熔盐催化法制备二维石墨化碳材料

为了降低石墨化碳材料的生产成本,以木屑为主要原料,氯化钴为催化剂前驱体,LiCl-KCl(LiCl和KCl的质量比为45 55)为熔盐介质,采用熔盐催化法制备了二维石墨化碳材料。研究了反应温度(700、800和900℃)、LiCl-KCl与干燥后木屑的质量比(分别设为0 1、10 1、20 1和40 1)对产物的物相组成和显微结构的影响。结果表明:产物主要为二维石墨化碳纳米片和碳纳米球,反应温度和盐料比对产物的石墨化程度影响显著。升高反应温度有助于碳原子的有序排列,促进产物的石墨化;但反应温度过高时,可能会导致催化剂颗粒的团聚,使催化剂失活,致使产物的石墨化程度降低。随着LiCl-KCl和木屑质量比的增加,石墨的结晶度先增加后降低。当热处理温度为800℃,LiCl-KCl和木屑质量比为20 1时,产物的结晶度为91%,碳纳米片的尺寸为5~10μm,厚度约为30 nm。

3D MoS_(2)/graphene nanoflowers as anode for advanced lithium-ion batteries

Vertical MoS2nanosheets were controllably patterned onto graphene as nanoflowers through a two-step hydrothermal method. The interconnected network and intimate contact between MoS2nanosheets and graphene by vertical channels enabled a high mechanical integrity of electrode and cycling stability. In particular, MoS2/graphene nanoflowers anode delivered an ultrahigh specific capacity of 901.8 mA·h/g after 700 stable cycles at 1000 mA/g and a corresponding capacity retention as 98.9% from the second cycle onwards.

Independent thickness and lateral size sorting of two-dimensional materials

Two-dimensional(2D)materials possess unique thickness-and lateral-size-dependent properties.Many efforts have been devoted to obtaining 2D materials with narrow structure heterogeneity while it is still challenging to independently control their thickness and lateral size,limiting their widespread applications.Here,we develop a three-step method which achieves independent thickness and lateral size sorting of 2D materials.Taking 2D h-BN flakes as an example,their thickness and lateral size are independently sorted to different fractions with thicknesses smaller than 6 nm.In addition,the 2D h-BN flakes possess narrow distributions of both thickness and lateral size.We further develop a force field extraction method and achieve scalable size sorting of 2D h-BN,which is universal for sorting other 2D materials including MoS2 and graphene oxide.This work reports an effective method to produce structure homogenous 2D materials and will help fundamental studies and applications of 2D materials where thickness and lateral size are of concern.

Flexible all-solid-state micro-supercapacitor based on Ni fiber electrode coated with MnO_2 and reduced graphene oxide via electrochemical deposition

Flexible and micro-sized energy conversion/storage components are extremely demanding in portable and multifunctional electronic devices, especially those small,flexible, roll-up and even wearable ones. Here in this paper, a two-step electrochemical deposition method has been developed to coat Ni fibers with reduced graphene oxide and MnO2 subsequently, giving rise to Ni@reduced-graphene-oxide@MnO2 sheath-core flexible electrode with a high areal specific capacitance of 119.4 mF cm^-2 at a current density of 0.5 mA cm^-2 in 1 mol L^-1 Na2SO4 electrolyte. Using polyvinyl alcohol（PVA）-LiCl as a solid state electrolyte, two Ni@reduced-grapheneoxide@Mn02 flexible electrodes were assembled into a freestanding, lightweight, symmetrical fiber-shaped micro-supercapacitor device with a maximum areal capacitance of26.9 mF cm^-2. A high power density of 0.1 W cm^-3 could be obtained when the energy density was as high as0.27 mW h cm^-3. Moreover, the resulting micro-supercapacitor device also demonstrated good flexibility and high cyclic stability. The present work provides a simple, facile and low-cost method for the fabrication of flexible, lightweight and wearable energy conversion/storage micro-devices with a high-performance.

Flexible high-performance microcapacitors enabled by all-printed two-dimensional nanosheets

Chemically exfoliated nanosheets have exhibited great potential for applications in various electronic devices.Solution-based processing strategies such as inkjet printing provide a low-cost,environmentally friendly,and scalable route for the fabrication of flexible devices based on functional inks of twodimensional nanosheets.In this study,chemically exfoliated high-k perovskite nanosheets(i.e.,Ca_(2)Nb_(3)O_(10)and Ca_(2)NaNb_(4)O_(13))are well dispersed in appropriate solvents to prepare printable inks,and then,a series of microcapacitors with Ag and graphene electrodes are printed.The resulting microcapacitors,Ag/Ca_(2)Nb_(3)O_(10)/Ag,graphene/Ca_(2)Nb_(3)O_(10)/graphene,and graphene/Ca_(2)NaNb_(4)O_(13)/graphene,demonstrate high capacitance densities of 20,80,and 150 nF/cm^(2) and high dielectric constants of 26,110.and 200,respectively.Such dielectric enhancement in the microcapacitors with graphene electrodes is possibly attributed to the dielectric/graphene interface.In addition,these microcapacitors also exhibit good insulating performance with a moderate electrical breakdown strength of approximately 1 MV/cm,excellent flexibility,and thermal stability up to 200℃.This work demonstrates the potential of high-k perovskite nanosheets for additive manufacturing of flexible high-performance dielectric capacitors.