Beyond the high entropy approach – highly functional, Sr-free, multicomponent cathodes for solid oxide fuel cells
Juliusz Dąbrowa a, Jan Adamczyk a, Karolina Bar a, Klaudia Zielińska b, Marek Zajusz a, Maria Szymczak c, Margarita Nowakowska a, Andrzej Mikuła a, Konrad Świerczek b d
a AGH University of Krakow, Faculty of Materials Science and Ceramics, Al. Mickiewicza 30, 30-059 Krakow, Poland
b AGH University of Krakow, Faculty of Energy and Fuels, Al. Mickiewicza 30, 30-059 Krakow, Poland
c AGH University of Krakow, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Krakow, Poland
d AGH Centre of Energy, AGH University of Krakow, ul. Czarnowiejska 36, 30-054 Krakow, Poland
Proceedings of 24th International Conference on Solid State Ionics (SSI24)
Emerging Materials for High-Performance Devices
London, United Kingdom, 2024 July 14th - 19th
Organizers: John Kilner and Stephen Skinner
Oral, Juliusz Dąbrowa, presentation 414
Publication date: 10th April 2024

The technology of solid oxide fuel cells (SOFCs) is widely considered to be one of the essential components of the next-generation power grid, offering unmatched efficiency, low pollution level, and the possibility of both producing (fuel cell mode) and storing energy (electrolysis mode). Its main deficiencies are high operating temperatures and still limited longevity, both factors being affected primarily by insufficient performance and degradation of the cathode materials. Unfortunately, in most state-of-the-art solutions, the excellent performance of materials walks hand in hand with their susceptibility to deterioration under cell’s operating conditions. A common reason for this behavior is the presence of alkali ions, mainly Sr and Ba, which on the one hand are considered indispensable for achieving sufficient catalytic activity, but on the other tend to form secondary phases, such as carbonates, which over time limit the amount of active cathode sites. One of the possible solutions proposed to counter these effects is the application of the high-entropy approach, which enables obtaining properties beyond the rule-of-mixture, and therefore overcoming some of the limitations of more conventional analogs. However, strict adherence to the high-entropy guidelines might become a limitation by itself, as the more elements we combine, the more difficult it becomes to preserve the single-phase structure and avoid the unwanted interactions between them.

In this study, we present the possibility of obtaining highly functional, alkali-free perovskites of superior performance, obtained through the progressing simplification of the starting La-Co-Cu-Fe-Mn-Ni and La-Cu-Fe-Mn-Ni-Ti high entropy systems. The properties of all materials are systematically studied, including their structure, oxygen nonstoichiometry, thermal expansion behavior, electrical properties, and stability against both typical electrolytes and under the operating conditions of the fuel cell. For the selected, most promising materials, the level of electrochemical performance is assessed using both symmetrical cells (cathodic polarization value Rp) and full cells (power output). The results show that most of the beneficial properties characterizing the base, high entropy systems, can be preserved in simpler, 3- and 4-component compositions while at the same bringing several new features, thanks to eliminating some of the suboptimal elements from the mixture. The electrochemical performance of the best materials, such as La(Co,Cu,Fe)O3 and La(Cu,Fe,Ni)O3, despite the lack of alkali ions is superior to the state-of-the-art LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) by a considerable margin, reaching the cathodic polarization value of 0.15 Ω·cm2 in the vicinity of 675 °C, making these materials potential candidates even for the low-temperature SOFCs (LT-SOFCs). This is especially impressive for the La(Cu,Fe,Ni)O3 composition, which not only does not contain alkali ions, but cobalt as well. Overall, it can be stated that the proposed approach can lead to materials characterized by a superior combination of functionality and electrochemical performance with respect to the currently utilized alternatives, while simultaneously addressing some of the most pressing issues of the SOFC cathode materials.

This research was funded in whole by National Science Centre, Poland, under project No. UMO-2021/41/B/ST8/04365.

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