Understanding the influence of particle size on the reaction mechanism in porous La0.6Sr0.4CoO3-δ air electrodes

Abstract

Enhancing the electrode performance of high-temperature devices such as solid oxide fuel cells and solid oxide electrolysis cells is essential for reducing their operating temperatures. One approach is to reduce the particle size in the porous electrodes, which has been shown to decrease their area specific resistance. In this study, we investigated the effect of particle size on the reaction mechanism of mixed-conducting La_0.6Sr_0.4CoO_3-δ electrodes by fabricating half-cells with 650 nm-thick films composed of 55 ± 15 nm particles (nanoporous) and 15 μm-thick films composed of ∼800 nm particles (microporous). Electrochemical impedance spectroscopy and analysis using the Gerischer model were performed. For both micro- and nanoporous electrodes, a consistent relationship was found between the reaction field and the particle size, with the reaction field being about three times the particle size under our conditions. The surface reaction resistance and the effective oxygen transport resistance of microporous and nanoporous electrodes show overall similar values, with differences on the order of 0.5–1 orders of magnitude, indicating that they are largely comparable. In the DC polarization measurements, the current density of the microporous sample, when multiplied by a constant factor, closely matched that of the nanoporous sample. This suggests that the reaction mechanisms at both these electrodes were similar. This study demonstrates that the improvement in electrode performance with reduced particle size does not arise from intrinsic changes in the material properties, but rather from the increase in specific surface area. These findings provide useful guidelines for designing high-performance mixed-conducting porous electrodes.