Synthesis And Electrochemical Performance Of Polymer-Derived Graphene-like Doped Materials

The physical and chemical properties of graphene can be greatly improved by changing the three dimensional structure of the carbon layer and/or doping with appropriate atoms.Graphene-based materials doped with nitrogen or sulfur are very promising candidates for the applications of supercapacitor,as it can improve the redox activity of the materials and the faradaic pseudocapacitance.In this paper,nitrogen and sulfur doped graphene-like material were prepared by high temperature carbonization of polymer precursor,the structures and their electrochemical properties were also investigated.Related work is as follows:(1)Chitosan was used as the carbon and nitrogen source,and potassium sulfate(K2SO4)was used as the sulfur source to prepare the nitrogen and sulfur co-doped graphene-like materials by a simple one-step method.The product shows a three-dimensional porous structure with a high doping content,in which the ratio of nitrogen and sulfur element is as high as 7.7%and 10.3%,respectively.Performance of the material as supercapacitive electrode was greatly improved by the synergistic effect of nitrogen and sulfur when using ionic liquid as the electrolyte.The specific capacitance is up to 147 F/g at an ultrahigh current density of 40 A/g,and our material can retain 93%of the initial capacitance after 1000 charge and discharge cycles at the current density of 10 A/g,showing a good cycle stability.(2)2-Methylimidazole zinc salt(ZIF-8)precursor was successfully prepared with an average size of 103 nm by using Zn(NO3)2·6H2O,2-methylimidazole and polyvinylpyrrolidone(K-30)as the reactants,which retained its structure after carbonization at 700 ?,and obtained a lot of microporous channels when the zinc element was removed by washing with concentrated hydrochloric acid.The final N-doped graphene-analogue has a large specific surface area and good conductivity,and so present good performances as the supercapacitive electrode:The specific capacitance is as high as 249 F/g at the current density of 3 A/g,and even at a high current density of 10 A/g,the specific capacitance is still retaining 120 F/g.