BaCo_0.4Fe_0.4Nb_0.1Sc_0.1O_3-δ perovskite oxide with super hydration capacity for a high-activity proton ceramic electrolytic cell oxygen electrode

Proton ceramic electrolytic cells (PCECs) are regarded as superior candidates for largescale hydrogen production by water electrolytic because they are efficient and weakly temperature-dependent. However, the intrinsically poor water-storage capability (hydration) and slow proton mobility of traditional PCEC oxygen electrodes retards the activity of electrochemical water decomposition to oxygen. The sluggish decomposition process has prevented the extensive application of PCECs. Herein, we report a Nb⁵⁺ and Sc³⁺ co-doped BaCo_0.4Fe_0.4Nb_0.1Sc_0.1O_3-δ (BCFNS) perovskite oxygen electrode that exhibits remarkably low polarization resistances (e.g., 0.079 Ω·cm² at 650 °C) in air humidified with 3 vol% H₂O. Both experiments and computational calculations linked this high performance to the synergistic effect of Nb⁵⁺ and Sc³⁺ in tuning the oxygen-vacancy concentration and the hydration reaction between oxygen vacancies and water molecules. This unique synergistic mechanism endows BCFNS with strong hydration capacity, boosting the formation of protonic defects and reducing the proton-migration barrier. Benefiting from these features, a single PCEC with a BCFNS oxygen electrode achieved much higher current densities than newly reported PCECs: 1224.91, 914.05, 622.18, and 314.89 mAcm⁻² at 1.3 V and 650 °C, 600 °C, 550 °C, and 500 °C, respectively. Such excellent electrolytic performance suggests that Nb⁵⁺ and Sc³⁺ co-doping can promote the hydration capability and proton mobility of electrode materials for high-performance PCECs.