Hu-n Li

Electrodeposited nickel hydroxide on nickel foam with ultrahigh capacitance.

Electrodeposited Ni(OH)(2) on nickel foam with porous and 3D nanostructures has ultrahigh capacitance in the potential range -0.05-0.45 V, and a maximum specific capacitance as high as 3152 F g(-1) can be achieved in 3% KOH solution at a charge/discharge current density of 4 A g(-1).

Lithium Insertion into TiO2 Nanotube Prepared by the Hydrothermal Process

A TiO 2 nanotube was prepared by a hydrothermal process. Transmission electron microscope tests showed that the products are uniform straight hollow tubes with the diam around 8 nm and the length over 300 nm. X-ray diffraction measurements indicate that the nanotubes crystallized in anatase TiO 2 . Cyclic voltammetry and galvanostatic charging and discharging tests showed that lithium-ion intercalation/deintercalation occured reversibly in the TiO 2 nanotube electrode, and a high capacity can be obtained. Electrochemical impedance spectra show that Li + ion intercalation occurs below 2.2 V. Around the 1.7 V plateau, the total electrochemical resistance reached a minimum.

Preparation of Mesoporous Nanocrystalline Co3O4 and Its Applicability of Porosity to the Formation of Electrochemical Capacitance

In this paper we describe a new synthesis strategy for preparing loose-packed porous materials with the particle diameter down scaled to nanometer size. Mesoporous nanocrystalline Co 3 O 4 was prepared using this method, and an attempt was made to apply it as an active electrode material for electrochemical capacitors. The composition and microstructure of the resulting nanocrystalline material were investigated by X-ray diffraction spectroscopy and high-resolution transit electron microscopy (HRTEM). Based on the value of d 1 1 1 from HRTEM, the molecular formula of Co 3 O 4 was obtained by comparing it with those of CoO and Co 2 O 3 . Static adsorption and desorption isotherm (SADI) analysis show that porous nanocrystalline Co 3 O 4 prepared by this method has a high Brunauer-Emmett-Teller (N 2 ) surface area (212 m 2 /g) with mesopore distributions. The formation mechanism of mesoporous nanocrystalline Co 3 O 4 was proposed based on Fourier transform infrared spectroscopy and SADI analysis. Electrochemical studies revealed that the electrode prepared with this kind of material exhibits a high specific capacitance of 401 F/g. The charge-storage mechanism of the measured capacitance was investigated. In addition, the electrochemical processes, such as ion transfer and electrical conduction, were investigated with electrochemical impedance spectroscopy. The correlation between the microstructure and the energy density as well as the power density is discussed.

Preparation and Electrochemistry of SWNT/PANI Composite Films for Electrochemical Capacitors

Single-walled carbon nanotube/polyaniline (SWNT/PANI) composite films were prepared by in situ electrochemical polymerization of an aniline solution containing different SWNT contents. Surface morphology and structural properties of these PANI-based films were examined by a scanning electron microscope and X-ray photoelectron spectroscopy. The electrochemical capacitance properties of these films were investigated with cyclic voltammetry, charge-discharge tests, and ac impedance spectroscopy. The composite film, based on the charge-transfer complex between well-dispersed SWNT and PANI matrixes, shows much higher specific capacitance, better power characteristics, and is more promising for applications in capacitors than a pure PANI film electrode.

Electrodeposition of ordered mesoporous cobalt hydroxide film from lyotropic liquid crystal media for electrochemical capacitors

A novel ordered mesoporous cobalt hydroxide film (designated HI-e Co(OH)2) has been successfully electrodeposited on titanium substrate from the hexagonal lyotropic liquid crystalline phase using surfactant Brij 56 as the structure-directing agent. Low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the film electrodeposited from the liquid crystal template has a regular nanostructure consisting of a hexagonal array of cylindrical pores. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the ordered mesoporous HI-e Co(OH)2 film electrode has excellent electrochemical capacitance between a potential range of –0.1–0.45 V, and a maximum specific capacitance as high as 1084 F g–1 could be achieved in 2 M KOH solution at a charge–discharge current density of 4 A g–1. Meanwhile, the properties of Co(OH)2 film electrodeposited from aqueous solution without templates (designated Aq-e Co(OH)2) are also discussed for comparison.

Mesoporous nanowire array architecture of manganese dioxide for electrochemical capacitor applications.

Mesoporous MnO(2) nanowire array architecture exhibits enhanced capacitive and charge/discharge performance for electrochemical capacitors.

