Fabrication and electrochemical properties of carbon nanotube film electrodes

Carbon nanotube (CNT) film electrodes were fabricated by a novel process involving the electrostatic spray deposition (ESD) of a CNT solution. Acid treated CNTs were dispersed in an aqueous solvent through sonication and then the CNT solution was electrostatically sprayed onto a metallic substrate by the ESD method. The CNT film electrodes showed well-entangled and interconnected porous structures with good adherence to the substrate. A specific capacitance of 108 F/g was achieved for the electrodes in 1 M H₂SO₄. In addition, the CNT film electrode showed good high rate capability.     

Electrochemical properties of double wall carbon nanotube electrodes

Electrochemical properties of double wall carbon nanotubes (DWNT) were assessed and compared to their single wall (SWNT) counterparts. The double and single wall carbon nanotube materials were characterized by Raman spectroscopy, scanning and transmission electron microscopy and electrochemistry. The electrochemical behavior of DWNT film electrodes was characterized by using cyclic voltammetry of ferricyanide and NADH. It is shown that while both DWNT and SWNT were significantly functionalized with oxygen containing groups, double wall carbon nanotube film electrodes show a fast electron transfer and substantial decrease of overpotential of NADH when compared to the same way treated single wall carbon nanotubes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

粘结剂对碳纳米管电极性能的影响

利用扫描电子显微镜．电极接触角和电极充放电等测试手段．研究了不同种类粘结剂和粘结剂含量对电极的影响．结果表明：采用酚醛树脂作为电极的粘结剂效果最好,当其质量占电极质量的15％时,电极的性能达到最佳。     

Influence of thin film properties on the electrochemical performance of diamond electrodes

The electrochemical properties of nanocrystalline diamond films grown by microwave-enhanced chemical vapour deposition from a helium–hydrogen–methane gas phase mixture on Ti substrates are explored. A range of important redox systems are examined in aqueous solution including the oxidation of hydroquinone and ascorbic acid, and the electrodeposition and stripping of Au and Cu. Compared to boron-doped diamond materials, the nanodiamond is found to be a highly active electrode material, with low overpotentials and high adherence of metallic electrodeposits, for the redox systems studied.     

Synthesis, characterization, and electrochemical capacitance of amino-functionalized carbon nanotube/carbon paper electrodes

Amino-functionalization of carbon nanotubes (CNTs) attached to carbon paper (CP) has been achieved using one synthesis protocol: (i) chemical oxidation, (ii) acyl chlorination, and (iii) amidation. The amidation reaction of the carboxylic groups in oxidized the CNT/CP hybrids enables the formation of terminal amino groups on the CNT sidewalls. The functionalized CNTs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, Fourier transformed infrared spectroscopy, thermal programmed desorption, and N₂ adsorption. The cyclic voltammetry curves of an amino-modified CNT-based capacitor showed a continuum of double-layer and pseudocapacitive behavior. The presence of surface oxides and amides on CNTs imparts not only hydrophilic coverage for the formation of double-layer (double-layer capacitance) but also active sites for the redox reaction (pseudocapacitance). Based on the result of the charge/discharge cycling test, the N-modified CNT/CP capacitor exhibits an enhanced capacitance, high-rate capability, and capacitance stability with high coulombic efficiency.     

Application of diamond electrodes to electrochemical processes

Conducting diamond thin film is a new electrode material that has received great attention recently because it possesses several technologically important characteristics such as an inert surface with low adsorption properties, remarkable corrosion stability, even in strong acidic media, and an extremely wide potential window in aqueous and non-aqueous electrolytes. Thanks to these properties diamond electrodes meet the requirements for a wide range of electrochemical applications. The object of this article is to summarise and discuss the recent results available in the literature concerning the application of diamond electrodes to electrochemical processes such as water treatment and electro-synthesis of organic and inorganic compounds.     

