The effect of group IIIA oxides on the oxygen reduction reaction at cathodes for intermediate-temperature solid oxide fuel cells

Abstract

This study investigates the effect of B2O3, Al2O3, Ga2O3 and In2O3, belonging to group IIIA, on the oxygen reduction reaction (ORR) at typical electrocatalysts, lanthanum strontium cobalt ferrite (LSCF) and lanthanum strontium ferrite (LSF), for intermediate temperature solid oxide fuel cells (SOFCs). Amongst these oxides, In2O3 significantly enhances the electrochemical performance by improving ORR as determined by AC impedance spectroscopy using symmetrical cells comprising samaria-doped ceria as the electrolyte. When 13.73 and 7.88 wt % In2O3 is impregnated into the porous LSCF and LSF electrodes, at 650 °C, the area specific interfacial polarization resistance (ASR) decreases from 0.41 to 0.27 Ω cm2 and from 0.99 to 0.39 Ω cm2, respectively. The distribution of relaxation time analysis suggests that In2O3 efficiently accelerates the charge transfer and oxygen incorporation processes. The chemical oxygen surface exchange coefficients are greatly increased by In2O3 deposition as demonstrated with the electrical conductivity relaxation technique. For example, at 800 °C, the deposition of 0.202 mg cm−2 In2O3 particles increases the coefficient from 4.53 × 10−5 to 2.81 × 10−4 cm s−1 and from 2.39 × 10−5 to 9.3 × 10−5 cm s−1 for LSCF and LSF, respectively.