Preparation of Solid Electrodes for Hydrogen Overpotential Studies

Makrides, A. C.; Coltharp, Marcellus T

doi:10.1149/1.2427721

Cited by 8 publications

(2 citation statements)

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“…Electrodes produced by cathodically activating a surface formed under highly oxidizing conditions are less likely to be contaminated than electrodes treated in any of the conventional ways, e.g., by heating in hydrogen at 400~176 (1, 3). The large exchange current found here is not caused by a high roughness factor as we have shown already (12).…”

Section: Exchange Currentsupporting

confidence: 82%

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Hydrogen Overpotential on Nickel in Alkaline Solution

Makrides¹

1962

J. Electrochem. Soc.

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The exchange current, Tafel slope, stoichiometric number, and limiting anodic current of the hydrogen reaction on nickel in 0.1N NaOH depend on the pretreatment and the polarization history of the electrodes. The discharge step of the Volmer-Tafel mechanism is rate-determining on surfaces characterized by high fractional coverage with adsorbed hydrogen. Such surface states are metastable however and are transformed on anodic-cathodic cycling to states which adsorb hydrogen weakly. The exchange currents for the discharge and combination steps are then about equal.The rate of the hydrogen reaction on nickel shows the familiar exponential dependence on potential; the Tafel slope b is about 0.1v and the exchange current io is in the range 10 -7 to 10 ~ amp/ cm ~. The hydrogen overpotential on nickel is intermediate therefore between the large overpotentials on mercury and lead (io ~ 10 -~ amp/cm ~-) and the relatively small overpotentials on metals of the platinum group (io ~-, 10 ~ amp/cm~).Nickel dissolves slowly in acid and at a negligible rate in alkaline solutions. Side reactions can be neglected in the latter if the solution is free from reducible impurities, mainly oxygen. In spite of the relative simplicity of this electrochemical system the mechanism of the reaction is in doubt. A number of authors (1, 3, 4, 8) concluded from the magnitude of the Tafel slope and from the value of stoichiometric number that the discharge step, H+q -e---) H,~., controls the over-all rate. A simple slow-discharge mechanism does not explain however the frequently observed time-dependence of overpotential, nor does it give correctly the change of overpotential with solution composition.Lukowzew, Lewina, and Frumkin (1) found that the potential of nickel cathodes which had been heated in H~ at 400~176 and cooled in a watersaturated hydrogen atmosphere drifted for some hours after switching on the current. They attributed the drift of potential to reduction of a nickel oxide film formed during cooling.Bockris and co-workers (3, 9) also found a potential drift in the first hour of cathodic polarization. Subsequent polarization curves did not follow the Tafel relation. Bockris and Potter (3) attributed the deviations from Tafel behavior to solution of hydrogen into nickel. They obtained satisfactory Tafel lines by making rapid measurements in the direction of increasing current density only and by using fresh electrodes for every run. Their procedure was opposite to that of Lukowzew, Lewina, and Frumkin (1) who carried out measurements after the potential had reached a steady value. Hoare and Schuldiner (10) found Tafel behavior (in acid solutions) with nickel electrodes i Present address: Tyco Laboratories, Inc., Waltham, Massachusetts.

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Section: Exchange Currentsupporting

confidence: 82%

“…(1, 3). The large exchange current found here is not caused by a high roughness factor as we have shown already (12).…”

Section: Exchange Currentsupporting

confidence: 82%

Hydrogen Overpotential on Nickel in Alkaline Solution

Makrides¹

1962

J. Electrochem. Soc.

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Pore Formation on n-InP

Schmuki

Santinacci

Djenizian

et al. 2000

phys. stat. sol. (a)

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The present work deals with localized dissolution processes of n-type InP(100). Pore growth can be electrochemically initiated on the n-type material in the dark in HCl, HBr and HF solutions and leads after extended polarization to the formation of a porous InP structure. The porous structures were characterized by SEM, AES, and PL measurements. The pore morphology depends strongly on the electrochemical conditions and the type of halogen acid present in the electrolyte. AES depth profiles show that the composition of the porous layer is strongly affected by the electrolyte. For all electrolytes depletion of In was observed; this effect is the strongest for HBr and the weakest for HF. Uptake of electrolyte anions is the highest for HBr and lowest for HF. From scratch experiments it is clear that the pore initiation process is strongly influenced by surface defects. The morphology of the dissolution process also strongly depends on illumination as assessed by an experiment using a laser beam for a local surface illumination. At high illumination intensity, electropolishing instead of pore formation takes place. The finest pore structure was obtained in the dark. Structures formed in HF show visible photoluminescence in the yellow to red range of the spectrum, whereas for HCl and HBr treated samples no significant visible PL was obtained.

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Pore formation on p‐type InP(100)

Schlierf

Lockwood

Graham

et al. 2005

Physica Status Solidi (a)

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PACS 81.05. Ea, 82.45.Vp The present work deals with anodization processes of p-type InP(100) in different halogenic acids. The morphology of the attack depends strongly on the electrochemical conditions and the type of anion present in the electrolyte. Only electropolishing was observed in HCl while the formation of a porous oxide layer was obtained in HF. In HBr, however, pore growth into the bulk material can be achieved.

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Preparation of Solid Electrodes for Hydrogen Overpotential Studies

Cited by 8 publications

References 7 publications

Hydrogen Overpotential on Nickel in Alkaline Solution

Hydrogen Overpotential on Nickel in Alkaline Solution

Pore Formation on n-InP

Pore formation on p‐type InP(100)

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