The electrochemical properties of imidazol-linked iron phthalocyanine—carbon electrodes

Electrodes for the electrochemical reduction of oxygen have been studied galvanostatically. The electrodes were of the activated carbon-polymeric iron phthalocyanine (FePc) type, made hydrophobic with a Teflon treatment. A link between the FePc and the carbon was achieved by covalently binding imidazol to the carbon surface and then letting the FePc co-ordinate to the free nitrogen of the imidazol molecule. In this way an initial improvement of the stability of the electrode potential and the polarization data was achieved. It has furthermore been established that the potential responds more rapidly to changes, i.e. it is more reversible, than an analogous electrode based on carbon that has not been treated with imidazol.     

Fabrication and electrochemical properties of carbon nanotube array electrode for supercapacitors

The multiwalled carbon nanotube (MWNT) array was fabricated by chemical vapor deposition (CVD) in the template of porous alumina from the carbonaceous source of C₂H₂ in the presence of a catalyst of ferric metals. To utilize the external surface other than the inner surface of the carbon nanotubes, 1 mol/L sulfuric acid was applied to remove off the most part of AAO template on the carbon nanotube electrode. The electrochemical performances of the carbon nanotube array electrode were investigated by use of the cyclic voltammetry, galvanostatic charge/discharge and ac impedance methods for its application in supercapacitors. The specific capacitance of 365 F/g of the electrode was achieved with the discharge current density of 210 mA/g in the solution of 1 mol/L H₂SO₄. In addition, the carbon nanotube array electrode was found to have low equivalent series resistance (ESR) and good cycling stability.     

Synthetic diamond electrodes: The effect of surface microroughnesson the electrochemical properties of CVD diamond thin films on titanium

The electrochemical behavior of B-doped diamond films on Ti substrates subjected to different pretreatment procedures (annealing, sand-blasting, and etching in HCl) is evaluated as a function of surface microroughness. Generally, the differential capacitance follows the true surface area of the electrodes. The width of the potential window also increases, but slightly, with the roughness. The electrode reversibility in the [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ redox system increases with increasing surface roughness. The apparent increase in the reversibility of the reaction may be also explained by the decrease in the true current density. Although the variations in the electrochemical parameters are not strongly pronounced, the tendencies observed can be used to optimise the electrode properties.     

The effect of CVD-diamond film thickness on the electrochemical properties of synthetic diamond thin-film electrodes

The electrochemical behavior of polycrystalline diamond films of different thickness (0.5–7 μm), grown by hot-filament CVD method, was studied by electrochemical impedance spectroscopy and cyclic voltammetry. The differential capacitance, background current, and potential window were measured in supporting electrolyte solution; the electrochemical kinetics, in [Fe(CN)₆]^3−/4− model redox system. With the increasing of the films thickness, the crystallite size increased; both the differential capacitance and background current in the indifferent electrolyte, as well as the transfer coefficients in the redox system, decreased; thus, the diamond electrode becomes as if less reversible. The effect of the films’ thickness is reduced to that of nondiamond (amorphous) carbon contribution from intercrystalline boundaries on the electrochemical behavior of the polycrystalline diamond electrodes.     

n-Type nitrogenated nanocrystalline diamond thin-film electrodes: The effect of the nitrogenation on electrochemical properties

Nitrogenated nanocrystalline diamond thin-film electrodes with controlled conductivity are grown from microwave- or arc-plasma in CH₄-Ar-H₂-N₂ gas mixtures. Their electrochemical behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. It is concluded from Mott-Schottky plots that the studied material has n-type conductance; the donor concentration is estimated. The character of electrode behavior is controlled by the degree of nitrogenation of the material. In particular, with the increasing of nitrogen concentration in the feeding gas (0-25%) supplied to plasma-chemical reactor, the potential window in the supporting electrolyte (2.5 M H₂SO₄) becomes somewhat narrower, the reversibility of electrochemical reactions in the [Fe(CN)₆]^3−/4− redox couple becomes more pronounced. Kinetic parameters of redox reactions in this couple are determined. By and large, with the increasing of the nitrogenation the electrochemical behavior of “poor conductor” gives way to that of metal-like conductor.     

