resumo
Among the most promising electrode choices for solid oxide cells, the misfit calcium cobaltite, with the nominal composition [Ca2CoO3-delta](0.62)[CoO2] (C349), is gaining special relevance due to its ability to provide good performance in oxidizing conditions, and also for possessing a thermal expansion coefficient similar to that of the standard electrolytes. In this work, we investigate the electrochemical behavior of the misfit C349 with the addition of an active interlayer made of Ce0.8Pr0.2O2-delta (CPO, + 2 mol% Co), compared to the electrode mechanism of an interlayer-free C349 electrode. A combination of three different approaches for the distribution function of relaxation times analysis permits a careful analysis on the characteristic time constants associated with the surface-exchange processes, revealing the existence of parallel reaction paths at higher temperatures, where the pathway through the C349 electrode may take on an important role. Conversely, at lower temperatures, due to the poor ionic conductivity of the C349 compound, the interlayer pathway may become predominant, since the CPO + Co provides much higher ionic conductivity than the C349. These results highlight the competition between an increased electroactive area and the role of the surface-exchange on the CPO + Co interface, where the latter becomes more relevant on decreasing temperature.
palavras-chave
OXYGEN REDUCTION REACTION; RELAXATION-TIMES; ELECTROCHEMICAL PERFORMANCE; TRANSPORT-PROPERTIES; IMPEDANCE; CERIA; KINETICS; CATHODES; MICROSTRUCTURE; CELLS
categoria
Chemistry, Physical; Electrochemistry; Energy & Fuels; Materials Science, Multidisciplinary
autores
Araujo, AJM; Loureiro, FJA; Holz, LIV; Graca, VCD; Grilo, JPF; Macedo, DA; Paskocimas, CA; Fagg, DP
nossos autores
Francisco José Almeida Loureiro
Bolseiro de investigação
João Paulo de Freitas Grilo
Investigador Júnioragradecimentos
This study was financed in part by the Coordenacao de Aperfeicoa-mento de Pessoal de Nivel Superior-Brasil (CAPES) -Finance Code 001. Allan J. M. Ara (jo acknowledges the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq/Brazil, reference number 200439/2019-7) . Joao P. F. Grilo, Carlos A. Paskocimas and Daniel A. Macedo also thank CNPq/Brazil (482473/2010-0, 446126/2014-4, 308548/2014-0, 307236/2018-8, 431428/2018-2 and 309430/2019-4) . The Aveiro team acknowledges the projects PTDC/CTM-CTM/2156/2020, PTDC/QUI-ELT/3681/2020, POCI-01-0145-FEDER-032241, UID/EMS/00481/2019-FCT, CENTRO-01-0145-FEDER-022083, funded by FEDER, Centro Portugal Regional Operational Pro-gramme (Centro2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) and by national funds (OE) , through FCT/MCTES. F.J.A. Loureiro acknowledge FCT for the Investigator Grant (CEECIND/02797/2020) .