In situ monitoring of hydrogen absorption-desorption in Pd sind Pd77Ag23 films by an electrochemical quartz crystal microbalance

A 10 MHz electrochemical quartz crystal microbalance (EQCM) was employed to study the hydrogen absorption-desorption behavior in Pd and Pd77Ag23 films . Each film of thickness varying from 100 to 200 nm was deposited on an AT- cut quartz crystal by magnetron sputtering. It was electrolytically charged -discharged with hydrogen in 0.1 M KOH solution by cyclic voltammetry at ro om temperature. The hydrogen absorbed or desorbed in the film was measured by EQCM through the variation of the oscillation frequency. The frequency s hift is caused by the synergistic effect of mass increase (or decrease) and the stress induced by hydrogen absorption in the film. Based on the integr ated oxidation current, the amount of hydrogen in the film was calculated. The magnitude of stress in the film could then be estimated from the freque ncy shift. The kinetic curves of hydrogen absorption at various reduction p otentials were also obtained and compared for Pd and Pd77Ag23 films. The Pd 77Ag23 film bird a faster hydrogen absorption rate but absorbed less hydrog en than the Pd film. It was also found that the hydrogen absorption rates i n both films were controlled predominantly by the surface effect and hydrog en fugacity. (C) 1999 Published by Elsevier Science S.A. All rights reserve d.