PbO effect on the oxygen reduction reaction in intermediate-temperature solid oxide fuel cell

Abstract

Ag paste is often used in solid oxide fuel cells (SOFCs) as the current collector. This study investigates the effect of lead oxide (PbO), which is usually present in Ag paste, on the oxygen reduction reaction (ORR) at the typical electrocatalysts, lanthanum strontium cobalt ferrite (LSCF) and lanthanum strontium ferrite (LSF), for intermediate-temperature SOFCs. The chemical oxygen surface exchange coefficients are greatly increased by the deposition of PbO particles on the LSCF and LSF bar surfaces as demonstrated by the electrical conductivity relaxation technique. For example, at 800 °C, the deposition of 0.074 mg cm−2 PbO particles increases the coefficients from 4.68 × 10−5 to 7.2 × 10−4 cm s−1 and from 2.62 × 10−5 to 1.60 × 10−4 cm s−1 for LSCF and LSF, respectively. Furthermore, the infiltration of PbO into porous LSCF and LSF electrodes significantly improves the ORR as determined with AC impedance spectroscopy using symmetrical cells comprising of samaria-doped ceria as the electrolyte. When 5.88 and 5.67 wt % PbO is infiltrated into the porous backbone of LSCF and LSF electrodes, at 650 °C, the area specific interfacial polarization resistance (ASR) is reduced from 0.26 to 0.14 Ω cm2 and from 1.34 to 0.37 Ω cm2, respectively. The distribution of relaxation time (DRT) analysis suggests that PbO efficiently accelerate the charge transfer and oxygen incorporation processes.