Platinum Black Electrodes Research Articles

Integrated microfluidic system with electrochemically actuated on-chip pumps and valves

A microfluidic system was constructed by integrating on-chip micropumps and check valves that function by means of a hydrogen bubble that is generated or extinguished electrochemically. Essential elements consisted of thin-film three-electrode systems, including a platinum black working electrode. Micro flow channels and containers for electrolyte solutions were formed on a polydimethylsilixane (PDMS) substrate. The growth and shrinkage of the bubble were controlled reproducibly by setting the working electrode potential at a constant value. The elastic nature of the bubble clogged in a valve compartment in the middle of the flow channel hindered the effective passage of the solution. The bubble was also effective in separating two different solutions. By making the valves open and close cooperatively, a solution could be introduced into the system and transported in the flow channel. When two dye solutions were transported and merged in a flow channel, sheath flows were observed, reflecting a low Reynolds number. As a model system, two solutions containing luciferin and luciferase were introduced separately, transported, and mixed. Chemiluminescence originating from the enzymatic reaction was observed.

Conductivity dependence of the polarization impedance spectra of platinum black electrodes in contact with aqueous NaCl electrolyte solutions

Abstract The polarization resistance and capacitance of platinum black electrodes in contact with aqueous NaCl solutions was investigated. A series of measurements were made at 25±0.1 °C in the 10 Hz to 10 MHz range using a HP 4192A Impedance Analyzer. The measurement cell has flat parallel platinum electrodes 15 mm in diameter, with a continuously variable spacing from 0.5 to 9 mm. They were platinized prior to each measurement. The electrolyte solution conductivities were in the 0.004–0.6 S m−1 range. The data were analyzed using an equivalent circuit consisting in a constant phase element in series with a parallel connection of a resistance and another constant phase element. The characteristic parameters of the model are presented as a function of the electrolyte solution conductivity.

Magnetosensitive enzyme electrode for hydrogen peroxide sensing

Peroxidase is one of the magnetosensitive enzymes, and has an important role in scavenging reactive oxygen species. In the present study, a surface of platinum black electrode was laminated by peroxidase molecules, and H2O2 decomposing processes by peroxidase and platinum black were monitored with and without magnetic fields of up to 14 T. An increase in the current reflected a decrease in the activity of peroxidase molecules. The current in the electrode with peroxidase increased significantly depending on the applied magnetic flux intensity. The increases of current during the magnetic field exposures were observed consistently both when the currents were transiently decreasing and at a constant level. It is suggested that the layers of peroxidase molecules on the platinum black cause a distortion by diamagnetic forces acting on the layers, and the distortion is concentrated on a catalytic part in the peroxidase resulting in the observed activity decreases.

Optimization of the geometry and porosity of microelectrode arrays for sensor design.

This paper describes the systematic investigation of a range of microelectrode arrays with varying dimensions fabricated by standard photolithographic and reactive-ion etching techniques. As expected from theory, the electrochemical behavior of microelectrode arrays with a constant individual diameter varied strongly with center-to-center spacing, the larger the spacing the more sigmoidal the recorded voltammogram. Furthermore, the behavior of arrays with a constant relative center-to-center spacing is shown to vary with individual electrode diameter, the arrays with the smallest electrodes producing strongly peaked voltammograms. Peak current densities and signal-to-noise ratios were also obtained for a variety of array geometries, and the use of electrodeposited platinum black electrodes was investigated. To demonstrate one advantage of using a loosely packed microelectrode array in electroanalysis, a ferrocene-mediated enzyme-linked assay involving the biocatalytic reduction of H2O2 was investigated. Results showed an improved temporal response, with current-time transients reaching a steady-state response more quickly using arrays with increased center-center spacings.

A reversible electrochemical nanosyringe pump and some considerations to realize low-power consumption

An electrochemical syringe pump was fabricated by micromachining. Two sets of thin-film three-electrode systems for actuation and sensing were formed on a glass substrate, whereas a microflow channel and a microcontainer for the internal electrolyte solution were formed on a silicon substrate. Hydrogen gas produced or consumed on a platinum black working electrode was used as a working medium. The rates of pumping for flushing and sampling could be varied by adjusting the potential of the working electrode at appropriate values to reduce and oxidize the related species. As a result, bi-directional pumping could easily be realized. During pumping repeated up to 20 times, the deviation of the pumping rates was distributed within 7% of the respective averages. The function of the micropump incorporated in a system was tested using a solution containing Cu 2+ ions and a distinct current increase accompanying the reduction of the ions was observed following the sampling. When the goal is to reduce power consumption, the material used for the auxiliary electrode is critical and Ag/AgCl was considered to be a good alternative for a platinum auxiliary electrode.

