Controllable Preparation Of Holey Graphene With Defects Or Edges And Electrocatalytic Performance For Oxygen Reduction Reaction

Defects or pinholes in graphene are important for tuning its properties to show excellent performance in various fields,such as supercapacitor and oxygen reduction reaction?ORR?.There are various methods to prepare defect or edge carbon on the basal plane of graphene.However,there are few studies on the quantitative relation between the edge carbon and its ORR performance.In this work,we controllably prepared holey graphene with defects by chemical method,meanwhile and the relationship between the ORR performance of holey graphene and its structure was studied.The main contents are as follows:?1?In Ar atmosphere,Co?OH?₂/GO was pyrolyzed to get CoO and partial reduced graphene.A simple carbothermal method was used to controllably form defects or pinholes in graphene by reacting graphene with CoO in argon atmosphere.The morphology of defects or pores and the reaction mechanism were investigated and discussed detailedly.The defects,the conductivity and the ORR performance of the holey graphene in alkaline electrolyte were quantitatively analyzed and correlated.The results show that the optimized annealing temperature is 700 ? based on the ORR activity.The content of defects or edge carbon atoms of holey graphene,that is the defect density,determining factor for the ORR activity,can be controlled by controlling the pore size and the density in the basal plane of graphene that was realized by adjusting the cobalt content in the precursor.10Co/G-700-HCl,possessing the highest edge or defective carbon content,reveals the optimal ORR performance with mixed 4eand 2e-ORR process,excellent stability and good methanol tolerance.?2?The holey graphene with pore size of about 11.5 nm was obtained in the condition of 700 ? and 10% H₂/Ar.In order to improve its ORR activity further,the obtained sample can be further treated under air condition at 300 ? to obtain the holey graphene with pore size of about 12.9 nm.Another simple method we adopted is treating Co?OH?₂/GO in 10% H₂/Ar atmosphere at 400 ? and then oxidizing at 250 ? in the air atmosphere.With this method,the holey graphene with pore size about 6.2 nm was obtained.Its ORR performance is higher than that of the first two samples and it shows a mixed 4e-and 2e-process.The Co particles in the samples were characterized by XRD and XPS.The edge or defect carbon content and the charge transfer resistance of the samples with different Co contents and different preparation methods were quantitatively evaluated by Raman spectra and Electrochemical impedance spectroscopy.The results show that the electron transfer resistances of all the samples were almost identical and the ORR performance of the samples is mainly dependent on the content of the defect or edge carbon.