Evaluation of Bi ₂V _0.9Cu _0.1O _5.35-an Aurivillius-type conducting oxide-as a cathode material for single-chamber solid-oxide fuel cells

The compound Bi ₂V _0.9Cu _0.1O _5.35, a typical Aurivillius-type fast oxygen ion conductor, was evaluated as a possible cathode material for single-chamber solid-oxide fuel cells operated under mixed propane and oxygen. The material was found to be structurally stable under various C ₃H ₈ + O ₂ environments over a wide temperature range and furthermore displayed low catalytic activity for propane oxidation. However, at temperatures above 650 °C, detrimental reactions between the cathode and the ceria electrolyte occurred, producing low conductivity interfacial phases. At these high temperatures the cathode additionally underwent extensive sintering and loss of porosity and, thus, stable fuel cell operation was limited to furnace temperatures of <600 °C. Even under such conditions, however, the partial oxidation occurring at the anode (a ceria nickel cermet) resulted in cell temperatures as much as 70-110°C higher than the gas-phase temperature. This explains the sharp decrease in fuel cell performance with time during operation at a furnace temperature of 586 °C. Under optimized conditions, a peak power density of ∼60 mW/cm² was obtained, which does not compete with recent values obtained from higher activity cathodes. Thus, the poor electrochemical activity of Bi ₂V _0.9Cu _0.1O _5.35, combined with its chemical instability at higher temperatures, discourages further consideration of this material as a cathode in single-chamber fuel cells.