Enhancing Oxygen Evolution Reaction and Stability in Proton-Conducting Solid Oxide Electrolysis Cells (p-SOECs) via a Porous Gadolinium-Doped Ceria Interlayer

Proton-conducting solid oxide electrolysis cells (p-SOECs) offer a promising pathway for intermediate-temperature (400-600 °C) hydrogen production. However, they still face critical challenges related to sluggish oxygen evolution reaction (OER) kinetics and low Faradaic efficiencies. In this work, we demonstrate that introducing a thin (∼0.8 μm) porous Gd0.1Ce0.9O1.95 (GDC) interlayer between a BaCo0.8Zr0.1Zn0.1O3-δ (BCZZ) oxygen electrode and electrolyte significantly enhances p-SOEC performance. The GDC interlayer reduces polarization resistance by 48% (from 0.54 to 0.28 Ω cm²) and increases Faradaic efficiency from 63% to 81% at -0.8 A/cm² and 600 °C. GDC interlayer p-SOECs display elevated effective H₂ current densities compared to control p-SOECs and reach up to -1.22 A/cm² at 1.3 V. Mechanistic studies on the interactions between GDC and BCZZ reveal that GDC intrinsically promotes OER kinetics by significantly reducing the polarization activation energy (Eap), dropping from 1.45 to 1.22 eV for full p-SOECs and from 0.98 to 0.76 eV for symmetric cells. This promotional effect is localized in the electrochemically active region near the electrolyte interface. Durability testing for over 1500 h under 50% H₂O conditions indicates that the GDC interlayer also improves long-term stability, with a degradation rate 53% lower than that of control p-SOECs. By pinpointing the interfacial region where GDC exerts its promotional effect, highlighting its role in enhancing OER kinetics, and establishing interlayer engineering as a powerful technique, this work provides a unified pathway to simultaneously improve p-SOEC activity, Faradaic efficiency, and durability.