Application In Intermediate-temperature Solid Oxide Fuel Cells Research Articles

Structural, thermal, surface, and electrical properties of Bi2O3 ceramics co–doped with Er–Ho–Tb rare earths

Face–centered cubic–Bi2O3 (δ–phase) material is a better ion conductor when compared to other types of solid electrolytes that have been declared in the literature due to its anion–defective crystal configuration, and hence it can be a promising solid electrolyte choice for intermediate temperature SOFC applications. In this research, Er–Ho–Tb co–doped Bi2O3 compounds were successfully synthesized by the solid–state reaction method and characterized using the XRD, TG & DTA, FPPT, and FE–SEM techniques. Apart from sample 4Er4Ho4Tb, each sample became stable with a cubic δ–phase at room temperature, according to XRD patterns. The DTA curves revealed no exothermic or endothermic peaks, implying a phase change in the constant heating cycle. The conductivity of Ho–rich compositions was higher than that of others, confirming the impact of cation polarizability on conductivity. In addition, at 700 °C, the sample 4Er8Ho4Tb with 1:2:1 content ratios had the highest conductivity of 0.29 S/cm. The porosity on the grain boundaries increased with doping, leading to higher grain boundary resistance, which could be responsible for the conductivity drop.

Ce-doped promotes the phase stability and electrochemical performance of SrCoO3-δ cathode for intermediate-temperature solid oxide fuel cells

The development of cathode with high oxygen reduction reaction (ORR) activity is crucial for intermediate-temperature solid oxide fuel cells (IT-SOFCs). SrCoO3-δ oxides, a mixed ion-electron conductivity (MIEC), are promising cathode materials. However, pure SrCoO3-δ exhibits a hexagonal or rhombohedral structure with poor electrical properties, limiting its application in IT-SOFCs. In this work, high-valence Ce4+ is doped at the A-site of SrCoO3-δ perovskite to improve the phase structural stability and electrochemical activity of SrCoO3-δ. The findings reveal that Ce4+ doping in small amounts significantly advances the conductivity and ORR activity due to enhanced structural stability. Among the series of samples, Sr0.95Ce0.05Co3-δ (SCC005) presents the best electrochemical performance. Moreover, the addition of Ce0.8Gd0.2O2-δ (GDC) further reduces polarization resistance by about ∼7 times. The peak power density of 1.3 W cm−2 is obtained at 750 °C for the SCC05-30%GDC cathode. The results indicate that A-site Ce doping is a promising strategy to enhance the ORR activity of SrCoO3-δ oxides.

Characterization of BaFe0.8Zn0.1Nb0.1O3-δ and BaFe0.6Zn0.3Nb0.1O3-δ Perovskite Cathode Materials for Intermediate-Temperature Solid Oxide Fuel Cells

This study explores the potentiality of the zinc and iron-based perovskite cathode materials in intermediate temperature solid oxide fuel cells (SOFCs), for which BaFe0.8Zn0.1Nb0.1O3-δ (BFZNO:1) and BaFe0.6Zn0.3Nb0.1O3-δ (BFZNO:2) materials with cubic crystal phase purity were considered. These materials have been effectively synthesized by employing the sol–gel autocombustion process. The structural details and phase purity of the synthesized nanomaterials were confirmed from the data obtained from the XRD patterns, while SEM images revealed that both materials are highly porous with grain sizes of 200–250 nm and 55–65 nm for BFZNO:1 and BFZNO:2, respectively. The DC electrical conductivity of BFZNO:1 was estimated as 3.98 S/cm and that of BFZNO:2 as 3.56 S/cm at 700 °C. The BFZNO:1 exhibited a superior current density of 1360 mAcm–2, a power density of 530 mW cm–2, and an open circuit voltage of 1.29 at an intermediate temperature of 700 °C, confirming the potential of Zn and Fe-based perovskite cathode materials for application in intermediate temperature SOFCs.

