Co-doped Ceria Research Articles

High Performance Low Temperature Solid Oxide Fuel Cells with Alkali Metal Carbonate Additives in Co-Doped Ceria Electrolyte

Doped ceria-carbonates composites are a new class of electrolytes for low temperature solid oxide fuel cells, these show very high ionic conductivity due to fast interfacial transport [1-2]. As reported by Chockalingum and Basu [3], 25 wt% (LiNa)2CO3-GDC electrolyte exibited an ionic conductivity of 0.17 S cm−1 at 550 °C and lowest activation energy of 0.127 eV in the temperature range 550–800 °C. To further improve the ionic conductivity, a series of calcium gadolinium/neodymium/samarium co-doped cerium oxide, M0.2CaxCe0.8-xO2 (x = 0.01 to x = 0.1) (M= Gd, Nd, Sm) have been synthesised by solgel method. The electrolytes have been physically and electrochemically characterized with respect to their thermal behaviour, phase, microstructure, elemental analysis and electrochemical performance using thermogravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy, Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy and electrochemical impedance spectroscopy respectively. The particle size of as synthesized electrolyte powders is ~ 20 nm as observed from the TEM. XRD results of the prepared electrolytes show that the powders are phase pure. The gadolinium calcium co-doped ceria lithium sodium carbonate (25% (LiNa)2CO3-Gd0.2Ca0.05Ce0.75O2) composite electrolytes exhibit high ionic conductivity (0.3 Scm-1 at 650°C), as it combines both the advantages of co-doping and the composite effect. Co-doped composite electrolytes show higher conductivity and stability due to the presence of calcium than the previously investigated composite electrolytes of (LiNa)2CO3-GDC [4, 5].

Processing and conductivity behavior of La, Sm, Fe singly and doubly doped ceria: As electrolytes for IT-SOFCs

Aliovalent doped ceria have shown enomorous potential to be used as electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). Dopant-induced oxygen vacancies lead to oxy-ion conductivity. Size-valency mismatch of dopant is vital to decide performance of the ceria-based electrolytes. In the present work, singly (La, Fe, Sm) and co-doped (La-Fe, Sm-Fe, La-Sm) ceria systems with optimized composition are studied. Crystal structure of all hydrothermally synthesized nano-scale doped ceria system are confirmed by X-ray diffraction (XRD) and data are well fitted using Rietveld refinement by Full-Prof suite. Microwave heating source (MS) have used for gas tight densification. Sinterability and microstructure are compared with conventionally (CS) sintered system. The ionic conductivity behaviours are investigated by impedance spectroscopy (IS) analysis in the intermediate operating temperature range 450–650 °C. The Arrhenius plot of total conductivity shows two different slopes indicating two different conduction mechanism. The exceptionally high oxy-ion conductivity (2.3 × 10−2 S cm−1 at 650 °C) is exhibited by MS-Ce0.85La0.075Sm0.075O2−δ composition, which is higher than singly doped MS-Ce0.85La0.15O2−δ (1.30 × 10−2 S cm−1) and MS−Ce0.85Sm0.15O2−δ (1.44 × 10−2 S cm−1). However, Fe-containing co-doped ceria system reveal reduction in conductivity. Microwave sintering offers massive energy and time savings for potential industrial production process.

Structures and electrical conductivities of Gd3+ and Fe3+ co-doped cerium oxide electrolytes sintered at low temperature for ILT-SOFCs

Gd3+ and Fe3+ co-doped cerium oxide electrolytes, Ce0.9Gd0.1‐xFexO2-δ (x = 0.00, 0.01, 0.03, 0.05, 0.07, 0.10), were prepared by co-precipitation for ultrafine precursor powders and sintering for densified ceramic pellets. The crystal and microscopic structures were characterized by XRD, FESEM and Raman spectroscopy and their electrical properties were studied by AC impedance spectroscopy and the measurement of single cell's outputs. In comparison with Ce0.9Gd0.1O1.95, the ceramic pellets of Ce0.9Gd0.1‐xFexO2-δ with a relative density of 95% can be obtained after sintered at 1000 °C for 5 h, showing a remarkably enhanced sintering performance with a sintering temperature reduction of 500 °C, which might be ascribed to the highly activated migration of constituent species in the cerium oxide lattice doped with Gd3+ and Fe3+ions. Moreover, the electrical conductivity of Ce0.9Gd0.1‐xFexO2-δ can be significantly enhanced depending on the mole fraction x, with Ce0.9Gd0.07Fe0.03O1.95 exhibiting the highest electrical conductivity of 38 mS/cm at 800 °C, about 36% higher than that of Ce0.9Gd0.1O1.95 electrolyte sintered at 1500 °C for 5 h. So, The Gd3+ and Fe3+ co-doped cerium oxide would be an excellent candidate electrolyte for ILT SOFCs due to its prominent sintering performance and enhanced electrical conductivity.

