A Comparison of Molten Sn and Bi for Solid Oxide Fuel Cell Anodes

Abstract

Molten Sn and Bi were examined at 973 and 1073K for use as anodes in solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. Cells were operated under “battery” conditions, with dry He flow in the anode compartment, to characterize the electrochemical oxidation of the metals at the YSZ interface. For both metals, the open-circuit voltages (OCVs) were close to that expected based on their oxidation thermodynamics, ∼0.93V for Sn and ∼0.48V for Bi. With Sn, the cell performance degraded rapidly after the transfer of approximately 0.5–1.5C∕cm2 of charge due to the formation of a SnnormalO2 layer at the YSZ interface. At 973K , the anode impedance at OCV for freshly reduced Sn was approximately 3Ωcm2 but this increased to well over 250Ωcm2 after the transfer of 1.6C∕cm2 of charge. Following the transfer of 8.2C∕cm2 at 1073K , the formation of a 10μm thick SnnormalO2 layer was confirmed by scanning electron microscopy. With Bi, the OCV anode impedance at 973K was less than 0.25Ωcm2 and remained constant until essentially all of the Bi had been oxidized to normalBi2normalO3 . Some implications of these results for direct carbon fuel cells are discussed.

Catalysis Center for Energy Innovation for Biomass Processing: Research Strategies and Goals

“…First, we need to understand oxygen transfer at the metal-electrolyte interface. For example, with molten Sn, we have found that formation of a thin, insulating layer of SnO 2 at that electrolyte interface limits the performance [37]. Potential reactions between the electrolyte and either the molten metal or its oxide also need to be investigated.…”

Direct carbon solid oxide Fuel Cell—a potential high performance battery

“…The DCFC is a potential technique with great promise for using coal cleanly and efficiently. Most DCFC research and development activities have been focused on liquid electrolyte fuel cells [1,2] or solid electrolyte fuel cells with some melt metal as the media for carbon delivering [3]. As the activation energy of carbon is generally high, DCFCs have to be operated at high temperatures, i.e., over 600 C. Any liquid-contained device operated at high temperature is dangerous because corrosion and leakage may occur to destroy the equipments.…”

Molten silver as a direct carbon fuel cell anode

“…Qualitatively, the characteristics in this region were highly repeatable and were observed also at a ramp rate of 1 mV s À1 . Unlike the case with molten Sn or In [9,10], where a maximum in the current was also observed in Vei curves measured using ramped potential due to formation of oxide films on the electrolyte, Ag 2 O formation is not possible in this case.…”

“…With metals that have stable solid phase oxides at the operating temperature (e.g. Sn and In), the impedance of the cells became very high after briefly drawing current through the electrolyte due to formation of an oxide film at the electrolyte interface [9,10]. We showed that this problem could be avoided using molten Sb because both Sb and Sb 2 O 3 are molten at reasonably low temperatures [8,9]; however, the OCV for cells with molten Sb anodes was only 0.75 V at 973 K, the potential established by equilibrium between Sb and Sb 2 O 3 .…”