Direct ammonia solid oxide fuel cells based on spinel ACo2O4 (A=Zn, Fe, Ni) composite cathodes at intermediate temperature

Direct ammonia solid oxide fuel cell (DA-SOFC) is a promising device to realize high-efficiency NH3-to-power. In this study, we fabricate a series of cobalt-based spinet ACo(2)O(4) (ACO, A = Zn, Fe, Ni) oxide as DA-SOFC cathodes using the citric acid complexing method. We prepare three cobalt-based spine] oxides with different A-site elements, i.e., Zn, Fe, and Ni, to establish the relationships between the valence and active site of ACO spinel oxide. The structural analysis based on XRD, XPS, TEC, and UV-Vis diffuse reflectance confirms that NCO exhibits smaller band gap, higher electronic conductivity, and better compatibility with electrolyte. The electrochemical results indicate that the cathodic surface of NCO containing rich Co3+ and O-ads leads to better oxygen reduction reaction (ORR) activity. The maximum power density of the DA-SOFC using NCO cathode reaches 1.06 W.cm(-2) at 800 degrees C, superior to those of using ZCO (0.83 W.cm(-2)) or FCO (0.92 W.cm(-2)) cathode. Kinetic analysis based on the distribution of relaxation time (DRT) and electrochemical impedance spectroscopy (EIS) indicates O-TPB - e(-) <-> O-TPB(-), is rate- limiting.