The adsorption of hydrogen on platinum

In contrast to the problem of oxygen adsorption, it has been clearly recognised since the work of Slygin and Frumkin [52] that a monolayer of hydrogen is adsorbed in the atomic form on Pt in the potential range from the equilibrium hydrogen potential to about 0.3 V more positive. They used equilibrium charging curves and later impedance measurements [53] but it 

Energy losses of 5.5 eV electrons on an oxidized platinum electrode surface 

It is evident that a satisfactory proof of the crystallographic origin of the multiple states of hydrogen adsorption depends on the ability to prepare and 

Each low-index face of Pt has comparable subtleties in its behaviour related to the method of preparation and also to the adsorbability of solution components, particularly anions. Pt is probably the extreme example of a surface which must be prepared and transferred with the utmost attention to the details of each step. At the time of writing, there appears to be a reasonable consensus of informed opinion about the voltammetric characteristics of a clean Pt surface of given orientation, although disagreements remain about the origin of some of the observed phenomena. 

As mentioned above, Hubbard and his co-workers has shown that the adsorption of iodine provides an excellent protective layer for Pt surfaces. This has led them to study the electrochemical properties of this surface and to provide a model of what the combination of ex-situ techniques combined with electrochemistry can provide in terms of detailed information about the structure of the surface layer. 

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Hence, it appeared that the story was complete and the adsorption of hydrogen on platinum understood. However, considerable controversy was arising even as the definitive experiments were being performed. In 1959, Schuldiner carried out kinetic measurements on the H2-evolution reaction... 

However, for some electrocatalytic reactions, such as the electrooxidation of alcohols, aldehydes or acides, and also the electro reduction of oxygen, lead adatoms can exhibit a promoting effect (3-7). Moreover, lead can change the selectivity in the case of electrocatalytic reductions of nitrocompounds (8), whereas it inhibits the adsorption of hydrogen on platinum (9,10),... 

Introduction to Experimental Approaches for the Adsorption of Hydrogen on Platinum... 

The first example concerns the adsorption of hydrogen on platinum in acid media. The second deals with the comparative adsorption of carbon monoxide on noble metals in aqueous medium, with a special emphasis on platinum and palladium. The third example is a discussion of the contribution of in situ reflectance spectroscopy to solving certain problems encountered in electrocatalysis. Finally, the last example concerns nonaqueous solvents in particular and the detection of species in the double layer. 

The adsorption of hydrogen on metal electrodes such as platinum has been studied extensively in electrochemical systems over the last several decades. The mechanism for the hydrogen oxidation reaction on a Pt electrode in an acid electrolyte proceeds through two pathways, Tafel-Volmer and Heyrosky-Volmer, both of which involve the adsorption of molecular hydrogen followed by a... 

Another empirical equation is the Temkin equation proposed originally by Slygin and Frumkin (1935) to describe adsorption of hydrogen on platinum electrodes in acidic solutions (chemisorption systems). The equation is (Rudzinski and Everett, 1992) ... 

Adsorption of Hydrogen on Platinum According to Measurements of the Capacity of Polarization, Zeit. Elektrochem. 55, 114-119. 

S. Cerny, M. Smutek, F. Buzek, The calorimetric heats of adsorption of hydrogen on platinum films. J. Catal. 38, 245-256 (1975)... 

Electrode processes can be retarded (i.e. their overpotential is increased) by the adsorption of the components of the electrolysed solution, of the products of the actual electrode reaction and of other substances formed at the electrode. Figure 5.43 depicts the effect of the adsorption of methanol on the adsorption of hydrogen at a platinum electrode (see page 353). 

Mention has been made variously that the rate of adsorption of hydrogen on nickel and iron is very fast at room temperature. In fact, the rate is so fast that the limiting factor appears to be the rate at which gases enter the reaction chamber through the stopcock from the reservoir. This essentially instantaneous adsorption has been observed for many other metals, including platinum, rhodium, palladium, tungsten, tanta-... 

Harting and Spohr investigated oxidation of methanol on the (2 11) face of a platinum single crystal.123 Similar to the reaction pathway on the (1 1 1) crystal face water plays an important role. That is the adsorption of methanol on charged and uncharged surfaces is strongly enhanced by the formation of a hydrogen bond to a... 

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