Mechanism-guided large-grain design of Sc-Ce co-doped BaCoO3 dual-phase oxygen electrodes for protonic ceramic cells

Protonic ceramic cells (PCCs) are promising mid-temperature electrochemical devices for hydrogen power generation and steam electrolysis, operating between 400 °C and 600 °C. They avoid severe high-temperature degradation and sealing challenges found in conventional solid‑oxide cells. Nevertheless, oxygen electrodes remain a major performance bottleneck due to slow oxygen-reduction/evolution kinetics and demanding long‑term stability under humid operating conditions.

In the development of oxygen electrodes, boosting specific surface area is a widely-adopted strategy to generate abundant catalytically-active sites. Approaches including nanofabrication, impregnation, and in-situ precipitation have proven effective for many electrode systems. This strategy fits well when electrode reactions are governed by surface-centred processes. Nevertheless, it carries an implicit prerequisite. When the overall reaction follows the hydrogenation-dehydrogenation route, bulk-phase proton transport can become a critical limiting factor. The abundant grain boundaries generated from nanostructured, high-surface-area electrodes may interrupt continuous proton-conducting pathways and restrict device output.

Researchers from the College of Materials Science and Engineering at Nanjing Tech University reported a mechanism-driven large-grain design for Sc-Ce co-doped BaCoO₃ dual-phase oxygen electrodes published in Journal of Advanced Ceramics. This work sets out to answer a key question: can oxygen-electrode microstructures be purpose-tailored according to the dominant proton-coupled oxygen reduction reaction (PC-ORR) mechanism?

The team published their work in Journal of Advanced Ceramics on September 30, 2026.

Recent literature has put forward an analytical framework that divides PC-ORR into two representative reaction pathways:

① hydration-dehydration pathway: The reaction rate is mainly controlled by the surface oxygen exchange process and is sensitive to the number of surface active sites;

② hydrogenation-dehydrogenation pathway: Protons directly participate in the electrode reaction, and the bulk proton transport may become the main limiting factor.

These two pathways impose distinct requirements on electrode microstructure. Electrodes operating via the hydration-dehydration pathway can take advantage of high specific surface area. In contrast, systems following the hydrogenation-dehydrogenation pathway demand well‑connected proton‑transport networks. It should be noted that the elementary steps and rate‑determining processes of PC-ORR are still under ongoing community discussion, and this classification framework is not universally applicable to every material system.

“Through conductivity relaxation, electrochemical impedance spectroscopy with DRT analysis and DFT calculations, the team classified electrode reaction pathways. The Sc-Ce co-doped electrode follows a hydrogen‑adsorption-desorption pathway where bulk proton transport partially limits performance, rather than a surface‑dominated hydration-dehydration mechanism.” said Lin.

In controlled comparisons with identical chemical compositions, micron‑sized large‑grain electrodes with low specific surface area (1.176 m² g⁻¹) outperformed nanostructured electrodes (10.707 m² g⁻¹). TOF-SIMS and Hebb-Wagner measurements confirmed higher bulk proton concentration and nearly one‑order‑of‑magnitude higher proton conductivity in large‑grain samples. The optimized large‑grain electrode achieves polarization resistance as low as 0.138 Ω cm² at 600 °C, a fuel-cell peak power density of 2.28 W cm^-2 at 700 °C, and electrolysis current density of 2.96 A cm^-2 at 1.3 V, alongside stable galvanostatic operation exceeding 120 hours.

“This work does not negate the value of high-surface-area nanostructures for surface‑controlled electrodes. Instead, our work demonstrates that when the proton‑coupled oxygen-reduction reaction follows the hydrogenation‑dehydrogenation mechanism, building continuous ion‑transport networks can deliver compelling performance,” said Associate Professor Lin Ge, corresponding author of this study. “Electrode microstructure selection should correspond to the dominant reaction mechanism, rather than relying on a one-size-fits-all design principle.”

The team reminds readers that oxygen-electrode reaction mechanisms for protonic ceramic cells are still actively debated in the community. These conclusions apply to the present Sc‑Ce co‑doped BaCoO₃ system, and further in-situ operando characterizations are required to fully clarify elementary reaction steps.

Co-authors include Xiaole Yu, Xinyuan Zhao, Bingyu He, Maoyi Hua, Yue Luo, Ziru Li, Jida Wang and Professor Sheng Cui.

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About Author

Lin Ge (corresponding author), an associate professor at Nanjing Tech University and a master's supervisor, is the deputy director of the Inorganic Materials Department.

Sheng Cui (corresponding author), Professor, Doctoral Supervisor, President of the School of Materials Science and Engineering at Nanjing University of Technology, mainly focuses on research in high-temperature insulation materials, photoelectric functional materials, and nano-composite materials.

 

Funding

This work was supported by the National Natural Science Foundation of China (Nos. 51502136), the Natural Science Foundation of Jiangsu Province (No. BK 20211260), Postgraduate Research & Practice Innovation Program of Jiangsu Province (26CXJH2720), the Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions and the Top-notch Academic Programs Project of Jiangsu Higher Education Institutions (TAPP).

 

DOI LINK: 10.26599/JAC.2026.9221387

 

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2025 IF is 14, ranking in Top 1 (1/34, Q1) among all journals in “Materials Science, Ceramics” category, and its 2025 CiteScore is 24.6 (6/133) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

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