Theoretical Study On The Electrocatalytic Performance Of Modified Fullerene Materials For Oxygen Reduction

As a new type of device for clean energy conversion,proton exchange membrane fuel cell(PEMFC)has attracted wide attention.It has high efficiency in energy conversion and the advantage of high energy density.However,the cathodic oxygen reduction reaction(ORR)limits the total reaction rate kinetically.At present,the platinum-based catalysts used commonly cannot be widely used in commercial application due to their high price and instability in catalytic process.In recent years,carbon-based catalytic materials have been widely studied as ORR catalysts,among which fullerene structure have attracted more attention because of high electrochemical stability and conductivity.And it is expected to become the main commercial catalytic materials from the view of cost.At present,there is no detailed study on ORR catalyzed based on C60 structure,and the selectivity between four-electron and two-electron reaction process in oxygen reduction reaction is not clear.Therefore,in this paper,the effect of modified C60 on the catalytic performance of oxygen reduction reaction is explored by density functional theory(DFT),and select respectively the superior structures for two-electron or four-electron reaction.And then,improve catalytic activity and selectivity further.The main contents of this paper are as follows:1.Taking C60 as the matrix structure,firstly,it is modified by embedding the transition metal atom(M@C60),and studied the electrocatalytic performance of oxygen reduction reaction.It is concluded that the overpotential of the four-electron reaction by the Mn@C60 structure is 0.44 V(the theoretical value of the precious metal platinum-based catalyst is 0.45 V).For the two-electron reaction,the reaction path follows the OOH ion reaction mechanism,and the limiting potential(UL)is used as the basis for judgment,and the Ti@C60 catalyzed two-electron reaction UL is 0.347 V(the theoretical maximum value is 3.55 V).Finally,the four-electron and two-electron reactions were screened,and it was concluded that the structures of Mn@C60 and Cu@C60 are conducive to the four-electron reaction to generate water,and Ti@C60 and Cr@C60 are conducive to the two-electron reaction to generate hydrogen peroxide.Finally,using the electronegativity of transition metal atoms and the electronegativity of oxygen and hydrogen together as descriptor,the ORR overpotential and limiting potential of C60 with different metal structures can be well predicted,thus the catalytic performance of the wrapped structure can be predicted.2.Adjust the modification method further,and use organic molecules to recombine with it to obtain a periodic molecular structure.And the electrocatalytic performance of oxygen reduction reaction was studied.The collaborators synthesized the N-C60-Ph structure in the experiment and analyzed the structure and catalytic performance.Based on the experimental results,we calculated and predicted that the structure was mainly a one-dimensional chain structure and verify the catalytic performance and conductivity before and after N doping have been significantly improved.The change of free energy proves that the N-C60-Ph structure is beneficial to catalyze the four-electron reaction.At the same time,combining the results of Chapter 3(the structure of Mn@C60 and Cu@C60 has good catalytic performance for the four-electron transfer reaction),the structure is adjusted again,and the Mn and Cu atoms are embedded in the N-C60-Ph structure.The results show that the single C60 The molecule is converted into a composite structure,the catalytic performance is improved,and the synergy between N,Mn,and Cu has a positive effect.Compared with the pure N-doped structure or the purely wrapped metal structure,the catalytic activity is further improved,and the calculated Mn The@C60-Ph-N structure catalyzed ORR overpotential was only 0.37 V.3.Next,the single atom MN4 form was used to modify C60 again,and its catalytic performance was studied.The over-potential of the four-electron reaction catalyzed by the CuN4-C60 structure was found to be only 0.32 V.The density of adsorption is analyzed by the density of states.Then based on the ionization energy,atomic radius and d-band center,a reasonable descriptor was found,which played a good role in predicting the ORR catalytic performance of the MN4-C60 structure.Finally,selective analysis was conducted and it was found that the generated H2O2 did not exist stably and would react further to produce water.In this paper,the catalytic performances of oxygen reduction reaction on C60-based modified structure were systematically studied,and the doping and connection methods were designed respectively to improve the catalytic performance of ORR.The structures that benefit to catalyze two-electron or four-electron reaction process were screened out,and the structure-activity relationship between C60-based structures and their catalytic performances was established from the electronic and atomic levels.Through this work,we not only give a deep solution to the problem of how to modify C60-based materials and improve their catalytic performance on ORR,but also predict and select C60-based materials with excellent catalytic performance,but also provide theoretical basis and guidance for the design and selection of other carbon-based catalytic materials.