A Review on the Process-Structure-Performance of Lanthanum Strontium Cobalt Ferrite Oxide for Solid Oxide Fuel Cells Cathodes

Asadi F., Ahangari M., Mostafaei J., Kalantari N., Delibas N., Asghari E., Niaei A.

In this study, L0.8Ba0.2Fe1-xMnxO3 (LBFM-x, x = 0.0, 0.2, 0.5, 0.8) perovskite materials were synthesized by a Sol-Gel combustion method and were investigated as an electrode material for a supercapacitor device. The morphology, crystalline structure and electrochemical performance of the samples were studied in detail. The active points, where the electrochemical redox reaction takes place to store faradaic energy, are the oxygen vacancies on the surface of perovskite oxides. Partial substitution in the B-site of the perovskite structure, which is directly related to the oxygen vacancy in BO6 octahedral, is effective in optimizing the electrochemical performance. Based on the results of structural analysis, LBFM-0.2 has the highest concentration of oxygen vacancies; thus, it showed a higher electrochemical performance compared to other samples. The supercapacitors prepared with this electrode material should have an acceptably high specific capacitance of 685 F.g−1 at a current density of 2.0 A.g−1. The partial substitution of Mnn+ at the B-site increases the oxidation state of Fe cations and the mobility of oxygen ions through the oxygen vacancy sites. The electrochemical stability of LBFM-0.2, was evaluated by applying long charge-discharge cycles. After 3000 charge-discharge cycles, the supercapacitor was able to maintain about 94 % of its initial capacity.

Omeiza L.A., Kabyshev A., Bekmyrza K., Kubenova M., Kuterbekov K.A., Baratova A., Adaikhan S., Bakar S.A., Azad A.K.

Efficient cathode materials are essential to the overall cell performance of solid oxide fuel cell (SOFC). The high linear thermal expansion coefficient (TEC) of traditional cobalt-containing cathode materials, cobalt poisoning, and the expensive nature of cobalt mean that cobalt-free cathode materials must be examined. Sr-doped cobalt-free BaZr0.8Ni0.2O3-δ cathode materials were synthesised using the conventional solid-state reaction method, and investigated as potential cathode materials for SOFC application. The synthesised Ba1-xSrxZr0.8Ni0.2O3-δ (BSZN0, BSZN25, BSZN5; x = 0, 0.25 and 0.5) samples were characterized via X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, dilatometer, and electrochemical impedance spectroscopy. The XRD analysis of the synthesised samples revealed a well-defined peak position at 2theta, and indexed as pm-3 m cubic space group. At 800 °C, the electrical conductivity in air for BSZN0, BSZN25, and BSZN5 were 72.24 S/cm, 80.46 S/cm and 85.55 S/cm, respectively. The average linear thermal expansion coefficient obtained for BSZN0, BSZN25, and BSZN5 at 25 to 1000 °C were 10.4 × 10–6 K−1, 10. 9 × 10–6 K−1, and 11.2 × 10–6 K−1, respectively. The improved linear thermal elongation of BSZN0, BSZN25, and BSZN5 will ensure compatibility with commonly used electrolytes in SOFCs.

Sumaiyah S., Ibrahim N., Mohamed Z., Rozilah R., Kazmi J., Masood A., Ali M.

The effect of Cr3+ on the electrical, magnetic and magnetoresistance effect in Pr0.75Na0.05K0.2Mn1−xCrxO3 (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) synthesised using the solid-state method are reported. An analysis at room temperature of X-ray diffraction data using the Rietveld refinement method showed all samples crystallised in the orthorhombic phase with Pnma space group. It is found that unit cell volume increased from 230.60 Å3 (x = 0) to 231.25 Å3 (x = 0.01) suggesting that substitution with a low concentration of Cr3+ may predominately substitute for Mn4+ site. However, further substituting Cr3+ caused a decrease in unit cell volume from 231.15 Å3 (x = 0.02) to 227.74 Å3 (x = 0.05), indicating at high concentration of Cr3+ dominantly substituted the Mn3+. Cr3+ substitution slightly decreased the Curie temperature $${(T}_{C})$$ value from 140.7 K (x = 0.00) to 139.7 K (x = 0.01) and 139.3 K (x = 0.02) indicates the substitution of Cr3+ slightly disturb ferromagnetic (FM) interaction between Mn3+–O2−–Mn4+. Interestingly, further substitution of Cr3+ increased the $${T}_{C}$$ to 140 K (x = 0.03), 140.7 K (x = 0.04) and 143.4 K (x = 0.05) which revealed the possibility of the existence of ferromagnetic interaction between Cr3+ and Mn3+ ions due to the similar electronic configuration of Cr3+ with that of Mn4+ ions. The observed large increased in resistivity with Cr3+ substitution and the decrease in metal insulator transition temperature (TMI) from 122 K (x = 0) to 90 K (x = 0.05) from resistivity versus temperature curve indicates the Cr substitution weakened mechanism and induce more competition between double-exchange (DE) and super-exchange (SE) mechanism involving Mn3+–O2−–Mn4+, Cr3+–O2−–Mn3+, Cr3+–O2−–Cr3+, Cr3+–O2−–Mn4+. The observation large magnetoresistance (MR) effect in Cr-substituted sample at low temperature region indicates enhancement of extrinsic MR effect, which likely arises from spin polarized tunnelling.

