Suitability of Sm3+-Substituted SrTiO3 as Anode Materials for Solid Oxide Fuel Cells: A Correlation between Structural and Electrical Properties

Abstract

Perovskite anodes, nowadays, are used in any solid oxide fuel cell (SOFC) instead of conventional nickel/yttria-stabilized zirconia (Ni/YSZ) anodes due to their better redox and electrochemical stability. A few compositions of samarium-substituted strontium titanate perovskite, Sm x Sr 1−x TiO 3−δ (x = 0.00, 0.05, 0.10, 0.15, and 0.20), were synthesized via the citrate-nitrate auto-combustion route. The XRD patterns of these compositions confirm that the solid solubility limit of Sm in SrTiO 3 is x < 0.15. The X-ray Rietveld refinement for all samples indicated the perovskite cubic structure with a Pm3m space group at room temperature. The EDX mapping of the field emission scanning electron microscope (FESEM) micrographs of all compositions depicted a lower oxygen content in the specimens respect to the nominal value. This lower oxygen content in the samples were also confirmed via XPS study. The grain sizes of Sm x Sr 1−x TiO 3 samples were found to increase up to x = 0.10 and it decreases for the composition with x > 0.10. The AC conductivity spectra were fitted by Jonscher's power law in the temperature range of 500-700 • C and scaled with the help of the Ghosh and Summerfield scaling model taking ν H and σ dc T as the scaling parameters. The scaling behaviour of the samples showed that the conduction mechanism depends on temperature at higher frequencies. Further, a study of the conduction mechanism unveiled that small polaron hopping occurred with the formation of electrons. The electrical conductivity, in the H 2 atmosphere, of the Sm 0.10 Sr 0.90 TiO 3 sample was found to be 2.7 × 10 −1 S·cm −1 at 650 • C, which is the highest among the other compositions. Hence, the composition Sm 0.10 Sr 0.90 TiO 3 can be considered as a promising material for the application as the anode in SOFCs.Energies 2019, 12, 4042 2 of 16 SOEC technology [1][2][3][4][5][6][7][8]. SOFCs are more efficient in comparison to a conventional power plant and lower temperature polymer-based fuel cells [9,10]. Electrolyte and electrodes are the essential component of a solid oxide fuel cell. Even if anionic, protonic [11,12] and dual-membrane cells [13] are reported, the first are the most studied in the literature. The state of the art material for the electrolyte is fluorite-structured yttria-stabilized zirconia (YSZ) because of its wide range of stability in oxidizing and reducing media [14], although doped ceria [15] and perovskite Sr-and Mg-incorporated lanthanum gallate (LSGM) are considered as alternatives for intermediate operative temperatures. Lanthanum strontium manganite (LSM)-YSZ composite and Sr-and Fe-doped lanthanum cobaltite (LSCF) are extensively used for cathodes, while Ni-based cermets are conventionally used as anode materials for SOFCs [16,17], although this Ni-based cermet anode material should demonstrate volume instability upon redox cycling and low-tolerance to carbon deposition when exposed to hydrogen [18]. Therefore, nickel-free, alternate-structured anode materials are essential to overcome these issues. Recen...

Investigating the effect of rGO on microstructural and electrical properties of La0.9Sr0.1Ga0.8Mg0.2O3 in intermediate temperature SOFCs

“…All the LSGM electrolyte samples are characterised by considerable compactness, uniform morphology, and distinct grains and grain boundaries. Density and relative densities of the electrolyte samples were determined by using the pycnometer method based on the Archimedes principle, 41 while the average grain size was estimated through a statistical approach associated with Image-J software. During experimental studies, the required precautions were considered and attention was paid to bubbles originating from water in the pycnometer.…”

Development of La and Mo Co-Doped SrTiO3 as Novel Anode Material for Solid Oxide Fuel Cell Applications

“…In air, the activation energy (E a ) for each regime was calculated using the Eq. ( 8) given below to investigate the mechanism of conductivity [27,28].…”

A Review of X-ray Photoelectron Spectroscopy Technique to Analyze the Stability and Degradation Mechanism of Solid Oxide Fuel Cell Cathode Materials

“…XPS is a well-established and widely used surface-sensitive spectroscopic technique for studying the elemental composition of the surface of SOFC cathode layers within the first few nanometers [ 2 ]. This photoelectron spectroscopic technique is used to quantitatively analyze the surface electronic structure of crystalline solid through the photoelectron spectra.…”

“…XPS provides details on the chemical composition near the surface region and the oxidation state of each element from the binding energy of particular core levels. Therefore, a highly surface-sensitive technique such as in situ synchrotron-based XPS can be used to understand how Sr segregation accelerates the degradation mechanism of the LSCF cathode, and this method often limits the surface catalytic activity for the ORR [ 2 ]. Figure 4 shows the typical XPS spectra of the LSCF cathode in the region with La 3d, Sr 3d, Co 2p, Fe 2p, and O 1s peaks.…”

“…Solid oxide fuel cells (SOFCs) are attractive and promising energy conversion devices for electricity production because of their high efficiency, fuel flexibility, and absence of precious noble metal catalyst [ 1 , 2 , 3 ]. A basic SOFC consists of a dense electrolyte, which is in contact with two porous and electro-catalytically active electrodes on either side ( Figure 1 ) [ 4 , 5 ].…”