| Since large-area films assembled by carbon nanomaterials have important applications in the fields such as energy storage,separation and filtration,and environment remediation,intense efforts are thus devoted to the development of methodology that can prepare the large-area,continuous macroscopic films.Macroscopic films not only present collective effects that are not achieved by the individual building blocks,but also facilitate their applications in realistic world.Traditional methods for the preparation of carbon nanomaterials-based films usually need the assistance of external forces,which bring the issues of low compactness and low degree of order.Chemical vapor deposition(CVD)methods are able to prepare high-quality carbon film,while they involve in severe conditions and high energy consumption.Therefore,we developed a metal-induced self-assembly method for the preparation of large-area,flexible carbon films.Successful examples include aero-dimensional carbon dots,one-dimensional carbon nanotubes,two-dimensional graphene,and three-dimensional carbon microspheres.Taking CNTs with excellent physical properties as the example,they can be assembled into highly-dense,order,and flexible films on the surface of copper.The thickness,size,and morphology the CNTs films can be controlled by tuning the experimental parameters.When compared to the CNTs films prepared by traditional vacuum-suction methods,CNTs films prepared via the self-assembly strategy are highly dense and exhibit good conductivity and mechanical performances.To demonstrate the generality of the self-assembly method,we extend the building blocks to carbon dots,carbon inks,and carbon microspheres,all of which are found to work.On the basis of the self-assembly results,we proposed the electric double layer theory to interpret the phenomena.Since CNTs films integrate excellent mechanical properties,conductivity,and surface/interface effects,they should be ideal candidates for flexible energy devices.For instance,supercapacitors assembled by the CNTs films will show adequate energy density,high power density,good antifatigue,and long cycle life.So,we fabricated the solid-state flexible supercapacitors by using the CNTs films supported by carbon cloth as the electrode and active materials,and H3PO4/PVA as the electrolyte and the separator.The results show that,at a current density of 1 A.g-1,the device has a mass specific capacitance of 26.8 F.g-1,an area specific capacitance of 3.4 mF.cm-2,an energy density of 3.5 Wh.kg-1,and a power density of 28.1 kW.kg-1.And the capacitance was kept at the 92%of the initial capacitance.When the isolated CNTs films were used as the active materials and current collectors to fabricate the all-solid-state supercapacitors,the devices were found to exhibit an energy density of 0.58 mWh.cm-3 and a power density of 0.39 W.cm-3.Moreover,the devices were found to have excellent durability and cyclability.They can maintain 94%of the initial capacitance after 15000 charge-discharge cycles and 90%of the initial capacitance after 5000 bending tests.When the supercapacitors are applied in the field of hybrid electric vehicles(HEV),high energy and power,long life,and stability will be the basic requirements.Currently,the studies on the supercapacitors for HEV are focusing on the promotion of the cruising power and service life while keeping the high power.A feasible solution to the above problems should be the combination of pseudocapacitance active materials with electric double layer active materials,by taking advantage of the high energy density of the former and the good durability of the latter.To this end,we fabricated the composite electrodes based on the CNTs films and multiple-valence metal oxides that have excellent ability to store charges,which were then applied to assemble high-performance supercapacitors with good stability.We firstly studied the high-capacitance compound of NiCoO2,which was grown on the surface of the CNTs films in the form of ordered nanosheets.At the current density of 5 mA cm-2,the electrodes based on NiCoO2@CNT@NF,NiCoO2@NF,and CNTs@NF show a capacitance of 3.3 mF.cm-2,1.2 mF.cm-2 and 0.6 mF.cm-2,respectively.For the asymmetric NiCoO2@CNT@NF//CNT@NF supercapacitor,it exhibited the energy density of 77 μWh.cm-3,and power density of P=40 W.cm-3,which outperformed the similar ones reported in the literatures.Besides NiCoO2,the compound of Co3O4 also showed god synergy with the CNTs,because the composite electrode based on the two components was found to exhibit much improved electrochemical performances than the electrode based on the isolated CNTs or Co3O4. |
