基于碳纳米管的柔性平面微型超级电容器

超薄电子器件的蓬勃发展和日益增长的人性化需求极大促进了可穿戴柔性微器件的发展,但是沉积电极材料在柔性基板上的技术仍处于起步阶段. 本文通过结合四面体制备器辅助涂层法和激光切割叉指构型技术,大规模地将碳纳米管沉积到商用印刷纸上作为电极,切割组装获得了柔性对称微型超级电容器. 制得的微型超级电容器的电化学性能可以通过简单地选择不同的四面体制备器模型制备不同厚度的碳纳米管薄膜进行调控. 优化获得的碳纳米管薄膜基微型超级电容器在0.02 mA的电流下,具有高达4.56 mF/cm²的面电容. 微型超级电容器经过连续10000次循环,器件的性能仍然可以保持接近100%. 四面体制备器辅助涂层方法和激光切割叉指构型技术为制备经济的微电子器件提供了新的视角. 附着碳纳米管的纸电极实现了可调控的面电容,在未来制备平面构型的不对称微超级电容器方面展示了广阔的应用前景.     

Systematic investigation on the properties of carbon nanotube electrodes with different chemical treatments

The functionalization of carbon nanotubes (CNTs) was carried out by using different chemical treatment methods. These functionalized CNTs were characterized by TEM image and FT-IR spectra. The CNT electrodes are measured by thermal resistivity and cyclic voltammetry experiments. The results showed that two important factors controlled the electrochemical properties of the CNT film electrode: one is the active functional group; another is activation energy of the CNT film. From our experiments, we have found the electrode of 10 min nitric acid treated CNTs have the optimal peaks in relation to carboxylic acids, the highest redox peak currents, the biggest value of k⁰ and well-defined quasi-reversible voltammograms for redox of iron couples, in which the two factors best match.     

An all chemical route to design a hybrid battery-type supercapacitor based on ZnCo2O4/CdS composite nanostructures

Recently, spinel-type binary metal oxides have attracted enormous interest in energy storage devices. In supercapacitors improving energy density is still challenging task and the composite nanostructures are found to address this issue in some extent. Herein, a composite nanostructure based on ZnCo₂O₄/CdS was synthesized on nickel foam using hydrothermal and successive ionic layer adsorption and reaction (SILAR) methods. A hydrothermally synthesized ZnCo₂O₄ nanoflowers were coated by CdS nanoparticles by varying SILAR cycles and studied its electrochemical performance. The ZnCo₂O₄/CdS nanostructured electrode with optimized four SILAR cycles of CdS coating exhibited a high areal capacity, energy density and power density of 2658 mCcm⁻², 517 μWhcm⁻² and 17.5 mWcm⁻² at 25 mA, which is higher than pristine ZnCo₂O₄. This work show ZnCo₂O₄/CdS nanostructure is a favorable electrode for supercapacitors.     

Template‐Free Fabrication of Hollow NiO–Carbon Hybrid Nanoparticle Aggregates with Improved Lithium Storage

Hollow NiO–carbon hybrid nanoparticle aggregates are fabricated through an environmental template‐free solvothermal alcoholysis route. Controlled hollow structure is achieved by adjusting the ratio of ethylene glycol to water and reaction time of solvothermal alcoholysis. Amorphous carbon can be loaded on the NiO nanoparticles uniformly in the solvothermal alcoholysis process, and the subsequent calcination results in the formation of hollow NiO–C hybrid nanoparticle aggregates. As anode materials for lithium‐ion batteries, it exhibits a stable reversible capacity of 622 mAh g^?1, and capacity retention keeps over 90.7% after 100 cycles at constant current density of 200 mA g^?1. The NiO–C electrode also exhibits good rate capabilities. The unique hollow structures can shorten the length of Li‐ion diffusion and offer a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. The hybrid carbon in the particles renders the electrode having a good electronic conductivity. Here, the hollow NiO‐C hybrid electrode exhibits excellent electrochemical performance.     

Ultrasound-assisted synthesis of 3D flower-like zinc oxide decorated fMWCNTs for sensitive detection of toxic environmental pollutant 4-nitrophenol

