Electrochemical performance of Li4Ti5O12/carbon nanofibers composite prepared by an in situ route for Li-ion batteries

A Li₄Ti₅O₁₂/carbon nanofibers (LTO/CNFs) composite has been synthesized by solid-state reaction with the in situ growth of CNFs using the chemical vapor deposition method in N₂/C₂H₂. The nanocomposite is characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms, and is investigated as an anode material for lithium-ion (Li-ion) batteries. The underlying mechanism for the improvement is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite shows better electrochemical performance than the bare LTO. The in situ formation of CNFs not only supply an efficient electronic conductive network but also reduce the particle size of LTO and increase in specific surface area, leading to increased electrical conductivity and rapider Li-ion diffusion in electrode/electrolyte interface and bulk electrode.     

Covalent immobilization of glucose oxidase on films prepared by electrochemical copolymerization of 3-methylthiophene and thiophene-3-acetic acid for amperometric sensing of glucose: Effects of polymerization conditions on sensing properties

For the purpose of glucose sensing, enzyme electrodes were fabricated via covalent immobilization of glucose oxidase on the films of conducting polymer. The films were prepared electrochemically by the copolymerization of 3-methylthiophene and thiophene-3-acetic acid. The properties of the films were investigated by taking into account the polymerization conditions (the kind of supporting electrodes, the current, the amount of passed charge, and the monomer concentration) and the dedoping treatment. The glucose sensing performance of the enzyme electrode was found to be affected markedly by the following three factors of the conducting polymer film: surface morphology, conductivity and cohesion with support electrodes. It was suggested that the ideal conducting polymer used for the enzyme electrode should be a thin film having high conductivity and ordered nanostructure.     

复合金属氧化物Sn-Sb-Mn/陶瓷粒子电极体系的电催化性能

通过热分解法制备了复合金属氧化物Sn-Sb-Mn/陶瓷粒子电极, 分别采用扫描电子显微镜(SEM)、能量色散X 射线能谱(EDS)、X射线衍射(XRD)和N2吸附-脱附等技术对电极的形貌、晶相组成、比表面积和孔径分布进行了表征. 考察了该三维粒子电极系统的析氧特性, 采用循环伏安法分析了三维系统的电催化性能, 并且进行了电化学催化降解苯酚的试验. 结果表明, 制备的陶瓷粒子电极涂层比表面较大、孔结构发达, 有利于电催化反应; 电催化降解主要发生在电化学析氧区; 粒子电极系统对苯酚降解作用显著, 明显高于二维电极系统, 苯酚的去除率为92.3%, 总有机碳(TOC)的去除率为66.7%. 研究结果表明, 该三维粒子电极系统具有优良的电催化性能.     

Electrocatalysis Using Porous Nanostructured Materials

The performance of electrochemical reactions depends strongly on the morphology and structure of the employed catalytic electrodes. Nanostructuring of the electrode surface represents a powerful tool to increase the electrochemically active surface area of the electrodes. Moreover, it can also facilitate faster diffusive mass transport inside three‐dimensional electrodes. This minireview describes recent trends in the development of synthesis routes for porous nanostructured electrode materials and discusses the respective important electrocatalytic applications. The use of structure‐directing agents will play a decisive role in the design and synthesis of improved catalysts.     

Electrochemistry at nanoporous interfaces: new opportunity for electrocatalysis

Physical and electrochemical features of nanoporous electrodes arising from their morphology are presented in this perspective. Although nanoporous electrodes have been used to enhance electrocatalysis for several decades, the origin of their capability was understood on the basis of enlarged surface area or crystalline facet. However, considerable attention should be paid to the fact that nano-confined space of nanoporous electrodes can significantly affect electrochemical efficiency. Molecular dynamics in nano-confined spaces is capable of offering much more chances of interaction between a redox molecule and an electrode surface. The mass transport in the nanoporous electrode depends on various pore characteristics such as size, shape, charge, connectivity, and symmetry as well as molecular properties such as size, charge, and kinetics. Moreover, when the pore size is comparable to the thickness of an electric double layer (EDL), the EDLs overlap in the porous structure so that electrochemically effective surface area is not the same as that of the real electrode surface. These unique properties come from simply nanoporous structure and suggest new opportunity to innovative electrocatalysts in the future.     

