Ammonia (NH₃) is attractive as a fuel for solid oxide fuel cells (SOFCs). NH₃ is free of carbon. Furthermore, the enthalpy of NH₃ reforming is low. These characters work better for SOFCs operation at intermediate-low temperature. However, the activity and long-term stability of Ni-based anodes in direct NH₃-fueled SOFCs drop around 700 ˚C [1, 2]. It is necessarily to improve the anode catalyst to explore further potentials of direct NH₃-fueled SOFCs.

We have studied the activity of Ni-Fe and Ni-Mo/Sm-doped CeO₂(SDC) as an anode for direct NH₃-fueled SOFCs at temperature of 700 to 900˚C [2, 3]. It was found that Fe and Mo enhanced the activity of the anode for NH₃ oxidation (NH₃ reforming, followed by hydrogen oxidation). From these results, we have proposed that the synergetic effect of Ni and Fe(Mo), which weakly and strongly bind to N atom, enhances the catalytic activity for NH₃oxidation. Here, we present the activity and stability of them at low temperature.

The Ni-Fe and Ni-Mo/SDC anodes exhibited the higher activity for the electrochemical oxidation of NH₃ even at temperature of 500 to 700 °C than the Ni/SDC anode. Furthermore, they exhibited the higher stability against heat cycle between 600 and 700 °C in NH₃ atmosphere than the Ni/SDC anode. It was found that Fe and Mo suppressed the deformation of the anode microstructure induced by the heat cycle in NH₃atmosphere. The formation of Ni-Fe and Ni-Mo alloy nitrides was confirmed in each anode. The relationship between the nitrides and the stability of the anodes are discussed.

Acknowledge

This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan.

Reference

[1] J. Yang et al., Appl. Mater. Interfaces, 7 (2015) 28701.

[2] W. Akimoto et al., Solid State Ionics, 256 (2013) 1.

[3] M. Hashinokuchi et al., Solid State Ionics, 285 (2016) 222.