Adsorption site blocker coverage

As a conclusion, the promoting effects of adsorption site blockers on H entry can be understood not by considering the effective diminution of 0 the overall coverage of OPD H (determined by integration of adsorption pseudocapacitance vs. potential curves [117-119]), but by considering the variation of x the local OPD H coverage in the sites not blocked [obtained by normahzation of 0 or from the Tafel and permeation slopes (see Tables 1 and 2)]. If the surfece-bulk transfer step is in equilibrium, a significant increase of the bulk H eoncentration can be induced by ASB surface effects only for the HER mechanism where the steps of electroadsorption and chemical combination are coupled. This analysis provides a quantitative explanation of the effects of promotion of H absorption into iron and ferrous alloys. [Pg.90]

Figure 12 Theoretical variations, for a coupled electroadsorption-chemical combination HER mechanism, of the overall H coverage 0jj (fiill line), the local H coverage Xjj (dotted line), the HER current (dashed line), and the bulk H fraction for charging (dashed line) with the coverage of adsorption site blocker (ASB). The represented case is for Langmuir type H adsorption and a geometric blocking effect, where one ASB atom blocks one H site, with random ASB adsorption 6h asb)% her cc asb) h Above a certain value of 0 gg...

$Figure 12 Theoretical variations, for a coupled electroadsorption-chemical combination HER mechanism, of the overall H coverage 0jj (fiill line), the local H coverage Xjj (dotted line), the HER current (dashed line), and the bulk H fraction for charging (dashed line) with the coverage of adsorption site blocker (ASB). The represented case is for Langmuir type H adsorption and a geometric blocking effect, where one ASB atom blocks one H site, with random ASB adsorption 6h asb)% her cc asb) h Above a certain value of 0 gg...$

On a surface irreversibly covered by an adsorption site blocker (ASB) on a significant range of potential, the H coverage at a given potential E/ 0H/ defined as the ratio of the density of H sites occupied by adsorbed H atoms to the total density of H sites existing on the clean surface (rj, can be expressed as... [Pg.140]

There is still a lack of experiments on the cathodic reaction with well-controlled surfece coverages by hydrogen, oxygen, and adsorption blockers. Such studies, as well as studies of the influence of the blockers on the occupancy of the subsurface sites, are necessary to understand fully the mechanisms of the hydrogen surface reactions involved in eorrosion phenomena. [Pg.92]

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