Fabrication Of Nitrogen-containing Activated Carbon Materials For Supercapacitor Applications

In the past few decades,supercapacitor has become one of the hot topics due to its many advantages,and has acquired good practical application in some fields.In order to deeply explore the factors that affecting the performance of supercapacitor,we based on the carbon-based material and fabricated the high performance nitrogen-contining activated carbon electrodes.Then,the mechanism of ionic effect on the capacitance of electrode material in aqueous electrolytes was also investgated.Firstly,the complex of melamine and citric acid was used as precursors for preparation of the carbon nitride materials,and the effects of different reaction conditions on the structure and supercapacitor properties of samples were studied.Secondly,to further improve the performance of electrodes,nitrogen-containing activated carbon was synthesized by a simultaneous pyrolysis/activation method from biomass bones under the different temperature.In addition,the mechanism of microporous ratio and nitrogen content on its capacitive properties was also studied.Finally,by using CMK-3 as research subject,the influence of electrolyte cation on their supercapacitor properties was explored by Raman spectroscopy.The main contents are as follows:（1）The design and synthesis of nitrogen-rich activated carbon materials is one of major topic for supercapacitors.Herein,porous activated carbon nitride（ACN）materials were obtained by a one-step pyrolysis/activation of melamine and citric acid complex at different temperature.In detail,the optimized ACN-700 electrode with a BET surface area of 716 m² g^-11 show a specific capacitance of 185 F g^-1 at the current density of 0.5 A g^-1.Then,the assembled symmetric cell based on ACN-700 can achieve the energy density of 16.9 Wh kg^-11 and 6.2 Wh kg^-11 in 2 M[BMIm]BF₄/AN and 6 M KOH,respectively.The enhanced performance of ACN-700 is mainly due to the introducing of nitrogen derived pseudo-capacitance,associated with the large surface area and surface oxygenation after activation.（2）Waste biomass of Pork bone,Blackfish bone and Eel bone were used as canbon/nitride source.The nitrogen-containing activated carbon was synthesized by a simultaneous pyrolysis/activation method,which can turn waste into treasure and reduce costs of processing.Then,the influence of pyrolysis temperature（500-800 ^oC）on the BET surface area and porous structure of activated carbon was studied,and acquired the highest specific surface area of 1522 m² g^-1.The electrochemical properties of nitrogen-containing activated carbon not only depended on the specific surface area,but also related to their micro-/mesoporosity ratio.Three samples PBAC-600,BFAC-600 and EBAC-600,which have higher ratio of micropore surface area,exhibit the enhanced specific capacitance of 263,302 and 264 F g^-1 in 6 M KOH electrolyte.Furthermore,the assembled symmetric supercapacitors based on PBAC-600 can achieve the higher energy density up to 7.0 and 26.2 Wh Kg^-1 in the aqueous and ionic liquid electrolyte,respectively.Such excellent performance can be attributed to the microporous structure,reasonable pore size distribution and nitrogen derived pseudocapacitance.Therefore,these results indicate that the waste bones have great potential for mass fabrication of the activated carbon electrodes.（3）The cation/anion of electrolyte on the electrochemical performance of materials cannot be ignored.Thus,probing the energy storage mechanism can help to improve the charge storage capacity of electrode material.Herein,we invegaste the charge transfer and ionic polarization of CMK-3 during energy storage process via differential phonon Raman spectroscopy（DPS）,and induce the hydrogen-bond（HB）relaxation and ionic polarization of aqueous electrolytes to understand the specific ion effect on their electrochemical performance.Results revealed that the specific capacitance of CMK-3 electrodes follows the sequence:KOH>NaOH>LiOH.At the same time,the polarizability of ions follows the sequence:Y（R,η）:Li⁺（0.78??,1.0）>Na⁺（0.98?,0.9）>K⁺（1.33?,0.8）.These results indicate that the smaller ion size,the bigger electronegativity and the stronger ionic polarization will perform the relatively poor specific capacitance.This method provides a novel idea to predict the matched-degree between electrolyte and electrode.