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

Abstract

We have so far developed Ni-Fe and Ni-Mo anodes with high catalytic activity for ammonia(NH3)-fueled SOFCs [1], and have proposed that the performance of NH3 -fueled SOFCs was determined by a balance between NH3 adsorption (Fe, Mo) and nitrogen(N2) desorption (Ni) capability [2]. Furthermore, we also found that both Ni-Fe and Ni-Mo anodes react with NH3 to form metal alloy nitrides (FeNx, γ-Ni2Fe2N and Ni0.2Mo0.8N) and metal Ni under the operation condition, while pure Ni anode does not form nitrides. These results suggested that the nitrides enhance NH3 adsorption at the anode and led to the high anode activity for NH3 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 NH3-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 NH3 oxidation, but Nb did not. XRD measurements of metal oxides (WO3, Ta2O5 and Nb2O5) after annealing in NH3 indicated that W and Ta in the anode reacted with NH3 to form nitrides, but Nb did not under the operation condition (i.e. at 973-1173 K in NH3). These results suggest that the easiness of the nitride formation is closely related to the high activity anode for NH3 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).