Effects of self-stress on the hydrogen absorption into palladium hydride electrodes of plate form under galvanostatic conditions

Abstract

Effects of diffusion induced stress on the hydrogen absorption into plate form electrodes of b-phase PdH x are discussed numerically based on the Volmer-Tafel route of the hydrogen evolution reaction, and thermodynamic considerations involving stress fields and non-ideal interactions of hydrogen in the electrode. It is found that the self-induced stresses enhance the absorption rate and may exceed the yield stress, especially when the thickness of the plate and/or charging current (or negative potential) increase. On the other hand, a plate with both sides exposed to electrolyte absorbs hydrogen more rapidly than that with only one side exposed to electrolyte under the same equivalent thickness and other conditions. Of course, the stresses developed in the former plate are always greater than those of the latter.

Numerical simulation of diffusivity of hydrogen in thin tubular metallic membranes affected by self-stresses

“…nH;0) has been canceled out by the boundary condition. This conclusion has also been proved by numerical simulation of hydrogen absorbing into a plate under galvanostatic charging [33]; it indicated that self-stress makes half-absorption time is less than the stress-free case although some details of the model di er from here. This could explain the fact ADCs increase with increasing nH and j0 (see Figs.…”

“…The ÿrst one is the term u nH shown in Eq. (4) or (15), which accelerates the di usion process and makes ADCs greater than the SFDC [33,36]. Although the term nH is the local value of hydrogen content in solid, only the increment (i.e.…”

“…Another factor omitted is the interaction between hydrogen atoms in metals (alloys) due to the conÿnement of discussion on the dilute solid solution here; otherwise, this factor will induce the di usivity changing with the hydrogen concentration and the UHD e ects will mix with the nonideal interaction in di usivity measurements for the metal hydride situation [33].…”

“…(15)- (19) and using the frame reported earlier [33]. In the calculation, the time step is 10 −6 and the space step is 10 −2 , and the precision is 10 −4 .…”

“…The actual metal (alloy) surface and bulk processes are complex [11,[32][33][34][35], for example, surface reactions (e.g. the Tafel and Heyrovsky steps) at electrode will diminish the permeation ux during hydrogen absorption [11].…”