Dilatometric and electrochemical measurements for studying hydrogen transport through oxide layers

Simultaneous dilatometric and electrochemical measurements are employed for studying the kinetic parameters and mechanism for hydrogen transport through metal oxides. As a model, CeO₂ layer on a palladium wire substrate is investigated. Hydrogen is dissolved in aqueous solutions where their acidity and the oxide layer thickness are the studied parameters. Based on both open circuit potential and length changes, it is deduced that molecular diffusion through pores and imperfections in the ceria lattice is the rate determining step and no chemical reactions are involved in the oxide bulk. The following diffusion coefficients are calculated by using a diffusional transport model: D_{(1 N KOH)} = 1.69 × 10^-11 cm² s^-1D_{(1 N H2SO4)} = 1.72 × 10^-11 cm² s^-1.