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A bilayer composite electrolyte comprising BaCe0.85Y0.15O3-d (BCY15) – Gd0.2Ce0.8O2-d (GDC20) at the anode side and BaZr0.85Y0.15O3-d (BZY15) – Nd0.1Ce0.9O2-d (NDC10) at the cathode side is designed for improving the stability of co-ionic conducting solid oxide fuel cells (SOFCs) in a cell imbalanced stack. Contrary to the single layer structured SOFCs, the bi-layer cell stably operates without electrode delamination under negative voltage conditions. We measure local internal p O 2 values using embedded Pt probes. Based on these values, local electronic conduction is estimated in combination with four probe DC conductivity measurements. It is found that n-type conductivity (∼10−3 Scm−1) and p-type conductivity (10−5–10−4 Scm−1) are developed in the BCY15-GDC20 near the anode side and in the BZY15-NDC10 near the cathode side, respectively. The results indicate that local electronic conduction in electrolyte regions near both the anode and cathode interfaces is a crucial factor for the durability of co-ionic SOFCs under negative voltage operation. We therefore suggest the bi-layer configuration as a practical solution to protect co-ionic SOFCs in a cell-imbalanced stack.

In the present study, the effects of the operation mode on the stability of anion exchange membrane water electrolyzers (AEMWEs) are investigated. AEMWEs are tested for ~1000 h under two different potentiostatic (1.95 V) conditions (short periodic and long periodic modes), and their degradation behavior are compared. Changes in ohmic and non-ohmic resistance are distinguished and traced out by regularly measuring the impedance spectra during the long-term test. The short periodic operation mode results in performance degradation due to the ohmic resistance, which is associated with the irreversible membrane degradation, while non-ohmic resistance follows increase and decrease patterns, which is associated with the nonpermanent bubble resistance. On the other hand, the long periodic operation mode results in a better stability with the ohmic and non-ohmic resistance value remaining almost constant during the test. The present study indicates that even a small operating factor such as the frequency of the rest time has a significant impact on the stability of cell. Thus, various possible operation modes with respect to the rest time should be taken into account for preventing an increase in the degradation rate of AEMWEs.

Local electronic conduction is spatially investigated through two types of co-ionic conducting composite electrolytes, BCY15 (BaCe0.85Y0.15O3-d) - GDC20 (Gd0.2Ce0.8O2-d) and BZY15 (BaZr0.85Y0.15O3-d) - NDC10 (Nd0.1Ce0.9O2-d), to understand their durability under abnormal operating conditions. Electrical potential variation is measured through the electrolytes using embedded Pt probes under open circuit conditions, from which we find that an effective electrolyte region (with high electronic resistance) is expanded in both composite electrolytes, in comparison with doped ceria (single phase) electrolyte. In BCY15-GDC20, most of the electrolyte region shows high electronic resistance, except for the region close to the anode. A contrast tendency is observed in BZY15-NDC10 showing mixed conduction in the region close to the cathode. Both types of composite electrolytes degrade under negative voltage conditions, but they are stable under positive voltage conditions. Post-analysis reveals that electrode/electrolyte delamination occurs at the cathode side in BCY15-GDC20 while it occurs at the anode side in BZY15-NDC10. Thus, we can say that the local electronic properties of composite electrolytes determine their stability, and the high electronic resistance region is vulnerable when the cell is subjected to abnormal conditions such as negative cell voltages.