Theoretical Study On The Performance Of High Efficiency Oxygen Reduction Electrocatalysts Based On Graphene

Since the discovery of graphene,Due to its exceptional electronic properties and huge surface-to-volume ratio, graphene has been used as a support for heterogeneous catalysts and thus has attracted tremendous attention. As a structural analog of graphene,the hexagonal boron nitride（h-BN） sheet has also attracted considerable attention due to its unique properties and wide applications。With the improvement of computational methods and computer capacity, the theoretical study is helpful not only to simulate the low dimensional nanostructures, but also to solve some problems, which is difficult to achieve in the current experimental conditions.In the present thesis, through density functional theory（DFT） computations, the geometry, electronic structure, and catalytic performance were systematically studied for metal-embedded two-dimensional material 。 First, we explore the structural,electronic, and magnetic properties of boron nitride nanosheet and grapheme,constructing on defects in their crystal lattices, then allowing the metal and M-P4 composites to embed their defects.（1） We explored the possibility of the Fe-embedded hexagonal boron nitride（h-BN）sheet as a novel electrocatalyst for ORR. Our results show that Fe atom can strongly bind with defective BN sheet and thus ensure its high stability. Moreover, O₂ molecule is found to be strongly chemisorbed on Fe-embedded BN sheet, which can server as precursors for ORR. Then activated O₂ molecule can be through a 4e process translate to H2 O molecules, Among them, the Gibbs free energy of elementary reaction are negative, indicating that reaction is spontaneous. Therefore, Fe doped boron nitride based on graphene has excellent catalytic performance can be as substitute for Pt and become orr catalyst.（2）The structure of M-P-C（Fe M=, Co） was used as the construction of ORR catalyst. Our computations have revealed that the Fe– and Co–P4 moiety-embedded graphenes possess good stability and high chemical reactivity for O₂ activation, thus facilitating the subsequent ORR steps, and a more efficient 4e pathway in both acidic and alkaline media is more energetically favorable. Furthermore, by analyzing thecomputed free energy profiles, the Fe–P4 species-embedded graphene is a more efficient electrocatalyst for the ORR in an alkaline medium than the Co–P4 species-embedded graphene.The results of this study can be used in the field of catalysis based on the properties of metal embedded defects graphene and boron nitride graphene, and provide useful guidance for the design of low and high efficiency catalysts.