Improved Ionic Transport Using a Novel Semiconductor Co_0.6Mn_0.4Fe_0.4Al_1.6O₄ and Its Heterostructure with Zinc Oxide for Electrolyte Membrane in LT-CFCs

Improving the ionic conductivity and slow oxygen reduction electro-catalytic activity of reactions occurring at low operating temperature would do wonders for the widespread use of low-operating temperature ceramic fuel cells (LT-CFCs; 450-550 °C). In this work, we present a novel semiconductor heterostructure composite made of a spinel-like structure of Co_0.6Mn_0.4Fe_0.4Al_1.6O₄ (CMFA) and ZnO, which functions as an effective electrolyte membrane for solid oxide fuel cells. For enhanced fuel cell performance at sub-optimal temperatures, the CMFA-ZnO heterostructure composite was developed. We have shown that a button-sized SOFC fueled by H₂ and ambient air can provide 835 mW/cm² of power and 2216 mA/cm² of current at 550 °C, possibly functioning down to 450 °C. In addition, the oxygen vacancy formation energy and activation energy of the CMFA-ZnO heterostructure composite is lower than those of the individual CMFA and ZnO, facilitating ion transit. The improved ionic conduction of the CMFA-ZnO heterostructure composite was investigated using several transmission and spectroscopic measures, including X-ray diffraction, photoelectron, and UV-visible spectroscopy, and density functional theory (DFT) calculations. These findings suggest that the heterostructure approach is practical for LT-SOFCs.