Analysis of anodic current transient and beam deflection transient simultaneously measured from Pd foil electrode pre-charged with hydrogen

Anodic current and beam deflection transients were measured simultaneously on a Pd foil electrode pre-charged with hydrogen at −0.02 and 0.09 V(RHE) in 0.1 M NaOH solution as a function of the hydrogen discharging potential. From the analysis of the anodic current transient measured, it is recognized that when the preceding potential jump is small enough to be below the transition discharging potential and this is followed by subjecting the electrode surface to a constant discharging potential, the hydrogen concentration corresponding to the discharging potential is not fixed at the electrode surface, but the change in surface concentration with time is then determined by the Butler–Volmer equation. From the hydrogen concentration profile transient simulated under the two constraints at the electrode surface depending on the discharging potential, we calculated numerically the transient of the deflection in the tensile direction caused by a smaller molar volume of α-PdHδ near the surface region than that in the inner region of the electrode during the hydrogen extraction. By comparison of the measured transient with that calculated, the movement of the maximum deflection in tensile and compressive directions was discussed in terms of the positive gradient of the molar volume towards the inner direction and the negative gradient due to the formation of a PdOH phase on the electrode surface, respectively.