Lowering the Temperature of Solid Oxide Electrochemical Cells Using Triple-Doped Bismuth Oxides.

Despite the great potential of solid oxide electrochemical cells (SOCs) as highly efficient energy conversion devices, the undesirable high operating temperature limits their wider applicability. Herein, a novel approach to developing high-performance low-temperature SOCs (LT-SOCs) is presented through the use of an Er, Y, and Zr triple-doped bismuth oxide (EYZB). This study demonstrates that EYZB exhibits > 147 times higher ionic conductivity of 0.44 S cm-1 at 600 °C compared to commercial Y-stabilized zirconia electrolyte with excellent stability over 1000 h. By rationally incorporating EYZB in composite electrodes and bilayer electrolytes, the zirconia-based electrolyte LT-SOC achieves the unprecedentedly high performance of 3.45 and 2.02 W cm-2 in the fuel cell mode and 2.08 and 0.95 A cm-2 in the electrolysis cell mode at 700 °C and 600 °C, respectively. Further, a distinctive microstructural feature of EYZB that largely extends triple phase boundary at the interface is revealed through digital twinning. This work provides insights for developing high-performance LT-SOCs.

Hydration of Proton-conducting BaCe0.9Y0.1O3-δ by Decoupled Mass Transport.

Mass relaxation profile of a perovskite-type oxide, BaCe0.9Y0.1O3-δ, was studied to understand decoupled diffusion of oxygen and hydrogen species during hydration/dehydration. The mass relaxation measurements are performed by thermogravimetric analysis (TGA) under various humidity conditions (Dry, -3.0 ≤ log(pH2O/atm) ≤ -1.6) at a constant oxygen partial pressure (log(pO2/atm) = -1.00 ± 0.01). The decoupled ions participated in hydration/dehydration reactions were proven to be at different ratios from the result introduced by the 8R m function. The enthalpy and entropy of non-stoichiometric hydration reaction, which considers each ratio of charge-carrier species, were -144.7 ± 3.7 kJ/mol and -147.8 ± 3.2 J/mol · K, respectively.

Spatial Distribution of Oxygen Chemical Potential under Potential Gradients and Theoretical Maximum Power Density with 8YSZ Electrolyte.

The maximum power density of SOFC with 8YSZ electrolyte as the function of thickness was calculated by integrating partial conductivities of charge carriers under various DC bias conditions at a fixed oxygen chemical potential gradient at both sides of the electrolyte. The partial conductivities were successfully taken using the Hebb-Wagner polarization method as a function of temperature and oxygen partial pressure, and the spatial distribution of oxygen partial pressure across the electrolyte was calculated based on Choudhury and Patterson's model by considering zero electrode polarization. At positive voltage conditions corresponding to SOFC and SOEC, the high conductivity region was expanded, but at negative cell voltage condition, the low conductivity region near n-type to p-type transition was expanded. In addition, the maximum power density calculated from the current-voltage characteristic showed approximately 5.76 W/cm(2) at 700 (o)C with 10 µm thick-8YSZ, while the oxygen partial pressure of the cathode and anode sides maintained ≈0.21 and 10(-22) atm.