Sonochemical synthesis of functionalized multi-walled carbon nanotubes (fMWCNTs) embellished 3D flower-like zinc oxide (ZnO) nanocomposite based novel electrochemical sensor for the detection of toxic environmental pollutant 4-nitrophenol (4-NP) is detailed in this paper. We have used laser-assisted synthesis technique in the development of 3D flower-like ZnO nanoparticles (NPs) and ultrasonication method was employed in preparation of ZnO NPs@fMWCNTs nanocomposite using a high-intensity ultrasonic bath DC200H with power of 200 W/cm² and 40 KHz frequency. The nanocomposite was meticulously fabricated on screen printed carbon electrode (SPCE) to carry out various electrochemical analysis. Different characterizations such as Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, UV visible spectroscopy (UV–Vis), X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) of the materials used in this work were taken. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques are used in electrochemical investigations. We have observed well-defined oxidation and reduction peak currents representing electrochemical mechanism of 4-NP at very low potentials for ZnO NPs@fMWCNTs/SPCE. Furthermore, we were able to achieve efficient electrochemical determination of 4-NP using the developed sensor with a high sensitivity of 11.44 μA μM⁻¹ cm⁻² and very low detection limit (LOD) of 0.013 μM in a broad linear range of 0.06–100 μM. All the significant features of a good sensor including anti-interference, good stability, excellent repeatability, and reproducibility were exhibited by the sensor. Moreover, we have tested practical feasibility of sensor by carrying out real sample analysis on different water samples.     

The In Situ Synthesis of Fe(OH)3 Film on Fe Foam as Efficient Anode of Alkaline Supercapacitor Based on a Promising Fe3+/Fe0 Energy Storage Mechanism

Herein, a simple in situ charge/discharge activation strategy is proposed to synthesize Fe(OH)3 film on Fe foam as an efficient anode of supercapacitors. The physical characteristics of electrodes are characterized and the electrochemical energy storage performances are investigated. Importantly, it is demonstrated the as‐synthesized Fe(OH)3@Fe foam electrode adopted a novel Fe³⁺/Fe⁰ redox reaction mechanism for energy storage in alkaline electrolytes. Compared with previously reported Fe³⁺/Fe²⁺ mechanisms, the Fe³⁺/Fe⁰ redox couple shows a more promising application value (e.g., higher theoretical‐specific capacitance, excellent conductivity of its reduction state). As for supercapacitor anodes, the electrode achieves high areal capacitance of 5.55–3.94 F cm⁻² at a current range of 20–200 mA cm⁻² and shows good stability for high‐rate and long‐term cycling. The assembled single supercapacitor device gives a high energy density of 11.64–7.43 Wh m⁻² at a power density of 157–1461 W m⁻². More importantly, the as‐adopted in situ activation strategy may also have potential value for synthesizing other transition metal oxide‐based products.     

Polyvinyl pyrrolidone-assisted synthesis of flower-like nickel-cobalt layered double hydroxide on Ni foam for high-performance hybrid supercapacitor

Nickel-cobalt layered double hydroxides (NiCo-LDH) were successfully deposited on nickel foam by a facile hydrothermal method using polyvinyl pyrrolidone (PVP) as the structure-directing reagent. The effect of PVP on the morphology and electrochemical performance of binder-free NiCo-LDH electrode for supercapacitor were investigated in detail. The prepared NiCo-LDH presented good dispersivity and appeared different flower-like structure via the addition of PVP. Specially, the NiCo-LDH electrode using 1 g of PVP exhibited a superior performance with a high-specific capacity of 724.9 C g^?1 at a current density of 1 A g^?1 and 577.1 C g^?1 at 10 A g^?1. In addition, a hybrid supercapacitor (HSC) based on the optimized NiCo-LDH as positive electrode and activated carbon as negative electrode was assembled with 6 M KOH as the electrolyte. The HSC device can deliver an energy density of 32.3 Wh kg^?1 at the power density of 387.1 W kg^?1. Moreover, the HSC device exhibited a good cycling stability with a retention rate of 94.0% after 2000-cycle charge-discharge test at 3 A g^?1.     

Ultrasonic assisted synthesis of Ni3(VO4)2-reduced graphene oxide nanocomposite for potential use in electrochemical energy storage

In the present study, Ni₃(VO₄)₂-reduced graphene oxide (NV/RGO) nanocomposite was synthesized for energy storage purpose. To this end, a mixture containing RGO nanosheets, Ni (CH₃COOH)₂ and Na₃VO₄ mixture was prepared under probe-type ultrasonic irradiation with frequency of 20 KHz and the optimized power of 100 W. The Raman and energy-dispersive X-ray spectroscopies confirmed the presence of RGO nanosheets, nickel and vanadium elements in the NV/RGO, respectively. In addition, field emission-scanning electron microscopy (FESEM) data showed the formation of the NV nanoparticles on the RGO nanosheets. NV/RGO nanocomposite was pasted on nickel foam (NF) and its performance was investigated in energy storage using a three-electrode cell containing 6 M KOH. In cyclic voltammogram of NV/RGO/NF, redox peaks for Ni (II)/Ni (III) with intensities higher than that for NV/NF were observed which confirms the synergistic effect of RGO on the performance of NV. Chronopotentiometry data revealed that the NV/RGO/NF electrode exhibits high capacity of 117.22 mA h g⁻¹ at 2 A g⁻¹. Electrochemical impedance spectroscopy also demonstrated an improvement in the electrical conductivity and electrochemical behavior of NV/RGO/NF nanocomposite compared to the RGO/NF and NV/NF. Furthermore, NV/RGO/NF electrode reserved about 88% of its initial capacity after 1000th potential cycle at 50 mV s⁻¹. Overall, the results of our study suggest that the NV/RGO nanocomposite prepared in the presence of ultrasonic irradiation might be regarded as a suitable active material for energy storage systems.     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

