Impact of ethyl cellulose variation on microstructural and electrochemical properties of spin coated YSZ electrolyte thin films for SOFCs: Slurry composition evolution

Abstract

The present work meticulously highlights the physical and electrochemical properties of slurry spin coated Yttria Stabilized Zirconia (YSZ) electrolyte thin films for solid oxide fuel cell (SOFC) applications wherein the concentration of ethyl cellulose (EC) is varied from 3.5 wt% to 6.5 wt% in the EC/YSZ/terpineol slurry. The TGA of the prepared mixtures reveals the complete mass removal of EC in temperature range of 380–400 °C. The dense and crack-free YSZ thin films on NiO/YSZ anode composites are developed by performing four separate coating cycles where each cycle is preceded by baking the films at 380 °C. The prepared YSZ electrolyte thin films showed polycrystalline nature with cubic phased prominent reflection corresponding to plane (111). The crystallite size of YSZ thin films is determined from W–H and Scherrer's relations which is obtained in the range of 18–26 nm and 21–26 nm, respectively. The 3D AFM projection shows hill-like topography where the average roughness is found to be increased from 3.01 nm to 8.49 nm with an increase in the EC content. FESEM analysis unveils smooth morphology along with the presence of some abscission zones in YSZ thin films after the removal of EC. The electrochemical properties are explored by fitting equivalent electrical circuit to the Nyquist data which confirms electrolytic response of the prepared coatings. The thermal activation of ionic conduction has been verified by observing the Arrhenius plots where conductivity is found to be varied in range 10 −4 -10 −5 S/cm with the respective increase in EC content. The activation energies of YSZ electrolyte thin films are found to be in the range of 1.09–1.18 eV which are slightly higher as compared to that of bulk YSZ.