Hydrogen and lithium transport through non-fractal and fractal electrodes of Pd alloys and transition metal oxides using quasi-steady-state and transient electrochemical methods based upon fractal Geometry

Abstract

The present work involves hydrogen and lithium transport through non-fractal and fractal electrodes of Pd alloys and transition metal oxides using quasi-steady-state and transient electrochemical methods based upon fractal geometry. Chapter III is concerned with the mechanism of hydrogen transport through Pd and $Pd_{82-y}Ni_ySi_{18}$ (y = 0 - 32) alloy electrodes. In chapter III-1, hydrogen transport through Pd foil electrode in the coexistence of two hydride phases of α-PdH and β-PdH was investigated in 0.1 M NaOH solution by the analysis of the anodic current transient. From the comparison of the initial anodic current experimentally obtained with that theoretically calculated from the Butler-Volmer equation in value, it was suggested that below the transition discharging potential, the hydrogen flux at the electrode/electrolyte interface is limited by the rate of interfacial charge transfer represented by the Butler-Volmer equation, whereas above the transition discharging potential, the hydrogen concentration corresponding to the discharging potential is fixed at the electrode surface. As the hydrogen discharging potential increased, the anodic current transient in the coexistence of two phases exhibited the transition in shape from the two-stage behaviour to the three-stage behaviour at the transition discharging potential. From the appearance of the three-stage current transient, it was inferred that hydrogen transport through the Pd foil electrode in the coexistence of two phases proceeds by the diffusion-controlled phase boundary movement in the second stage. In chapter III-2, hydrogen transport through amorphous $Pd_{82-y}Ni_ySi_18$ alloys (y = 0 - 32) was examined in 0.1 M NaOH solution by analysis of the anodic current transient. It was found that the anodic current transient showed the non-Cottrell behaviour, but its shape and value remained nearly constant regardless of the hydrogen discharging potential. From the coincidence of the anodic cur...