Low-Temperature Deposition of Undoped Ceria Thin Films in scCO2 As Improved Interlayers for IT-SOFC

Abstract

Cerium oxide films were deposited onto various yttria-stabilized zirconia (YSZ) electrolytes using supercritical fluid deposition (SFD) in a cold wall reactor. Deposition of ceria thin films (20–240 nm) was carried out via hydrolysis of a Ce precursor at 250–300 °C (typically 30 min) in supercritical CO2 (scCO2). The as-deposited films were continuous, dense and crystalline. They exhibited some carbon contamination which was eliminated in all cases by postannealing the films at 400 °C. Film microstructure depends on the hydrolysis conditions (water to cerium molar ratio), on the substrate nature (Si wafers or YSZ pellets) and on the YSZ pellet thickness (100 μm or 1 mm). Ceria films were then used as interlayers for intermediate temperature solid oxide fuel cells (IT-SOFC) between the YSZ electrolyte and the Nd2NiO4+δ cathode layer subsequently deposited. The electrochemical properties of the SOFC symmetrical half cells were investigated by electrochemical impedance spectroscopy (EIS). The presence of the undoped ceria layer deposited in scCO2 lowers the resistance of the cell, compared both to cells with an optimized doped ceria layer deposited by screen printing and to cells without any interlayer.