Analysis of stresses generated during hydrogen transport through a Pd foil electrode under potential sweep conditions

Abstract

In the present work, the stresses generated during cyclic voltammetric measurements on a Pd foil electrode in 0.1 M NaOH solution have been analysed by using a laser beam deflection technique combined with cyclic voltammetry. From the linear relationship between the anodic peak current density and the scan rate on a logarithmic scale, it is recognised that the hydrogen concentration at the electrode surface is determined by the applied potential above the transition scan rate, whereas the change in the hydrogen concentration at the electrode surface with time is specified by the Butler–Volmer equation below the transition scan rate. The deflection transient measured simultaneously with the cyclic voltammogram shows that in the high scan rate range, the compressive deflection increases to a maximum value and then is completely relaxed. In the low scan rate range, however, the deflection transient is characterised by the occurrence of a maximum compressive deflection, a transition of compressive to tensile deflection, a maximum tensile deflection and finally a complete decay of the tensile deflection in sequence. From the hydrogen concentration profile transient simulated under the two constraints at the electrode surface, we simulated the deflection transients as a function of the scan rate. From the coincidence of the calculated deflection transient with that measured, the movement of the deflection in the compressive and tensile directions can be accounted for in terms of the difference in the molar volume of α-PdH δ across the whole electrode, developed during hydrogen diffusion.