Physicochemical properties of the Crofer 22 APU steel with La0.6Sr0.4Co0.2Fe0.8O3-δ protective-conductive coatings prepared by pulsed laser deposition

Commercial La0.6Sr0.4Co0.2Fe0.8O3-? powder was used for preparation of corresponding perovskite films on commercial Crofer 22 APU high chromium steel by pulsed laser deposition. The obtained films PLD1 and PLD2 with a thickness of 1.1 and 0.35 ?m, respectively, were dense and homogeneous, with good adhesion to the polished surface. Oxidation studies of the samples were carried out in air at 800?C for 200h. The calculated parabolic rate constant kp after isothermal oxidation for the PLD1 sample was 4.10 ? 10?14 g2cm?4s?1 and was approximately four times lower than the oxidation rate determined for the PLD2 sample. As a result of the oxidation process, in both cases, a thin oxide layer of chromia and Mn1.5Cr1.5O4 spinel was formed on the steel/film interface. In addition, small amounts of manganese-chromium spinel crystals were observed on the films? surfaces. Values of the specific electrical resistance at 800 ?C after 100 h of the experiment were 0.06 and 0.038W?cm2 for PLD1 and PLD2, respectively. The results indicate that the applied coatings meet the criteria set upon protective-conductive layers for interconnect materials, for the IT-SOFCs (intermediate-temperature solid oxide fuel cells) applications.

Development of oxide composite materials for cathode element of IT-SOFCs

Investigating the properties of composite oxide for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been done as a new cathode material. Using a solid-state reaction method, the metallic oxide material has been employed to create the composite model system. During the sintering process, a model system of Sm0.5Sr0.35Ba0.15FeO3-δ (SSBF15) was constructed. Thermal gravimetric analysis (TG) was played to utilize the oxygen content and weight loss of the model. In the meantime, the structure of the composite was characterized using X-ray diffraction (XRD), and the conductivity properties were tested by thermal conductivity. The structural design was made possible by the findings, which revealed that the composite model structure exhibited the crystalline structure with perovskite phase. Weight losses during the construction of the structure were reflected in the decomposition and evaporation of the composite's constituent parts. After the calcination process up to 950 °C, the model system's formation oxygen content was obtained of 2.94 in 800 °C. The electrical conductivity maximum obtained in 12.2 S·cm-1 at 430 °C. At low temperatures, the conductive behavior was affected by the metallic element, while at higher temperatures, it was influenced by the ionic structure. As a result, mixed ionic and electric conductors (MIEC) were extensively utilized in the process of generating the conductive properties. The SSBF15 composite has a good chance of being used as an alternative cathode material with a perovskite single phase for future IT-SOFCs applications based on the structure and conductivity results. Additional testing and observation are required to determine the resistance's value when incorporated into the electrolyte and its heat expansion properties

Investigation on high entropy alloys as interconnect material for intermediate temperature solid oxide fuel cells

Investigation of Solid Oxide Fuel Cells (SOFCs) is receiving great attention due to its higher efficiency and zero environmental pollution during operation. Interconnects are a critical part of the SOFC stack which connects the cells in series and combines the electricity produced. The present study aims to investigate High Entropy Alloys (HEAs) for interconnect application in intermediate temperature SOFC. Towards this, FeCoCrNi, FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs are prepared by vacuum arc melting and examined for its phase evaluation. Thermal stability, thermal expansion, resistivity, oxidation, and Area Specific Resistance (ASR) are investigated up to 800 °C. Oxidation studies show the formation of multicomponent oxide in the HEAs which suppresses the growth of Cr2O3 layer. FeCoCrNiMn0.1, FeCoCrNiMn0.5, and FeCoCrNiMn HEAs possess ASR values less than 100 mΩ.cm2 in the temperature range of 600–800 °C which ensure the superior performance of the SOFC stack.

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

Perovskite-structured La1-xSrxCo1-yFeyO3-δ (LSCF) is a promising mixed ionic/electronic-conducting material that exhibits excellent electro-catalytic activity toward oxygen reduction and oxygen evolution reactions. LSCF offers potential applications in many processes, such as electrodes for solid oxide fuel cells (SOFCs), oxygen sensors, and dense membrane for oxygen separation and thus have been studied extensively in various fields. However, its physical and electrochemical properties are substantially influenced by dopant concentration, dopant type and processing conditions (synthesis methods, composite cathode effect, fabrication conditions, and chromium poisoning). Understanding and correlating the effect of LSCF composition, its synthesis methods, fabrication conditions, and its parameters are essential to enhance the performance of LSCF cathode for high- to- intermediate temperature SOFC applications. This review emphasizes the importance of enhancing the performance of LSCF cathode by optimizing the influential factors to facilitate and expedite research and development efforts for SOFC commercialization in the near future. Various synthesis and fabrication methods used to prepare and fabricate LSCF and LSCF-based composite cathodes are discussed in detail. Moreover, their pros and cons in optimizing the microstructure of LSCF cathodes are highlighted. Finally, the strategies to improve the long-term microstructural stability and electrochemical performances of the LSCF cathode are discussed.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