掺硼金刚石电极电化学再生粉末活性炭

使用200目粉末活性炭吸附苯酚模拟废水至饱和,用BDD电极作为阳极再生饱和炭,以再生效率为评价指标,研究不同因素对活性炭再生效果的影响。在电解质为0.05 mol/L的Na_2SO_4溶液,pH为7,电流密度为50 mA/cm~2,再生时间为2 h条件下,活性炭再生率达74.8%。同时不同电解质对再生效果也有不同影响,硫酸钠优于氯化钠,再生效率随着pH的增加而增加。采用正交实验方法对影响再生效果的各因素进行评价,其影响的主次顺序是:电解质浓度、pH、电解时间。     

掺硼金刚石电极电化学再生粉末活性炭

使用200目粉末活性炭吸附苯酚模拟废水至饱和,用BDD电极作为阳极再生饱和炭,以再生效率为评价指标,研究不同因素对活性炭再生效果的影响。在电解质为0.05 mol/L的Na_2SO_4溶液,pH为7,电流密度为50 mA/cm²,再生时间为2 h条件下,活性炭再生率达74.8%。同时不同电解质对再生效果也有不同影响,硫酸钠优于氯化钠,再生效率随着pH的增加而增加。采用正交实验方法对影响再生效果的各因素进行评价,其影响的主次顺序是:电解质浓度、pH、电解时间。     

Ordered array of diamond ultramicroband electrodes for electrochemical analysis

Boron-doped diamond ultramicroband arrays with different array densities and interelement spacings were fabricated using silicon technology and selective diamond deposition (SAD) technique to yield microvoltammetric electrodes. The electroactive ultramicroband elements were designed with one microscopic critical dimension to impart microelectrode behavior while the other dimension was made larger to yield an increase in signal current. Cyclic voltammetry studies in this work showed that with sufficient interelement separation, the ultramicroband arrays display sigmoidal pseudo-steady-state cyclic voltammograms characteristic of microband electrodes. The ultramicroband arrays yielded higher faradaic current per unit area, than either square ultramicroelectrode array or conventional planar diamond electrode from earlier reported work. This is due to enhanced mass transport to the ultramicroband elements at slow scan rates. Larger current density and higher signal-to-noise (S/N) ratio leads to better limits of detection, making it possible to fabricate a more sensitive electrode for applications such as electroanalysis, electrocatalysis, trace element analysis, mechanistic and fast transfer kinetics studies, electrochemistry in highly resistive media, as well as sensors in flow and biological system.     

Characterization of boron-doped diamond electrodes by electrochemical impedance spectroscopy

Charge transfer on boron doped diamond (BDD) electrodes was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The diamond films of 5 μm thickness and boron content between 200 ppm and 3000 ppm were prepared by the hot filament CVD technique on niobium substrate and mounted in a Teflon holder as rotating disk electrodes. The electrochemical measurements were carried out in aqueous electrolyte solutions of 0.5 M Na₂ SO ₄ + 5 mM K₃[Fe(CN)₆]/K₄[Fe(CN)₆]. Significant deviation in the redox behaviour of BDD and active Pt electrodes was indicated by a shift of the peak potentials in the cyclic voltammograms with increasing sweep rate and lower limiting diffusion current densities under rotating disk conditions. In the impedance spectra an additional capacitive element appeared at high frequencies. The potential and rotation dependence of the impedance spectra can be described quantitatively in terms of a model based on diffusion controlled charge transfer on partially blocked electrode surfaces. Direct evidence for the non-homogeneous current distribution on the diamond surface was obtained by SECM measurements.     

