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

Abstract

A 10 MHz electrochemical quartz crystal microbalance (EQCM) was employed to study the hydrogen absorption–desorption behavior in Pd and Pd 77 Ag 23 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 room temperature. The hydrogen absorbed or desorbed in the film was measured by EQCM through the variation of the oscillation frequency. The frequency shift is caused by the synergistic effect of mass increase (or decrease) and the stress induced by hydrogen absorption in the film. Based on the integrated oxidation current, the amount of hydrogen in the film was calculated. The magnitude of stress in the film could then be estimated from the frequency shift. The kinetic curves of hydrogen absorption at various reduction potentials were also obtained and compared for Pd and Pd 77 Ag 23 films. The Pd 77 Ag 23 film had a faster hydrogen absorption rate but absorbed less hydrogen than the Pd film. It was also found that the hydrogen absorption rates in both films were controlled predominantly by the surface effect and hydrogen fugacity.