High Efficiency Direct Ammonia Type Fuel Cells based on BaZrxCe0.8-XY0.2O3/Pd Oxide-Metal Junctions

Friday, 28 July 2017: 15:20
Grand Ballroom West (The Diplomat Beach Resort)
Y. Aoki (JST-PRESTO, Hokkaido University), T. Yamaguchi, S. Kobayashi, C. Zhu, and H. Habazaki (Hokkaido University)
Recently, ammonia has attracted a considerable interest as a prospective carbon-free fuel source for fuel cells due to the low cost, ease in liquefaction and transportation at ambient temperatures, and high volumetric energy density. The proton conducting ceramic fuel cells (PCFCs) using proton-conducting oxides, such as BaZrxCe0.8-xY0.2O3-d, as an electrolyte is promising as a direct ammonia type fuel cells. The water formation in PCFCs is mainly progressive at the cathode side, unlike solid oxide fuel cells (SOFCs), and therefore, the contamination of the ammonia fuels into the exhaust water is precluded, thereby eliminating re-purification of water exhaust and simplifying total systems. Hydrogen membrane fuel cell (HMFC), which was firstly proposed by Ito et al., consists of an ultrathin proton conducting ceramic electrolyte supported on a dense hydrogen permeable metal anode. The cell facilitates efficient power generation, giving 900 mW cm-2 at 400°C, since reduced electrolyte thickness can significantly decreases the ohmic loss at lower temperatures. This unique cell configuration could be advantageous for ammonia fuel cells because 1) the NOx formation at the anode is perfectly prevented because NH3 gases are isolated from the oxide electrolytes by Pd solid anode and 2) Pd is expected to capture efficiently the hydrogen gases produced by the pyrolysis of ammonia due to the large ahydrogen sorption ability. Herein, we demonstrated the high efficiency power generation of the direct ammonia type HMFC due to the hydrogen pumping effects realized by BaZr0.1Ce0.7Y0.2O3-d (BZCY) and Pd heterointerface. Ohmic characteristics of the heterojunctions, altogether with hydrogen solubility of Pd, can facilitate the hole proton exchange between Pd and BZCY regardless of the lowered hydrogen concnetartion in NH3-fed anodes. The cell gained the maximum power density of 0.52 W cm-2 at 600°C, which was much higher than the champion data of ammonia PCFCs.