The influence of hydrogen partial pressure, current density, and temperature on the anodic oxidation of sorbed H and the anodic generation of sorbed O were determined. Electrode processes were evaluated and separated to give the following quantities: (a) the amount of H associated with a Pt surface and its immediate vicinity, (b) the extent of reaction of H atoms, absorbed in the metal interior, that migrate to the surface of the metal and are either ionized or react with O atoms, (c) the extent of reaction of H2 from the solution phase, (d) the amount of O adsorbed on the Pt surface, and (e) the amount of O absorbed in the Pt surface layers (skin).The kinetics of the open‐circuit reaction of galvanostatically determined amounts of sorbed O with H2 were determined. This investigation showed that absorbed O in Pt significantly affects coulometric measurements at pulse lengths longer than about 1000 µsec. The presence of absorbed O in the Pt can also materially affect the reaction rate of chemisorbed O with H2. Under the experimental conditions, transport of reactants on the solution side was fast enough so that diffusion did not limit processes in either the H ionization or O sorption regions. The data indicated that migration of adsorbed species on the Pt surface to active sites was rate controlling in the O sorption region, except in the case of reaction of adsorbed O with H2 when significant amounts of O were absorbed in the skin of the Pt. In this case the chemical reaction rate between adsorbed O and H2 was retarded so that this chemical step appeared to be rate determining. Reaction rates of the adsorbed O and H2 reaction under open‐circuit conditions were determined at varying temperatures, adsorbed and absorbed O concentrations, and H2 partial pressures.

Under potentiostatic, steady-state conditions and at anodic potentials above 0.7v (NHE), the rate of oxidation of molecular hydrogen decreases at a high activity Pt electrode in 1M H2SO4. It is shown that this decrease is not owing to the formation of oxygen species on the electrode surface. It is believed that this passive behavior of Pt is due to anion adsorption, at least between 0.7 and 1.2v. Depending on potential and previous potential sequence, passivity in this region is evidently sensitive to the amount of sulfate ion adsorbed, its heat of adsorption, and the presence of dermasorbed oxygen. At higher potentials both sorbed oxygen species and sulfate ion may be present and may contribute to the passivity. In the 0.7-1.2v passive region, hydrogen oxidation is electrochemical. There is no significant chemical oxidation via an oxygen intermediate. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 142.58.129.109 Downloaded on 2015-05-31 to IP

A technique was used which allowed the confirmation of surface cIe'mliness of bright platinum electrodes during overw)lt,~ge me'tsurcments.As the current density was increased, three consecutive ~ vs. i relationships were observed, n = a: + bLi (I) , = a~ --(0.026 -4-.003) log i (II) n = aa --(0.105 4-.015) log i.(III) The current density at which the transition from (II) to (III) occurred was dependent on the rate at which hydrogen ion diffused into the double layer. The mechanism of hydrogen overvoltage on platinum is discussed in view of these results. The true are~t of the platinum electrode was determined from double-layer capacity me~surements. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 35.8.191.249 Downloaded on 2015-03-08 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 35.8.191.249 Downloaded on 2015-03-08 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 35.8.191.249 Downloaded on 2015-03-08 to IP

The effect of hydrogen pressure on the hydrogen overvoltage of bright platinum was determined in acid. From the anodic and cathodic overvoltages, kinetic parameters were determined. A mechanism controlled by slow combination of hydrogen atoms adsorbed on the platinum surface fits the experimental data. From the Langmuir adsorption isotherm it is shown that the surface of the active platinum electrode at equilibrium is sparsely covered with hydrogen atoms.

The potential of saturated α-palladium in hydrogen-stirred solution compared to a Pt/H2 electrode in the same solution is 0.0495±0.0005 v. The potential-determining reaction on α-palladium is independent of hydrogen pressure. The potential-determining equilibrium is postulated to be, H++e= lim Pd(Pd−H)α. Pure palladium spontaneously absorbs hydrogen in hydrogen-stirred solution until the saturation limit of the α phase is reached. This limiting atomic ratio of H/Pd=0.025±0.005. Between a H/Pd atomic ratio of 0.03 to 0.36 both the α and β phases coexist and the mixed potential is determined by that of the α domains. In the H/Pd region 0.36 to 0.6, the potential is a function of the hydrogen content of the palladium.