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 throu gh metal oxides. As a model, CeO2 layer on a palladium wire substrate is in vestigated. Hydrogen is dissolved in aqueous solutions where their acidity and the oxide layer thickness are the studied parameters. Based on both ope n circuit potential and length changes, it is deduced that molecular diffus ion through pores and imperfections in the ceria lattice is the rate determ ining step and no chemical reactions are involved in the oxide bulk. The fo llowing diffusion coefficients are calculated by using a diffusional transp ort model: D-(1 N KOH) = 1.69 X 10(-11) cm(2) s(-1)D((1 N H2SO4)) = 1.72 X 10(-11) cm(2) s(-1). (C) 2001 Elsevier Science Ltd. All rights reserved.