The Desigin And Application Of Two-dimensional Graphene-based Materials As Electrodes For Supercapacitors

Two-dimensional?2D?nitrogen-containing porous carbon nanosheets are prepared in the presence of graphene oxide?GO?as a structure-directing agent by a simple yet facile hydrothermal method.It is found that GO can effectively turn the morphologies of the hydrothermal carbonaceous products,resulting in the unique 2D structures.The as-obtained2D nitrogen-containing porous carbon nanosheets as electrodes for supercapacitors exhibit a high specific capacitance of 301.6 F g^-1 at a current density of 0.5 A g^-1 and superior rate capability with a capacitance retention of 70.5%at the high current density of 20 A g^-1.The2D nitrogen-containing porous carbon nanosheet electrodes also exhibit good cycling performance,possessing the high capacitance retention over 92.3%after 5000charge-discharge cycles at the current density of 5 A g^-1.Two-dimensional?2D?N,S co-doped porous carbon nanosheets are prepared in the presence of graphene oxide?GO?from expired wheat four.It is found that GO can effectively turn the morphologies of the activated products,resulting in the unique 2D structures.The as-obtained 2D N,S co-doped porous carbon nanosheets as electrodes for supercapacitors exhibit a high specific capacitance of 291 F g^-1 at a current density of 0.5 A g^-1 and superior rate capability with a capacitance retention of 70%at the high current density of 30 A g^-1.The2D N,S co-doped porous carbon nanosheet electrodes also exhibit good cycling performance,possessing the high capacitance retention over 93%after 5000 charge-discharge cycles at the current density of 5 A g^-1.Experimental and theoretical results reveal that the high pseudocapacitive effect of the N and S species can improve the electrochemical performance.Ultrathin 2D nitrogen-doped carbon nanosheets have been facilely synthesized from potato starch by using graphene oxides?GO?as the structure-directing agent.The addition of GO to the potato starch can increase the surface areas as well as the pyridinic-N and pyrrolic-N ratios of the as-made 2D carbon nanosheets.The as-obtained ultrathin nitrogen-doped carbon nanosheets possess a high capacitance of 301 F g^-1 at 0.5 A g^-1,superior rate capability of 81%at 50 A g^-1,and a good cycling stability.Experimental and theoretical results show that high pyridinic-N and pyrrolic-N ratios in the NCNSs are beneficial for improving the electrochemical performance.A novel 1D/2D hybrid design is reported for synthesizing a high performance NiCo-hydroxide nanowires/graphene?NiCo-NWs/G?composite.The oxygen-containing groups on the graphene oxide surface can act as anchoring sites for uniformly adsorbing the metal seeds,leading to the dispersed formation of thin NiCo-NWs on the graphene surface.The existence of graphene in NiCo-NWs/G can provide a conductive network to boost the faradaic reaction.In addition,the bimetallic NiCo-NWs possess rich redox reaction sites and the thin nanowire structure ensures that electrons can move rapidly from the reaction sites to the current collectors.Owing to the synergic effects of 1D NiCo-NWs and 2D graphene,the developed NiCo-NWs/G electrode exhibits the excellent performance of 1449 F g^-11 at a current density of 1 A g^-1,high rate capability of 61%at 20 A g^-1,and a good cycling stability.Moreover,the asymmetric supercapacitor with NiCo-NWs/G as a positive electrode and active carbon as a negative electrode delivers a high energy density of 42.1 Wh kg^-1 at a power density of 0.8 kW kg^-1.This work may pave a promising new way for the development of 1D/2D composite based on pseudocapacitive hydroxides and carbon materials for high-performance asymmetric supercapacitors.