chapter 5,the electrochemical properties of(NH2Ph)(CH3Ph)2CorCo(PPh3)was studied and a mechanism of electron transfer was then proposed.this cobalt corrole undergoes two irreversible reductions and three reversible oxidations in CH2Cl2 contaning 0.1 mol/L TBAP as the supporting electrolyte.The catalytic activity of this compound for ORR in 1.0 mol/L HClO4 was also examined using rotating-disk electrode.The results indicate that,the cobalt corrole has catalytic activity for the reduction of oxygen in 0.1 mol/L HClO4.The number of electron transfer in the oxygen reduction process is 2,the product of the reaction thus is 100%H2O2.In Chapter 6,graphene oxide(GO)which has a similar structure with graphene was firstly prepared by the modified Hummers method and reacts with SOCl2 to give GOCl which can react with the NH2 group of the A2 B type corrole(CorCo)to give a functionalized cobalt corrole which was covalently bonded to GO via the amidation reaction to generate the organic inorganic hybrid material represented as GO-CorCo.This hybrid matieral was characterized by the Raman,FTIR,TEM and AFM techniques.The catalytic activity of the hybrid material was examined in detail in a solution contained 0.1 mol/L KOH or 0.5 mol/L H2SO4.The results was then compared to that of the precursors(GO and the A2 B type cobalt corrole)for synthesis of the material as well as the mixure of GO and CorCo.The experimental results showed that a 2-electron process is seen under the acidic conditions regardless of the voltage responding the starting or steady state limiting currents for the catalytic reactions.It indicates that cobalt corrole functionalization using graphene oxidecannot improve its catalytic performance for ORR in acid solutions.However,in alkaline solutions,If the reduction potentials were controlled at-0.80 V or more negative,the GO-CorCo has higher catalytic activity for the reduction of oxygen,the number of electrons transferred(n)during the oxygen reduction process is 4 and H2 O is the reaction product.Thus,it can be concluded that GO-CorCo can be used as an ideal catalyst for oxygen reduction reaction. |
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