Platinum electrodes aging

FIGURE 1.2 Tafel plots as electrode potential, E, versus the logarithm of the current density, logy, for mercury ( - ), platinized mercury to 1% (o-o), platinized mercury as thin film (a-a), fresh etched silver ( - ), aged etched silver (O-O), polished silver ( - ), bright platinum (H—h), and spongy platinum electrodes (c-c). 

Roughness factors for carbon-supported platinum electrodes are typically between 600 and 2000 [6], and can decrease with age and operation due to catalyst sintering and morphological changes due to stresses in the catalyst layer. When the roughness factor is used as a separate parameter, the BV expression is then shown as... 

Recently data have also been obtained to show that the activity of the platinum changes with change in its degree of dispersion. Thus, it was found in [171] that the specific activity of smooth platinum in stationary electrochemical oxidation of methanol is two to three times greater than that of platinized platinum. The activity of a platinized platinum electrode increases with aging. According to data in [207], the adsorption and electrochemical... 

In studies on Pt dotted silicon electrodes, PMC measurements revealed that tiny Pt dots increased the interfacial charge transfer compared with bare silicon surfaces in contact with aqueous electrolytes. However, during an aging effect, the thickness of the oxide layer between the silicon and the platinum dots gradually increased so that the kinetic advantage again decreased with time.11... 

Types of aging processes such as those described for the adsorption of oxygen and methanol on platinum are also characteristic of the adsorption of other substances and of adsorption on other electrodes. In some cases these changes manifest themselves as a change (mostly an increase) in the adsorption energy with time. In... 

Gold, platinum, cold-rolled steel, and aluminum electrodes were coated with FEP Teflon and then mounted on a plane circular-rotating stage in the gas chamber in such a way that each in turn could become the stationary electrode of a parallel-plate condenser whose vibrating electrode was an aged, uncoated, aluminum... 

The silver-silver chloride electrode consists of a mounted platinum screen that has been heavily plated with silver from a cyanide bath, rinsed, aged in an acidified silver nitrate solution, rinsed, coated with a thin layer of silver chloride by anodizing in a dilute HCl solution (preferably no more than a few days before use), and kept in dilute HCl pending use. This is mounted in a glass sleeve with a small hole in the bottom to admit the cell... 

Electrode-Preparation and Aging. Electrode preparation procedures are given by Keston (14) and by Ives and Janz (II). Electrodes were prepared from a paste containing 90% silver oxide and 10% silver bromate placed on a platinum spiral and heated in a furnace for 7 min at 650°C. Janz and Taniguchi (12) have reviewed the preparation, reproducibility, and stability of this electrode. Taylor and Smith (13) found the equilibrium potential to be stable within 0.02 mV. Electrodes... 

A major difficulty with contact potential work is the provision of a completely inert reference electrode. Poisoned nickel has been used, but aged gold or platinum is more widely applicable. Bewig and Zisman have described reference electrodes of gold and platinum coated with Teflon resin. These electrodes were more stable than the bare metals in wet and dry oxygen, nitrogen and in carbon dioxide, hydrogen and helium. 

Since Pt dissolution is favored by high electrode potential, relative humidity, and temperature, the possibility to limit the risk of electrocatalyst aging is based on the use of Pt-alloy catalyst instead of pure platinum, at least for the cathode, which is characterized by higher potential with respect to anode, and by adoption of operative conditions not too severe in terms of humidity and temperature. While this last point requires interventions on the membrane structure, the study of catalyst materials has evidenced that a minor tendency to sintering can be obtained by the addition of non-noble metals, such as Ni, Cr, or Co, to the Pt cathode catalyst [59, 60], suggesting a possible pathway for future work. On the other hand also the potential application of non-platinum catalysts is under study, in particular transition metal complexes with structures based on porphyrines and related derivatives have been proposed to substitute noble metals [61], but their activity performance is still far from those of Pt-based catalysts. 

The decomposition mechanism of hydrogen peroxide at a metal surface was investigated in greatest detail by R. and H. Gerisher [19], who recorded the electrochemical characteristics of the process in parallel with measurements on the decomposition rate. It was noticed first of all that the condition of the platinum surface had a great effect on all the measured quantities and that the measurements were insufficiently reproducible owing to aging of the electrodes ... 

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