Electrochemical and Catalytic Behavior of Ni-Based Cermet Anode for Ammonia-Fueled SOFCs

Solid oxide fuel cells (SOFCs) are one of the promising power generation devices due to their high energy conversion efficiency and low emissions. Hydrogen fuel can be used as an environmentally clean energy carrier for SOFCs. However, the storage and transportation are major obstacles for the large-scale application because of the low volumetric density and boiling point. Thus, high fuel flexibility of SOFCs has attracted much attention for a simplified power generation system.

Recently, ammonia was considered as a promising fuel for SOFCs because of following reasons; high energy density, ease in liquefaction (–33.4ºC at atmospheric pressure or 8.46 atm at 20ºC), no greenhouse gas emission, narrower flammable range than hydrogen. Much effort has been devoted to enhance the performance of direct ammonia fuelled SOFCs employing oxide-ion [1, 2] or proton [3, 4] conducting electrolytes. Meng et al. [2] fabricated a 10-μm thick SDC electrolyte with 50wt% Ni–SDC as an anode and BSCF as a cathode. A peak power density of 1190 mW/cm² was achieved at 700 °C, which was the highest performance reported in literatures for the direct NH₃-SOFC using oxygen ion conducting electrolyte.

In this report, the mechanism of electro-oxidation of ammonia over Ni-based cermet anode was studied. Especially, we focused on the correlation between the catalytic activity of anode for ammonia decomposition and cell performance. This systematic investigation has revealed that ammonia is catalytically decomposed to H₂ and N₂, and then H₂ produced is electrochemically oxidized over anode. Furthermore, the operating temperature and hydrogen concentration had a great impact on ammonia decomposition as well as cell performance. These results provided the strategy for the development of anode materials for direct ammonia-fueled SOFCs.

[1] Qianli Ma, Jianjun Ma, Sa Zhou, Ruiqiang Yan, Jianfeng Gao, Guangyao Meng, Journal of Power

Sources 164 (2007) 86–89.

[2] Guangyao Meng, Cairong Jiang, Jianjun Ma, Qianli Ma, Xingqin Liu, Journal of Power Sources

173(2007) 189–193.

[3] N. Maffeia, L. Pelletierb, J.P. Charlandb, A. McFarlanb, Journal of Power Sources 140 (2005)

264–267.

[4] N. Maffei, L. Pelletier, J.P. Charland , A. McFarlan, Journal of Power Sources 162(2006) 165–167.