Transport properties and electrochemical activity of YBa(Co,Fe)4O7 cathodes

The layered phases derived from YBaCo4O7 exhibit a relatively low thermal expansion, significant mixed conductivity and attractive electrochemical activity in contact with doped LaGaO3 solid electrolyte. These properties may be of interest for intermediate-temperature SOFC cathodes. Moderate doping of yttrium-barium cobaltite with iron decreases slightly the total conductivity, predominantly p-type electronic, and have no essential effect on the oxygen ion transport and cathodic polarization at 1073 K. However, hexagonal YBaCo4O7, where the average cobalt oxidation state is + 2.25, and its derivatives appear metastable at temperatures below 1050–1100 K. Oxygen uptake at intermediate temperatures in air leads to the phase decomposition, accompanied by increasing conductivity and dramatic volume contraction.