Platinum black electrode

The electrophoresis cell usually consists of a horizontal glass tube, of either rectangular or circular cross-section, with an electrode at each end and sometimes with inlet and outlet taps for cleaning and filling (Figures 7.5 and 7.6). Platinum black electrodes are adequate... 

Bagnell LJ, Jeffery EA. Electrolytic hydrogenation and hydrogenolysis of phenols at platinum black electrodes. Aust J Chem 1980 33 2565-2569. 

Hydrogen electrode — A gas electrode where purified hydrogen gas is dissolved, usually in an aqueous solution, in which an inert electrode, preferably a - platinized platinum (- platinum black, -> electrode materials) electrode is inserted. The hydrogen electrode is of exceptional importance in electrochemistry because the -> standard hydrogen electrode (SHE) provides by convention a reference potential for all half reactions and thus the thermodynamic reference point for all energy calculations. An alternative form is the -> dynamic hydrogen electrode (DHE). 

Electrodeposition of glucose oxidase and bovine semm albumin on a platinum black electrode followed by glutaraldehyde cross-linking and covered with a polyethylene glycol-polyurethane outer membrane Blood glucose [38]... 

If the discharge step in the hydrogen electrode reaction, as discussed earlier, really is Reaction 13 then for platinum black electrode this would represent the step e (Pt) —> e aq. The following cycle is thus worth considering... 

Only if E°in = 0—i.eif the standard hydrogen electrode is zero on an absolute scale—can one deduce from Baxendale s considerations that the potential neecssary to produce e aq in its standard state from a platinum black electrode is —2.6 volts. In fact in our work we used total potential differences across the cell much less than 2.6 volts. (One can of course make E°= 0 on an absolute basis simply by selecting the appropriate standard state of e iPt) for this to be so, even if it turns out to be 1040. However, if one arbitrarily takes some reasonable standard state for e Ft) then E°i0 0 on an absolute basis). 

The ability of an element to be oxidised or reduced in a cell is used to obtain a value for the electrode potential. If an electrode is immersed in one molar hydrochloric add and hydrogen gas at a pressure of I atmosphere is bubbled over the platinum black electrode to maintain equilibrium, it is possible to obtain a value for the electrode potential of any clement. 

The platinum electrode can be improved by an active electrolytic process forming a platinum black surface. The reduced polarization impedance is due to an increased effective metal surface area (fractal surface). The electrode is prepared in an electrolyte containing (e.g., 3% platinum chloride), with the platinum as the cathode. Platinum black is deposited on the surface, and also here there are optimum values for current density and quantity of electricity a current density of about 10 mA/cm and a quantity of electricity (charge) of about 30,000 mA s/cm is recommended (Schwan, 1963). Best results are obtained if the platinum surface is sandblasted before platinum black deposit. However, the surface may be fragile, and a protein layer formed with tissue contact may easily smooth the micro-rough surface and increase polarization impedance. Platinum black electrodes are best stored in distilled water and short-circuited (Schwan, 1963). 

Figure 7.16 Polarization impedance for monopolar platinum black electrode in physiological saline solution. Constrictional series resistance subtracted. Data from Schwan (1963),...

The series capacitances of some other metal/electrolyte interfaces are given by Geddes (1972). They are always lower than the AgCl or platinum black electrodes in 0.9% NaCl. For. stainless steel, it was given as 40 pF/cm at 20 Hz ( = 500 pS/cm ). 

Fig. 14.5. A.c. and d.c. conductivities of tin-exchanged mordenite with R = 0.2. Platinum black electrodes. The cell is purged with hydrogen saturated with water at 20 C. Measuring temperature 25 °C. Symbols , d.c. conductivity O, a.c. conductivity. At a relative exchange of 40 the cell was purged with dry hydrogen for one week s (with permission).

For materials with mixed electronic and ionic conduction e.m.f. measurements on a concentration cell have often been used to separate the different contributions. In this method a concentration gradient is established across the sample, which is equipped with electrodes reversible to only one ion, e.g. platinum black electrodes and different hydrogen partial pressures. The potential difference is measured, preferably at several partial pressure differences. The transference number of the ion can then be deduced from the deviation from the Nemst law behaviour by use of the equation " ... 

A simplification of the technique, applicable for protonic conductors is shown in Fig. 27.2. The cell is here equipped with platinum black electrodes, which can be made blocking/non-blocking for protons by purging the cell with either nitrogen or hydrogen gas. This system has been used, for example, by Maiti Freund (1981) on hydroxyapatite. 

Niedrach has used constant current transients to study the adsorption of several hydrocarbons from acid and alkaline electrolytes at 25°C on supported platinum black electrodes. An... 

Figure 10. Galvanostatic oxidation curves for hydrocarbons adsorbed on platinum black electrodes at 25°C from 5N H2SO4 (1) C2H4, (2) C4H10, (3) C3H8, (4) C2H6, (5) CH4, (6) H2 [from Niedrach, J. Electrochem. Soc. Ill...

Foral MJ, Langer SH (1988) The effect of preadsorbed sulfur on nitric oxide reduction at porous platinum black electrodes. Electrochim Acta 33 257... 

The porous platinum black electrodes were fabricated by compressing platinum black powder under high pressure (DeRosa et al, 1971). 

Fig. 4 Carbon monoxide stripping scan of a DMFC cathode at different times in a life test. The reference shown is for a pure platinum black electrode. (Reproduced from Choi et al. 2005)...

The first new system is shown in Fig. 1.3 and is the so-called hydrogen electrode. It comprises a platinum black electrode dipping into a solution of hydrochloric acid. Hydrogen gas is bubbled over the surface of the electrode. The reaction which determines the electrode potential again depends on the transfer of an electron between the Fermi level of the electrode and an ion in solution ... 

A similar idea concerning the combination of charging curves and gas chromatography in the study of carbonaceous species on a Teflon-bonded platinum-black electrode was used in reference 60. The species were formed by adsorbing propane first and dehydrogenating the species afterwards. However, the amount of CO2 cannot be deteripined quantitatively since diffusion of CO2 into the electrolyte takes place. Only the amount of carbon dioxide that leaves the side of the electrode adjacent to the gas phase was determined. 

Practical units of fuel cells could not operate without porous electrode structures. Porous electrodes with their large electrochemically active surface allow reasonable currents to be supplied at acceptable losses due to polarization (see section 2 of chapter II). Although a few properties, like maximum available surface of electrocatalyst and hydrogenation and dehydrogenation of carbonaceous species for Teflon-bonded platinum black electrodes, and formation of oxygen layers for Raney nickel electrodes, have been discussed in preceding chapters, a discussion of the parameters that determine the operation of porous electrodes had to be offered in a separate chapter. While the empirical aspects concerning the operation of porous electrodes are covered in this chapter, theoretical aspects are dealt with in chapter XVI. 

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