Omeiza L.A., Kuterbekov K.A., Kabyshev A., Bekmyrza K., Kubenova M., Afroze S., Bakar S.A., Azad A.K.

Intermediate-temperature solid oxide fuel cell (IT-SOFC) work at moderate temperature range (600—800 ℃), thereby eliminating the issue of thermal degradation of electrode materials, reduce operational cost, increase flexibility of material selections, and enhance electrochemical stability of cell components. At intermediate-temperature range, there exists sluggish cathodic reaction, high activation energy and slow oxygen reduction reaction (ORR) at the cathode. Several cobalt-containing cathode perovskite materials with mixed ionic and electronic properties have been developed, which has helped in resolving sluggish ORR and enhances cathodic reaction, thereby increasing the overall performance of IT-SOFC. The expensive nature of cobalt, high evaporation rate and poor thermal expansion coefficient (TEC) means cobalt-free cathode materials need to be investigated. The present study gives an insight into the current trends of cobalt-free cathode materials development in IT-SOFC. Literature reviewed showed composite La0.65Ca0.35FeO3-δ-Gd0.2Ce0.8O2-δ (LCF-GDC), and La0.7Sr0.3Cu0.15Fe0.85O3-δ cathode materials has good polarisation resistance of 0.28 Ωcm2 at 750 ℃, and 0.0153 Ωcm2 at 700 ℃, respectively. Limitations, challenges, gaps were identified, and possible future research direction was recommended. The study also analysed the use of symmetrical electrodes, as it will help resolve the complexity of developing different electrode materials for cathode and anode in IT-SOFC. Holistic efforts were devoted to ensuring that the literature reviewed was recent (within the last 4yrs), and relevant to the current constraints impeding cathode materials use in IT-SOFC. This review study is meant to serve as a reference material to related researchers, and industry experts looking for the most recent accomplishments in cobalt-free cathode materials development.

Samreen A., Ali M.S., Huzaifa M., Ali N., Hassan B., Ullah F., Ali S., Arifin N.A.

AbstractThe high‐temperature solid oxide fuel cells (SOFCs) are the most efficient and green conversion technology for electricity generation from hydrogen‐based fuel as compared to conventional thermal power plants. Many efforts have been made to reduce the high operating temperature (>800 °C) to intermediate/low operating temperature (400 °C<T<800 °C) in SOFCs in order to extend their life span, thermal compatibility, cost‐effectiveness, and ease of fabrication. However, the major challenges in developing cathode materials for low/intermediate temperature SOFCs include structural stability, catalytic activity for oxygen adsorption and reduction, and tolerance against contaminants such as chromium, boron, and sulfur. This research aims to provide an updated review of the perovskite‐based state‐of‐the‐art cathode materials LaSrMnO3 (LSM) and LaSrCOFeO3 (LSCF), as well as the recent trending Ruddlesden‐Popper phase (RP) and double perovskite‐structured materials SOFCs technology. Our review highlights various strategies such as surface modification, codoping, infiltration/impregnation, and composites with fluorite phases to address the challenges related to LSM/LSCF‐based electrode materials and improve their electrocatalytic activity. Moreover, this study also offers insight into the electrochemical performance of the double perovskite oxides and Ruddlesden‐Popper phase materials as cathodes for SOFCs.