Development of cobalt-free oxide (Sm0.5Sr0.5Fe0.8Cr0.2O3-δ) cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs)

A cobalt-free perovskite oxide Sm0.5Sr0.5Fe0.8Cr0.2O3-δ (SSFC) has been exploited as a novel cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The cathode model was synthesized with the addition of the chromium element in the B side of the composite metallic oxide system, which was then formed by the solid-state reaction method. The model system was further characterized in detail for getting the properties behavior. The solid-state reaction of the SSFC system was observed through thermal gravimetric analysis. Meanwhile, the structural properties were investigated by x-ray diffraction, and the weight loss was examined by the thermal gravimetric analysis as well. Furthermore, the thermal expansion coefficient was determined by the thermal-mechanical analysis, and the conductivity properties were tested by the thermal conductivity analysis. The result showed that the SSFC cathode demonstrated the crystalline structure based on the design with a perovskite phase. The oxygen content created on the model structure was obtained to be 2.98 after the calcination process. The average thermal expansion coefficient was achieved up to 5.0×10-6 K-1 as the heating given up to 800 °С. Moreover, the conductivity value reached from 2 S∙cm-1 at 400 °С and it increased to be a maximum of 7.5 S∙cm-1 at 700 °С. In addition, the presence of Cr6+ cation valence coordinated with the oxygen anion could lead to generating a large concentration of oxygen vacancies on the cathode surface, facilitating the transport of the O2− anion in the cathode system. Based on these results, the SSFC cathode has good properties as a composite system promising for IT-SOFCs application in the future

Effects of Cr/Ti co-doping on the electrical and thermal properties of tantalum-based electrolyte materials for solid oxide fuel cells

New triclinic oxide material Ta1−x−yTixCryO2.5−δ (x = 0.077, y = 0–0.053) was synthesized via an oxalate co-precipitation method and tested as a novel electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Structural, electrical, and thermal properties of tantalum-based electrolyte co-doping with Cr3+/Ti4+ content were studied. X-ray powder diffraction showed that the crystal structure changed from orthorhombic to triclinic due to co-doped, and its high-temperature triclinic (pseudo-tetragonal) phase of tantalum pentoxide (H-Ta2O5) structure was stabilized to room temperature by doping. The crystalline phase facilitates the generation of more oxygen vacancies, which increases the electrical conductivity. The appearance of oxygen vacancies in the crystal with triclinic structure was confirmed with Raman spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy results exhibited the grain size decreases gradually with doping. Impedance curves showed high total ionic conductivity (1.48 × 10–1 S/cm at 700 °C) and low activation energy (Ea = 0.857 eV) for Ta0.9Ti0.067Cr0.033O2.5−δ. Thermal expansion coefficients (3.09 × 10–6 K−1) for co-doped samples were much lower in comparison to other electrolytes. Based on the results reported in this work, Ta1−x−yTixCryO2.5−δ can be an excellent oxygen conductor and recommended as solid electrolytes for IT-SOFC applications.

