Effect of Co-existing Substances on the Sorption Rate of Hydrogen by Palladium Sheets

Abstract

The effect of co-existing substances on the rate of sorption of hydrogen by a palladium sheet exposed to carbon dioxide, methane, oxygen, or carbon monoxide at pressure less than 20 Torr before the sorption experiments. Exposure treatment of Pd sheets with carbon dioxide, methane, or oxygen at room temperature gave no effect on the sorption rate. The oxidation of the surface of Pd sheets at high temperature brought an induction period in the hydrogen sorption. In the case of carbon monoxide, the amount of hydrogen sorbed in a Pd sheet was proportional to the square root of time (Fig.1), but its proportionality constant 77 was lower than that for a clean Pd sheet. The value of i was affected by the exposing pressure of carbon monoxide and pretreatments of Pd sheets (Fig.3). The results were explained with the assumption that the rate-determining step is the hydrogen diffusion process in the 8-phase bringing the a-8 phase transition and that the adsorption of carbon monoxide lowers the concentration of dissolved hydrogen in the vicinity of Pd surface.