Powder Microelectrode Research Articles

Carbon nanotube powder microelectrodes for nitrite detection

Multi-wall carbon nanotubes (MWCNTs) are filled in the cavity at the tip of a microelectrode to form a carbon nanotube powder microelectrode (CNTPME) for testing the nanotubes under various conditions. Anodic treatment is found to cut the nanotubes into shorter species, increase double layer capacity, and make the nanotubes able to strongly adsorb Os(bpy) 3 2+. The CNTPME modified with anodic pretreatment and pre-adsorbed Os(bpy) 3 2+ (CNTPME-Os(bpy) 3 2+) shows high catalytic activity for nitrite reduction in acidic solutions. The sensitivity, temperature coefficients of such modified electrode for nitrite detection are 4.9 and 6.8 A cm −2 M −1, 0.14 and 0.16% (°C) −1 for steps 1 and 2 of nitrite reduction, respectively with a lower detection limit 10 −7 M for S/N=4. These features plus the miniaturizability make the CNTPME-Os(bpy) 3 2+ a very promise candidate for nitrite sensor.

A study of calcium zincate as negative electrode materials for secondary batteries

The properties of calcium zincate as negative electrode materials for secondary batteries were examined by powder microelectrode, cyclic voltammetry, charge–discharge cycle measurements and X-ray diffraction (XRD) analysis. The results show that the cycleability of calcium zincate is obviously superior to that of ZnO and that of the mixture of ZnO and Ca(OH) 2 (the molar ratio of Zn:Ca=2:1). Calcium zincate forms zinc metal during the charging and exhibits an initial discharge capacity 230 mAh g −1. With the discharge cut-off voltage of 1.0 V, the discharge capacity of the experimental Zn/NiOOH cell does not decay much during 500 cycles, exhibiting good prospect for practical use.

Studies on the behaviors of PbSO4/Pb and PbO2/PbSO4 electrodes prepared from lead carbonate by powder microelectrode technique

The behaviors of PbSO4/Pb and PbO2/PbSO4 electrode prepared from PbCO3 have been examined using powder microelectrode(PME) technique and cyclic voltammetry(CV). Firstly, PMEs packed with PbCO3 transformed into PbSO4 PME in 1.0 mol/L H2SO4 solution at 30 °C, and then the PbSO4 in the PMEs were formed to Pb or PbO2 using an unsymmetrical signal (Qa/Qc for PbSO4/Pb electrode andQc/Qa for PbO2/PbSO4 electrode being 0.1–0.3) in 2.5 mol/L H2SO4 solution. The results show that the CV characteristic of either PbSO4/Pb or PbO2/PhSO4 PME prepared from PbCO2 are as good as that of both electrodes made from lead oxide powder produced by ball mill.

Elimination of the interference of ascorbic acid in the amperometric detection of biomolecules in body fluid samples and the simple detection of uric acid in human serum and urine by using the powder microelectrode technique

Abstract A study of the electrochemical behaviour of ascorbic acid (AA) at the powder microelectrode revealed that exhaustive electrolysis of AA could be achieved within a narrow range of potential. As a result, the interference of AA in the amperometric detection of bioactive molecules in body fluid samples can be practically eliminated by employing the powder microelectrode technique. Elimination of the interference of AA can be further improved if the monitored biomolecules are strongly adsorbed on the surface of carbon powder. A good example of such a bioactive compound is uric acid (UA), which can be strongly adsorbed on the surface of acetylene black powder. In a mixture containing 0.8 μM–0.4 mM UA and a large excess of AA in 0.1 M phosphate buffer solution, the separation between the potentials of oxidation current peaks of UA and AA reaches 400 mV, and the height of the UA peak is linear with respect to the UA concentration. A very simple procedure for the detection of UA in human serum and urine samples has been worked out to illustrate the above-stated principle. Application of the same principle in the amperometric detection (and probably simultaneous determination) of other electroactive biomolecules also seems promising.

Powder Microelectrodes for Capillary Electrophoresis with Amperometric Detection

In this paper, we first report the use of powder microelectrodes (PMEs) as the amperometric detector for thiols, hydrazine and hydroxylamine in capillary electrophoresis (CE). This PME, with graphite-supported metalloporphyrin powder as catalyst, offers a few advantages as an amperometric detector in CE. Concentration limit of detection and mass limit of detection obtained for L-cysteine at the PME could reach 88 nM and 230 amol, respectively. The response of thiols at the PME was very reproducible since the electrode fouling was reduced. A relative standard deviation of peak heights (n = 8) of 1.8% and a relative standard deviation of migration time (n = 8) of 1.0% can be obtained for L-cysteine. The material packed in the PME can easily be changed. Hence, it is very convenient to choose suitable catalysts to detect special analytes, and this specially designed microelectrode should be applicable to many other compounds of biological interest.