Synthesis, structural and morphological studies of Sr2+ and Gd3+ co-doped Ceria electrolyte system for LT-SOFC

This paper reports the effect of Sr2+ addition on the structural, microstructural properties of Ce0.8Gd0.2O2-δ(GDC) electrolyte for low temperature solid oxide fuel cell application. The Sr2+ (0, 0.5, 1 and 2 mol %) doped GDC solid electrolytes have been prepared by solid state method. The sintered densities of the samples are around 95%. XRD study reveals the cubic fluorite structure. The microstructure of the samples resulted into grain sizes in the range of 4.3 to 0.868 μm. Raman spectra also confirms the presence of GDC single phase.

Promising solid electrolyte material for an IT-SOFC: crystal structure of the cerium gadolinium holmium oxide Ce0.8Gd0.1Ho0.1O1.9 between 295 and 1023 K.

The crystal structure of Ce0.8Gd0.1Ho0.1O1.9 (cerium gadolinium holmium oxide) has been determined from powder X-ray diffraction data. This is a promising material for application as a solid electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Nanoparticles were prepared using a novel sodium alginate sol-gel method, where the sodium ion was exchanged with ions of interest and, after washing, the gel was calcined at 723 K in air. The crystallographic features of Gd and Ho co-doped cerium oxide were investigated around the desired operating temperatures of IT-SOFCs, i.e. 573 ≤ T ≤ 1023 K. We find that the crystal structure is a stable fluorite structure with the space group Fm-3m in the entire temperature range. In addition, the trend in lattice parameters shows that there is a monotonic increase with increasing temperature.

Alkaline earth metal and samarium co-doped ceria as efficient electrolytes

Co-doped ceramic electrolytes M0.1Sm0.1Ce0.8O2−δ (M = Ba, Ca, Mg, and Sr) were synthesized via co-precipitation. The focus of this study was to highlight the effects of alkaline earth metals in doped ceria on the microstructure, densification, conductivity, and performance. The ionic conductivity comparisons of prepared electrolytes in the air atmosphere were studied. It has been observed that Ca0.1Sm0.1Ce0.8O2−δ shows the highest conductivity of 0.124 Scm−1 at 650 °C and a lower activation energy of 0.48 eV. The cell shows a maximum power density of 630 mW cm−2 at 650 °C using hydrogen fuel. The enhancement in conductivity and performance was due to increasing the oxygen vacancies in the ceria lattice with the increasing dopant concentration. The bandgap was calculated from UV-Vis data, which shows a red shift when compared with pure ceria. The average crystallite size is in the range of 37–49 nm. DFT was used to analyze the co-doping structure, and the calculated lattice parameter was compared with the experimental lattice parameter.

Structural analysis of Ce0.83Dy0.14Ca0.03O1.90 (CDC) and enhanced electrical conductivity of its composites with alkali carbonates for LT-SOFCs

Present work mainly deals with two important aspects of co-doped ceria based solid electrolytes. First, the occurrence of micro-strain or structural distortions in ceria lattice on doping of Dy3+ and Ca2+ at the place of Ce4+. Second, an enhancement in electrical conductivity by formation of nano-composites of Ce0.83Dy0.14Ca0.03O1.90 (CDC) and eutectic mixture of sodium and lithium carbonates [(Li0.52Na0.48)2CO3] (LNCO). CDC ceramic powder was synthesized by citrate-nitrate auto-combustion route. Nano-composites were prepared by mixing the CDC powder with LNCO using a ball mill. X-ray diffraction studies were carried out to analyze the crystal structure of CDC and to study the amorphous nature of carbonates in the nanocomposites. Thermal behavior of the nanocomposites was studied by differential scanning calorimetry (DSC). XRD data of CDC were refined by Rietveld analysis to determine the lattice parameters, atomic positions, bond lengths, bond angles, oxygen deficiency and possible micro-strain. Microstructures of the specimens were studied using scanning electron microscope. Electrical conductivity of the nanocomposites was investigated by using complex plane impedance analysis. A significant improvement in electrical conductivity was observed in nanocomposites with varying concentration of carbonates. Maximum conductivity, 1.05× 10−1 S cm−1 at 500 °C, was observed in the composite with 30 wt% (CDC/30LNCO) of carbonates content.

Investigation on La3+ and Dy3+ co-doped ceria ceramics with an optimized average atomic number of dopants for electrolytes in IT-SOFCs

