Estimation of Charge-Transfer Resistivity of La[sub 0.8]Sr[sub 0.2]MnO[sub 3] Cathode on Y[sub 0.16]Zr[sub 0.84]O[sub 2] Electrolyte Using Patterned Electrodes

Yttria-stabilized zirconia (YSZ) electrolyte disks with patterned Sr-doped LaMnO 3 (LSM) electrodes having different three-phase boundary (TPB) lengths ( l TPB ) , but the same electrode-electrolyte interface area, were prepared using photomicrolithography. Impedance spectra for half-cells were obtained under oxygen partial pressures; p O 2 , ranging from 10 − 3 to 1 atm and temperatures from 650 to 800°C. Area specific charge-transfer resistance, R ct , was found to vary inversely with l TPB . While the charge-transfer resistance is inversely proportional to l TPB , consistent with the charge-transfer reaction occurring mainly at the TPB, at 800°C some transport through LSM also appears to occur. The estimated value of charge-transfer resistivity, ρ ct , corresponding to the charge-transfer reaction occurring at the TPB in air at 800°C ( 1.26 × 10 5 Ω cm), is in good agreement with that estimated from actual fuel cell tests using quantitative stereological analysis of LSM-YSZ composite electrodes. R ct and ρ ct were found to decrease with increasing p O 2 and with increasing temperature. The activation energy for the overall charge-transfer reaction was estimated to be ∼1.5 eV.