| Owning large specific area,decent conductivity,rich porous structure,superior thermal conductivity and the ability to absorb microwaves,graphene aerogel has great contribution and potential in the fields of catalyst,energy storage,adsorption,thermal applications and electronic device.It is worthwhile to study the complex fabrication process in which every single step can influence the properties of graphene aerogel.Meanwhile,graphene aerogel is an electric double layer material which mainly depends on its surface area to provide capacitance that,however,is unsatisfying and still needs to be improved.Aimed at above problems,nitrogen,iodine and manganese doping have been adopted to improve the performance of the aerogel.The purpose of nitrogen doping is to enhance the structure of the aerogel and enlarge its specific surface area.And doping iodine is to decrease its resistance and offer some pseudocapacitance.The addition of manganese is to test the performance of the aerogel as a carrier of pseudocapacitance materials.Meanwhile the influence of hydrothermal reaction time in the doping process has been studied.To identify the effects of doping,the materials have been tested in both three electrode and two electrode configuration using 1M KOH as electrolyte.The details of the experiments are listed below.(1)Study of nitrogen-doped graphene aerogel.Nitrogen-doped graphene was synthesized using ethanediamine and ammonia as additive via a hydrothermal method.The effects of hydrothermal reaction time,drying method and the proportion of additive to the performance of the aerogel were studied.It was found that more reaction time brought about better self assemble process which,as a result,gave larger specific surface area and pore volume.However,when the time past 18 h,the increase of specific surface area started to slow down and the pore volume began to shrink.And the experiment also revealed the different roles that ethanediamine and ammonia played in nitrogen doping.It turned out that nitrogen helped to enhance the structure of the aerogel and offer a larger surface area while ethanediamine gave rise to increase in capacitance.And through this method,surface area was enlarged and nitrogen-doped graphene aerogel with specific area of 848.383 m~2/g and pore volume of 2.632 ml/g was obtained.With above structure,the nitrogen-doped graphene aerogel showed specific capacitance of 145 F/g at 0.5 A/g in a three-electrode configuration.Been assembled into a coin type supercapacitor,it showed 100%retention after 1000 cycles in life span test.(2)Study of iodine-doped graphene aerogel.Iodine-doped graphene aerogel was prepared via a two step hydrothermal method where hydroiodic acid was used as the doping source.Reaction time of the hydrothermal process and the concentration of hydroiodic acid had been studied as factors affecting the performance of the aerogel.It was found that more reaction time and higher density of iodine addition could increase specific surface area and decrease pore volume.And iodine doping could indeed provide lower resistance and pseudocapacitance.Finally,iodine-doped graphene with specific area of 718.421 m~2/g and resistance of 198 m?cm was synthesized and its conductivity and capacitance were enhanced.Tested in a tree electrode system,it possessed specific capacitance of 246 F/g at 0.1 A/g.And it held a steady capacitance of108 F/g after 1000 cycles in two electrode system.(3)Study manganese-doped graphene aerogel.Manganese graphene aerogel was fabricated via a hydrothermal method using manganese dichloride as doping source.The influence of the amount of manganese additive was studied.It was found that larger addition of manganese led to the decrease of specific surface area and pore volume.And the aerogel synthesized presented capacitance of 180 F/g at 0.1 A/g showing evident pseudocapacitance behavior.And it was assembled into coin type supercapacitor to run cycle span test and showed a retention of 93%after 1000 cycles in two electrode configuration. |
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