Investigations of the Kinetics of Hydrogen and Oxygen Reactions on a Platinum Electrode in Acid Solution Using Pulse and Decay Techniques

Abstract

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.

Sorption Behavior of the Overpotential‐Deposited H Species in the Cathodic H 2 Evolution Reaction at Pd and Pt‐Pd Electroplated Composite Electrodes

“…2b) in acidic solution suggests formation of hydride or "dermasorbed" hydrogen (38,39) in a few atomic layers, just below the surface, and this causes the short, almost fiat, potential arrest in the decay curves, an effect not observed at active bright Pt electrodes in alkaline solution. In the case of Pd, due to the appreciable amount of H absorbed (normally >> H adsorbed), it takes a much longer time (>30s) than for Pt (ca.…”

The Mechanism of Electrochemical Oxidation of Organic Fuels

“…However, the implicit assumption of a simple stoichiometry on the surface, that is, the assumption that one oxygen or hydrogen atom is adsorbed per metal atom at saturation, may be questioned. Furthermore it has recently been shown 101 that substantial amounts of hydrogen and even oxygen may be absorbed in platinum, so that care must be exercised in using hydrogen and oxygen charging methods for surface-area determination.…”

On the Differential Thermal Analysis of the Platinum‐Oxygen System

“…This threepronged peak may be interpreted in terms of the desorption of adsorbed hydrogen from two and possibly three kinds of adsorption sites known (14)(15)(16) to exist on the Pt surface. The large background AT may be accounted for by the desorption of dermasorbed (25) and dissolved hydrogen (26,27) in the bulk metal. From x-ray diffraction studies of HNO3 passivated Pt-O alloy samples (1), it was found that the Pt lattice had been expanded suggesting that the dissolved oxygen had entered the Pt lattice.…”