Enhancement of electrochemical properties of screen-printed carbon electrodes by oxygen plasma treatment

Plasma treatment is frequently used to clean and modify the surface of materials, including polymers and graphite. However, very limited information has been reported concerning the modification of a matrix, such as a screen-printed carbon electrode (SPCE) which is consisted of a mixture of graphite and pasting binder, using plasma. In this study, the surface characteristics and electrochemical properties of the plasma-treated SPCEs were investigated. The plasma-treated SPCEs performed a good electrochemical response (enhanced about 80-fold compared with those untreated electrode) and exhibited good reproducibility (CV of 4.8%). The response of plasma-treated electrodes was comparable with the electrodes modified with noble metal and superior to those electrode modified with carbon nanotube (CNT) (ca. 20-fold). SEM imaging revealed that an effective decomposition or removal of impurities and pasting binder on the surface of SPCEs during oxygen plasma treatment. The plasma treatment increases the step-like defects on the surfaces of graphite particles resulting in the generation of numerous edge planes. The phenomena could be responsible for the improvement of the electrochemical properties of SPCEs. The results also suggest that the plasma treatment condition is important. Over-erosion on the SPCE surface by high powered plasma may lead to the poor reproducibility of the SPCEs.     

Biological applications of diamond electrodes; electrochemical studies of riboflavin

The electrochemical study of flavines is a challenge using many solid-state electrode materials, since pronounced adsorption effects are observed which have deleterious effects on the recorded observations. In the present work three distinctive types of diamond electrode are employed to measure electrochemical charge transfer to riboflavin. At nanodiamond, it is found that rapid charge-transfer kinetics are observed, between the electrode and an adsorbed layer of around 2 monolayers thickness which rapidly forms at the electrode surface. In contrast, high phase purity microcrystalline diamond electrodes, show little adsorption, enabling solution phase diffusion controlled electrochemistry to be observed. Studies of the pH dependence of the observed electrochemistry are presented, which show results comparable to those observed at dropping mercury electrodes, and electrochemical measurements in the presence of power ultrasound are also described.     

Investigations of electrochemical oxygen transfer reaction on boron-doped diamond electrodes

In this paper, the electrochemical oxygen transfer reaction (EOTR) is studied on boron-doped diamond electrodes using simple C₁ organic compounds (methanol and formic acid). The kinetics of both oxygen evolution (side reaction) and organics oxidation (main reaction) has been investigated using boron-doped diamond microelectrodes-array (BDD MEA). Oxygen evolution, in the high-potential region, takes place with a Tafel slope of 120 mV dec⁻¹ and zero reaction order with respect to H⁺. In the presence of organics, a shift of the polarization curves to lower potentials is observed while the Tafel slopes remain close to 120 mV dec⁻¹. A simplified model of C₁ organics oxidation is proposed. Both water discharge and organics oxidation are assumed to be fast reactions. The slowest step of the studied EOTR is the anodic discharge of hydroxyl radicals to oxygen. Further in this work, electrolysis of formic acid on boron-doped diamond macroelectrode is presented. In order to achieve 100% current efficiency, electrolysis was carried out under programmed current, in which the current density was adjusted to the limiting value.     

Microwave activation of electrochemical processes: High temperature phenol and triclosan electro-oxidation at carbon and diamond electrodes

The electrochemical oxidation of phenolic compounds in aqueous media is known to be affected by the formation of electro-polymerized organic layers which lead to partial or complete electrode blocking. In this study the effect of high intensity microwave radiation applied locally at the electrode surface is investigated for the oxidation of phenol and triclosan in alkaline solution at a 500 μm diameter glassy carbon or at a 500 μm × 500 μm boron-doped diamond electrode. The temperature at the electrode surface and mass transport enhancement are determined by calibration with the Fe(CN)₆^3−/4− redox system in aqueous 0.3 M NaOH and 0.2 NaCl (pH 12) solution. The calibration shows that strong thermal and mass transport effects occur at both glassy carbon and boron-doped diamond electrodes. The average electrode temperature reaches up to 390 K and mass transport enhancements of more than 20-fold are possible. For the phenol electro-oxidation at glassy carbon electrodes and at a concentration below 2 mM a multi-electron oxidation (ca. 4 electrons) occurs in the presence of microwave radiation. For the electro-oxidation of the more hydrophobic triclosan only the one-electron oxidation occurs. Although currents are enhanced in presence of microwave radiation, rapid blocking of the electrode surface in particular at high phenol concentrations still occurs.