Effect of electrodeposition temperature on the electrochemical performance of a Ni(OH)2 electrode

The effect of the electrodeposition temperature on the electrochemical performance of Ni(OH)2 electrode was investigated in this report. Ni(OH)2 was electrodeposited directly on nickel foam at different temperatures. The crystalline structure, morphology and specific surface area of the prepared Ni(OH)2 were characterized by X-ray powder diffraction (XRD), field emission scanning electronic microscopy (FESEM) and Brunauer–Emmett–Teller (BET). Electrochemical techniques such as cyclic voltammetry (CV), chronopotentiometry, and electrochemical impedance spectra (EIS) were carried out to systematically study the electrochemical performance of various Ni(OH)2 electrodes in 1 M KOH electrolyte. The results demonstrated that the electrodeposition temperature had obviously affected the properties of the Ni(OH)2. A pure α-Ni(OH)2 phase could be observed at low temperature. When the temperature increased to 65 °C, the β-Ni(OH)2 phase together with α-Ni(OH)2 phase were present. Moreover, the sample synthesized at 65 °C possessed a porous honeycomb-like microstructure and the corresponding specific capacitance was up to 3357 F g−1 at a charge–discharge current density of 4 A g−1, which suggested its potential application as an electrode material for supercapacitors.

Ni/CdS Bifunctional Ti@TiO2 Core-Shell Nanowire Electrode for High-Performance Nonenzymatic Glucose Sensing

In this work, a Ni/CdS bifunctional Ti@TiO2 core-shell nanowire electrode with excellent electrochemical sensing property was successfully constructed through a hydrothermal and electrodeposition method. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were employed to confirm the synthesis and characterize the morphology of the as-prepared samples. The results revealed that the CdS layer between Ni and TiO2 plays an important role in the uniform nucleation and the following growth of highly dispersive Ni nanoparticle on the Ti@TiO2 core-shell nanowire surface. The bifunctional nanostructured electrode was applied to construct an electrochemical nonenzymatic sensor for the reliable detection of glucose. Under optimized conditions, this nonenzymatic glucose sensor displayed a high sensitivity up to 1136.67 μA mM(-1) cm(-2), a wider liner range of 0.005-12 mM, and a lower detection limit of 0.35 μM for glucose oxidation. The high dispersity of Ni nanoparticles, combined with the anti-poisoning faculty against the intermediate derived from the self-cleaning ability of CdS under the photoexcitation, was considered to be responsible for these enhanced electrochemical performances. Importantly, favorable reproducibility and long-term performance were also obtained thanks to the robust frameworks. All these results indicate this novel electrode is a promising candidate for nonenzymatic glucose sensing.

High performance asymmetric supercapacitor based on MnO2 electrode in ionic liquid electrolyte

In this work, the electrochemical properties of a MnO2 nanocomposite electrode were investigated in 1-butyl-3-methyl-imidazolium hexafluorophosphate ([Bmim]PF6)/N,N-dimethylformamide (DMF) electrolyte. The [Bmim]PF6/DMF electrolyte with different volume fractions exhibits significant influence on the electrochemical properties of the electrode. When the volume ratio of [Bmim]PF6 and DMF was 1 : 1, the electrode showed the best electrochemical performance. The operation potential window of the MnO2 nanocomposite electrode in ionic liquids was 2.1 V and the specific capacitance according to the mass of MnO2 was 523.3 F g−1 at 3 A g−1. Then, a high-voltage (3 V) MnO2 asymmetric supercapacitor was successfully fabricated, using the MnO2 nanocomposite electrode, activated carbon and [Bmim]PF6/DMF as the positive electrode, negative electrode and electrolyte, respectively. The MnO2 asymmetric supercapacitor displayed a maximum specific energy of 67.5 W h kg−1 at a specific power of 593.8 W kg−1 and a maximum specific power of 20.4 kW kg−1 at a specific energy of 8.5 W h kg−1. The impressive results showed that [Bmim]PF6/DMF could be a promising electrolyte for MnO2 supercapacitors.

Sol–gel template synthesis and structural properties of a highly ordered LiNi0.5Mn0.5O2 nanowire array

A highly ordered LiNi0.5Mn0.5O2 nanowire array was prepared using a porous anodic aluminium oxide (AAO) template from a sol–gel solution containing Li(OAc), Ni(OAc)2 and Mn(OAc)2. Electron microscopy results show that LiNi0.5Mn0.5O2 nanowires of uniform length and diameter are obtained, and that the length and diameter of the LiNi0.5Mn0.5O2 nanowires are dependent upon the pore diameter and the thickness of the applied AAO template. X-Ray diffraction and electron diffraction investigations demonstrate that the LiNi0.5Mn0.5O2 nanowires have a layered structure of LiNi0.5Mn0.5O2. X-ray photoelectron spectroscopy indicates that a nearly stoichiometric layered LiNi0.5Mn0.5O2 material has been obtained.