The Preparation And Electrochemical Properties Of The Transition Metal Oxides On Porous Nitrogen Carbon Surface

The lithium-air electrochemical system is a representative energy conversion and storage technology with the preponderance of high efficiency and environmental protection.In the structure of it,the electricity catalyst plays a key role in the chemical process,but the performance of the whole system is always limited by insufficient catalytic activity,short cycle life and high cost,it is a long-standing problem.In the basic of developing high efficiency,low cost and durable electric catalyst,putting forward the theory that inorganic nanocrystals nucleate,grow and anchor directly in nanocarbon substrate,developing strong inorganic nanocrystals/hybrid nanocarbon materials,to improve the catalytic activity and stability.In this paper,the present situation,composition and challenges of rechargeable nonaqueous lithium-air battery are described.The oxygen reduction/oxygen evolution?ORR/OER?bifunctional catalyst was prepared by anchored Co₃O₄ nanocrystals on the surface of nitrogen doped porous carbon materials through hydrothermal method via the bonds of Co-N.The research work focused on exploring and discussing the key influence factors of the electrode electrochemical performance;the charging/discharging cycle performance of lithium-air battery and presenting a new theoretical and experimental basis for the application of porous bifunctional catalyst in lithium-air batteries.The following conclusions are drawn:1)The results of TEM and BET demonstrate that the prepared NHCNs is porous structure.The pore diameter is mainly distributed around 30 nm.The NHCNs heated temperature under 1000?has specific surface area of 360.6 m²/g,while the Co₃O₄/NHCNs comprised with the content of 30%cobalt and heated temperature under500?has lower specific surface area of 278.3 m²/g due to crystal stacked.Electrochemical test and analysis present that the catalyst with the content of 30%cobalt heated temperature under 500?showed better catalytic properties.The prepared Li-Air batteries illustrate the cycling performance of the prepared electrode with the specific capacity of 500 mAhg^-1 after 15 cycles which provide the theoretical and experimental support for the application of such porous composite catalysts in lithium-air batteries.2)After exploring the influence of carbonization temperature on the electrochemical properties,the results show that NDPC heated under 800?has more positive half wave potential,excellent durability and the surface area of 56 m²/g.Element analysis results show that the samples heated under 700?and 800?have the same nitrogen content,while the sample heated under 900?possess the lower content of nitrogen and carbon which could be due to the higher carbonization temperature leading lower stability of the edge of the nitrogen and carbon atoms.3)The morphologies and the content of Co of the Co₃O₄/NDPC materials are investigated with TEM and element analysis.The results demonstrate that the addition of Co ion amount in the first step of hydrothermal play a key role on the final Co content of the prepared materials.Also,the hydrothermal time controlling is an effective method to adjust Co content and crystal size.By comparing the electrochemical performance of different catalyst samples show that the synergistic effect existing between Co and N atoms has a very significant improvement on performance compared than physical mixture material.