Platinum electrodes, platinized

FIGURE 4 Bode plot of the impedance (a) magnitude and (b) phase of a microfabricated interdigated microsensor electrode array measured over the range 0.1 mHz to 100 kHz in 0.5 M KCl at 25°C. Showing the effect of electrode platinization ( ) unplatinized platinum electrodes ( ) platinized platinum electrodes. 

Sometimes the term normal hydrogen electrode (and respectively normal potential instead of standard potential) has been used referring to a hydrogen electrode with a platinized platinum electrode immersed in 1 M sulfuric acid irrespectively of the actual proton activity in this solution. With the latter electrode poorly defined diffusion (liquid junction) potentials will be caused, thus data obtained with this electrode are not included. The term normal hydrogen electrode should not be used either, because it implies a reference to the concentration unit normal which is not to be used anymore, see also below. 

FIGURE 10.9 Galvanostatic charging curve for a platinized platinum electrode in 0.1 M H2SO4 solution (1) anodic scan, (2) cathodic scan. 

Podlovchenko Bl, Petrii OA, Frumkin AN, Lai H. 1966. The behaviour of a platinized-platinum electrode in solutions of alcohols containing more than one carbon atom, aldehydes and formic acid. J Electroanal Chem 11 12-25. 

Christensen PA, Hamnett A, Weeks S A. 1988. In-situ FTIR study of adsorption and oxidation of methanol on platinum and platinized glassy carbon electrodes in sulphuric acid solution. J Electroanal Chem 250 127-142. 

The glass tubes contain mercury and are firmly fixed in the ebonite cover of the cell so that the distance between the electrodes may not change during the experiment. Contact with the platinum electrodes is made by dipping the copper wires of the circuit in the mercury contained in the tubes. The coating of the electrodes with platinum black is carried out in order to inhibit polarization. When examining certain electrolytes, platinized electrodes cannot be used since platinum black may catalyze the decomposition or the oxidation of the electrolyte. The cell is maintained at constant temperature thermostatically, as conductivity increases rather significantly with temperature. 

The differential capacity can be measured primarily with a capacity bridge, as originally proposed by W. Wien (see Section 5.5.3). The first precise experiments with this method were carried out by M. Proskurnin and A. N. Frumkin. D. C. Grahame perfected the apparatus, which employed a dropping mercury electrode located inside a spherical screen of platinized platinum. This platinum electrode has a high capacitance compared to a mercury drop and thus does not affect the meaurement, as the two capacitances are in series. The capacity component is measured for this system. As the flow rate of mercury is known, then the surface of the electrode A (square centimetres) is known at each instant ... 

Fig. 2.1. Electrode potential during the oxidation of methanol and hydrogen on a platinized platinum electrode (real area = 130 cm2) at constant current i = 5 mA. Base electrolyte = 0.5 M H2S04, room temperature. 

Although a 1,2-diene is not a conjugated diene, it is also electrochemically reducible with platinized platinum electrode in acidic solution to the monoolefin and a saturated alkane18. 

A platinum disk electrode was electrolytically platinized in a platinum chloride solution to increase the surface area and enhance the adsorption power. The platinized platinum electrode was then immersed in a solution containing 10 mg ml l ADH. 0.75 mM and 6.2 mM NAD. After sufficient adsorption of these molecules on the electrode surface, the electrode was transferred into a solution containing 0.1 M pyrrole and 1 M KC1. Electrochemical polymerization of pyrrole was conducted at +0.7 V vs. Ag/AgCl. The electrolysis was stopped at a total charge of 1 C cm 2. An enzyme-entrapped polypyrrole membrane was deposited on the electrode surface. 

The conductance of a solution is the inverse of its resistance, and conductance has units of ohms 1 or mohs. The higher the conductance of a solution, the lower is its electrical resistance. A conductivity meter and conductivity cell are used to determine the effective resistance of a solution. The conductivity cell consists of a pair of platinized platinum electrodes with an area of approximately 1.0 cm2 with spacers designed to hold the electrodes rigidly parallel and at a fixed distance from each other. The cell can be standardized with solutions of known conductivity to obtain the cell constant, k so that the instrument response R... 

Chemically platinized platinum with the roughness factor ISO was used for the same experiment. The resTilt is shown in Fig. 2-43. The oxidation cmrent for eoCOad forms a small peak rather than just a shoulder. Since the roughness factors are almost same for both chemically and electrochemically platinized platinum electrodes, the difference probably stems from the morphology of the platinum. 

