Platinum electrodes particles

Electrophoresis. Electrophoresis, the movement of charged particles in response to an electric potential, has become very important in biochemistry and colloid chemistry. In the present study an apparatus similar to that described by Burton( M2-M5) was used. A U-tube with an inlet at the bottom and removable electrodes at the two upper ends was half filled with acetone. The a Au-acetone colloidal solution was carefully introduced from the bottom so that a sharp boundary was maintained between the clear acetone and the dark purple colloid solution. Next, platinum electrodes were placed in the top ends of the U-tube, and a DC potential applied. The movement of the boundary toward the positive pole was measured with time. Several Au-acetone colloids were studied, and electrophoretic velocities determined as 0.76-1.40 cm/h averaging 1.08 cm/h. 

Ikariyama [2] described a unique method for the preparation of a glucose oxidase (GOD) electrode in their work. The method is based on two electrochemical processes, i.e. electrochemical adsorption of GOD molecules and electrochemical growth of porous electrode. GOD immobilized in the growing matrix of platinum black particles is employed for the microfabrication of the enzyme electrode. It demonstrated high performance with high sensitivity and fast responsiveness. 

Electrodes may be classified into the following two categories as shown in Fig. 4-3 one is the electronic electrode at which the transfer of electrons takes place, and the other is the ionic electrode at which the transfer of ions takes place. The electronic electrode corresponds, for instance, to the case in which the transfer of redox electrons in reduction-oxidation reactions, such as Fe = Fe + e,occurs and the ionic electrode corresponds to the case in which the transfer of ions, such as Fe , , = Fe, occiirs across the electrode interface. Usually, the former is found with insoluble electrodes such as platinum electrodes in aqueous solution containing redox particles and the latter is found with soluble metal electrodes such as iron and nickel. In practice, both electron transfer and ion transfer can take place simultaneously across the electrode interface. 

Fig. 8-40. Transfer currents of redox electrons observed on a platinum electrodes covered with a thin platinum oxide film of PtO in acidic solutions as a function of film thickness hydrated redox particles Fe /Fe at 0.98 V he in acidic solution at pH 0 hydrated redox particles Ce /Ce at 1.0 in acidic solution at pH 3. [From Schultze, 1978 Schultze-Vetter, 1973.]...

Goldmann [4] observed quite curious phenomena when a spark is passed between platinum electrodes. In a mixture containing 3% H2 no flame forms when a charge is introduced tiny particles of platinum fly off the electrodes... 

Nanomaterials can also be applied to glucose biosensors to enhance the properties of the sensors and, therefore, can lead to smaller sensors with higher signal outputs. Carbon nanotubes have been incorporated in previously developed sensors and seen to increase the peak currents observed by threefold.89 Platinum nanoparticles and single-wall carbon nanotubes have been used in combination to increase sensitivity and stability of the sensor.90,91 CdS quantum dots have also been shown to improve electron transfer from glucose oxidase to the electrode.92,93 Yamato et al. dispersed palladium particles in a polypyrrole/sulfated poly(beta-hydro-xyethers) and obtained an electrode response at 400 mV, compared to 650 mV, at a conventional platinum electrode.94... 

Activation (of noble metal electrodes) — Noble metal electrodes never work well without appropriate pretreatment. Polycrystalline electrodes are polished with diamond or alumina particles of size from 10 pm to a fraction of 1 pm to obtain the mirror-like surface. The suspensions of polishing microparticles are available in aqueous and oil media. The medium employed determines the final hydrophobicity of the electrode. The mechanical treatment is often followed by electrochemical cleaning. There is no common electrochemical procedure and hundreds of papers on the electrochemical activation of -> gold and platinum (- electrode materials) aimed at a particular problem have been published in the literature. Most often, -> cyclic and - square-wave voltammetry and a sequence of potential - pulses are used. For platinum electrodes, it is important that during this prepolarization step the electrode is covered consecutively by a layer of platinum oxide and a layer of adsorbed hydrogen. In the work with single-crystal (- monocrystal) electrodes the preliminary polishing of the surface can not be done. 

Platinum Hydrosol or Colloidal Platinum.—A solution of platinum hydrosol or colloidal platinum in water is easily prepared by sparking between platinum electrodes immersed in ice-cooled water,8 a current of about 10 amperes and 40 volts being employed. The electrodes consist of thick platinum wire, and, when placed from 1 to 2 mm. apart, sparking takes place, particles of the metal being tom off and suspended in the water. The liquid thus obtained is allowed to stand overnight, and decanted from any sediment. It has a dark colour, but the individual metallic particles cannot be distinguished even with the aid of a microscope. 

On the other hand, Chen et al. developed polypyrrole film electrodes containing nanodispersed platinum particles and investigated their catalytic properties for the electro-oxidation of hydrogen [13]. They confirm the remarkable electrocatalytic activity of these PPy/Pt films compared to bulk platinum electrodes, as the film thickness increases to 5 pm. 

Fig. 20.10. Point-by-point platinum NMR spectra of carbon-supported platinum electrodes. (1) As received, 2.5 nm average particle diameter (2) cleaned, 2.5 nm (3) cleaned, 2.0 nm (4) cleaned, 8.8 nm. The...

Impedance samples of 13 mm diameter and 0.3 mm thickness were pressed in a die, mounted between platinum electrodes in an oven and the complex impedance measured between 10 Hz and 10 MHz. The spectra shown in Fig. 1 show a low frequency inter-particle relaxation (of no further interest to us) and an intra-particle relaxation associated with cation exchangeable sites. These relaxations have peak frequencies which exhibit the simple Ahrrenius behaviour shown in Fig. 2, ie... 

In 1976 Leban et used this approach to study the interaction of a platinum electrode with several particles, among them the water molecule and halide ions. The cluster used was taken to be a model of the Pt( 111) surface and contained only five platinum atoms. In this work the iterative extended Huckel molecular orbital (lEHT) method was used. The stability of the adsorption of the water molecule and of the ions was tested by computing the charge transfer to the cluster and the total energy of the system for various positions of the adsorbate on the surface. 

Similar observations concerning the electro-oxidation of methanol were made by Ulmann et al, using platinum micro-particles dispersed into polypyrrole films (from 100 to 700 nm thickness) deposited by cyclic voltammetry on a gold electrode [152]. The platinum loading was varied from 10 pg/cm to 300 pg/cm, leading to an increase in the current density (recorded after 12 hours of methanol oxidation at a constant potential) for platinum loadings up to 150 pg cm after which the current density reaches a plateau. 

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