Electrode-Supported Protonic Ceramic Electrolysis Cells for Electrochemically Promoted Ammonia Synthesis at Intermediate Temperatures

• Published in: ACS omega Vol. 8; no. 43; pp. 40299 - 40308
• Main Authors: Okazaki, Moe, Otomo, Junichiro
• Format: Journal Article
• Language: English
• Published: American Chemical Society 31-10-2023
• ISSN: 2470-1343; 2470-1343
• DOI: 10.1021/acsomega.3c04478

Protonic ceramic electrolysis cells (PCECs) have attracted attention for their applications in electrochemical ammonia synthesis, but their low Faradaic efficiency and thermodynamic constraints at high operating temperatures have led to low ammonia formation rates. In this work, electrode-supported PCECs with a noble-metal-free Ni-BaZr0.8Y0.2O3−δ cathode and a spin-coated proton-conducting electrolyte were developed for ammonia electrosynthesis, conducted in a single-chamber reactor cofed with N2 and H2. Ammonia formation rates increased non-Faradaically with applied voltage, reaching up to 1.1 × 10–8 mol s–1 cm–2 at 400 °C, which corresponds approximately to a 150 °C reduction in operating temperature compared to previously reported works conducted in mixed N2 and H2. The improved performance at intermediate temperatures by using a Ni catalyst is attributed to the electrochemical promotion of catalysis upon cathodic polarization. By fabrication of a cell with low Ohmic losses and improved contact resistance at the anode–electrolyte interface, sufficient cathodic polarization to accelerate ammonia formation was achieved, even at 400 °C. A combined water electrolysis and ammonia synthesis system is proposed, where the hydrogen byproduct from water electrolysis can be efficiently utilized via a recycling process; such a system requires enhanced ammonia formation in a mixed N2/H2 atmosphere, as demonstrated in this work.