Characteristic Functions and Parameters in the Theory of Hydrogen Overpotential

Castellan, Gilbert W.

doi:10.1149/1.2428062

Cited by 5 publications

(8 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…is found to be 7.25 x 10 -3 A/cm 2. Equation [13] is similar to the one derived by Castellan (10). Schuldiner (8) has shown that for 0.05 to 0.7V, im is independent of potential.…”

Section: H2 Dissociation 41mentioning

confidence: 69%

Mechanisms and Kinetics of H2 Dissociation and Open-Circuit Accumulation of H Atoms during the Formation of the Equilibrium H2/H+ Electrode on Platinum

Rosen

Schuldiner²

1970

J. Electrochem. Soc.

View full text Add to dashboard Cite

The rate at which dissolved H2 dissociates and accumulates on a clean, H-and O-free Pt electrode as the reversible H2/H + electrode is formed has been studied under dissociation, diffusion, and mixed control. The kinetics of the open-circuit hydrogen accumulation reaction (h.a.r.) in H2-saturated (I atm) IM H2SO4 were determined by a galvanostatic double-pulse method in which the first pulse strips the surface, and the second pulse measures the amount of H accumulated in a given time. Under dissociation control, the accumulation of the first 70% of the equilibrium concentration of H obeys a second-order kinetic relation in which the maximum rate at zero time is 4.46 mA/cm 2. As the h.a.r, proceeds, the initial reaching of zero volt cannot be equated with equilibrium of the H2/H + reaction. A slower rearrangement of adsorbed and dermasorbed H atoms occurs before thermodynamic equilibrium is reached. The hydrogen oxidation limiting current density of 2 mA/cm 2 (0.05-0.7V, vigorous H2 stirring) is shown to be the geometric average of idiss,rnax (4.46 mA/cm '2) and idiff,max (geom) (7.25 mA/cm2). This mixed control indicates that diffusion causes the effective H2 partial pressure at the electrode surface to be reduced from 1 to 0.45 atm. Only a small fraction of the total number of Pt atoms which are associated with H atoms at equilibrium are active dissociation sites. Non-faradaic charging corrections were found to be complex and involved adsorption/desorption processes as well as doublelayer charging.

show abstract

“…is found to be 7.25 x 10 -3 A/cm 2. Equation [13] is similar to the one derived by Castellan (10). Schuldiner (8) has shown that for 0.05 to 0.7V, im is independent of potential.…”

Section: H2 Dissociation 41mentioning

confidence: 69%

Mechanisms and Kinetics of H2 Dissociation and Open-Circuit Accumulation of H Atoms during the Formation of the Equilibrium H2/H+ Electrode on Platinum

Rosen

Schuldiner²

1970

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…Using these definitions, the steady-state conditions are written in detail and in their functionality. i--j = ]2(01, Cl) [9] i --j = f3 (cl) [10] j = f4(01, ul) [11] j = I5(ltl, u2) [ …”

Section: The Steady-state Conditionsmentioning

confidence: 99%

“…Considering only the functionality we conclude from Eq. [8], [9], and [10] that s can be expressed as a function of i and i-j only. Successive elimination of c2, 82, u2, Ul, cl, and 81 from Eq.…”

Section: Solution Of the Equationsmentioning

confidence: 99%

“…Quantities such as (d81/ds)o, (dul/dS)o, etc., are then eliminated between these equations. The calculation is simplified considerably if parameters of a type described earlier (10) are introduced in place of (d81/ds)o, etc. We obtain finally…”

Section: The Initial Slopementioning

confidence: 99%

“…Otherwise hydrogen would not enter the membrane when it is made cathodic. If i6o were larger than ilo the palladium would have to be anodic for hydrogen to enter (10). Vetter (11) quotes the two possible values of 10.1 or 0.099 for the ratio, i6o/ilo, which were determined by Knorr (12) from the mixed potential of a supersaturated Pd-H alloy in 2N H2SO4.…”

Section: The Initial Slopementioning

confidence: 99%

See 2 more Smart Citations

The Transmission of Electrolytically Deposited Hydrogen through a Palladium Membrane Electrode

Castellan

1964

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

A sequence of elementary steps is postulated to describe the transport of hydrogen through a palladium membrane electrode. The amount of hydrogen transmitted per square centimeter of the membrane is described by a current density, --j, while the rate of deposition of hydrogen per square centimeter is described by a polarization current density,--i. It is shown in general, without reference to the particular mechanism, that j is a linear function of i at low values of i, and that the derivative, (di/dj)i=o, is a linear function of the membrane thickness L, provided only that Fick's law in simple form holds; the slope of the plot of (di/dj)~=o vs. L is independent of conditions on the exit side of the membrane. It is also shown in general that if conditions are the same on both sides of the membrane at equilibrium, no more than one-half of the hydrogen deposited can be transmitted. The postulated mechanism predicts that the rate of transmission should reach a limiting value, --Jm, at high values of --i. For thin membranes, 1/('--jm) should be a linear function of L. The slope of 1/(--jm) vs. L depends on the diffusion coefficient of hydrogen atoms in palladium and is independent of the rates of the surface reactions, although in some instances it depends on 0o, the equilibrium coverage of the surface by hydrogen atoms. In Parts II and III some experimental data are treated in terms of this mechanism.We have studied the transmission of electrolytically deposited hydrogen through palladium. In this paper, a mechanism is postulated and the rate equations are arranged in a form suitable for graphical treatment of the data. (The side of the membrane on which hydrogen atoms are deposited will be called the entrance side, or side 1; the other side will be called the exit side, or side 2.) In Part II (1) data are presented on the transmisison of hydrogen if the exit side of the foil is in contact with a solution of a strong oxidizing agent, e.g., Ce +4, and if it is in contact with hydrogen gas. In Part III (2) the effects of varying the temperature and the hydrogen pressure on the exit side of the foil are described. ExperimentalThe experiment may be described as follows. Two compartments are separated by a palladium foil. The compartment on the entrance side contains a sulfuric acid solution and a platinum anode; the entrance side of the palladium foil is the cathode. The compartment on the exit side was filled in different ways; we have used Ce(SO4)2 solution, H2SO4 solution, gaseous hydrogen, and water. A current, i (amp/cm2), is passed in the entrance compartment between the palladium membrane cathode and the platinum anode. The rate of deposition of hydrogen atoms on the entrance side of the foil is --i. The amount of hydrogen transmitted to the compartment on the exit side is measured and expressed as an equivalent current density, --j.The problem is to determine the dependence of j on the parameters of the system, particularly on the polarization current density, i, and the membrane thickness, L. Some General Prope...

show abstract

Electrode Processes

Schuldiner

1964

Recent Progress in Surface Science

View full text Add to dashboard Cite

Characteristic Functions and Parameters in the Theory of Hydrogen Overpotential

Cited by 5 publications

References 4 publications

Mechanisms and Kinetics of H2 Dissociation and Open-Circuit Accumulation of H Atoms during the Formation of the Equilibrium H2/H+ Electrode on Platinum

Mechanisms and Kinetics of H2 Dissociation and Open-Circuit Accumulation of H Atoms during the Formation of the Equilibrium H2/H+ Electrode on Platinum

The Transmission of Electrolytically Deposited Hydrogen through a Palladium Membrane Electrode

Electrode Processes

Contact Info

Product

Resources

About