Synergistic Coupling of Proton Conductors BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ and La₂Ce₂O₇ to Create Chemical Stable, Interface Active Electrolyte for Steam Electrolysis Cells

For the first time, proton conductors BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) and La2Ce2O7 (LCO) are combined to create an interface active and steam-tolerant electrolyte for high-performance proton-conducting solid oxide electrolysis cells. LCO shows good chemical compatibility with BZCYYb. The readily fabricated LCO/BZCYYb bilayer electrolyte can be densified at a temperature of as low as 1300 °C versus ∼1600 °C for the benchmark steam-stable BaZr0.8Y0.2O3−δ electrolyte. With Pr2NiO4+δ as the anode and Ni as the cathode catalyst, this bilayer electrolyte cell yields a current density of 975 and 300 mA/cm2 under a 1.3 V applied potential at 700 and 600 °C, respectively. This performance is among the best of all H-SOECs equipped with a chemically stable electrolyte so far. A BZCYYb layer in the bilayer electrolyte promotes the hydrogen evolution reaction at the cathode side, resulting in a 108% improvement over the cell without this layer. The LCO layer, on the other hand, effectively protects this functional BZCYYb layer from the high concentration of steam in a practical SOEC operation condition. The cell without the LCO layer shows degradation in terms of an increased electrolyzing potential from 1.07 to 1.29 V during a constant 400 mA/cm2 operation at 700 °C. In contrast, the bilayer electrolyte cell maintains the same electrolyzing potential of 1.13 V under the same conduction for a 102 h operation. These findings demonstrate that this synergic bilayer electrolyte design is a vital strategy to overcome the dilemma between performance and stability faced by the current benchmark Zr- or Ce-rich Ba(CeZr)O3−δ electrolysis cells to achieve excellent performance and stability at the same time.