Direct Ammonia Fuel Cells with Hydrogen-permeable Metal-supports

Abstract

Direct ammonia type intermediate temperature fuel cell is examined by means of a hydrogen membrane fuel cell (HMFC) comprising 1 𝜇m-thick BaZr_0.1Ce_0.7Y_0.2O₃₋₅ (BZCY) thin film electrolyte, and Pd solid anode. It generates the maximum power density of 0.58 W cm^-2 at 600℃ with ammonia fuels, and this value is found to be three times larger than the champion data of the recently-reported direct ammonia type proton-conducting ceramic fuel cells (PCFCs). AC impedance spectroscopy is performed to determine the interfacial polarization resistances, disclosing that the anodic overpotentials of HMFCs are at least one order of magnitude smaller than those of anode-supported PCFC under relatively high DC outputs. The anode charge transfer reactions are driven by the oxidation of monoatomic hydrogen dissolves at the BZCY/Pd solid-solid interface, mediated via proton transfer from Pd to BZCY. The electrochemical analysis reveals that the proton pumping caused by the BZCY/Pd heterojunction facilitates the incorporation of proton from Pd side and thus the pyrolysis of NH₃ gas is promoted in order retain the high concentration of H dissolves near the heterojunction. This would decrease the anode concentration overpotentials.