Electrocatalytic hydrogenation of alkenes on LaNi5 electrodes

Abstract In this paper a new electrocatalytic hydrogenation process is reported based on the use of LaNi5 electrodes. The charge/discharge of hydrogen within the intermetallic compound through cyclic voltammetry experiments was observed using a powder microelectrode in classical aqueous KOH medium, as well as in other buffered aqueous or hydro-organic media. Most voltammograms are modified in the presence of unsaturated compounds, which indicates that a hydrogenation reaction occurs. Electrocatalytic hydrogenation on a preparative scale was carried out with three unsaturated compounds taken as models (methyl vinyl ketone, 1-decene, 5-hexen-2-one) and it was found that only the CC bond is hydrogenated with Faradaic efficiencies up to 100%.

Powder Microelectrode Modified with Nafion-Os(bpy)_3~( 2+) and PVP Composite and Its Catalysis for NO_2 - Reduction

Powder Microelectrode Modified with Nafion-Os(bpy)_3~( 2+) and PVP Composite and Its Catalysis for NO_2 - Reduction

Surface diffusion and the spillover of H-adatoms and oxygen-containing surface species on the surface of carbon black and Pt/C porous electrodes

Abstract The cyclic voltammetric behavior of Vulcan XC-72 ∣ Nafion® and carbon-supported Pt ∣ Nafion® interfaces was studied by using the powder microelectrode technique. It was concluded that catalyst particles not in direct contact with Nafion® also contributed to the cyclic voltammograms although the electrode ∣ Nafion® interfaces formed only at the end face of the electrodes. The phenomena were interpreted in terms of surface conductivity and spillover of adsorbed species over the surface of catalyst particles. The effects of electrochemical pretreatment of the electrodes and the prolonged potential cycling on the cyclic voltammograms have been observed, which indicated that surface conductivity, and surface diffusion as well as spillover were sensitive to the surface status of the catalyst particles.

Nitrite reduction at powder microelectrodes

Abstract The limiting current of nitrite reduction in acid media is usually controlled by a preceding chemical reaction occurring in a very thin reaction zone. We propose that the apparent current density of this kind of reaction can be effectively enhanced by using a porous electrode and, for analytical purposes, the powder microelectrode (PME) is a convenient version. The apparent limiting current densities of nitrite reduction at the PMEs made from Au and carbon powders are found to be 50 and 100 times larger, respectively, than those obtained with smooth electrodes. For the carbon PME, the current is linear with nitrite concentration spanning five orders of magnitude with a lower detection limit of 4.4 μmol l−1.

Electrochemical studies of Li/LixMn2O4 by using powder microelectrode

Abstract In this work, cyclic voltammogram, AC impedance and potential step method have been used to study the electrochemical properties of Li/Li x Mn 2 O 4 system using a powder microelectrode technique. The results show that the diffusion of lithium ions in Li x Mn 2 O 4 particles is the rate-determining step. The diffusion coefficient of lithium ion and the exchange current density have been measured at different x values of Li x Mn 2 O 4 .

Two reduction processes for hydrogen adsorption and absorption at MmNi 5-type alloy electrodes

The electrochemical hydrating/dehydrating behavior of MmNi 5-type alloy electrodes in an alkaline solution was investigated with cyclic voltammetry, scanning electron microscopy and X-ray photoelectron spectroscopy analysis. At an Mm(Ni 3.8Co 0.5Al 0.4Mn 0.3) 5 powder microelectrode, a hydrogen absorption peak was observed at more negative potential than that of the water electroreduction and hydrogen adsorption peak in its cyclic voltammograms. In addition, the electrochemical mechanism of the hydrogen absorption and desorption at the hydride electrodes in the alkaline solution is discussed.

