A novel CuFe₂O₄ ink for the fabrication of low-temperature ceramic fuel cell cathodes through inkjet printing

Inkjet printing is a mask-free, contactless, and precise thin film and coating fabrication technique, which can tailor the electrode microstructure of solid oxide fuel cells to provide a larger surface area with more reaction sites. For the first time, printable and functional CuFe₂O₄ inks were developed by analyzing particle size, viscosity, surface tension, density, and thermal properties. Two inks, named Ink (1) and Ink (2), were formulated with different compositions. Ink (2), containing 20 wt% 1,5-pentandiol, exhibited smaller particle sizes (0.87 μm) and a lower activation loss compared to Ink (1). For further optimization, NLK-GDC porous electrolyte substrates were inkjet printed with 30, 40, 50, 100 and 200 layers of Ink (2), with estimated thicknesses of 4.2, 5.6, 7, 14, and 28 μm. The best performance was achieved with a 100-layer inkjet-printed symmetric cell, exhibiting an ASR of 9.91 Ω cm². To enhance the rheological properties of Ink (2), cyclopentanone was added, resulting in Ink (2) - Samba, which had improved characteristics. Ink (2) - Samba possessed an average particle size (D50) of 0.68 μm and a Z number of 3.89. Finally, EIS analysis compared a 100-layer inkjet-printed symmetric cell with Ink (2) - Samba to a drop-cast cell with the same ink to evaluate how the fabrication technique influences cell performance. Inkjet printing demonstrated a hierarchical porous microstructure, increased reaction sites, and reduced ASR from 19.59 Ω cm² to 5.99 Ω cm². Additionally, SEM images confirmed that inkjet printing reduced the particle size distribution during deposition. These findings highlight the significant impact of manufacturing techniques on electrode quality and fuel cell electrochemical performance.