The voltammogram for oxidation of COad Is shown Fig. 2—47. The coverage was calculated as 0.7. Like the chemically platinized platinum electrode without Nafion, oxidation current of eoCOad is seen at as low as 330 mV. 

Chemically and electrochemically platinized platinum electrode (180 as roiighness factors for both electrodes) were used as high area platinum electrodes. While they showed slightly different COad oxidation characteristics, their methanol oxidation characteristics were virtually the same. Therefore, the results will be shown for only chemically platinized platinum electrodes. 

Tin was electrochemically deposited on smooth and high area (chemically platinized) platinum electrodes at -300 mV for 10 s. The thermodynamic potentials for tin metal and its ions are ... 

Electrical conductance The conductance measurements were made in a glass cell consisting ot two equivalent electrode sections. Circular platinized platinum electrodes parallel to the plane of the membrane were embedded in each section. The membrane area was 0.98 cm2. Resistance measurements were made with and without the membrane in O.IN NaCl solution. 

The effect of inorganic cations on the electroreduction of nitrate ions at platinized platinum electrodes has been studied in [56, 57]. 

An analog of the platinized platinum electrode is the black or gray nickel electrode, which under certain experimental conditions can be used as the hydrogen electrode instead of the platinum electrode [65]. This electrode can be obtained by electrochemical deposition of nickel under the experimental conditions described in [65]. The real surface areas of these electrodes significantly surpass their geometric surface areas. In addition, potential-dependent adsorption of hydrogen occurs on the nickel surface and the measurement of the hydrogen capacity of the electrode in alkaline medium offers a tool for the determination of the real surface area [66]. 

It was demonstrated that the radiotracer method, using labeled anions, is an adequate tool to follow anion adsorption in the course of voltammetric measurements and to gain simultaneous information on hydrogen and anion adsorption [163]. Coupling voltammetric and radiometric measurements in the study of platinized platinum electrodes gave insight in the anion-hydrogen atom coadsorption process. 

A fast repetitive triangular potential sweep (lO" V s between 0.05 and 1.5 V for 2 h) was applied to platinized platinum electrode [217]. This treatment resulted in a considerable decrease in the real surface area and in the formation of a (lOO)-type preferentially oriented surface structure. 

Fig. 6 Cyclic voltammograms of a platinized platinum electrode (type II) in (a) 0.25 mol dm H2SO4, (b) 0.25 mol dm H2SO4 + 10 mol dm HNO3, and (c) 0.25 mol dm H2SO4 - -10 mol dm HNO3. Sweep rate,...

Even though one is considering the simplified situation of equilibrium, one is still faced with the fact that the absolute potential differences across single interfaces are experimentally inaccessible (Section 6.3.1). However, one can always resort to the convention (see Section 6.3.4) of referring all potentials to an SHE which would consist, e.g., of a platinized platinum electrode in contact with hydrogen gas at 1 atm pressure and a solution of hydrogen ions at unit activity. 

R. Lorenz and H. Wehrlin have also shown that the use of platinized platinum electrodes increases the maximum concentration of the hypochlorite. Carbon electrodes have a 10 to 28 per cent, porosity and the soln. which fills the pores is electrolyzed, but the dissolved salt in the pores cannot be renewed as rapidly as the soln. about the surface of the electrode, and consequently the evolution of oxygen and the production of chlorate, begin sooner, and the maximum concentration of the hypochlorite is less than with platinum electrodes. Part of the oxygen also oxidizes the carbon, and this makes the electrolyte slightly acid, thus favouring chlorate production. 

At a platinum electrode that is slightly activated by platinization, the dissolved hydrogen in various solvents is oxidized nearly reversibly by H2= 2H+ + 2c. We can determine by cyclic voltammetry the standard potential of this process. If the standard potentials in various solvents are compared using a common potential scale, the Gibbs energies of transfer of H+ can be obtained [44], With electrodes other than platinum, it is difficult to observe reversible oxidation of dissolved hydrogen [44 b],... 

It is desirable to measure R (and thus G) at a high frequency in order to reduce Xc to a negligible value compared to R. Unfortunately, other complications arise if the frequency is increased above a few kilohertz, and therefore other means must be devised to decrease Xc. A commonly used remedy is to increase the surface area and thus the capacitance of the electrodes as much as possible. A 100-fold area increase is obtained by platinizing the electrodes, that is, electrodepositing a layer of platinum black onto the platinum electrodes, usually from a solution of chloroplatinic acid [8]. 

Six conductance cells, LC-1 through LC-7, each constructed of borosilicate glass with platinized platinum electrodes, are shown in Figure 5 (LC-7 is similar to LC-5 and... 

---