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.

In a high‐purity closed system, potential regions at which very slow reactions are rate‐controlling were accurately separated and measured. Tafel regions and the possible reaction mechanisms on a Pt electrode in helium‐saturated 1MH2SO4 normalfrom the H2 normalto the O2 formation reactions were determined. Effects of dermasorbed H and O atoms on transient and steady‐state reaction rates were shown. Maximum oxidizable and reducible impurity levels were quantitatively determined both in solution and as adsorbed species on the working electrode surface. It was shown that the impurity levels were very low. Very small additions of hydrogen or oxygen in the critical transition region from net cathodic to anodic reactions did not appear to have catalytic effects. However, at oxygen partial pressures above 10−7 atm, a poisoning effect was apparent.

A tight electrochemical system was constructed in which the PO2 above the cell solution was <10−9 atm. Comparing potentials with data from a previous paper (1) showed that very small amounts of O2 leaking into a closed system can have marked effects on potential behavior at low PH2 . Reduction of the oxygen leak to negligible proportions showed that: (a) the Nernst equilibrium relation for the H+/H2 couple holds only for PH2 in excess of 10−6 atm; (b) at low PH2 , trace amounts of O2, even in the presence of several orders of magnitude more hydrogen, acted as an electrode poison causing a positive deviation from the theoretical Nernst behavior; (c) in O2‐free solution, at PH2 normalbelow 10−6 normalatm , the potential remained at 0.18v positive to NHE and was independent of PH2 . The potential‐determining reaction in this region may be an exchange of H− in solution with H atoms dermasorbed in the Pt. The potential vs. oxygen partial pressure relation was essentially the same as found in previous work from this laboratory. Residual hydrogen associated with Pt at potentials from 0.18 to 0.2v did not react with oxygen.

The open‐circuit potential on bright platinum in 1M H2SO4 was measured as a function of oxygen or hydrogen partial pressure from 10−2 to 10−7 atm. The very low rates of H2 or O2 flow which were required were produced by a special gas generator. Potentials predicted by the Nernst equation for the H+/H2 couple were not observed below 10−4 atm H2 partial pressure. A Nernst relation with a slope of 0.06 v/decade of oxygen partial pressure was found. The oxygen leak into the closed system used was found to be about 10−7 atm. Based on the assumption that the resultant dissolved O2 decreases the dissolved H2 concentration in the solution at the electrode surface, an equation was developed for obtaining the effective H2 partial pressure.

Using single anodic constant‐current pulses, the steady‐state concentration of carbon monoxide already adsorbed on the surface of a bright Pt electrode in 1MH2SO4 and the additional amount of CO adsorbed during the application of the pulse has been determined. At potentials of 0.3–0.4v (NHE), surface coverage of one molecule of CO per surface Pt atom was observed at very low CO partial pressures; for CO partial pressures up to 1 atm the coverage increased to about 1.06 CO molecules per Pt atom, indicating that additional CO physically adsorbs on the base chemisorbed layer. At 1.0–1.3v the rate of adsorption of CO was slower than the rate of diffusion (25°C), and indirect evidence suggests that CO is not adsorbed at potentials above 1.3v. The mechanism of oxidation of CO appears to be an electrochemical oxidation of water to form chemisorbed oxygen atoms, which then rapidly react with chemisorbed CO to form CO2 .