球磨形成的Ni-Mo纳米晶复合镀层上的析氢反应

采用复合电镀的方法将不同球磨时间制备的高催化活性的纳米晶，Ｎｉ－Ｍｏ合金粉直接镀于电极表面，并用稳态极化曲线及交流阻抗技术测试了这些电极析氢的电化学活性，同时用Ｘ射线衍射，透射电镜及扫描电镜监测了Ｎｉ－Ｍｏ合金粉的物相结构，晶粒尺寸及复合电极表面的形貌，并初步探讨了这些复合电极的析氢机理，实验结果表明，球磨不仅可使镍钼粉合金化成为纳米晶，同时随着球磨时间的增加，纳米晶晶粒继续细化，电极的析氢催化活     

Effect of starting materials on electrochemical performance of sol-gel-synthesized Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode materials for lithium-ion batteries

In this study, the effect of the sol-gel starting materials with different particle sizes on the sol-gel-synthesized spinel Li₄Ti₅O₁₂ (LTO) was systematically investigated. The physical and electrochemical properties of the synthesized materials were characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller-specific surface area analyses, galvanostatic charge/discharge tests, cyclic voltammetry, and electrochemical impedance spectroscopy. It was found that the initial particle size of sol-gel starting material played a crucial role on the properties of as-prepared LTOs. The LTO synthesized with the relatively finer particle size of starting materials possessed relatively smaller particle size and larger specific surface area and therefore resulted in the superior electrochemical properties. The initial discharge capacity of the as-prepared LTO exhibited 168.2, 150.6, and 142.7 mAh g^?1 at current densities of 1, 5, and 10 C, respectively, and up to 95, 95, and 90 % of the corresponding initial discharge capacity was retained after 50 cycles.     

Surface modification of neural probes with conducting polymer poly(hydroxymethylated-3,4-ethylenedioxythiophene) and its biocompatibility

A novel conducting polymer, poly(hydroxymethylated-3,4-ethylenedioxy-thiophene) (PEDOT-MeOH), was electrochemically deposited onto the electrodes of micromachined neural probes. Uniformly distributed film was obtained from aqueous solution when doped with polystyrenesulfonate. The surface morphology was rough and had good cellular adhesion. Impedance spectroscopy showed that the magnitude of coated electrode was lower than that of the bare gold over a range of frequencies from 10⁰ to 10⁵ Hz. Since the biocompatibility of the interface between the neural probes and brain tissue plays an important role when the probes are implanted in the central nervous system for long-term application, biomolecules were incorporated into the coating. Nonapeptide CDPGYIGSR was codeposited as the counterion in the conducting films. The surface morphology of the coating was fuzzy, providing many bioactive sites for interaction with neural cells. The magnitude of impedance was as low as 53 kω at the biologically relevant frequency of 1 kHz. An in vitro experiment demonstrated that the neuroblastoma cells grew preferentially on the PEDOT-MeOH/CDPGYIGSR-coated electrode sites and spread beyond the electrode area.     

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 μM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.     

Immobilization of glucose oxidase on carbon paper electrodes modified with conducting polymer and its application to a glucose fuel cell

A carbon paper electrode was modified with the conducting copolymer of 3-methylthiopene and thiophene-3-acetic acid prepared electrochemically on the electrode, and an enzyme electrode was fabricated by covalent immobilization of glucose oxidase on the modified electrode. The modification with the conducting copolymer increased the surface area of the electrode and the amount of the immobilized enzyme. As a result, the enzyme electrode showed a high catalytic activity. Moreover, it was found that the increased surface area led to a high rate of electron transfer reaction between the electrode and p-benzoquinone employed as an electron mediator. The enzyme electrode fabricated with the modified carbon paper gave a larger glucose oxidation current than that fabricated with the bare one. In addition, the glucose oxidation current was found to increase with increasing content of the conducting copolymer in the modified carbon paper. Corresponding to the large glucose oxidation current, high performance was confirmed for the glucose fuel cell constructed with the enzyme electrode based on the modified carbon paper.     

Effect of Electrode Pattern on the Column Structure and Yield Stress of Electrorheological Fluids

For electrorheological (ER) suspensions, the aggregate structures of particles were observed in electric fields by the use of transparent cells with different electrode patterns. Although the suspension is dispersed to noninteracting particles without electric fields, many aggregates are formed on the electrode surface in electric fields. Since the dipole–dipole interactions cause chain structures of particles and equilibrium conformations of chains are always aligned with electric field, the aggregates indicate the presence of columns spanning the electrode gap. The particle concentration in columns which are developed between parallel-plate electrodes is about 22 vol %. In striped electrodes, the particles construct striped aggregates along the electrodes and no particles remain in the insulating region. The particle concentration in striped aggregates is about 35 vol %. The nonuniformity of electric field is responsible for the high particle concentration. The increase in particle concentration of column lead to the high yield stress of electrified suspension. Therefore, the ER performance of suspension as an overall response can be improved by the electrode design.     