Magnetically disturbed activity of immobilized catalase on an electrode in hydrogen-peroxide buffer

A catalase-immobilized platinum black electrode was used to measure the catalytic decomposition of hydrogen peroxide by catalase. The superconducting current of an 8 T superconducting magnet was swept between 0 T and 8 T, and the catalase electrode's current was monitored continuously under a voltage-stabilized condition. The sensor's current changed in correspondence with the varying magnetic fields. During the magnetic field exposures, the electrode's current increased nearly 200%. The clear and reproducible increase in the electrode's current under magnetic fields indicated that the catalytic activity of catalase was disturbed under magnetic field exposure of up to 8 T and at a threshold between 1 to 2 T.

Fabrication and Characterization of Gold–Platinum Black Electrode

Abstract Gold–platinum black layer was electrochemically deposited on a platinum electrode in the mixed solution of tetrachloroaurate, hexachloroplatinate, and lead acetate. The surface of the electrode after the deposition was characterized by scanning electron microscopy, X-ray microanalysis, and cyclic voltammetry. There was no evidence of the localization of gold and platinum, and the deposition ratio of gold and platinum was proportional to the concentration of tetrachloroaurate and hexachloroplatinate.

白金黒表面における固定化酵素活性の磁場による抑制効果

白金黒表面における固定化酵素活性の磁場による抑制効果

Preparation and characterization of platinum black electrodes

We have investigated properties of electrochemically deposited platinum black by atomic force and scanningelectron microscopy. Platinum black was deposited on evaporated platinum electrods. Deposition time and cure temperature was found to influence the quality and morphology of the platinum black layer. Morphological inclusions were readily observed in filmsdeposited for duration of less than 60 seconds at a bias of 1.5 V against a platinum counter electrode. Shorting of themicrofabricated electrodes due to lateral outgrowth of high surfacearea platinum black was observed when current densities on the orderof 100 mA cm−2 were employed. We further show that reproducibility ofhighly adherent platinized electrodes is achieved.

Control of the orientation of human erythrocytes by magnetic and electric fields

The orientation of human red blood cells (RBCs) was controlled by the application of magnetic and electric fields. Because of their anisotropic diamagnetism, RBCs orient parallel to strong magnetic fields. The electric orientation of erythrocytes is also caused by electric dipoles induced by an electric field. The RBCs orientation is parallel to both the electric and magnetic fields. A 4–5 kV/m alternating current (ac) electric field (10–200 kHz, sine wave) was applied to RBCs suspended in a phosphate buffer solution using a pair of platinum black electrodes spaced 200–250 μm apart. An 8 T magnetic field was applied to the RBCs perpendicular to the direction of the electric field. It was observed that all RBCs were oriented in the same direction and parallel to the electric and magnetic fields. By the application of a horizontal 8 T magnetic field and a 4 kV/m ac electric field positioned perpendicular to one another, the RBCs oriented horizontally and their sedimentation rate was decreased by 18%. The flowing rate of the 10% RBCs suspension was decreased by 7.6% with the application of an 8 T magnetic field and a 4 kV/m ac electric field perpendicular to the direction of the suspension flow. It was observed that flowing RBCs were oriented perpendicular to the direction of the flow by the application of the fields, when the velocity of the suspension of RBCs was less than 300 μm/s.

Low Cost Electrodes for Proton Exchange Membrane Fuel Cells: Performance in Single Cells and Ballard Stacks

For widespread exploitation of proton exchange membrane fuel cells (PEMFCs) the cost of the stack must be reduced, and the performance per unit volume increased. Significant cost reduction has been achieved by the development of a high‐volume, low cost, electrode manufacturing process and from reductions in the electrode precious metal catalyst loadings. The performance of membrane electrode assemblies (MEAs) employing printed cathodes (⩽0.6 mg Pt/cm2) and anodes (⩽0.25 mg Pt/cm2, 0.12 mg Ru/cm2) in Ballard Mark V single‐cell and advanced‐stack hardware are at least comparable to current stack MEAs comprising high loading unsupported platinum black electrodes containing 4.0 mg Pt/cm2. Optimum cell performance has provided high power densities of 0.42 W/cm2 at 0.7 V. Furthermore, under motive and utility test conditions, the low‐cost electrodes show minimal loss in performance after over 3000 h of stack operation and, in short and full sized stacks, the cell‐to‐cell reproducibility is excellent, highlighting the high consistency of product available from the electrode manufacturing process. Incorporation of the low cost electrodes in commercial PEMFC stacks is anticipated in the near future.

