Abstract
Solid oxide fuel cells (SOFCs) are promising alternatives to combustion technology for electric energy production due to no emission and high efficiency in chemical to electric energy conversion. Despite such advantages, the commercialization of SOFCs is hindered by the high operating temperature, resulting in a few problems, such as expensive system cost and short lifetime. Thus, while reduced-temperature SOFCs have been a long-lasting interest in the SOFC community, the sluggish oxygen reduction reaction (ORR) occurring at the oxygen electrode at intermediate temperature is the most critical challenge for the enhanced overall performance of SOFCs. As a promising strategy to achieve higher catalytic activity of oxygen electrode, the infiltration method has been employed due to not only extended active site for ORR by electrode surface decoration with active nanoparticle catalysts, but enriched oxygen vacancies additionally formed on the surface of infiltrates. Furthermore, heterointerface engineering in the infiltrated oxygen electrode has, more recently, emerged as a promising approach to optimize oxygen electrode performance. The lattice strain, induced by lattice parameter mismatch in heterostructured materials, can significantly influence the ORR/OER (oxygen evolution reaction) kinetics by changing oxygen defect formation energy and migration barrier. We report the enhancement in the electrochemical performance of the La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) based heterostructured oxygen electrode, when infiltrated with aliovalent cation doped La2-xAxNi1-yByO4 (Ruddlesden-Popper, RP), leading to different intrinsic catalytic ability according to dopant; Sr and Co for A and B site, respectively, to generate oxygen defect (e.g., oxygen vacancy or interstitial O2-). This study demonstrates the impact of the oxygen defect in the infiltrates on the heterointerface, dominating ORR & OER kinetics in the heterostructured oxygen electrode, and investigate the primary oxygen defect for RP structured infiltrate to realize high ORR & OER activity. To characterize the morphology of infiltrates anchored on the oxygen electrode surface and the heterointerface synthesized between infiltrated layers and backbones, scanning electron microscope (SEM) and transmission electron microscopy (TEM) are performed. The electrochemical performances of the infiltrated SOFCs were examined by electrochemical impedance spectroscopy and analyzed in terms of the distribution of relaxation time (DRT) from impedance data. Thermogravimetric analysis (TGA) and iodometric titration are conducted to understand the correlation between oxygen defect produced by aliovalent doping and electrochemical ORR activity.
Published Version
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