Congpu Mu

Fabrication of NiCo2-Anchored Graphene Nanosheets by Liquid-Phase Exfoliation for Excellent Microwave Absorbers

Graphene nanosheets (GNSs) were prepared by an efficient liquid-phase exfoliation method, and then the NiCo2/GNS nanohybrids were fabricated using the single-mode microwave-assisted hydrothermal technique. The NiCo2/GNS composites with different GNS proportions were investigated as microwave absorbers. Morphology investigation suggested that NiCo2 nanocrystals were uniformly anchored on the GNS without aggregation. The electromagnetic parameters of NiCo2/GNS nanohybrids could be artificially adjusted by changing the GNS proportion, which led to an exceptional microwave-absorbing performance. A reflection loss (RL) exceeding -20 dB was obtained in the frequency range of 5.3-16.4 GHz for the absorber thicknesses of 1.2-3.2 mm, while an optimal RL of -30 dB was achieved at 11.7 GHz for a thickness of 1.6 mm. The enhanced microwave-absorbing performance indicated that the NiCo2/10 wt % GNS composite has great potential for use as an excellent microwave absorber.

Flexible Black-Phosphorus Nanoflake/Carbon Nanotube Composite Paper for High-Performance All-Solid-State Supercapacitors

We proposed a simple route for fabrication of the flexible BP nanoflake/carbon nanotube (CNT) composite paper as flexible electrodes in all-solid-state supercapacitors. The highly conductive CNTs not only play a role as active materials but also increase conductivity of the hybrid electrode, enhance electrolyte shuttling and prevent the restacking between BP nanoflakes. The fabricated flexible all-solid-state supercapacitor (ASSP) device at the mass proportion of BP/CNTs 1:4 was found to deliver the highest volumetric capacitance of up to 41.1 F/cm3 at 0.005 V/s, superior to the ASSP based on the bare graphene or BP. The BP/CNTs (1:4) device delivers a rapid charging/discharging up to 500 V/s, which exhibits the characteristic of a high power density of 821.62 W/cm3, while having outstanding mechanical flexibility and high cycling stability over 10 000 cycles (91.5% capacitance retained). Moreover the BP/CNTs (1:4) ASSP device still retains large volumetric capacitance (35.7 F/cm3 at the scan rate of 0.005 V/s) even after 11 months. In addition, the ASSP of BP/CNTs (1:4) exhibits high energy density of 5.71 mWh/cm3 and high power density of 821.62 W/cm3. As indicated in our work, the strategy of assembling stacked-layer composites films will open up novel possibility for realizing BP and CNTs in new-concept thin-film energy storage devices.

Fabrication of multifunctional carbon encapsulated Ni@NiO nanocomposites for oxygen reduction, oxygen evolution and lithium-ion battery anode materials

Multifunctional carbon encapsulated Ni@NiO nanocomposites (Ni@NiO@C) were synthesized for applications in oxygen reduction reactions (ORR), oxygen evolution reactions (OER) and lithium-ion batteries (LIB). The morphology was investigated via SEM and TEM, suggesting that the Ni@NiO@C nanocomposites have uniform and spherical core-shell structures. When the Ni@NiO@C nanocomposite is used as the catalyst in ORR, 90% of the initial current density can be maintained after 15 h in O2-saturated 0.1 mol L−1 KOH at 0.3 V under a rotation speed of 1600 rpm. As a catalyst for OER, the highest activity overpotential of the Ni@NiO@C nanocomposite electrocatalyst is 380 mV (vs. RHE) under the current density of 10 mA cm−2, and the Tafel slope was calculated to be 55 mV dec−1 by linear fitting. Electrochemical performances of the Ni@NiO@C nanocomposites used as LIB electrodes exhibited a long cycling life with a high capacity of 750 mA h g1 after 400 cycles under 200 mA g−1.摘要本文成功合成了多功能的碳包覆Ni@NiO纳米复合材料, 并将其用作析氧反应和氧还原反应催化剂以及锂离子电池的负极材料. 扫描电镜和透射电镜照片表明Ni@NiO@Cm米复合物具有均一的球形核壳结构. 将Ni@NiO@C纳米复合物用作氧还原反应的催化剂时, 在浓度为0.1 mol L−1的氢氧化钾溶中以1600 rpm转速下连续反应15小时后, 电流密度仍然可以保持在初始值的90%以上. 作为析氧反应的催化剂时, 在电流密度为10 mA cm−2时Ni@NiO@C纳米复合物的活性电位是380 mV (vs. RHE). 同时线性拟合的塔菲尔斜率为55 mV dec−1. Ni@NiO@C纳米复合物被用作锂离子电池的负极材料时, 在电流密度为200 mA g−1下循环400圈后, 电池容量还可以达到750 mA h g−1. 结果表明Ni@NiO@Cm米复合物用于氧还原反应、 析氧反应和锂离子电池均具有优异的电化学性能.

