Tailoring Electrocatalytic Properties of Solid Oxide Fuel Cell Composite Cathodes Based on (La_0.8Sr_0.2)_0.95MnO_3+δ and Doped Cerias Ce_1–xLn_xO_2–δ (Ln=Gd, La, Er, Pr, Tb and x=0.1–0.2)

Abstract

Composites made of different doped cerias and (La0.8Sr0.2)0.95MnO3+δ were studied as potential solid oxide fuel cell cathodes. Tb, Pr, Gd and Er have been introduced as ceria dopants to enhance the electrocatalytic properties of (La0.8Sr0.2)0.95MnO3+δ composites fabricated within. Different electrochemical behaviors were observed for the studied composites depending on lanthanide cation nature, i.e., whether they can exhibit different oxidation states or not. Specifically, (La0.8Sr0.2)0.95MnO3+δ/ceria composites with a mixed valence dopants (Tb and Pr) in the CeO2 structure are the best performing and present a limiting step at low frequencies; whereas those with ceria‐doping elements with fixed oxidation state (Gd and Er) exhibit the limiting processes at higher frequencies. This fact is related to the higher magnitude of the TPB enlargement in the composite cathode achieved thanks to the promotion of mixed ionic‐electronic conductivity in the Pr/Tb‐doped ceria phase. The best cathode performance was obtained with (La0.8Sr0.2)0.95MnO3+δ_Ce0.8Pr0.2O2–δ cathodes with the lowest values for the polarization resistance in the 900–700 °C temperature range.

Influence of Ln elements (Ln = La, Pr, Nd, Sm) on the structure and oxygen permeability of Ca-containing dual-phase membranes

“…Besides, the CPO-PCFO membrane exhibits much higher oxygen permeation flux than that of the CSO-SCFO membrane, which may be related to the fact that CPO has both higher ionic conductivity and non-negligible electronic conductivity [44]. As can be seen, the oxygen permeation flux through CPO-PCFO membrane can sustain around 0.25 mL cm -2 min -1 over the 40 hours, which is dissimilar with previously reported on the phenomenon of single-phase membranes, in which the oxygen permeation flux through Ba0.5Sr0.5Fe0.2Co0.8O3-δ (BSFCO) membrane promptly drop from 1.5 mL cm -2 min -1 to 0 within 10 hours [21,25,51].…”

“…This is also consistent with the above analysis. mixed valence of Pr 3+ and Pr 4+ , some polarons can hop between different valence states, resulting in improvement in the electronic conductivity of Ce0.9Pr0.1O2-δ phase [43,44].…”

“…It is noticeably seen that the CPO-PCFO composite exhibits the highest oxygen permeability among our investigated four CLnO-LnCFO membranes and yields an oxygen permeation flux of 0.51 mL cm -2 min -1 at 1000 o C. On the one hand, it may be in connection with the non-negligible electronic conductivity of CPO, whereas other lanthanide elements in CLnO only own the fixed valence (+3). As the Pr element has mixed valence of Pr 3+ and Pr 4+ , some polarons can hop between different valence states, resulting in improvement in the electronic conductivity of Ce0.9Pr0.1O2-δ phase [43,44].…”

“…For example, the electronic conductivity of Ce0.8Pr0.2O2-δ is the 0.021 S/cm at 800 o C in the oxygen partial pressure gradient 1/0.21 bar, which is the same order of magnitude comparing with the ionic conductivity (0.077 S/cm) [45]; whereas other electronic conductivity of lanthanide-doped ceria is negligible, such as Ce0.9Gd0.1O2-δ phase (~10 -3.8 S/cm) at 800 o C [46]. Since Ce0.9Pr0.1O2-δ owns both high ionic conductor and non-negligible electronic conductivity, the reaction sites for oxygen permeation cover the whole membrane surfaces for CPO-PCFO, which is not confined to the triple-phase boundary (TPB) and the surface of perovskite phases, thereby improving the oxygen permeability [44,47]. On the other hand, it may be concerned with the electronic conductivity of perovskite.…”

Improving the performance of oxygen transport membranes in simulated oxy-fuel power plant conditions by catalytic surface enhancement

“…As shown in the Bode plot (Figure 9.a), processes contributing to the high frequencies part of the spectra are mainly responsible for the large Rp value. These processes are related to the transport of species through the 10Sc1YSZ-MCO/Ce-doped material interface [50], which could indicate that a lack of electronic conductivity limits the performance of this backbone. When the content of the electronic conducting phase was increased from 1).…”