Enhancement of the oxygen reducing reaction in nanostructured La0.6Sr0.4CoyFe1-yO3 and La0.8Sr0.2MnO3 SOFC cathodes

JOAQUIN SACANELL; AUGUSTO MEJIA GOMEZ; JIMENA SIEPE; HERNÁN MARTINELLI; ANA GABRIELA LEYVA; DIEGO G. LAMAS

Conferencia; The Energy and Materials Research Conference; 2015

La1-xSrxCoyFe1-yO3 (LSCF) and La0.8Sr0.2MnO3 (LSM) are the most commonly used cathodes in Solid Oxide Fuel Cells (SOFC). A significant increase of the specific area of the cathode can be achieved by preparing structures on the nanometric scale and thus, an improved performance can be expected. However, the high operating temperature (~ 1000°C) of LSM-based SOFCs hinders their stability, so it is important to enhance the electrochemical properties at lower temperatures. In the present work, we have developed nanostructured cathodes prepared from LSCF and LSM nanotubes of enhanced performance, allowing its use at 700-800°C. We observed that our cathodes have qualitative improvements compared with microstructured materials: - In the case of LSCF, improved electrochemical properties are related to the increase of the specific surface area and also to the reduced size of the nanoparticles that form the cathode, giving rise to higher grain-boundary O2--anion diffusivity. - In the case of LSM, the diffusion in the gas phase is optimized to a negligible level and also we observed evidence of ionic conduction though the cathode, which is extremely rare in LSM cathodes. In Figure 1 we show typical SEM images of the cathodes obtained with LSCF and LSM nanotubes. In some cases the hollowed structure of the tubes disappeared and thus the electrode is formed by a collection of nanotubes or dense rods after performing the sintering of the cathode (a porous thick film), depending on the size of the precursor nanotubes. Figure 2 shows: (a) the reduction of the area specific resistance (ASR) in LSCF cathodes made with smaller diameter nanotubes and (b) in LSM cathodes, the gas phase transport contribution at low frequency contribution only appears at reduced oxygen partial pressures (P(O2))