The Oxygen Reduction Reaction Property Of Nitrogen-doped Mesoporous Graphene Spheres Prepared By Spray Drying

Oxygen reduction（ORR）reaction is a chemical reaction occurring at the cathode of fuel cell.As an important factor to promote oxygen reduction reaction,it is especially important to develop a durable oxygen reduction catalyst with excellent performance.This paper focuses on oxygen reduction catalysts and nitrogen-doped graphene materials.Oxygen reduction（ORR）reaction is a chemical reaction occurring at the cathode of fuel cell.As an important factor to promote oxygen reduction reaction,it is especially important to develop a durable oxygen reduction catalyst with excellent performance.This paper focuses on oxygen reduction catalysts and nitrogen-doped graphene materials.First,the principle and structure of fuel cell are described in detail.This paper introduces current several mainstream status and lack of oxygen reduction catalyst,including Pt catalysts,transition metal oxides,metal nitrides and nitrogen doped graphene materials four.And focuses on the influence of structure and nitrogen content of nitrogen doped graphene on the electrocatalytic activity of the modified methods and research status.Secondly,nitrogen doped mesoporous graphene spheres were prepared by spray drying.Melamine,gas phase SiO₂ and graphene oxide were used in the preparation of raw materials.We found that the addition of SiO₂ helped the formation of graphene ball structure.This structure enables the nitrogen source to be better encapsulated by graphene,reducing the loss of nitrogen during heat treatment and increasing the nitrogen content of the final product to 5.78%.Thus,it can increase the active site and improve the catalytic activity of oxygen reduction.After removing SiO₂,the mesoporous structure with high specific surface area can be obtained.The specific surface area is up to 155 m² g^-1,which can improve the mass transfer efficiency of materials and further improve the catalytic performance of oxygen reduction.Then,we further explored the nitrogen doped mesoporous graphite microspheres in the previous experiment.By changing the content of nitrogen source melamine,the effect of nitrogen source content on the oxygen reduction performance of nitrogen doped mesoporous graphene microspheres prepared by spray drying was investigated.We used three groups of different raw materials in different proportions.The mass ratios of melamine,gas phase SiO₂ and go were 1:1:2,2:1:2 and 3:1:2 respectively.Using the same preparation method as in the previous experiment,we obtained three groups of products.Through testing,analysis and comparison,we found that the oxygen reduction performance of the product whose raw material ratio is 2:1:2 is the best.In a certain range,the higher the nitrogen source content,the higher the nitrogen content.Excess nitrogen sources make it harder for materials to form stable spheres.Therefore,moderate nitrogen content is the most beneficial to improve the catalytic performance of oxygen reduction.Finally,based on the above work,we made a summary and prospect,hoping to further optimize and explore the experiment.