Detection of dopamine in the presence of a large excess of ascorbic acid by using the powder microelectrode technique

Abstract The powder microelectrode technique is employed in the detection of ultra-low concentrations of dopamine (DA), which can be adsorbed and thus preconcentrated on the inner surface of a carbon black packed powder microelectrode. The apparent reversibility and kinetics of the oxidation of DA were found to improve significantly, and separation of the oxidation current peaks of DA and ascorbic acid (AA) reaches about 300 mV. In the presence of 0.6 mM AA in solution, the oxidation current peak due to 20 nmol of DA remains clearly evident. After correction of the background current of AA, the height of the oxidation current peak of DA oxidation is proportional to the concentration of DA in solution, and is not affected by the presence of large excess of AA. The low limit of DA detection is ca. 20 nM in acidic solution, and less than 1 μM in neutral solution. Detection of DA in concentrations as low as 5 nM can be achieved after prolonged immersion of powder microelectrode in solution.

Study of the powder/membrane interface by using the powder microelectrode technique I. The Pt-black/Nafion® interfaces

The polarization behavior of a Pt microdisk electrode, a platinized Pt microdisk electrode and a Pt-black powder microelectrode immersed in sulfuric acid solution, in contact with a moist Nafion® membrane were studied by cyclic voltammetry. The experimental results reveal that the surface diffusion of the adsorbed species plays an important role in determining the kinetics of interfacial reactions taking place at the powder/Nafion® membrane interface. The weakly adsorbed hydrogen atoms diffuse significantly faster than the strongly adsorbed hydrogen and the oxygen-containing surface species. Surface active sites in the range of tens of microns from the powder/Nafion® interface can be involved in interfacial reactions. The apparent coefficients of diffusion of various surface species were estimated from the variation of peak current with scan rate of potential. The apparently higher irreversibility of electrode reaction observed at the powder/membrane composite electrode is explained by considering mechanism of current generation of this type of electrode.

Application of SPE composite microelectrodes to the study of the spillover of adsorbed species on electrode surfaces

The electrochemical behavior of ferrocene in acetonitrile at the platinum|Nafion® interface was investigated using SPE composite microelectrodes. Two parallel reactions take place at the interface. The redox reaction of ferrocene|ferricinium ions predominates at the platinum|Nafion® composite microdisk electrode, while the adsorption or desorption of atomic hydrogen predominates at the platinum black|Nafion® composite powder microelectrode. This fact implies that the electrochemical reactions take place only at the interface and the adsorption of atomic hydrogen can occur on surface sites remote from the interface. The SPE composite microelectrode seems to be a potential technique of investigating the spillover of adsorbed species on the electrode surface.

Improvement of the output characteristics of amperometric enzyme electrode by using the powder microelectrode technique

Application of the powder microelectrode technique to the fabrication of enzyme electrodes can result in significant improvement of the output behaviours of an amperometric enzyme electrode. The theoretical kinetic equation of the powder enzyme electrode is derived and compared with that of the planar enzyme electrode, together with a simple method for the estimation of apparent Michaelis constant K m′ from the response of the powder enzyme electrode. The glucose oxidase (GOD) electrode is used as the model to verify the theoretical equations. Values of K m′ estimated from experimental data obtained with powder electrodes are closer to the intrinsic values of the same enzyme system in bulk phase. The working life of the enzyme electrode was found to improve and the interfering effects of various bioactive molecules were found to be less in the case of powder enzyme electrodes.

M—SPE composite powder microelectrodes used in organic electrosynthesis

We investigate the electrochemical behavior of 2-ethyl anthraquinone at the powder graphite|Nafion® membrane interface of a solid polymer electrolyte composit powder electrode.

Quantitative Evaluation of Electrochemical Properties of MH alloy by powder microelectrode

Quantitative Evaluation of Electrochemical Properties of MH alloy by powder microelectrode

Improvement of the Anti-interference Characteristics of GOD Electrode by Using the Powder Microelectrode Technique

Improvement of the Anti-interference Characteristics of GOD Electrode by Using the Powder Microelectrode Technique

Powder microelectrodes

We have shown that powder microelectrodes are a potentially useful technique for electroanalytical chemistry and the study of the electrochemical kinetic and cyclic behavior of various powdery materials. The main merits of this type of electrode are as follows. 1. (1) It is possible to achieve a significantly enhanced electrode surface and homogeneous polarization simultaneously. Improved reversibility, a better developed limiting diffusion current and easier analysis of experimental data should render this type of electrode applicable in many areas of electroanalytical chemistry and electrode kinetics studies. 2. (2) Electrochemical study of powders is easy and rapid. The powder microelectrode is much simpler to prepare than the porous electrode, and the cyclic charge—discharge behavior of electroactive materi als can be studied much more rapidly with the powder microelectrode than with the conventional porous electrode method. Results obtained with the porous electrode and with the powder microelectrode are usually in good agreement with each other.