Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance Spectroscopy

摘要

Proton-conducting solid-electrolyte perovskite ceramics based on acceptor-doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600℃. Protonic conductivity in yttrium-doped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300℃. Conductivity data obtained from impedance spectroscopy on BaCe_(0.9)Y_(0.1)O_(3-α) over the extended temperature range of 100°-900℃ are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate-limiting processes occur in series with a breakover transition at ～250℃. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one-half of the low-temperature value, is proposed, based on curve fitting of the high-temperature data.