Effects of electrode size and surface morphology on electrode polarization in physiological buffers

Electrode polarization (EP) is inevitable in high conductivity buffers at low AC frequencies due to the accumulation of free charges at the electrode/electrolyte interface. Electrode miniaturization increases EP effect on impedance measurements. In this paper, six gold planar (GP) electrodes having different diameters () were used to investigate the size effect on EP with parallel plate electrode geometry. GP electrode surface was electrochemically deposited with gold nanostructures (GNs) to minimize the EP effect. Equivalent circuit model was used to attain electrode/electrolyte interfacial impedance. Constant phase element model was used to analyze the relation between the size and morphology of electrodes on EP. The surface morphology of gold nanostructured electrodes was examined using SEM, and the influence of different applied potential on the growth of GNs was elucidated with Nernst equilibrium condition. Surface roughness and wettability characteristics were examined performing surface roughness and contact angle measurements, respectively. The improvement of GNs deposited electrode performance was investigated by analytically generated Jurkat cell suspension spectra. The results show that the error in estimating the subcellular properties can be drastically reduced by using GNs deposited electrodes.     

Size effects on the electrochemical oxidation of oxalic acid on nanocrystalline platinum

The electrocatalytic activity of platinised platinum (Pt Pt) electrodes in the electrooxidation of oxalic acid was found to be dependent on the degree of ageing. Pt Pt electrodes prepared by electrodeposition were aged by cycling the potential with an upper positive potential limit corresponding to Pt surface oxidation. This procedure results in surface reconstruction with an increase of mean particle size. The changes of surface area and roughness of Pt Pt during ageing have been discussed in terms of sintering processes for supported catalysts or ceramic materials. An increase of mean particle size is accompanied by a decrease in oxygen adsorption, e.g. through changes in the surface concentration of defects on the particle surface. Two possible mechanisms for the electrooxidation of oxalic acid involving either an oxygen adsorbate species (CE mechanism) or direct electrode transfer can be distinguished. Changes of oxidation rate are related to changes of oxygen coverage with ageing.     

Effects of Precursors and Carbon Nanotubes on Electrochemical Properties of Electrospun Nickel Oxide Nanofibers-Based Supercapacitors

Supercapacitors have been considered as one of the main energy storage devices. Recently, electrospun nanofibers have served as promising supercapacitor electrodes because of their high surface area, high porosity, flexibility, and resistance to aggregation. Here, we investigate the effects of electrospinning parameters and nickel precursors on the nanostructure of electrospun nickel oxide (NiO), as well as on their electrochemical performance as supercapacitor electrodes. In contrast to the case of using nickel nitrate, increasing the nickel acetate molar concentration maintains the flexible fibrous sheet morphology of the as-spun sample during the polycondensation and calcination of NiO. As a result, our flexible electrode of NiO nanofibers derived from nickel acetate (NiO-A) exhibits much better electrochemical performance values than that of nickel nitrate-derived NiO. To further improve the electrochemical storage performance, we combined NiO-A nanofibers with single-walled carbon nanotubes (CNTs) as a hybrid electrode. In both half-cell and full-cell configurations, the hybrid electrode displayed a higher and steadier areal capacitance than the NiO-A nanofibers because of the synergetic effect between the NiO-A nanofibers and CNTs. Altogether, this work demonstrates the potency of the hybrid electrodes combined with the electrospun NiO-A nanofibers and CNTs for supercapacitor applications.     

Carbon Composite Electrodes for Liquid Chromatography/Electrochemistry: Optimizing Detector Performance by Tailoring the Electrode Composition

Abstract

Results obtained in this laboratory and elsewhere suggest that carbon composite electrodes may possess a signal-to-noise (S/N) advantage compared to continuous electrodes such as glassy carbon when used for detection of analytes in flowing streams. One succomposite electrode which appears partic- ularly attractive in this regard is the Kel-F-graphite (Kelgraf) electrode, compression molded from Kel-F and powdered graphite and containing 5 to 30% graphite by weight. Studies of the electrode surface by scanning electron microscopy and X-ray photoelectron spectroscopy in conjunction with electrochemical investigations employing chronoamperometry, cyclic voltammetry, and capacitance measurements have led us to view the electrode surface as an ensemble of rnicroelectrodes, the dimensions of which can be varied by changes in particle size and/or ratio of Kel-F to graphite in the composite. The S/N advantage of the composite electrode apparently arises from a signal (current) enhanced by radial diffusion of analyte to the individual microelectrodes, resulting in a response greater than that obtained from a continuous electrode of equal active area. Since detector noise is generally assumed proportional to the active area of the electrode, S/N enhancement results.

For composite electrodes employed in a thin-layer channel design LC detector, the observed variations in the S/N ratio with changes in (1) composite composition (%C), (2) particle size of Kel-F used in fabrication of the composite, and (3) area of composite exposed in the flow channel are discussed within the context of the microelectrode ensemble model. It is further demonstrated that the ability of the electrode to resist fouling can be modified by variation in composite composition.     

