Effects of Nitride Formation on Anode Catalytic Activity in Ammonia-Fueled SOFCs

We have so far developed Ni-Fe and Ni-Mo anodes with high catalytic activity for ammonia(NH 3 )-fueled SOFCs [1], and have proposed that the performance of NH 3 -fueled SOFCs was determined by a balance between NH 3 adsorption (Fe, Mo) and nitrogen(N 2 ) desorption (Ni) capability [2]. Furthermore, we also found that both Ni-Fe and Ni-Mo anodes react with NH 3 to form metal alloy nitrides (FeN x , γ-Ni 2 Fe 2 N and Ni 0.2 Mo 0.8 N) and metal Ni under the operation condition, while pure Ni anode does not form nitrides. These results suggested that the nitrides enhance NH 3 adsorption at the anode and led to the high anode activity for NH 3 oxidation. In the present study, we prepared three kinds of anodes, Ni-W, Ni-Ta and Ni-Nb and evaluated their performance as anode in NH 3 -fueled SOFCs to investigate the correlation between the nitride formation and the anode activity. These anodes were synthesized by impregnating W, Ta and Nb precursor solutions into a pre-sintered Ni-SDC anode cermet. The addition of W and Ta enhanced the anode activity for NH 3 oxidation, but Nb did not. XRD measurements of metal oxides (WO 3 , Ta 2 O 5 and Nb 2 O 5 ) after annealing in NH 3 indicated that W and Ta in the anode reacted with NH 3 to form nitrides, but Nb did not under the operation condition (i.e. at 973-1173 K in NH 3 ). These results suggest that the easiness of the nitride formation is closely related to the high activity anode for NH 3 oxidation. Acknowledge This work was supported by the Kyoto Environmental Nanotechnology Cluster from MEXT, Japan. Reference [1] W. Akimoto et al., Solid State Ionics , 256 , 1–4 (2014). [2] W. Akimoto et al., ECS Trans. , 57 (1), 1639-1645 (2013).