Nuclear Magnetic Resonance Spectroscopic Study of the Electrochemical Oxidation Product of Methanol on Platinum Black

The adsorbate resulting from the potentiostatic, catalytic decomposition of methanol (0.1 M CH3OH in 0.5 M H2SO4) on a platinum black electrode has been studied via 13C nuclear magnetic resonance spectroscopy, at open cell potential. Cyclic voltammetry results indicate that coverage is a function of electrodecomposition time and potential. The spin−spin relaxation time T2 is dependent on surface coverage and ranges from ∼3 to ∼1.8 ms at coverages ranging from 0.3 to 0.75 ML, due to the increased effectiveness of 13C−13C dipolar interactions at high coverage. At 0.5 ML, the temperature dependence of the 13CO T2 (in a 2H2O-exchanged electrolyte system) has been determined from 80 to 250 K. There is a well-defined peak in relaxation rate at ∼170 K which can be modeled using a simple diffusional model having an activation energy of 7.9 ± 2.0 kcal/mol. Spin−lattice relaxation results from 10 to 250 K reveal Korringa behavior, with a T1T product (and Knight shift) that is independent of surface coverage, and has the same value for the electrochemical adsorbate as gas phase CO adsorbed on Pt. The similarity in T1T, T2, Knight shift, and activation energy for surface diffusion are in general accord with values previously measured in gas phase heterogeneous catalyst systems and strongly support the idea of primarily on top CO with C-down, on one major type of surface site.

Enzyme sensors prepared by electrodeposition on platinized platinum electrodes

Platinized Pt (platinum black) electrodes were employed as a base electrode for the immobilization of glucose oxidase (GOD). The GOD sensors were prepared by first electrodeposition of GOD/ BSA(bovine serum albumin) mixture on platinized Pt and subsequent cross-linking with glutaraldehyde. The roughness factor and morphology of the platinized Pt surfaces significantly depended on the platinization potential between 0.0 and −0.25 V (vs. sat. Ag AgCl ). At more positive potentials, small Pt crystallites were uniformly deposited to give a flatter layer, while dendritic crystallites were prominent at the other extreme resulting in higher roughness factors. A preferred exposition of Pt(110) planes was also observed on the dendritic crystallite surfaces, onto which the protein molecules deposited with a faster rate than onto the Pt(100) planes. The current intensities to glucose of the resulting GOD sensors gradually increased as the plating potentials for the base electrodes were more negative, which was accounted for from the fact that larger amounts of the protein molecules deposited on those highly roughened and preferentially Pt(110)-exposed Pt black surfaces. In addition, the highly roughened Pt black electrodes gave rise to a better signal to noise ratio in the current signals of the resulting sensors. It is likely that the plantinization process imparts a higher hydrophilic character on the Pt black surfaces such that adhesion of oxygen bubbles is greatly suppressed.

Determination of acetylcholine and choline with platinum-black ultramicroarray electrodes using liquid chromatography with a post-column enzyme reactor

A method for the highly sensitive determination of acetylcholine (ACh) and choline (Ch) was developed using platinum (Pt) black microarray electrodes as detectors in a microbore liquid chromatography (LC) with a post column enzyme reactor. The electrodes were prepared by plating a gold (Au) film electrode with sub-μm Pt-black particles. Since hydrogen peroxide generated by the enzymatic reaction of ACh and Ch was oxidized only at the Pt-black microarray electrode, each Pt-black particle (typically 0.1–0.2 μm in size) operated as an ultramicroelectrode. A high signal-to-noise ratio was achieved because of the high current density at the Pt-black microarray electrodes and because the Au film has a much lower baseline noise than the Pt. Detection limits of 5.7 (ACh) and 6.0 (Ch) fmol were obtained, with a wide linear range. The ACh and Ch signals with an Au film electrode modified with Pt-black particles retained more than 70% of their initial value after 5 days with continuous potential application. This is better stability than for a bare platinum electrode which retained only 40% of its initial response under comparable conditions.

Who introduced the tetrapolar method for measuring resistance and impedance?

