Theoretical Study Of Graphene With Defects Electrocatalysts For Oxygen Reduction Reaction

This thesis systematically studied Heteroatom-doped defective graphene?H-Gra?electrocatalytic performance for oxygen reduction reaction?ORR?within Density functional theory?DFT?.The main contents and results are summarized as follows:?1?the activity in acid medium of nitrogen and sulphur co-doped graphene with carbon defect(_V-N,S-gra)is investigated,including the activity sites,the reaction pathways as well as free energy diagrams.Six kinds of O₂ adsorption configurations are found and the reaction sites are all carbon atoms adjacent to the dopants.However,they are physisorption in the neighboring carbon of nitrogen,unlikely to initialize the ORR process.Otherwise if the adsorption sites are in the adjacent carbon of sulphur,the catalyst activity is associated with the adsorption energy,that is,we find a best ORR pathway with a gentle adsorption?-0.03eV?.An energy barrier of 0.82eV is found in this favorable process in which the adsorbed O₂ molecular is prone to be hydrogenated continuously to give rise to H₂O molecular,promising a four-electron pathway.At last the effect of electrode potential is simulated and for the best reaction pathway all the elemental reactions are downhill until the potential is as large as 0.31eV.?2?the activity of FeN_x?x=1-4?doped graphene?FeN_x-gra?for both ORR and OER are comparatively studied.It is found that the overpotential for both ORR and OER are disturbed by the doping concentration and configuration of nitrogen.Among all the studied FeN_x-gra?x=1-4?,the FeN₄-gra is identified as the best candidate with the calculated overpotential of 0.87eV and 0.78 eV for the OER and ORR,respectively.The high activity of FeN₄-gra stems from its high asymmetry spin density.