The chemical stability of a nanoscale yttria-doped barium cerate (Y-BaCeO3 or BCY) thin film electrolyte for low temperature solid oxide fuel cells (SOFCs) are investigated in the temperature range of 300 -400 degrees C. The micro-SOFCs using 300 nm-thick BCY electrolyte show a poor fuel cell performance and continuous decrease in open circuit voltage (OCV) with higher operating temperatures. Characterization results from X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the observed degrading fuel cell performance is attributed to the rapid decomposition of BaCeO3 into BaCO3, Ba(OH)(2), and CeO2 from reactions with CO2 and H2O during fuel cell test. The lattice parameters of BCY expanded during fuel cell test, resulting in the formation of micro cracks along the electrolyte that possibly induced the OCV drop. The reactions of nano thin film BC? with CO2 and H2O are both active at temperature between 300 and 400 degrees C, which is unlike bulk BCY material where only the reaction with CO2 is significant. The reduction of Ce4+ species into Ce3+ in the BCY electrolyte has also lead to an electronic conduction in BCY that lowered OCVs. (C) 2014 Elsevier B.V. All rights reserved.