Preparation of SmxCe1 − xO2(SDC) electrolyte film with gradient structure via a gas-phase controlling convection–diffusion approach on porous substrate

A SDC electrolyte film with gradient structure rooted on porous alumina substrate has been prepared by using a gas-phase controlling convection–diffusion approach. Investigation on the fabrication principles and the co-precipitation kinetics turned out the gradient distribution of hydroxide product of Ce(OH)3 and Sm(OH)3 in a porous substrate could be formed as induced by the down-toward diffusion of NH3·H2O in polar solvent along vertical direction and the up-toward convection of Sm3+ and Ce3+ ions over the cross-section of porous substrate, and the aim ratio of Ce to Sm of 4:1 in the sediment phase would be achieved by controlling component concentration in bulk solution. As a result, Sm0.2Ce0.8O2.0(SDC) electrolyte film with gradient microstructure could be fabricated after a subsequent sintering treatment at a high temperature. Investigation of crystal phase, structural, compositional characteristics of the sintered SDC/substrate specimens proved that a uniform and dense SDC film with an average grain size of ∼ 500 nm spread over on the surface of substrate, and a correct cubic fluorite phase has been formed. Gradient variation presented in both the microstructure of SDC/substrate and the component contents over the cross-section of the SDC/substrate. Numerical analysis on the EDX data presented three component parts were sectioned, including a dense SDC layer of ∼ 25 μm, a uniform filling layer of ∼ 140 μm and a successive diffuse layer stretching as far as ∼ 250 μm. Effect of bulk pH on thickness and surface microstructure of SDC film has been discussed. This microstructure-optimization approach will be applicable to fabricate electrode-supported gradient electrolyte films for IT-SOFC.