Potentiostatic Current-Potential Measurements on a Platinum Electrode in a High-Purity Closed System

The anodic oxidation of platinum in 1N H2SO4 is studied by using opencircuit transients to determine Tafel slopes and by following film growth optically with an ellipsometer. The Tafel slope values are found to be proportional to the film thicknesses measured with the ellipsometer. This result is interpreted in terms of an ionic conduction model in which the overpotential appears across the anodic oxide film, and the logarithm of the ionic current density is proportional to the field in the oxide. The results are compared with the results of similar measurements on iron and tantalum. Although platinum, iron, and tantalum have quite different chemical properties, and their oxides span a thickness range from a monolayer to several thousand angstroms, it is concluded that the same basic process is responsible for the anodic oxidation of the three metals." Electrochemical Society Active Member.Electrochemical Society Student Member.

Section: Methodssupporting

confidence: 72%

“…Vagramyan and Sutyagina (9) reported that alternating current can effect the grain size, brightness, and porosity of electrodeposited metals. Marchese (I0) showed that the superposition of a.c. on d.c. reduces internal stresses in electrodeposited nickel.…”

Section: The Effect Of Superimposedmentioning

confidence: 99%

The Anodic Oxidation of Platinum: Evidence for a High-Field Ionic Conduction Mechanism

Ord

1971

“…As noted by Schuldiner et al (29), the dissolved oxygen penetrated more deeply than the derma when Pt was anodized at 1.7v because the effects of the dermasorbed oxygen could be detected for extended periods of time after the potential had been lowered below lv. This observation was explained by diffusion of absorbed oxygen from the metal interior into the dermasorbed region.…”

Section: Discussionmentioning

confidence: 73%

On Dissolved Oxygen in Bulk Platinum

Hoare

1969

The hydrogen overvoltage was determined on the front side of a bright Pt foil in 2N H2SO4 solution while the solution on the back side was stirred with H2, N2, or 02. No change in the ~ was detected when the foil was connected as a diaphragm and when H2 stirring was replaced with 02 stirring on the back side. With the foil connected as a bielectrode, the ~ increased after an induction period depending on the thickness of the .foil when H2 stirring was" replaced with 02 stirring on the back side. These results indicate that under anodic polarization, oxygen can be dissolved in Pt. The dissolved oxygen can penetrate to the front side of the Pt foil where its presence as dermasorbed oxygen modified the catalytic activity of the Pt surface for the H2 evolution reaction. In the absence of anodization, oxygen sorbed from solution can penetrate the Pt lattice no further than the dermasorbed region.

“…Brief aqua regia treatment reduced to to 50 msec, and three representative points were redetermined. (7). 1 of ref.…”

Section: Resultsmentioning

confidence: 98%

On the Activity of Platinum Catalysts in Solution

Warner¹,

Schuldiner²,

Piersma

1967

Self Cite

The effects of thermal treatment and chemical etching of platinum on the specific rate of the chemical reaction of chemisorbed oxygen with hydrogen were determined. The hydrogen was present in electrochemically clean 1M H2SO4 and in the derma of the metal. On successive thermal treatments of bright Pt beads, which were heated to the melting point and then slowly recrystallized under high temperatures, the specific rate varied randomly from trial to trial. Where heating was more uniform, and the cooling rate slower, reaction of hydrogen with Pt-O was usually faster. Repeated aqua regia etching of a given Pt bead caused monotonic improvement until a rate between 0.014 and 0.021 amp/cm 2 was attained. Rates on Pt wire electrodes, which probably differed from the flame-formed Pt beads both in average crystallite size and in number of defects (created by the drawing process and only partially removed by subsequent annealing), were highly variable, but considerably lower than on beads. Surfaces whose activity for the Pt-O/ hydrogen reaction differed manyfold showed no differences in anodic charging curves nor did electrochemical rates of water oxidation at +0.617 and ~0.587v (NHE) or reduction of hydrogen ions at +0.300v differ. It appears that many electrochemical reactions are insensitive to these differences in surface condition. Because of its great sensitivity to catalyst pretreatments, the Pt-O/ hydrogen reaction is identified as a "demanding reaction," especially useful for identifying and examining certain variables affecting contact catalysis in solution. Since impurity sorption is one such variable, the rate of this reaction is one of the most responsive cleanliness tests available. Boudart et al. (1) have pointed out that the rates of ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74