ReBaCo_2-xMn_xO_5+δ (Re: rare earth element) layered perovskites for application as cathodes in Solid Oxide Fuel Cells

Abstract

Decrease of the operation temperature is considered as one of the most important targets in development of Solid Oxide Fuel Cells (SOFC), as it leads to considerable extension of their long-term operation and makes construction and utilization of the SOFC generators cost-effective. Relatively high value of the activation energy of the oxygen reduction reaction (ORR) occurring at the cathode, and consequently, large cathodic polarization resistance at lower temperatures is a major obstacle hindering usage of SOFCs at decreased temperatures. In this work possibility of application of manganese-doped cobalt-based cation-ordered perovskites as candidate cathode materials in the intermediate temperature (IT, ca. 600-800 °C) range is discussed. The considered oxide materials, depending on chemical composition, i.e. choice of Re element and Mn-doping level exhibit high values of mixed ionic-electronic conductivity, as well as good catalytic activity toward the oxygen reduction and moderate thermal expansion. Cathode layers manufactured on a basis of selected ReBaCo2-xMnxO5+δ oxides show low polarisation resistance.

Peculiar Properties of Electrochemically Oxidized SmBaCo2−xMnxO5+δ (x = 0; 0.5 and 1) A-Site Ordered Perovskites

“…Moreover, the Rietveld refinements of all the XRD data are presented in Figure 4a-c. On the basis of previous works, different space groups were selected for the as-synthesized materials: Pmmm for SmBaCo 2 O 5+δ , P4/mmm for SmBaCo 1.5 Mn 0.5 O 5+δ , and Cmmm for SmBaCoMnO 5+δ . For more details regarding the selection of the crystal structure for compounds with equilibrium oxygen content, see [15,17,31,32]. simple perovskites [5,6,12], the discussed effect might be related to the preferential, layered placement of the oxygen vacancies in the initial samples.…”

High-entropy approach to double perovskite cathode materials for solid oxide fuel cells: Is multicomponent occupancy in (La,Pr,Nd,Sm,Gd)BaCo2O5+δ affecting physicochemical and electrocatalytic properties?

“…The calculated values of the electrode polarization resistance exhibit a linear dependence on temperature in log R p -T −1 coordinates, as is shown in Figure 7. The established activation energy is 1.21 eV, which can be considered moderate (Zheng et al, 2012;Pelosato et al, 2014;Olszewska and Świerczek, 2019). The lowest recorded value of R p equals to 0.037 Ω cm 2 at 900 °C, while it increases to 0.175 Ω cm 2 at 750 °C.…”

“…While doping at the B-site of Co-based double perovskites (e.g., with Fe, Mn, or Cu) has been relatively thoroughly studied (Karppinen et al, 2002;Zhang, 2004;Tsvetkov et al, 2011;Kim et al, 2013;Broux et al, 2014;Tsvetkov et al, 2016;Kong, 2018;Olszewska and Świerczek, 2019;, in the case of this type of double perovskites, the occupancy of the A-sites can have an equally great impact on the properties of the materials, creating further opportunities for their tailoring. In fact, most of the properties, such as oxygen non-stoichiometry, electronic conductivity, ionic conductivity, or thermal expansion coefficient (TEC), can be directly correlated to the ionic radius of the A-site lanthanide and/or its difference when compared to Ba cations, see also Supplementary Figure S1 (Lee et al, 1998;Du et al, 2014;Kim and Manthiram, 2015;Olszewska, Świerczek, et al, 2019).…”

“…While doping at the B-site of Co-based double perovskites (e.g., with Fe, Mn, or Cu) has been relatively thoroughly studied (Karppinen et al, 2002;Zhang, 2004;Tsvetkov et al, 2011;Kim et al, 2013;Broux et al, 2014;Tsvetkov et al, 2016;Kong, 2018;Olszewska and Świerczek, 2019;, in the case of this type of double perovskites, the occupancy of the A-sites can have an equally great impact on the properties of the materials, creating further opportunities for their tailoring. In fact, most of the properties, such as oxygen non-stoichiometry, electronic conductivity, ionic conductivity, or thermal expansion coefficient (TEC), can be directly correlated to the ionic radius of the A-site lanthanide and/or its difference when compared to Ba cations, see also Supplementary Figure S1 (Lee et al, 1998;Du et al, 2014;Kim and Manthiram, 2015;Olszewska, Świerczek, et al, 2019). In most cases, the selection of bigger RE ions, such as La or Pr, helps in enhancing the transport properties, however, at a price of increasingly high TEC values (Kim and Manthiram, 2015) (e.g., from 18.2 to 29.5•10 -6 K −1 for YBaCo 2 O 5+δ and LaBaCo 2 O 5+δ , respectively) (Olszewska, Świerczek, et al, 2019) Similarly, the oxygen nonstoichiometry also changes drastically, varying at room temperature from δ ≈ 0.41 to δ ≈ 1 for Y-and La-based compositions, respectively, and can be further modified by substituting Ba with other smaller alkali ions such as Sr or Ca (Kim and Manthiram, 2015).…”

“…In fact, most of the properties, such as oxygen non-stoichiometry, electronic conductivity, ionic conductivity, or thermal expansion coefficient (TEC), can be directly correlated to the ionic radius of the A-site lanthanide and/or its difference when compared to Ba cations, see also Supplementary Figure S1 (Lee et al, 1998;Du et al, 2014;Kim and Manthiram, 2015;Olszewska, Świerczek, et al, 2019). In most cases, the selection of bigger RE ions, such as La or Pr, helps in enhancing the transport properties, however, at a price of increasingly high TEC values (Kim and Manthiram, 2015) (e.g., from 18.2 to 29.5•10 -6 K −1 for YBaCo 2 O 5+δ and LaBaCo 2 O 5+δ , respectively) (Olszewska, Świerczek, et al, 2019) Similarly, the oxygen nonstoichiometry also changes drastically, varying at room temperature from δ ≈ 0.41 to δ ≈ 1 for Y-and La-based compositions, respectively, and can be further modified by substituting Ba with other smaller alkali ions such as Sr or Ca (Kim and Manthiram, 2015). However, despite the profound effect of the A-site occupancy on the properties of the double perovskites, the studies concerning the utilization of multiionic A-site arrangement (with multiple lanthanide ions) are still much less popular than those of B-site modifications.…”