General Synthesis and Lithium Storage Properties of Metal Oxides/MnO2 Hierarchical Hollow Hybrid Spheres

Metal oxides/MnO₂ hierarchical hollow hybrid nanostructures have attracted significant attention because of their wide potential applications. However, the exploration of a general synthetic approach for fabricating hierarchical hollow hybrid nanostructures is still a great challenge. Herein, a “penetration‐carbonization and reduction‐coating–annealing” route is presented for the generalized synthesis of metal oxides/MnO₂ hierarchical hollow hybrid spheres, including NiO/MnO₂, Co₃O₄/MnO₂, and CuO/MnO₂. Because of the unique hierarchical hollow hybrid nanostructures, NiO/MnO₂ nanomaterials possess a desirable capacity (1520 mA h g⁻¹) and outstanding cyclic stability (909 mA h g⁻¹ at the 200th cycle) as Li‐ion battery anode materials. The work reported herein can not only pave the way for the generalized synthetic strategy of metal oxides/MnO₂ hierarchical hollow hybrid nanostructures, but also provide a promising application of NiO/MnO₂ nanomaterials for Li‐ion battery anode.     

Sensible design of open-porous spherical architectures for hybrid supercapacitors with improved high-rate capability

Hybrid supercapacitors show high energy densities with good long-term cycling stability when used as energy sources. However, their poor rate performance as a consequence of their low ionic diffusion capability at high currents during cycling should be improved. Here, we propose using a spray-drying process to fabricate a novel structure comprising open-porous spherical lithium manganese oxide as an electrode material for hybrid supercapacitors. The resultant hybrid supercapacitor comprising full-cell systems shows a high specific capacitance (33.8 F cm⁻³ at a current of 1 A) and remarkable high-rate performance (25.6 F cm⁻³ at a current of 16 A). Moreover, outstanding cycling stability of 83% was attained at a current of 2 A after 5400 cycles. Our new strategy provides a useful methodology to increase the abundance of electrochemically active sites by fabricating a spherical structure using nanosized primary particles, which also leads to shorter diffusion pathways and to improved ionic electron transport because of the open-porous structure of the electrode materials.     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

Graphene oxides and carbon nanotubes embedded in polyacrylonitrile-based carbon nanofibers used as electrodes for supercapacitor

This study investigates the use of graphene oxides (GOs) and carbon nanotubes (CNTs) embedded in polyacrylonitrile-based carbon nanofibers (GO–CNT/CNF) as electrodes for the supercapacitor. GO–CNT/CNF was prepared by electrospinning, and was subsequently stabilized and activated. The specific capacitance of GO–CNT/CNF is 120.5 F g⁻¹ in 0.5 M Na₂SO₄ electrolyte, which is higher than or comparable to the specific capacitances of carbon-based materials in neutral aqueous electrolyte, as prepared in this study. GO–CNT/CNF also exhibits a superior cycling stability, and 109% of the initial specific capacitance after 5000 cycles. The high capacitance of GO–CNT/CNF could be attributed to the edge planes and the functional groups of GO, the highly electrical conductivity of CNT, and the network structure of the electrode.     

Electrochemical properties of high-power supercapacitors using ordered NiO coated Si nanowire array electrodes

Highly ordered NiO coated Si nanowire arrays are fabricated as electrode materials for electrochemical supercapacitors (ES) via depositing Ni on electroless-etched Si nanowires and subsequently annealing. The electrochemical tests reveal that the constructed electrode has superior electrical conductibility and more active sites per unit area for chemical reaction processes, thereby possessing good cycle stability, high specific capacity, and low internal resistance. The specific capacity is up to 787.5 F g⁻¹ at a discharge current of 2.5 mA and decreases slightly with 4.039% loss after 500 cycles, while the equivalent internal resistance is ∼3.067 Ω. Owing to its favorable electrochemical performance, this ordered hybrid array nanostructure is a promising electrode material in future commercial ES.     

