Preparation Of Heteroatom Doped Carbon Nanosheets Based On Boron Nitrogen Synergistic Effect And Research On The Capacitive Energy Storage Performance

Supercapacitors have attracted great attention as next-generation energy storage devices because of the high power density,superior lifetime,and good safety.Carbon materials are widely used for supercapacitors due to the large surface area and good conductivity.Particularly,nitrogen-doped carbon has been mostly investigated because of the high electronegativity and excellent compatibility of nitrogen atoms towards carbon skeleton.However,nitrogen-doped carbon materials confront with a severe issue of low nitrogen content because the nitrogen-containing functional groups are unstable at high treating temperature.Aiming at the above mentioned issues,herein,we developed a simple boric acid-assisted strategy to effectively trap nitrogen in B,N co-doped carbon nanosheets（BN-CNSs）.Using graphene quantum dots（GQDs）with an initial nitrogen content of 5.0 at.%as precursors,the effect of different carbonization temperature and boric acid dosage on the physicochemical properties and electrochemical properties of the BN-CNSs were investigated.Besides,we discussed the energy storage mechanism of the BN-CNSs.The research details of the paper are as follows:1.Firstly,the different carbonization temperature and boric acid dosage of BN-CNSs capacitive energy storage performance were studied.We found that the percentage of nitrogen atoms showed increasing firstly and then dereasing,while the percentage of boron atoms showed increasing firstly and then decreasing.We also found that the results with the increase of boric acid dosage（1:5,1:10,1:15）:the percentage of nitrogen atoms and boron atoms showed increasing firstly and then dereasing.Besides,we found that the largest percentage of heteroatoms and the best electrochemical energy storage performance were obtained when the carbonization temperature was 800℃ and the ratio of graphene quantum dots to boric acid was1:10 through the electrochemical performance test.Under the optimal conditions,the BN-CNSs show an increased nitrogen content of 7.2 at.%and a boron content of 4.4at.%.When used in three electrode,the BN-CNSs present high capacitance of 252 F g^-1 at 1 A g^-1,good rate performance of 150 F g^-1 at 50 A g^-1,excellent cyclic stability without capacitance fading after 10,000 cycles at 10 A g^-1.When used in two electrode,the BN-CNSs present high capacitance of 287 F g^-1 at 1 A g^-1,good rate performance of 150 F g^-1 at 50 A g^-1,excellent cyclic stability without capacitance fading after 10,000 cycles at 10 A g^-1.So the BN-CNSs with high nitrogen content and high performance were prepared at the appropriate carbonization temperature and boron doping rate.2.The BN-CNSs were prepared by boron fixation can significantly enhance the electrical energy storage performance.So the electrical energy storage mechanism is discussed.We also prepared nitrogen doped carbon nanosheets using similar GQDs by Mg（OH）₂ template method,and compared with BN-CNSs at physicochemical properties and electrochemical energy storage performance.According to the physicochemical property characterization and electrochemical energy storage test results of CNSs,the energy storage mechanism of BN-CNSs is obtained.When used in three electrodes,the CNSs show pseudocapacitancecontribution 16%at 10 m V s^-1.However,the BN-CNSs show high pseudocapacitance contribution 48%at 10 m V s^-1 owing to abundant active sites from highly doped boron and nitrogen atoms.So,we researched the N_1sand B_1s of XPS.We found that the nitrogen atom content of BN-CNSs was not only higher than the nitrogen atom content of the CNSs but also higher than the nitrogen atom content of GQDs.In addition,the nitrogen-containing functional groups of BN-CNSs compared with the CNSs and GQDs not only has the same functional groups of pyridine N,pyrrolic N,pyridine-N-oxide and graphitic N but also has the new functional groups C-N-B and BCO₂.In conclusion,the synregistic effect between nitrogen and boron atoms is not only beneficial to the co-doping carbon materials but also beneficial to the improvement of the carbon materials electrochemical properties.Our work use the graphene quantum dots（GQDs）with an initial nitrogen content of 5.0 at.%as precursors,the BN-CNSs were obtained by boron nitrogen fixation,which show the specific surface 817 m²g^-1,an increased nitrogen content of7.2 at.%and a boron content of 4.4 at.%.As an exemplified application for supercapacitors,the BN-CNSs perform a specific capacitance of 287 F g^-1at 1 A g^-1with high pseudocapacitive contribution owing to abundant active sites by highly doped heteroatoms.They also present a good rate capability of 150 F g^-1 at 50 A g^-1as well as remarkable cycle stability with no obvious capacitance fading after 10,000cycles at 10 A g^-1.Our work make use of the synergistic effect not only prepares BN-CNSs with high nitrogen content but also broadens the avenue to design highly-doped functional carbon materials.