Characterization of stainless steel electrode modified by a thin film of polyaniline containing pt particles and its electrocatalytic activity for methanol oxidation

The catalytic behavior of stainless steel (SS) electrode modified by a thin film of polyaniline (PANI) containing platinum particles was studied for electrooxidation of methanol and compared with a platinated Pt/PANI electrode in acidic aqueous solution. Cyclic voltammetry (CV), chronoamperometry, CO stripping techniques were used to investigate electrochemical properties and electrocatalytic activity of SS/PANI/Pt and Pt/PANI/Pt electrodes. The morphology and particle size of Pt catalysts were characterized by Transmission Electron Microscopy (TEM) measurement. The effects of various parameters such as thickness of polymer film, medium temperature and stability of the modified electrodes on methanol oxidation were also investigated. The results indicated that the modified SS electrode exhibited a considerably high electrocatalytic activity on the methanol oxidation as well as the modified Pt electrode.     

A Porous Mooncake-Shaped Li4Ti5O12 Anode Material Modified by SmF3 and Its Electrochemical Performance in Lithium Ion Batteries

Reasonably designing and synthesizing advanced electrode materials is significant to enhance the electrochemical performance of lithium ion batteries (LIBs). Herein, a metal–organic framework (MOF, Mil-125) was used as a precursor and template to successfully synthesize the porous mooncake-shaped Li₄Ti₅O₁₂ (LTO) anode material assembled from nanoparticles. Even more critical, SmF₃ was used to modify the prepared porous mooncake-shaped LTO material. The SmF₃-modified LTO maintained a porous mooncake-shaped structure with a large specific surface area, and the SmF₃ nanoparticles were observed to be attach on the surface of the LTO material. It has been proven that the SmF₃ modification can further facilitate the transition from Ti⁴⁺ to Ti³⁺, reduce the polarization of electrode, decrease charge transfer impedance (R_ct) and solid electrolyte interface impedance (R_sei), and increase the lithium ion diffusion coefficient (D_Li), thereby enhancing the electrochemical performance of LTO. Therefore, the porous mooncake-shaped LTO modified using 2 wt % SmF₃ displays a large specific discharge capacity of 143.8 mAh g⁻¹ with an increment of 79.16 % compared to pure LTO at a high rate of 10 C (1 C=170 mAh g⁻¹), and shows a high retention rate of 96.4 % after 500 cycles at 5 C-rate.     

以金属有机骨架材料HKUST-1为模板制备多孔聚苯胺电极及其超级电容器性能研究

以涂敷在碳布基体上的金属有机骨架多孔材料HKUST-1为硬模板,使用单极脉冲法沉积聚苯胺制备了具有电活性的多孔复合电极Micro-PANI/CC,同时以空白碳布(Carbon Cloth,CC)为基体制备了聚苯胺电极PANI/CC,并研究、比较了它们的电化学电容器性能. 使用XRD、SEM分析了所得电极的结构,结果显示电极Micro-PANI/CC表面具有大量的纳米孔状结构. 在0.5 mol·L^-1硫酸为电解液的体系中测试了循环伏安、恒电流充放电、阻抗以及稳定性等特性,在扫速为2 mV·s^-1 时,电极Micro-PANI/CC和PANI/CC的比电容分别为895.6 F·g^-1和547.6 F·g^-1,在其它测试条件相同的情况下,前者的比电容保持在后者的1.64倍以上,且具有更好的倍率特性、更低的电阻和较好的稳定性等特点,说明这种以HKUST-1为模板形成的多孔聚苯胺更适于超级电容器电极材料.     

Efficient modification of Cu electrode with nanometer-sized copper tetracyanoquinodimethane for high performance organic field-effect transistors

We report high performance organic field-effect transistors (OFETs) with the modified Cu bottom-contact electrodes. Efficient modification of the Cu electrodes with nanometer-size copper tetracyanoquinodimethane (Cu-TCNQ) increases the electrode/organic layer contact area and reduces contact resistance. We investigated the effect of the Cu-TCNQ morphology on the device performance. The pentacene-based OFETs with the modified Cu bottom-contact electrodes exhibited high device performance. The field-effect mobility up to 0.31 cm(2)/V s was achieved. To the best of our knowledge, this is the highest device performance for the OFETs with the bottom Cu electrodes ever reported. Consequently, our results provide an effective approach to fabricate high performance and low-cost OFETs.     

Nanoconfinement effects in electrochemical reactions

Nanostructuring materials in the aims to enhance its catalytic activity has long been indispensable in electrocatalyst development. In particular, nanoporous electrodes with numerous pores in the nanoscale, are widely utilized owing to its enlarged surface area as well as activated surface characteristics. In the geometrical point of view, nanocavities of nanoporous electrodes offer unique spatial environment that confine reactant molecules, resulting in enhanced interaction between the reactant molecule and the electrode surface. Such electrocatalytic effects stemming from the morphology of nanoporous electrodes have been denoted as nanoconfinement effects. This review introduces the concept of nanoconfinement effects in electrochemical systems, the recent progress, and perspectives in this field.