Hydrogen‐Atom Direct‐Entry Mechanism into Metal Membranes

Abstract

The hydrogen-atom direct-entry mechanism is used to explain why the steady-state hydrogen permeation current density through a metal membrane is directly proportional to the cathodic current density, i~, and is independent of the membrane thickness when io is small.

Mechanism of hydrogen adsorption/absorption at thin Pd layers on Au(111)

“…However, there is still discussion of the mechanism of hydrogen absorption. Two mechanisms were proposed: (a) indirect absorption, in which the hydrogen goes through an adsorption step [1,2] and (b) direct absorption mechanism [3][4][5][6][7]. These two mechanisms and their consequences were discussed in our earlier papers [7][8][9].…”

Investigation of hydrogen adsorption–absorption on iron by EIS

“…The first one is the classical two-step indirect absorption process, via the H ads adsorbed intermediate, first proposed by Bockris et al [20], whose rate constants are k 1 , k −1 , k 4 , k −4 . The second one can be seen as a generalization of the one-step Frumkin direct insertion process [21][22][23], which generates the H * abs in a thin sublayer, which was already proposed for the Pd/H system, and whose rate constants are k 5 , k −5 . In the sublayer, the absorbed monoatomic hydrogen, H abs , and the "trapped" hydrogen, H * abs , are supposed to interact through k t , k r .…”

Determination of hydrogen absorption isotherm and diffusion coefficient in Pd81Pt19 alloy

“…(i) one-step or direct absorption mechanism in which the proton is reduced and transferred (absorbed) into the metal [25][26][27][28][29][30] M þ H þ þ e ¢ M À H abs;0 ð1Þ…”