(373e) Molten Mixed Metal Anodes for Solid Oxide Fuel Cells

Increasing demand for energy calls for efficient use of solid carbonaceous fuels such as coal and waste biomass.  Solid oxide fuel cells using molten metal anodes have shown sufficient promise in utilization of solid carbon fuels for energy generation ^1,2.  Recently, we have shown that cells with molten Sb anodes have been able to generate electric power densities exceeding 300 mW/cm² at 973 K using sugar char as fuel³.  The research presented in this work is directed toward understanding the chemistry associated with use of a low melting metal mixtures including Sb as anodes in fuel cells in a battery mode (i.e. without added fuel).  Various mixtures of Sn, Bi, In and Pb, each with Sb have been used as anodes.  In all cases, metals having the higher tendency to oxidize are preferentially oxidized, and the cell behaves much as it would with that metal in pure form as the anode.  In cases where the oxide formed from this preferential oxidation has a higher melting point than the operating temperature of the cell (e.g. SnO₂ with T_mp =  1903 K or In₂O₃ with T_mp =  2185 K in cells operating at around 1000 K or less), the oxide may deposit on the electrolyte-anode interface resulting in degradation of cell performance.  In the Sb-Pb system, although PbO melts well above the 973 K operating temperature ( T_mp =  1161 K), Sb is preferentially oxidized and the cell behaves similarly to that using pure Sb.  Experiments involving extended periods of operation for the cell using mixture of molten Sb and Pb as anode were conducted and it was observed that the cell performs until 100% of the Sb is oxidized.  This is a significant improvement compared with a cell using the same amount of pure Sb as the anode, which degrades after 10% oxidation of Sb³.  Characterization of cross-sections from quenched mixed metal anodes is underway to better understand the nature of the observed improvement in performance.

1)       Jayakumar, A.; Lee, S.; Hornes, A.; Vohs, J. M.; Gorte, R. J. A Comparison of Molten Sn and Bi for Solid Oxide Fuel Cell Anodes. J. Electrochem. Soc. 2010, 157, B365–B369.

2)      Jayakumar, A.; Vohs, J. M.; Gorte, R.J. Molten-Metal Electrodes for Solid Oxide Fuel Cells, Ind. Eng. Chem. Res. 2010, 49,10237-10241.

3)      Jayakumar, A.; Küngas, R.; Roy, S.; Javadekar A.; Buttrey D. J.,; Vohs, J. M.; Gorte, R.J. Electrical Power Generation Using Solid Fuels in a Solid Oxide Fuel Cell with a Molten Antimony Anode, Submitted.