Study Of Oxygen Reduction Reaction Based On Nitrogen-doped Carbon Materials As Catalysts

With the development of science and technology,the accelerated consumption of fossil fuels has induced increasing energy and environment problems.The development of energy devices suitable for the environment and sustainable development has become the focus of research.Currently,fuel cells have attracted great attention as a new energy device with almost zero pollution to the environment,high energy conversion efficiency,and good safety.In the conventional technology,Pt-based catalysts are the best catalysts for oxygen reduction reactions?ORR?in fuel cells.However,Pt-based catalysts have disadvantages such as easy degradation of catalytic activity,high cost,and poor stability,which makes them difficult to achieve further application of fuel cells.Therefore,this article focuses on the ORR catalyst of the direct methanol fuel cell?DMFC?cathode,and aims to accelerates the rate of oxygen reduction reaction by further optimizing the structure and composition of the catalysts.IThe research contents and achievements of this article are as follows:1?By using different precursors and different heat treatment temperatures.It is concluded that urea in a muffle furnace can be heated at a heating rate of 5°C min^-1 to 550°C and held for 4 hours to obtain a more obvious U-g-C₃N₄ hierarchical structure with a larger specific surface area(85 m² g^-1)and more catalytic performance?-0.321 V?.However,the conductivity of g-C₃N₄ itself is very poor.Therefore,we modified g-C₃N4 by mixing with graphene or adding metal elements.2?We developed a facile and economic strategy to prepare Cobalt and nitrogen co-doped carbon nanotubes for efficient ORR application.The g-C₃N₄ is used as the template and N source,Citric acid is used as the carbon source and Cobalt nitrate hexahydrate is used as the cobalt source.Through simple hydrothermal treatment and calcination,Co-N co-doped carbon nanotubes structures with high specific surface area(523 m² g^-1)and a rich nitrogen content?4.58%?can be obtained.It has excellent catalytic performance under alkaline conditions,such as onset voltage-0.087 V,half-peak voltage-0.140 V,limit current density of 3.57 mA cm^-1,good resistance to methanol crossover effects and 4e^-reaction path and so on.3?Adding g-C₃N₄ to graphene oxide can prevent graphene oxide from agglomerating during hydrothermal?180°C?process to obtain a multi-folded three-dimensional layered g-C₃N₄@rGO substrate,and then adding g-C₃N₄ quantum dot solution by physical method ?ultrasonic and stirring?to obtain g-C₃N₄@rGO/g-C₃N₄QDs composite material.After addition of quantum dots,the nitrogen content increased significantly?8.87%?,which provided more active sites for the reaction.Under alkaline conditions,the cyclic voltammetry curve?CV?has a more perfect rectangle and excellent peak voltage?-0.214 V?.According to the K-L equation,the ORR process is 4e^-reaction,and it has good resistance to methanol crossover effect and stability.