A catalyst support for direct-ammonia solid-oxide fuel cell anodes based on lanthanum titanium oxynitride

Abstract

Ammonia is considered a promising fuel for solid-oxide fuel cells (SOFCs) owing to its ease of transportation, hydrogen density, and energy content. Direct-ammonia solid-oxide fuel cells (DA-SOFCs) have been shown to undergo degradation faster than SOFCs fueled by hydrogen; therefore, there is a pressing need to develop stable anodes from new materials for DA-SOFCs. Herein, nickel (Ni) and iron (Fe) nanoparticles were supported on a lanthanum titanium oxynitride support and mixed with copper (Cu) and gadolinium-doped ceria (GDC) to form a novel DA-SOFC anode. Cells with the oxynitride-based anode catalyst exhibited a current density and power density of 939 mA cm⁻² and 228 mW cm⁻², respectively, at 750 °C. The electrochemical activity obtained is among the best for electrolyte-supported DA-SOFCs, particularly with a thick electrolyte. Unlike YSZ-based anodes for DA-SOFCs, the oxynitride-based anode performed particularly well under temperature cycling and long-term chronoamperometry with no signs of physical degradation to the cell or delamination. Furthermore, mass spectroscopy of the anode exhaust revealed that a negligible amount of NO_x gases was produced during operation using the oxynitride anode. To our knowledge, this is one of the first reports showing the use and stability of an oxynitride phase for an SOFC electrode. These results suggest that oxynitride-based supports, which are themselves synthesized from ammonia at high temperatures, are a stable and active class of materials for use in DA-SOFC anodes.