Electrochemical performance of novel NGCO-LSCF composite cathode for intermediate temperature solid oxide fuel cells

In this study, a co-dopant CGO was synthesized to produce more efficient cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Neodymium (Nd) was doped into CGO in four different weight ratios in the formula NdxGd0.15Ce0.85-xO2-δ (NGCO); the selected percentages for x were 1%, 3%, 5% and 7%. XRD patterns showed pure phase for all synthesized compositions and good compatibility at high temperature under static air with the most common ceramic cathode material in IT-SOFC (La0·60Sr0·40Co0·20Fe0·80O2-ä, LSCF). Impedance spectroscopic characterization of symmetrical cells of the composite NGCO-LSCF at different temperatures (650–800 °C in steps of 50 °C) and a frequency range of 0.1–1 MHz in synthetic air revealed interesting results. The lowest polarization resistance (Rp) was achieved for Nd0.05Gd0.15Ce0·80O2-δ (0.06 Ω cm2 at 800 °C, 0.17 Ω cm2 at 750 °C, 0.31 Ω cm2 at 700 °C, and 0.59 Ω cm2 at 650 °C). The expected decrease in Rp was not observed for the sample with higher Nd content (7% Nd). Thus, it can be said that there is a distinction between the compositions Nd0.05Gd0.15Ce0·80O2-δ and Nd0.07Gd0.15Ce0·78O2-δ; the co-doping of Nd in NGCO incremented the oxygen ion diffusion path, thereby optimization in the triple phase boundary (TPB) sites was obtained. Furthermore, SEM and TGA measurements were conducted to clarify the reasons of such improvements. This work showed that an NGCO-LSCF composite can be considered as a potential candidate for cathode material for future IT-SOFC applications.

Superionic conductive La3+ and Pr3+ Co-doped cerium oxide for IT-SOFC applications

La3+ and Pr3+ co-doped cerium oxide compositions were synthesized and examined as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications. The cubic fluorite structure was confirmed with powder X-ray diffraction (XRD) and Raman studies. High-resolution scanning electron microscope (HR-SEM) micrographs depicted the distribution of particles in a narrowed manner on the porous structure and high-resolution transmission electron microscope (HR-TEM) image exhibited the particles are roughly in a spherical shape. Ultraviolet and photoluminescence spectra affirmed the formation of oxygen vacancies. Thermal analysis at an intermediate temperature range affirmed the high thermal stability without any structural transitions and decompositions. High thermal expansion coefficient values were observed at the intermediate temperature range. The ionic conductivity drastically enhanced with the incorporation of La3+ dopant and Ce0.8La0.1Pr0.1O2−δ solid electrolyte expressed the highest conductivity of 1.84 × 10−1 S/cm at 600 °C. Hence, Ce0.8La0.1Pr0.1O2−δ solid electrolyte is an excellent candidate in the IT-SOFC field.

Preparation and electrochemical properties of an La-doped Pr2Ni0.85Cu0.1Al0.05O4+δ cathode material for an IT-SOFC

The cathode material Pr2-xLaxNi0.85Cu0.1Al0.05O4+δ (PLNCA, x = 0, 0.2, 0.5 and 1.0) was synthesized by an EDTA-citrate process for use in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The phase structure and compatibility of the PLNCA with a La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) electrolyte was characterized by X-ray diffraction analysis. A test of thermodynamic stability shows that only PrLaNi0.85Cu0.1Al0.05O4+δ can work for 72 h at 700 °C without decomposition. The average thermal expansion coefficient of the PLNCA material matches well with that of the LSGM electrolyte. The electrical conductivity of the PLNCA material varies in the range of 40–80 S cm−1 at 400 °C. The area specific resistance of the PLNCA cathode on LSGM electrolyte was determined to be 0.029, 0.035, 0.036 and 0.037 Ω cm2 for x = 0, 0.2, 0.5, 1.0 at 800 °C, respectively. Moreover, the power density of the electrolyte supported single cell for x = 0, 0.2, 0.5, 1.0 was determined to be 392, 357, 350 and 341 mW cm−2 at 700 °C, respectively. Among PLNCA materials, PrLaNi0.85Cu0.1Al0.05O4+δ shows the best compromise between electrochemical properties and thermodynamic stability and could serve as a potential cathode material for application in IT-SOFCs.

