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 degreesC). The electrochemical properties of Pr-doped barium godolinium cerate [Ba(Ce0.8-yPryGd0.2)O-2.9] have been investigated as parr 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 rural conductivity of Ba(Pr0.8Gd0.2)O-2.9 exceeds similar to0.75 S/cm at 800 degreesC 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(Ce0.8Gd0.2)O-2.9 electrolyte fuel cells. For example: the cathodic overpotential resistance of a Ba(Pr0.8Gd0.2)O-2.9 cathode is 0.47 Ohm cm(2) at 800 degreesC at current densities <100 mA/cm(2). This is the lowest cathodic overpotential resistance reported fur a perovskite electrode on a proton-conducting electrolyte fuel cell at this temperature. (C) 2000 The Electrochemical Society. S0013-4651(00)08-027-7. Ali rights reserved.