Research On Electrocatalytic Water Splitting Based On Metal Corrole Compounds

At present,molecular catalysts are mainly used in homogeneous catalysis in the field of electrocatalysis.The relationship between structure and performance can be deeply understood through mechanism study.By combining molecular catalysts with nanocarbon materials to form heterogeneous composites,the improvement of catalytic performance of the molecule in aqueous solution can be achieved and the scope of practical application can be expanded.Corrole ligands can not only stabilize the high valence metal ions,but also improve the reduction ability of the low valence metal ions due to the high electron density around the corrole ring,and thus improving the redox properties of the complexes.Therefore,in the study of electrocatalytic water splitting,we choose metal corrole as molecular catalyst.In this work,we focus on the preparation and electrocatalytic properties of the carbon nanotube composites covalently modified with cobalt corrole(Col).In addition,we synthesized and characterized cobalt corrole(Co3)and iron corrole compounds(Fel?Fe2).They were designed to investigate the mechanism of oxygen-oxygen bonding in the catalytic cycle of water oxidation.The main results obtained are as follows:1.Two corrole ligands,LI and L2,were synthesized.By coordinating with Cu and Co salts,metal corrole complexes Cul/Cu2 and Col/Co2 were obtained.Their structures were confirmed by NMR and MS,and the crystal structure of complex Co2 was determined by single-crystal X-ray diffraction.The electrochemical measurements of Cul,Cu2,Col and Co2 showed that Cul and Cu2 were catalytic inactive for water splitting,while complexes Col and Co2 catalytic active in acetonitrile.Therefore,cobalt corrole was chosen as molecular catalyst for surface functionalization of carbon nano tubes.2.In this paper,catalysts were linked to carbon nanotubes by two amidation methods.Methode A:carboxyl groups of carbon nanotubes were activated by SOCl2 forming exterior acyl chloride which reacted with amino group of catalyst Col forming amide bond,thus composite CoCor-CNT-A were obtained.Methode B:the amino group of catalyst was directly coupled with carboxyl group in carbon nanotubes by using coupling agents(DCC,DMAP,HOBt),obtaining composite CoCor-CNT-B.The functionalized metal corrole-carbon nanotube composites(CoCor-CNT-A/B)were characterized by IR,UV,Raman,SEM,TEM and XPS.After modificated with Col,the ID/IG value of CoCor-CNT-B was almost unchanged compared with that of blank CNTs.However,the ID/IG value of CoCor-CNT-A increased significantly compared with that of blank CNTs,indicating that the ordered structure of CNTs has changed,which was consistent with the results observed by scanning electron microscopy and transmission electron microscopy.The reason may be that the ordered structure of CNTs has been destroyed by strongly acidic,strongly oxidative SOCl2 and high temperature(110?).The electrochemical tests showed that the electrocatalytic activity of CoCor-CNT-B for OER and HER was better than that of CoCor-CNT-A in aqueous solutions at pH 0,7 and 14.This may be due to the retention of large specific surface area and good conductivity of CNTs in amidation reaction under mild conditions.3.Coordinated with 5,10,15-tri(pentafluorophenyl)corrole,cobalt corrole complex Co3 was used to study the mechanism of oxygen-oxygen bonding during catalytic water oxidation.Co? was oxidized to Co?=O with iodobenzene as oxidant,and then the reaction between Co?=O species and hydroxide ions was studied.Based on ultraviolet absorption spectra and mass spectrometry data,it is preliminarily speculated that the formation of oxygen-oxygen bond by the nucleophilic attack of H2O on Co?=O is a feasible mechanism of water oxidation.4.Iron corrole complexes-Fel and Fe2,were synthesized and characterized.Next,the mechanism of electrocatalytic oxygen production of iron corrole compounds will be explored.