Applications Of Nitrogen Deficient Graphitic Carbon Nitride In Energy Storage And Conversion

Global population and economic expansion are dramatically accelerating the energy consumption.At present,fossil fuels?such as oil,gas and coal?remain the main composition of the energy sources,whose combustion is accompanied by harmful gas emissions,seriously pollution to the environment.Therefore,the development of sustainable technology and equipment for energy conversion/storage become one of the hottest topics in science.In the future energy structure,new energy storage and conversion devices represented by fuel cells and lithium ion batteries will play a key role in the sustainable development of energy.Fuel cell can directly convert chemical energy into electric energy.Lithium-ion batteries can store electric energy with high energy density.Graphitic carbon nitride?g-C3N4?showing great thermal stability,appropriate electronic structure,abundant nitrogen content and tunable porous structure,has been widely concerned owing to its great potential in energy conversion and storage devices as electrode material or electrocatalyst.The utilization of g-C3N4 in these fields still faces many problems and challenges.For lithium ion battery systems,poor conductivity and serious irreversible capacity loss induced by the high nitrogen content of g-C₃N₄ needs to be solved first.For fuel cell,although g-C₃N₄ shows excellent durability and resistance to carbon monoxide poisoning,the small specific surface area,poor electrical conductivity and low catalytic activity limited its development.Based on these problems,we modified g-C₃N₄ by a magnesiothermic denitriding technique to prepare nitrogen-deficient carbon nitride?ND-g-C3N4?,and investigated its energy conversion and storage performance.The research content and results are as follows:?1?The temperature dependence on the preparation of ND-g-C₃N₄-n?n=650,675,700,750oC?via magnesiothermic denitriding method was studied.It was found that when the critital reaction temperature was 675?.At 675oC,nitrogen content would decrease sharply,and thus the conductivity of ND-g-C3N4 greatly increased.Meanwhile,the ohmic resistance remarkably decreased with the introduction of graphene skeleton.Therefore,high specific capacity,long cycle life and excellent rate performance have been obtained.At the current density of 1000 mA g^-1,the capacity reached 2820 mA h g^-1 after 1080 cycles.When the heat treatment temperature was higher than 675?,the reversible lithium storage capacity decreased because of the increase of the unstable graphitic nitrogen during the lithiation process.This work will provide a new strategy for the application of ND-g-C₃N₄ in LIB electrode.?2?Using ND-g-C₃N₄ as supports,Pt was uniformly loaded on the surface of ND-g-C3N4 by a sol method and studied as electrocatalyst for oxygen reduction reaction?ORR?.Compared with Pt/C,Pt/ND-g-C₃N₄ catalyst showed excellent ORR activity and stability.The doping of nitrogen atoms could accelerate the nucleation and growth of Pt,thus improving the dispersion and the utilization of Pt.Moreover,pyridine nitrogen and graphitic nitrogen of the material could serve as active sites,beneficial to improving of catalytic activity.In addition,the presence of nitrogen atoms strengthened the interaction between Pt and the supports,prevented the dissolution and agglomeration of the Pt nanoparticles,and thus enhanced the durability of the catalyst.