The technique of using an outer pair of electrodes to inject current and an inner pair of electrodes to measure potential eliminates electrode/electrolyte impedance errors when measuring the resistivity of a conducting substance. A pressing problem of the late 1800s was the accurate measurement of the resistivity of an electrolyte that was placed between a pair of electrodes in a container. Kohlrausch (1897) working in Charlottenburg, Germany, solved the problem in a limited way by 1) using 1000 Hz current and 2) creating the platinum-black electrode. By using what was then a high frequency, the electrode impedance became low. By placing a velvety-like deposit of platinum on a platinum electrode, the effective surface area was increased, thereby reducing the electrode impedance. Such blackened platinum electrodes are still used in conductivity cells designed to permit measurement of electrolytic resistivity. Working in Paris, France, well before Kohlrausch, Lippmann had solved the problem of measuring electrolytic resistivity in a simple and elegant way by introducing the tetrapolar method in conjunction with his capillary electrometer, a sensitive and rapidly responding potential indicator. Lippmann (1873) had become interested in the shape of a drop of mercury in a solution of sulfuric acid. When an iron wire was placed into the sulfuric acid and then contacted the mercury, the contour of the mercury changed. The combination of the iron wire, mercury, and electrolyte caused the charge distribution on the surface of the mercury to change, thereby altering the surface tension and, hence, the contour. Lippmann used the phenomenon of electrocapillarity, as it became known, to construct a sensitive and rapidly responding electrometer.

Control of molecular adsorption by a bias-voltage applied Langmuir-Blodgett technique

The authors have investigated organic thin films fabricated by a bias-voltage applied Langmuir-Blodgett (LB) technique, which is based on the adsorption LB method. The bias voltage is applied between a conductive indium-tin-oxide coated glass substrate and a subphase through a platinum black counter electrode. Malachite green and 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (C 12TCNQ) are used as an adsorbing and a spreading molecule from the aqueous subphase, respectively. Ultraviolet-visible absorption spectra of the LB films demonstrate that the quantity of adsorbing and spreading molecules can be controlled by applying the bias voltage.

Amorphous alloy electrodes for anodic oxidation of sulfite

Amorphous Ni-valve metal alloys containing a few atomic per cent of platinum group elements were prepared by rapid quenching and were employed for electrochemical oxidation of sulfite in 0.075 M Na 2B 4O 7 + 0.3 M H 3BO 3 + 1 M Na 2SO 3 at 30°C. Of the amorphous alloy electrodes containing ruthenium, rhodium, iridium or platinum, the platinum-containing electrodes showed the highest activity, which was almost the same as or even higher than that of the platinized platinum black electrode. Furthermore, the combined addition of platinum and ruthenium enhanced the catalytic activity. When ruthenium was substituted for part of the platinum, the maximum activity for amorphous Ni40Nb xPt(1 − x)Ru alloys was observed at about 0.8 at.% Pt.

A solid polymer electrolyte-bases electrochemical carbon monoxide sensor

A solid polymer electrolyte (SPE)-based electrochemical sensor for carbon monoxide detection has been designed, fabricated and evaluated. Nafion membrane is used as the solid electrolyte, and a hydrophobic Teflon-based platinum black thin-layer electrode is used as the working electrode. The sensor is tested over the CO concentration range 0-1.04% and shows good reproducibility. The response time to a step change of carbon monoxide is about 3 s. Operation of the sensor over 90 days in an ambient environment shows good sensor stability.

Selective detection of acetylene gas extracted from isolation oil by an electrochemical sensor using a gold electrode

The selective detection of acetylene in gases extracted from isolation oils has been studied to develop an electrochemical sensor for the diagnostic monitoring of the condition of in-service electrical instruments. Effects of coexisting gases (CH4, C2H6, C2H4, H2 and CO) on the oxidation current of C2H2 were tested using gas-permeable gold-coated and platinum-black electrodes as the sensor. The gold-coated electrode showed good behaviour for the selective current detection of acetylene under potentiostatic conditions (−0.1 V/Pt-black reference electrode) in 10m H2SO4 electrolyte solution.

Amorphous nickel-valve metal-platinum group metal alloy electrodes for hydrogen-oxygen sulphuric acid fuel cells

Powder catalysts were prepared by immersion of amorphous Ni-40Zr and Ni-40Ti alloys containing a few at % of platinum group elements in HF solution. This treatment led to preferential dissolution of the valve metal and nickel with a consequent formation of microcrystalline alloy powders consisting of concentrated platinum group elements and some nickel and valve metal. Porous gas-diffusion electrodes prepared by using these alloy catalyst powders were employed for electrochemical reduction of oxygen and oxidation of hydrogen in 1 M H2SO4 at 25°C. The activity of the electrodes prepared from the amorphous alloys containing Pt−Ru, Pt−Rh, Pt and Pd for oxygen reduction was considerably higher than that of the platinum black electrode. Oxidation of hydrogen occurred readily close to the equilibrium potential. Amorphous alloy electrodes containing Pt−Ru, Pt−Rh and Pt were more active than the platinum black electrode for the hydrogen oxidation.