Facile synthesis and excellent electrochemical performance of CoP nanowire on carbon cloth as bifunctional electrode for hydrogen evolution reaction and supercapacitor

In this paper, we report CoP nanowires supported on carbon cloth (CC) (CoP/CC) as a bifunctional electrode for hydrogen evolution reaction (HER) and supercapacitor. CoP/CC possess an excellent electrocatalytic performance for HER, with a Tafel slope of 56 mV/dec and a low overpotential of 68 mV to achieve a current density of 10 mA cm-2. Remarkably, the bifunctional CoP/CC used as electrode for supercapacitor exhibit a higher specific capacitance of 674 F g-1 at a scan rate of 5 mV s-1 and maintains long-life cycling stability, retaining 86% of the initial capacitance after 10,000 cycles. CoP/CC will be a promising candidate as electrode for HER and supercapacitor.摘要本文利用微波辅助水热法在碳布上快速合成了 CoP纳米线阵列(CoP/CC)双功能电极材料可用于析氢反应(HER)和超级电容器的电 极.CoP/CC用于Hm时展现了优越的电化学性能,其塔菲尔斜率为56 mV/dec.当电流密度为10 mA cm-2时,其电位低至68 mV. 值得注意 的是, CoP/CC也可用于超级电容器的电极.在扫描速率为5 mVs-1时, 其比电容高达674 F g-1.同时具有高的循环稳定性, 在循环10000次 后, 比电容仍然可以维持在初始值的86%.本文结果表明, CoP/CC可以作为HER和超级电容器电极的有力候选者.

Strain Release Induced Novel Fluorescence Variation in CVD-Grown Monolayer WS2 Crystals

Tensile strain is intrinsic to monolayer crystals of transition metal disulfides such as Mo(W)S2 grown on oxidized silicon substrates by chemical vapor deposition (CVD) owing to the much larger thermal expansion coefficient of Mo(W)S2 than that of silica. Here we report fascinating fluorescent variation in intensity with aging time in CVD-grown triangular monolayer WS2 crystals on SiO2 (300 nm)/Si substrates and formation of interesting concentric triangular fluorescence patterns in monolayer crystals of large size. The novel fluorescence aging behavior is recognized to be induced by the partial release of intrinsic tensile strain after CVD growth and the induced localized variations or gradients of strain in the monolayer crystals. The results demonstrate that strain has a dramatic impact on the fluorescence and photoluminescence of monolayer WS2 crystals and thus could potentially be utilized to tune electronic and optoelectronic properties of monolayer transition metal disulfides.

Dynamic susceptibility of onion in ferromagnetic elliptical nanoring

Micromagnetic simulation was performed to investigate the equilibrium state and dynamic susceptibility spectra of magnetic elliptical nanoring. There are two equilibrium states (onion and vortex) obtained in elliptical nanoring. The onion state can be used to record information in MRAM. And it is important to investigate the dynamic susceptibility spectra of onion state, which is closely related to writing and reading speed of magnetic memory devices. Those results show that two or three resonance peaks are found under different thickness of elliptical nanoring with onion state, respectively. The low resonance frequency of two resonance peaks is increasing with the arm width of the elliptical ring, but is decreasing with the thickness. However, the high frequency of two resonance peaks is decreasing with the arm width of the elliptical ring.

