DFT Study Of Oxygen Reduction Reaction On O-doped Graphene-supported Pt-based Alloys With 3d Transition Metals

Fuel cells,which have high efficiency of energy conversion and low pollutant emission,are considered as a strong support for the sustainable development of energy in the future.However,the large-scale commercial applications of fuel cells are hampered by the sluggish kinetics of oxygen reduction reaction?ORR?at the cathode.The highly efficient alloy electrocatalysts with less content of noble metals for ORR should be studied to reduce the cost of fuel cell.Therefore,it is significant for the design and development of alloy electrocatalysts to understand the ORR mechanism and study the parameters to estimate the ORR activity over alloy electrocatalysts.In this dissertation,oxygen adsorption,consecutive hydrogenation and molecular water desorption during ORR process were studied on Pt₄ and Pt-based alloys with 3d transition metals Pt₃M?M=Ti?V?Cr?Mn?Ni?Co?Fe?clusters supported on O-doped graphene.Oxygen adsorption structures and energy were examined on supported Pt₄and Pt₃M,every element step was calculated and analyzed,in addition the free energy profiles were made.The results demonstrated that the early 3d transition metals and late 3d transition metals in Pt-based alloys influenced ORR process differently.The oxygen was dissociated to two separated O atoms and absorbed with strong oxygen binding energy on supported Pt₃Ti,Pt₃V,Pt₃Cr clusters,which lead to the subsequent higher hydrogenation energy against for ORR.In contrast,oxygen is adsorbed in the form of O₂ molecule on supported Pt₄ and Pt₃Mn,Pt₃Fe,Pt₃Co,Pt₃Ni clusters.The weaker oxygen binding energy leads to the first step of hydrogenation with lower energy on them,which is promotive for ORR.The ORR activity rule was examined and compared on O-doped graphene supported Pt₄ and Pt-based alloys Pt₃M with different 3d transition metals.Specifically,the oxygen binding energy,formation energy of two OH*and formation energy of two H₂O*are comprehensively analyzed over Pt and Pt₃M for ORR activity.The results show over those Pt-based alloy catalysts?Pt₃Fe?Pt₃Co?Pt₃Ni?with similar oxygen binding energy to that of pure Pt,the formation energy of two OH*and two H₂O*is relative smaller than that over other Pt-based alloy catalysts with oxygen binding energy away from that of pure Pt,Thus the ORR activity of supported Pt₃Fe?Pt₃Co?Pt₃Ni are better,which is in agreement with experimental research.