The correlation between internal chemical potential, and durability of anode-supported BCY (BaCe0.85Y0.15O3-delta) electrolyte cells, was investigated as a function of electrolyte thickness. Internal hydrogen and oxygen chemical potentials were measured on thin (similar to 10 mu m) and thick (similar to 50 mu m) BCY electrolyte using an embedded Pt probe. As the electrolyte thickness decreased, the internal chemical potential became dominated by the gases surrounding the cathode, indicating that the thin BCY cell may be vulnerable to water vapor produced at the cathode during operation. Constant -current tests were conducted on a thin (-10 mu m) BCY electrolyte cell with a BCY+ LSCF ((La,Sr)(Co,Fe)O3-delta) cathode, and a thick (similar to 35 mu m) BCY electrolyte cell with a BZY (BaZr0.85Y0.15O3-delta)+ LSCF cathode, under positive and negative voltage conditions. Consistent with the results of the internal chemical -potential measurements, the former showed a significant rate of degradation due to changes in BCY composition in the electrolyte and cathode, while the latter showed much better durability, regardless of the sign of cell voltage. Thus, the present work shows the effect of BCY electrolyte thickness and selection of cathode material, on the durability of BCY based cells, in terms of their internal chemical potential. (C) 2016 Elsevier Ltd. All rights reserved.