Over the past decade, nano-sized Mixed Ionic Electronic Conducting (MIEC) – micro-sized Ionic Conducting (IC) composite cathodes produced by the infiltration method have received much attention in the literature due to their low polarization resistance (RP) at intermediate (500-700°C) operating temperatures. Small infiltrated MIEC oxide nano-particle size and low intrinsic MIEC oxygen surface exchange resistance (Rs) have been two critical factors allowing these Nano-Micro-Composite Cathodes (NMCCs) to achieve high performance and/or low temperature operation. Unfortunately, previous studies have not found a reliable method to control or reduce infiltrated nano-particle size. In addition, controversy exists on the best MIEC infiltrate composition because: 1) Rs measurements on infiltrated MIEC particles are presently unavailable in the literature, and 2) bulk and thin film Rs measurements on nominally identical MIEC compositions often vary by up to 3 orders of magnitude.Here, two processing techniques, precursor nitrate solution desiccation and ceria oxide pre-infiltration, were developed to systematically produce a reduction in the average La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) infiltrated nano-particle size from 50 nm to 22 nm. This particle size reduction reduced the SOFC operating temperature, (defined as the temperature where RP=0.1 Ωcm2) from 650°C to 540°C. In addition, Rs values forinfiltrated MIEC particles were determined for the first time through finite element modeling calculations on 3D Focused Ion Beam-Scanning Electron Microscope (FIB-SEM) reconstructions of electrochemically characterized infiltrated electrodes.
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