Improving the field-emission properties of carbon nanotubes by magnetically controlled nickel-electroplating treatment

A novel magnetically controlled Ni-plating method has been developed to improve the field-emission properties of carbon nanotubes (CNTs). The effect of the magnetic field and Ni-electroplating on CNT field-emission properties was investigated, and the results are demonstrated using scanning electron microscopy, J-E and the duration test. After treatment, the turn-on electric field declines from 1.55 to 0.91 V/μm at an emission current density of 100 μA/cm², and the emission current density increases from 0.011 to 0.34 mA/cm² at an electric field of 1.0 V/μm. Both the brightness and uniformity of the CNT emission performance are improved after treatment.     

EDLC characteristics with high specific capacitance of the CNT electrodes grown on nanoporous alumina templates

Well-ordered nanoporous alumina templates were fabricated by two-step anodization method by applying a constant voltage of 40 V in oxalic acid solution or of 25 V in sulfuric acid solution. The cylindrical pore diameter and pore density of the templates utilized for the carbon nanotube (CNT) growth were 86 ± 5 nm and 1.2 × 10¹⁰ cm⁻² in oxalic acid solution and 53 ± 1 nm and 3.1 × 10¹⁰ cm⁻² in sulfuric acid solution, respectively. The CNTs with uniform diameter of 50 ± 10 nm (oxalic acid) and 44 ± 2 nm (sulfuric acid) were grown on the porous alumina template as electrode materials for the electrochemical double layer capacitor (EDLC). The EDLC characteristics were examined by measuring the capacitances from cyclic voltammograms and the charge–discharge curves. The specific capacitances of the CNT electrodes are 30 ± 1 F/g (Φ = 50 ± 10 nm) and 121 ± 5 F/g (Φ = 44 ± 2 nm). The high specific capacitance of the CNT electrode was achieved by using nanoporous alumina templates with the high pore density and the small and uniform pore diameter.     

Superior electrochemical performance of carbon cloth electrode-based supercapacitors through surface activation and nitrogen doping

A simple and low-cost strategy is developed to fabricate three-dimensional (3D) nitrogen-doped carbon cloth electrode through surface activation and nitrogen-doping process. The process can exfoliate the smooth surfaces of micro carbon fibers into nanostructures together with the doping of nitrogen-containing species. The as-fabricated carbon cloth electrode shows excellent areal capacitances of 882.36 and 706.68 mF cm^?2 at the current density of 1 and 60 mA cm^?2, respectively, exhibiting good rate performance. It also exhibits outstanding cycling stability with 98.7 % retention of its initial capacitance after 30,000 continuous charging/discharging tests. When the electrodes were assembled and tested as a symmetric supercapacitor, it also demonstrates superior electrochemical performance. It is believed that the 3D carbon structures with enlarged surface area, improved conductivity and electrode/electrolyte wettability, and enhanced pseudocapacitance by doping of nitrogen lead to the vast improvement of electrochemical performance.     

A High‐Performance Anode Material for Li‐Ion Batteries Based on a Vertically Aligned CNTs/NiCo2O4 Core/Shell Structure

3D vertically aligned carbon nanotubes (CNTs)/NiCo₂O₄ core/shell structures are successfully synthesized as binder‐free anode materials for Li‐ion batteries (LIBs) via a facile electrochemical deposition method followed by subsequent annealing in air. The vertically aligned CNTs/NiCo₂O₄ core/shell structures are used as binder‐free anode materials for LIBs and exhibit high and stable reversible capacity (1147.6 mAhg^?1 at 100 mAg^?1), excellent rate capability (712.9 mAh g^?1 at 1000 mAg^?1), and good cycle stability (no capacity fading over 200 cycles). The improved performance of these LIBs is attributed to the unique 3D vertically aligned CNTs/NiCo₂O₄ core/shell structures, which support high electron conductivity, fast ion/electron transport in the electrode and at the electrolyte/electrode interface, and accommodate the volume change during cycling. Furthermore, the synthetic strategy presented can be easily extended to fabricate other metal oxides with a controlled core/shell structure, which may be a promising electrode material for high‐performance LIBs.     

Titanium buffer layer for improved field emission of CNT based cold cathode

Carbon nanotube (CNT) based cold cathodes are considered to be the most promising material for fabrication of next generation high-performance flat panel displays and vacuum microelectronic devices. Adhesion of CNTs with the substrate and the contact resistance between them are two of the important issues to be addressed in CNT based field emission (FE) devices. Here in this work, a buffer layer of titanium (Ti) is deposited prior to the catalyst deposition and the growth was carried out using chemical vapor deposition (CVD) technique. There was significant increase in emission current density from 10 mA/cm² to 30 mA/cm² at the field of 4 V/μm by the use of titanium buffer layer due to much less dense growth of CNTs of smaller diameter. Field emission results suggest that the adhesion of the CNTs to the substrate has improved. The titanium buffer layer has also lowered the contact resistance between the CNTs and the substrate because of which a stable emission of 30 mA for a longer duration was obtained.