Influence of processing conditions on the ionic conductivity of holmium zirconate (Ho2Zr2O7)

Nanopowders of holmium zirconate (Ho2Zr2O7) synthesised through carbon neutral sol-gel method were pressed into pellets and individually sintered for 2 h in a single step sintering (SSS) process from 1100 °C to 1500 °C at 100 °C interval and in a two step sintering (TSS) process at (I) −1500 °C for 5 min followed by (II) - 1300 °C for 96 h. Relative density of each of the sintered pellet was determined using the Archimedes’ technique and the theoretical density was calculated from crystal structure data. Grain size was obtained from SEM micrographs using ImageJ. Pellets processed by TSS have been found to be denser (98 %) with less grain growth (1.29 μm) as compared to the pellets processed using SSS process. Ionic conductivity of Ho2Zr2O7 pellets sintered by two different processes was measured using ac impedance spectroscopy technique over the temperature range of 350 °C–750 °C in the frequency range of 100 mHz–100 MHz for both heating and cooling cycles. The temperature dependence of bulk (2.67⨯10−3 Scm−1) and grain boundary (2.50⨯10−3 Scm−1) conductivities of Ho2Zr2O7 prepared by TSS process are greater than those processed by SSS process suggesting the strong influence of processing conditions and grain size. Results of this study, indicates that the TSS is the preferable route for processing the holmium zirconate as it can be sintered to exceptionally high densities at lower temperature, exhibits less grain growth and enhanced ionic conductivity compared with the samples processed by SSS process. Hence, holmium zirconate can be considered as a promising new oxide ion conducting solid electrolyte for intermediate temperature SOFC applications between 350 °C and 750 °C temperature range.

Evaluation of Fe-Doped CGO Electrolyte for Application in IT-SOFCs

A challenge encountered with intermediate temperature solid oxide fuel cells (IT-SOFCs) is lowering the densification temperature of the doped ceria electrolyte and improving its ionic conductivity. Ceria doped with 10 mol% gadolinium oxide and 0, 1, 5 mol% iron oxide were synthesized by a low temperature precipitation route based on hexamethylenetetramine as the precipitating agent. The as-synthesized precursors are nanocrystalline powders with a homogeneous morphology. Co-doping with Fe3+ changes the sintering behaviour of the doped cerium oxide and favours densification at lower temperatures. Through a comprehensive elementary, structural, microstructural and electrochemical analysis of the co-doped cerium oxide, it was established the doping mechanism of Fe3+ and its effect on the bulk and grain boundary conductivities. The overall aim is to evaluate its suitability for application as an electrolyte in IT-SOFC applications.

Study of a Promising Co-Doped Double Perovskite Cathode Material for IT-SOFCs

Based on the high catalytic activity and mixed ionic and electronic conductivity, double layered perovskites have been recognized as advanced cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). A recent study has outlined that the synergic effect of co-doping high valence cations (Nb5+ and Ta5+) on a simple perovskite (SrCo1.8Ta0.1Nb0.1O5+δ) has created an optimal balance of oxygen vacancies, ionic mobility and surface electron transfer which results with a drop of the ASR and a promising power density of the fuel cell. In this study, a co-doped double layered perovskite, LnBa0.5Sr0.5Co1.8Ta0.1Nb0.1O5+δ (Ln = Sm and Pr), was evaluated as IT-SOFC cathode material. The properties of the materials were analyzed with yttria stabilized zirconia and gadolinium-doped ceria electrolytes. As result, the Ta-Nb co-doped materials exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance over 100 hours, making them as a promising cathode material for applications in IT-SOFCs.

Use of waste water glass as silica supplier in synthesis of pure and Mg-doped lanthanum silicate powders for IT-SOFC application

Water glass in alkali solution (Na2SiO3/NaOH) an abundant effluent, generated in the alkaline fusion of zircon sand, represents a potential silica source to be converted in useful silica technological application. Actually, the generation of energy by environmental-friendly method is one of the major challenges for researchers. Solid Oxide Fuel Cells (SOFC) is efficient and environmentally clean technique to energy production, since it converts chemical energy into electrical power, directly. Apatite-type lanthanum silicates are promising materials for application as an electrolyte in intermediate temperature SOFC (IT-SOFC) because of their higher ionic conductivity, in temperatures of range 600–700 °C, than conventional zirconia electrolytes. In this work, pure (La9,56(SiO4)6O2,34) and Mg-doped (La9,8Si5,7Mg0,3O26,4) lanthanum silicate were synthesized, from that rich effluent. Using the sol-gel followed by precipitation method, the single crystalline apatite phase of both silicates was obtained by thermal treatment at 900 °C of their precursors. Sintered ceramic samples reached density of higher than 90%.

