Ceria‑iron electrocatalysts for ammonia electrosynthesis using protonic ceramic electrolysis cells

• Published in: Solid state ionics Vol. 414; p. 116649
• Main Authors: Okazaki, Moe, Otomo, Junichiro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2024
• Subjects: Ammonia electrosynthesis; CeO2-Fe2O3; Electrode adhesion; Protonic ceramic electrolysis cell; Solid-state diffusion; Ammonia electrosynthesis; Solid-state diffusion; Protonic ceramic electrolysis cell; Electrode adhesion; CeO2-Fe2O3
• ISSN: 0167-2738
• DOI: 10.1016/j.ssi.2024.116649

Iron has proven to be a simple yet high-performing electrode for ammonia electrosynthesis, particularly when used with protonic ceramic electrolysis cells. On a proton-conducting BaCe0.9Y0.1O3−δ (BCY) electrolyte, iron oxide forms an interfacial layer during sintering due to solid-state cation diffusion. In this work, we found that the ceria‑iron layer that is formed in-situ both enables electrode adhesion and is active for ammonia electrosynthesis. Cells with electrodes fabricated from CeO2-Fe2O3 at a weight ratio of 1:1 (CeFe11) and 6:1 (CeFe61), designed to replicate the composition of the interfacial layer, resulted in ammonia formation rates similar to those of cells with pure Fe electrodes, reaching 1.1–1.2 × 10−8 mol s−1 cm−2 at an applied voltage of −1 V at 600 °C. The ceria‑iron catalysts exhibited higher catalytic activity and a moderate electrochemical activity. A comparison of these electrodes suggests that the regions where ceria and iron are in proximity are the most active for ammonia electrosynthesis. Furthermore, CeFe11 demonstrates similar ammonia formation rates on BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb1711) as on BCY; as BZCYYb is more stable than BCY in the presence of water vapor, the development of ceria‑iron electrodes could widen the application of iron-based electrodes to ammonia electrosynthesis combined with water electrolysis.
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•Solid-state diffusion between BCY electrolyte and Fe2O3 aids electrode adhesion.•Ceria-based interfacial layer formed by diffusion is active for ammonia synthesis.•CeO2-Fe2O3 electrodes exhibit activity for ammonia electrosynthesis in N2/H2.