Attenuating the metal‑oxygen bonds in BaCo0.4Fe0.4Zr0.1Y0.1O3-δ to achieve a high efficiency bifunctional oxygen electrode for reversible solid oxide cells

Proton-conducting reversible solid oxide cells (P-RSOCs) have the potential to enable interconversion between power and green hydrogen at low to intermediate temperatures. However, the large-scale application of P-RSOCs is significantly hindered by inefficient oxygen reduction (ORR) and evolution reaction (OER) kinetics in air electrode at reduced temperatures. Herein, this investigation introduces a straightforward approach of doping 5 % Zn into the BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BCFZY) lattice to form Ba(Co_0.4Fe_0.4Zr_0.1Y_0.1)_0.95Zn_0.05O_3-δ (BCFZYZ) as an exceptional efficiency and durable air electrode for P-RSOC. The introduction of Zn doping is anticipated to weaken the coulombic forces between B-site metallic ions and oxygen ions, thereby increasing the oxygen vacancies and proton defect concentration. Experimental results identify that the incorporation of Zn significantly enhances oxygen vacancies generation and hydration, and facilitates oxygen/proton surface exchange and bulk diffusion rates, thereby accelerating the ORR and OER kinetics. The BCFZYZ electrode exhibits relatively smaller polarization resistance and corresponding reaction activation energy (E_a = 1.198 ev). The P-RSOCs using BCFZYZ air electrode deliver impressive bifunctional performance at 650 °C, the cell achieves a peak power density of 946 mW cm⁻² in fuel cell operation, and 1175 mA cm⁻² electrolysis current density at 1.3 V in water splitting process. Moreover, the BCFZYZ full cell maintains stable voltage for 120 h and exhibits robust stable reversibility over a 100 h cycling period. This work provides an effective design strategy to facilitate the ORR and OER kinetics of BCFZY for high performance and durable air electrode of P-RSOC.