Structure, Properties And Electrocatalytic Oxygen Reduction Mechanism Of Doped Fullerenes

With the increasing environmental pollution and energy crisis,it is urgent to find a new alternative energy source.At present,the best alternative energy is fuel cells,among which hydrogen-oxygen fuel cell is the most potential fuel cell due to its unique advantages.In hydrogen-oxygen fuel cells,the oxygen reduction reaction(ORR)is crucial.The reaction rate of ORR can be accelerated by catalyst.So far,Pt is the most effective ORR catalyst.However,Pt has seriously hindered the commercialization of hydrogen-oxygen fuel cells due to its high cost and low content.Therefore,the research that finds a kind of non-Pt or even non-metallic catalyst is the hot spot.In this paper,the structure,property and ORR catalytic activity of fullerene have been investigated by computational chemistry based on DFT.(1)The ORR mechanisms and catalytic abilities of pure and N-doped fullerenes were investigated via DFT computations.Four different sized fullerenes,C20,C40,C60,and C180,were utilized to investigate the size effect on the ORR performance.The results reveal that the smallest(C20 and N-doped one)and the largest(C180 and C179N)fullerenes are not effective ORR catalysts candidates.However,N-doped C40 and C60,with the adsorption energies much close to those on Pt(111),manifest high ORR activity potentials.Further analysis of the relative energy diagram shows that the ORR processes on C19N and C179N are completed through a H2OO dissociation mechanism,while on C39N and C59N,they undergo an OOH dissociation pathway.In addition,the C39N has the largest decreased energy of rate-determining step in the relative energy profile,suggesting its ORR activity is the best among all the different sizes of fullerenes we studied.(2)The oxygen reduction reaction catalytic activity and poisoning-tolerance ability of endohedral metallofullerene Fen@C60(n=1-7)catalysts are investigated in detail by using density functional theory calculations.The calculation predicts very low catalytic activity of the pristine C60 fullerene,but significant activity enhancement is obtained when encapsulating iron clusters into C60 cage due to improved energy gaps.With the increase of the size of encapsulated Fen cluster,the adsorption energies of all the oxygen reduction intermediates,such as OOH,O,and OH,become jointly stronger.Among all the screened Fen@C60(n=17)catalysts,Fe3@C60 possesses the highest oxygen reduction activity,with a predicted limiting potential of about 0.73 V that is comparable to that of Pt(111)surface(0.79 V).The limiting potentials for Fe2@C60,Fe4@C60 and Fe5@C60 are also relatively high,with the values of 0.64,0.69,and 0.64 V,respectively.In addition,the above screened Fen@C60 catalysts also exhibit excellent poisoning tolerance ability to SO2,H2S,CO,NO,and NH3 species.(3)On the basis of density functional theory,the ORR catalytic activities of Mn@C60(M=Mn,Co,Ni,Cu;n=2-5)have been investigated systematically.At first,the structures of the studied model can be obtained by relaxing the C60 cage that contains a lowest energy structure of metal cluster inside.And then,the active site was determined by charge distribution analysis.The calculated results uncover that there is almost linear relationships between the adsorption energies of OOH,O and that of OH intermediate,and the OH can be used as a good descriptor in predicting ORR activities of catalysts.Further analysis of the reversible potentials of ORR uncovers that Mn5@C60,Cu4@C60,Co2@C60,and Ni4@C60 have relatively better ORR activities,with the calculated reversible potentials of 0.71,0.70,0.64,and 0.62 V,respectively.In addition,these four screened EMFs that have good activities toward ORR are also have good poisoning-tolerance abilities to some impure gases such as SO2 and CO.However,the influences of fuel molecules such as methanol,formic acid,and ethanol to these four EMFs are not neglected.(4)The ORR activity on metalfullerene C58M(M=Mn,Ni,Co,Fe and Cu)have been investigated by DFT calculations.The most stable calculation model can be elected by relaxing the different doped models.Meanwhile,the binding energy have been analyzed.Subsequently,the corresponding free energy curve was drew and the curve indicated that C58Co is the best ORR catalyst.The results uncover that there is a linear relation between?G*OOH,?G*O and ?G*OH.And the ?G*OH can be used to predict ORR activity.Further analysis of ORR overpotential proves C58Co possesses the highest catalytic property.