Electrochemical Characterization of Mixed Conducting Ba(Ce[sub 0.8−y]Pr[sub y]Gd[sub 0.2])O[sub 2.9] Cathodes

The high proton conductivities of doped barium and strontium cerates has led to their consideration as electrolytes in fuel cells operating at intermediate temperatures (600-800°C). The electrochemical properties of Pr-doped barium gadolinium cerate [ Ba ( Ce 0.8 − y Pr y Gd 0.2 ) O 2.9 ] have been investigated as part of our assessment of new mixed-conducting electrodes in fuel cells with barium cerate electrolytes. Substitution of Pr for Ce increases the total and electronic conductivities, and the total conductivity of Ba ( Pr 0.8 Gd 0.2 ) O 2.9 exceeds ∼0.75 S/cm at 800°C in dry air. Electromotive force measurements indicate that the Pr-substituted samples also retain high proton and oxygen-ion conductivities despite their decreased ionic transport numbers. Cathodes prepared using these mixed-conducting Pr-doped barium-gadolinium cerates exhibit low cathodic overpotentials in Ba ( Ce 0.8 Gd 0.2 ) O 2.9 electrolyte fuel cells. For example, the cathodic overpotential resistance of a Ba ( Pr 0.8 Gd 0.2 ) O 2.9 cathode is 0.47 Ω cm 2 at 800°C at current densities < 100 mA / cm 2 . This is the lowest cathodic overpotential resistance reported for a perovskite electrode on a proton-conducting electrolyte fuel cell at this temperature.