Mechanism and Activity of Ni-Based (Ni-M: M = Fe, Mo, W, Ta) Cermet Anodes for Ammonia Oxidation in SOFCs
We have investigated the activity of anodes prepared with transition metals nickel(Ni), iron (Fe) and their alloy for NH3-SOFCs[2,3]. The Fe/Sm-doped ceria (SDC) cermet anode was more active for NH3 oxidation than Ni/SDC. We also found that the activity of the Ni40-Fe60//SDC for NH3 oxidation was highest by optimizing the metal composition. These results suggested that the rate limiting steps in a direct NH3 oxidation (or reforming NH3) at the anode were (i) NH3 adsorption and (ii) N2 desorption. We concluded that Fe and Ni atoms had the roles of accelerating reactions (i) and (ii), respectively, and the synergetic effect of Fe and Ni resulted in the enhancement of the anode activity for NH3oxidation.
On the basis of the mechanism of NH3 oxidation at the anode, we prepared the anode of Ni and Molybdenum (Mo) since Mo has the high ability of NH3 adsorption, and evaluated their performance for NH3-SOFCs. The Ni-Mo/SDC anodes were fabricated by impregnating a MoCl5 aqueous solution into a Ni/SDC pre-sintered cermet on an electrolyte. It was revealed that the optimum addiction of Mo enhanced the anode activity for NH3 oxidation. Our experimental results suggested that the anode activity for NH3 oxidation was determined by a balance between abilities of NH3 adsorption and N2desorption.
This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan.
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