Vanadium (oxy)nitride as a new category of anode for direct ammonia solid oxide fuel cells cells

Abstract

Ammonia (NH3) is considered a potential energy carrier to be used as a fuel in energy conversion devices, such as solid oxide fuel cells (SOFCs). Nonetheless, in the presence of NH3, traditional Ni-containing anodes may suffer from poor chemical stability, resulting in its partial conversion to nickel nitride. We, therefore, propose a new composite anode for direct ammonia solid oxide fuel cells made of a metallic conducting phase, vanadium (oxy)nitride (VON), and an oxygen-ion conducting phase, (ZrO2)0.92(Y2O3)0.08 (YSZ). X-ray diffraction (XRD) reveals that the VON material is chemically compatible with YSZ. Good thermal stability was also shown under reducing conditions by thermogravimetry (TGA). Electrochemical impedance spectroscopy (EIS) showed that peak performing composition is composed of 50:50% vol of VON:YSZ at 850 °C, yielding comparable performance to that of previous reports on traditional Ni-YSZ cermets. The electrode mechanism under NH3 fuel was found to be similar to that of traditional Ni-based cermet compositions using hydrogen fuel, due to the predicted thermal decomposition of ammonia under the studied operation temperatures, i.e., ≥650 °C, while sensitivity to flow rate considerations was also highlighted. To the best of our knowledge, this work reports a completely new category of anodes for SOFC applications.