Electrode Platinizing Technique

Chemical-deposition Electrode. Chemical techniques can also be employed in the fabrication of catalyst layers by platinizing the surface of a Nafion membrane. One approach [65, 66] is to expose one side of the Nafion membrane to a reductant solution (e.g., hydrazine solution) and the other side to a platinic acid solution. The reductant diffuses across the membrane to react with platinic acid and form a Pt catalyst layer. In another impregnation-reduction method [3, 67, 68] a cationic salt, such as Pt(NH3)4Cl2, is first impregnated into the Nafion membrane, followed by exposing this membrane to a reductant, such as NaBUj. As shown in Figure 19.13, a dense and porous platinum film can be formed using this chemical deposition technique. 

The basic technique is as follows Coarse (10-30/x) capillary tubes are drawn out. The metal to be used is then melted into the tube lumen. The metal-filled tubes are then heated and drawn down to 1 /x or less (see Section 4.3 for pulling techniques). The electrode tips may then be plated, and they are usually platinized. Platinizing technique was discussed in Chapter 2. 

In the choice of an analytical technique for following the course of a reaction, it is important to recognize that no aspect of the measurement should affect the kinetic processes occurring in the system. For example, a solution conductivity method that uses platinized electrodes should not be used in the study of a reaction that is catalyzed by platinum black. 

Impedance diagram technique. The polarization cell consisted in a transparent plastic tube that was adhered to the paint surface by means of a silicone sealer. The tube contained distilled water and a 25 cm platinized titanium sheet, which was used as auxiliary electrode. Measurements were made with... 

The similarity of the shape of the voltammetric curves of platinized system to those reported for electrodes treated by the fast repetitive potential perturbation technique or obtained by annealing electrodeposited platinum and the appearance of signs characteristic for stepped surfaces allows us to assume that these phenomena should be ascribed to the similarities in the surface structure. 

There is a continuous interest in the spectroscopic studies of adsorbed species (for instance, [EMIRS], potential modulated reflectance spectroscopy [PMRS]). The EQCM technique was used recently for the study of chemisorption and oxidation of methanol at polycrystalline (platinized) Pt. It was found that accumulation of strongly adsorbing species at the electrode surface is accompanied by a decrease in the mass, relative to the background electrolyte, and the rate of this decrease is an indication how the surface becomes covered by adsorbates. 

A possibility to consider polyciystalline platinum surface as some combination of low index surfaces or as some disordered single crystalline surface surely caimot be immediately concluded from the values of zero charge potentials exclusively. Experiments with some intermediate model systems more or less reduceable to simple additive combinations of several planes, or of terraces and steps, are of increasing interest. Microfacetted electrodes, various types of nanoparticles prepared by precise non-electrochemical techniques, non-coalesced electrodeposited particles, " and single platinum microspheres deposited on micro-electrodes, as well as highly ordered templated electrdeposits can be considered as most ordered real platinum materials helpful to discover stractural effects at atomic level. However they all are still too simple to compare with, to say, platinized platinum, and attempts to electrodeposit the dispersed metallic multilayers of more and more ordered type ° are also relevant. 

A technique for effectively increasing the electrical area of an electrode without increasing its mechanical dimensions is platinization. Colloidal platinum black is plated onto the metallic electrode surface. The surface granularity thus produced can increase the effective electrode surface by as much as 10,000 times, with an equivalent reduction in current density at the interface. The granularity produces more points at which current lines can... 

The preparation of platinized electrodes consists of depositing colloidal platinum (platinum black) upon the working surfaces. This is accomplished by the use of conventional electroplating techniques. The electrode to be platinized is connected as the cathode, and a piece of pure platinum sheet forms the anode of an electrolytic cell. Kohlrausch and Holborn formula platinizing solution is employed as the electrolyte. Its chemical composition is platinum chloride (H2PtCl2) 3 % dissolved in 0.025 % lead acetate solution. This platinizing solution may be obtained in 2-oz bottles from the Hartman-Leddon Co. in Philadelphia or from the Arthur H. Thomas Co., also of Philadelphia. 

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