Metal–organic framework derived cobalt phosphosulfide with ultrahigh microwave absorption properties

Nanostructure composites of ferromagnetic materials embedded in nanoporous carbon (NC) derived from metal-organic frameworks (MOFs) have attracted enormous attention due to their potential application in many fields, such as microwave absorption, energy storage, and conversion. The rational design of nanocomposites holds a determinant factor for overcoming the challenges involving the microwave absorption performance. Herein, CoS2/NC, CoP/NC, and CoS2-xPx/NC with a rhombic dodecahedral structure have been successfully fabricated by using the template cobalt-based MOFs (ZIF-67). A morphology analysis indicates that ferromagnetic nanoparticles are embedded in NC matrix. It is obvious that the rhombic dodecahedron can be maintained after the phosphorization and sulfurization of Co/NC derived from the thermal decomposition of ZIF-67. The microwave absorption performance can obviously be improved by the phosphorization and sulfurization of Co/NC. CoS2-xPx/NC exhibits an excellent microwave absorption property and the minimum reflection loss (RL) of CoS2-xPx/NC can reach -68 dB at 14.6 GHz with a thickness of 1.5 mm. An RL value less than -10 dB can be achieved in the microwave frequency range of 12.7-17.3 GHz (4.6 GHz) with a thickness of 1.5 mm for CoS2-xPx/NC. This article offers a novel way to fabricate cobalt-based materials/carbon composites for an excellent microwave absorber.

Grain wall boundaries in centimeter-scale continuous monolayer WS2 film grown by chemical vapor deposition

Centimeter-scale continuous monolayer WS2 film with large tensile strain has been successfully grown on oxidized silicon substrate by chemical vapor deposition, in which monolayer grains can be more than 200 μm in size. Monolayer WS2 grains are observed to merge together via not only traditional grain boundaries but also non-traditional ones, which are named as grain walls (GWs) due to their nanometer-scale widths. The GWs are revealed to consist of two or three layers. Though not a monolayer, the GWs exhibit significantly enhanced fluorescence and photoluminescence. This enhancement may be attributed to abundant structural defects such as stacking faults and partial dislocations in the GWs, which are clearly observable in atomically resolved high resolution transmission electron microscopy and scanning transmission electron microscopy images. Moreover, GW-based phototransistor is found to deliver higher photocurrent than that based on monolayer film. These features of GWs provide a clue to microstructure engineering of monolayer WS2 for specific applications in (opto)electronics.

Liquid-Exfoliation of S-doped Black Phosphorus Nanosheets for Enhanced Oxygen Evolution Catalysis

Black phosphorus (BP) has recently drawn great attention in the field of electrocatalysis due to its distinct electrocatalytic activity for the oxygen evolution reaction (OER). However, the slow OER kinetics and the poor environmental stability of BP seriously limits its overall OER performance and prevents its electrocatalysis application. Here, sulfur (S)-doped BP nanosheets, which are prepared using high-pressure synthesis followed by liquid exfoliation, have been demonstrated to have much better OER electrocatalytic activity and environmental stability compared to their undoped counterparts. The S-doped BP nanosheets display a Tafel slope of 75 mV dec-1, which is a favorable value refered to the kinetics of OER in electrochemical tests. Notably, there is no degradation of S-doped BP nanosheets after six days exposure to ambient, indicating an excellent environmental stability of the S-doped BP. The density functional theory calculations show that the OER activity of BP originate from its crystal defects and heteroatom S doping can effectively enhance its OER activity and stability. These results highlight the doping effect on electrocatalytic activities and stability of BP and provide a simple and effective method to design highly efficient OER catalysts based on the modification of BP.