Crystal structure analysis of double perovskite (Bi,Sr)(Co,Fe)O6-δ for intermediate temperature solid oxide fuel cells (IT-SOFCs): A preliminary study

Double perovskite-type BixSr2-xCo0.5Fe1.5O6-δ (BiSCF) oxides with various A-site (x = 0.6, 0.7, 0.8, designated as BiSCF06, BiSCF07, BiSCF08, respectively) have been synthesized by a solid-state reaction technique, and investigated on their structure properties of perovskite powder for application of intermediate-temperature solid oxide fuel cells (IT-SOFCs) purpose with related to the calcination temperatures at 950, 1000 and 1050°C. The crystal structure of the BiSCF powder was analyzed by X-ray diffractometer (XRD), and determined by Rietveld refinement. The results show that BiSCF07 powder which calcined at 950 ° C shows the best structure of cubic perovskite with space group Pm-3m and a lowest impurity at room temperature indicated structure stability and offers a higher mobility of oxygen vacancies. Based on this result, BiSCF07 powder has a potential to be developed as cathode for IT-SOFCs applications.

Synthesis and characterization of Pr/Gd co-doped ceria by using the citric acid–nitrate combustion method

A series of Ce0.8Gd0.2−xPrxO1.90 (x = 0–0.10) compositions have been synthesized by citric acid–nitrate combustion method for intermediate temperature solid oxide fuel cells (ITSOFCs). Characterization studies were carried out with X-ray diffraction (XRD), scanning electron microscopy (SEM) and AC impedance spectroscopy. X-ray diffraction results showed that a single-phase fluorite structure formed at a relatively low calcination temperature which is 600 °C. Dense Ce0.8Gd0.2−xPrxO1.90 pellets were successfully prepared by sintering at 1400 °C for 6 h. The relative density of Ce0.8Gd0.2−xPrxO1.90 samples was over 94% of the theoretical density. The two-probe AC impedance spectroscopy was used to study the ionic conductivity of co-doped ceria samples. According to the electrochemical impedance spectroscopy results, the conductivity of the Ce0.8Gd0.10Pr0.10O1.90 (σTotal,750 °C = 5.1 × 10−2 S/cm) composition was found to be higher than that of gadolinia-doped ceria (Ce0.8Gd0.20O1.90 (σTotal,750 °C = 3.4 × 10−2 S/cm). Due to higher ionic conductivity, it is thought that this composition can be a potential candidate to be used as an electrolyte material in ITSOFCs applications.

Structural, electrical and thermal studies on microwave sintered Dy and Pr co-doped ceria ceramics as electrolytes for intermediate temperature solid oxide fuel cells

The present study was focused on the effects of co-doping on the conductivity enhancement of CeO2-based solid ceramics for application as electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) and the correlation of ionic conductivity variations with micro structural alterations resulting from the addition of co-dopants. Nano-crystalline Dy and Pr co-doped ceria Ce0.8Pr0.2−xDyxO2−δ solid solutions were successfully synthesized by sol–gel auto-combustion and innovative densification by energy efficient microwave sintering (MS) at 1300 °C. The XRD results in concurrence with Raman studies ascertained the formation of cubic fluorite structure in the entire range of composition. The lattice parameters obtained by Rietveld refinement showed lattice contraction with increased dysprosium content. MS has resulted in improved densification and the relative densities of all the samples were noticed above 96% of the theoretical density. TEM images confirmed the nano-crystalline character in the as-prepared samples with the particle sizes measured around 20 nm. SEM micrographs showed spherical faceted near-uniform grains (average grain sizes around 225 nm) with distinct grain boundaries and negligible porosity. Formation of oxygen vacancies and their concentration in all the samples was assessed with the help of Raman spectroscopy. Total ionic conductivity values and activation energies were measured depending on the Dy content. The ionic conductivity of the best composition was found to be 6.8 mS cm−1 at 500 °C. Thermal expansion co-efficient of the samples was matched with that of the commonly used electrode materials. These results gave rise to the firm conclusion that the investigated co-doped ceria has the potential to be utilized as an electrolyte for IT-SOFC applications.