Hydrogen permeation kinetics

The electrochemical hydrogen permeation technique has proved to be a valuable tool in the study of these reaction mechanisms. This is mainly due to the ability to estimate the amount of an intermediate (Hads) in the reaction scheme. Such studies have been presented, for example, by Devanathan and Stachurski, by Bockris et and by Iyer et The applicability of the Volmer-Tafel reaction scheme can be evaluated by considering the kinetic expressions for reactions (22) and (23), together with equilibrium in the absorption process (25)... 

Surface Kinetics of Hydrogen Permeation in Mixed Proton-Electron Conductors 21... 

To the best of our knowledge, there is yet no literature example where surface kinetics has been proven to limit the hydrogen permeation across a mixed pro-ton-electron conducting oxide, and seemingly membrane thicknesses below Lc have thus never been reached. 

The reaction stages and species involved may be expected to be similar on the feed and permeate sides of a hydrogen membrane. If the flux is driven by reaction with oxygen on the permeate side, this side may naturally be quite different, both in terms of ionic species and electronic (holes versus electrons). The formation or presence of water vapor may also play a significant role in hydrogen exchange kinetics. 

Tab. 8 Relationships between the kinetics of hydrogen evolution and hydrogen permeation...

IPZ analysis of the experimentally measured steady state hydrogen permeation rates through AISI 4340 steel are used to estimate hydrogen kinetic diffusion constants and hydrogen diffusivity within the ahoy. Atomic hydrogen permeation transients through an AISI 4340 membrane for different appHed potentials were studied in an electrolyte... 

Table E8.1 Kinetic Data for Hydrogen Evolution and Hydrogen Permeation in AISI 4340 Steel...

Table E8.2 Kinetic Data for Hydrogen Evoiution and Hydrogen Permeation for Samples A and B...

E8.4. The hydrogen kinetic parameters were calculated by fitting the experimental data to the IPZ model. The results for samples A and B are presented in Table E8.2. Predict which sample shows better resistance to hydrogen permeation. 

Table E8.4 Kinetic Parameters for Hydrogen Permeation Through Cd Coated Steei a ( o (A/cm ) k (mol/cm ) (mol/s cm )...

For mechanistic modeling, CF results must be coupled with transient electrochemical reaction kinetics, hydrogen permeation, and hydrogen trapping analyses described elsewhere in this manual. 

The dependence of l/J on L can therefore be used to evaluate from the intercept provided that the value of 6 is known independently. If k hydrogen permeation is controlled only by surface entry kinetics when the membranes are too thin with respect to the hydrogen dififusivity for the metal of interest. 

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