Formation Of Hollow Carbon Microspheres For Oxygen Reduction Reaction

In order to alleviate the problem of energy crisis and environmental pollution,renewable green energy storage and conversion devices are in urgent need of development,such as metal air batteries,fuel cells and so on.The application of these storage and conversion devices which are based on oxygen reduction reaction(ORR)are restricted because of the sluggish kinetics of ORR reaction kinetics.Therefore,it is necessary to develop the effective ORR catalyst to alleviate the problem.At present,carbon materials have become a research hotspot due to its’ stable physical and chemical properties,excellent electrical conductivity,high specific surface area,abundant sources,low prices and a series of advantages.The hollow carbon material as a special porous carbon material which possesses unique morphology and structure has great application prospect in the field of ORR catalysts.In this paper,the hollow carbon was prepared through hydrothermal and heat treatment with carbon black and ammonia water as raw materials.The thickness of shell was adjusted by adjusting the temperature and time of heat treatment.After hydrothermal treatment,the hollow structure of the solid hollow carbon spheres appeared initially,but the spherical shell was thicker.After the heat treatment under ammonia gas,the thickness of the hollow carbon spheres was greatly reduced.It means that the hollow structure was optimized.When the heat treatment temperature is 900 ℃ and the heat treatment time is 2 h,the thickness reaches the lowest value and has the best electrocatalytic activity,the half-wave potential tested is 0.85 V vs RHE.In order to further improve the activity of hollow carbon,preoxidation,carbonization and ammonia heat treatment were used to cover the surface of carbon sphere with organic matter to form the C/C core-shell structure for in-situ nitrogen doping.Because the electrocatalytic activity increases with the increase of pyridine nitrogen and graphite nitrogen content.So,the content ofpyridine nitrogen and graphite nitrogen was regulated by the change of organic species,addition amount,carbonation time and temperature.When the organic matter is chitosan,the mass ratio of organic matter to carbon is 10:1,the carbonization temperature is 650 ℃ and the carbonization time is 2 h,the sample obtain the best performance,and the half-wave potential is 0.88 V vs RHE.Next,iron atoms were added during the hydrothermal process in order to form the iron containing compounds to improve the activity.By controlling the iron source and amount can control the kinds of iron compounds.The sample made from FeCl3 and iron and carbon atom ratio of 3:1000 can form Fe5C2 which can achieve the best electrochemical performance and the half-wave potential is raised to 0.89 V vs RHE.