In the present study, we investigate the fundamental properties of CeO2 by selecting La3+ (57), and Dy3+ (66) as dopants with optimized average atomic number of 61.5, which lies in between Pm3+ (62) and Sm3+ (62) in accordance with the criteria for optimum doping. A system of co-doped ceria ceramics Ce1–x–yLaxDyyO2-δ ((x, y) = (0.00, 0.00), (0.025, 0.025), (0.05, 0.05), (0.075, 0.075), (0.10, 0.10), (0.00, 0.20) and (0.20, 0.00)) as electrolytes for intermediate temperature solid oxide fuel cells were successfully prepared by a well-known sol-gel auto-combustion route. In order to obtain dense samples, the prepared pellets were sintered in air at 1300°C for 4h using conventional furnace and relative densities of all the samples were found to be higher than 95%. Single phase cubic structure, microstructural density and elemental composition analysis of all the samples were studied by powder X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy techniques, respectively. Raman spectroscopy analysis confirmed the formation of concentrated O2-–vacancies in the co-doped ceria system. Impedance spectroscopy measurements revealed the high value of total ionic conductivity and low activation energy for the composition Ce0.85La0.075Dy0.075O2−δ i.e., 2.08 × 10–2 S cm–1 and 0.58eV, respectively. Linear thermal expansion analyses of all the samples revealed the matched thermal expansion coefficients. Finally, these results recommend that the Ce0.85La0.075Dy0.075O2−δ sample can be useful as a solid electrolyte in IT-SOFC applications.

Preparation and characterization zirconium and samarium co-doped ceria solid electrolytes for IT-SOFC applications

Zirconium and Samarium co-doped ceria solid electrolyte materials Ce0.8–xSm0.2ZrxO2-δ (x=0, 0.05, 0.10, 0.15 and 0.20) for intermediate temperature-solid oxide fuel cells were synthesized by citrate-nitrate auto combustion synthesis technique. Powder x-ray diffraction results reveal that all the synthesized samples show a single-phase with cubic fluorite structure. The lattice parameter values were calculated from the powder x-ray diffraction data. Samples with high density were obtained by sintering the samples at 1300°C for 4h. The average crystallite sizes were calculated from the Scherer formula. Surface morphologies of all the samples were obtained by using the scanning electron microscope. The total ionic conductivity of all the samples was carried out from impedance analysis in the temperature range RT – 500°C. The highest total ionic-conductivity with lowest activation energy values were observed for Ce0.65Sm0.2Zr0.15O2-δ at 500°C makes it as a useful solid electrolyte material for intermediate temperature-solid oxide fuel cells (IT-SOFCs) applications.

Thermally drivenin situexsolution of Ni nanoparticles from (Ni, Gd)CeO2for high-performance solid oxide fuel cells

Ni:Gd co-doped ceria (GNDC) was synthesized to thermally exsolve NiO nanoparticles and subsequently reduced to a Ni nanocatalyst to achieve a high-performance SOFC despite a low Ni content (∼2 vol%).

Electrical Properties of Sr2+ and Gd3+ Codoped Ceria Electrolyte System for LT-SOFC

Electrical Properties of Sr2+ and Gd3+ Codoped Ceria Electrolyte System for LT-SOFC

Structure, densification and electrical properties of Gd3+ and Cu2+ co-doped ceria solid electrolytes for SOFC applications: Effects of Gd2O3 content

Ceria-based solid electrolytes exhibit superior electrical conductivity compared to traditional yttria-stabilized zirconia ceramics. However, they require high sintering temperatures to achieve full densification. Transition metal oxides exhibiting low melting points, such as CuO, have been used as additives to lower the sintering temperature of these materials. In this context, the present work is focused on the evaluation of the effects of gadolinium oxide (Gd2O3) content on the structure, densification and electrical properties of ceria co-doped with CuO. Nominal compositions of Ce0.99−xGdxCu0.01O2-δ (0 ≤ x ≤ 0.3) were synthesized by the polymeric precursor method. The precursor powders were characterized by simultaneous thermogravimetry and differential thermal analysis (TG/DTA) and the calcined powders were studied by X-ray diffraction (XRD) and Rietveld refinement to obtain crystallographic parameters. The sinterability of green bodies was evaluated by dilatometry up to 1200°C. The relative density was determined in samples sintered between 950 and 1050°C and the microstructural characterization was performed by scanning electron microscopy (SEM). The electrical properties were investigated by impedance spectroscopy (IS). The XRD results confirms the formation of a cubic fluorite type structure in the entire composition range. The lattice parameters obtained by Rietveld refinement showed a reduction in the crystallite size with increasing gadolinium content. Densification was improved with increasing Gd-content up to x = 0.15. The electrical conductivity was enhanced by gadolinium addition, reaching a maximum of 7.81mScm−1 at 600°C for the composition x = 0.15 sintered at a temperature as low as 1050°C.

Low temperature microwave sintering of yttrium and samarium co-doped ceria solid electrolytes for IT-SOFCs

Nanocrystalline co-doped ceria Ce0.8Sm0.2−xYxO2−δ solid electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were synthesized through sol–gel auto-combustion method. The prepared samples were sintered via microwave sintering at 1200 °C for 1 h. The X-ray diffraction analysis of co-doped ceria system reveals formation of the samples with a single-phase cubic fluorite structure. The lattice parameter values were calculated from X-ray diffraction patterns. The calculated crystallite sizes of all the samples were found to be in the range of 17 and 28 nm. Surface morphologies and elemental analysis of all the samples were carried out by using SEM and EDS analysis. The existence of chemical bonding in the samples was studied by FTIR spectroscopy. The presence of oxygen vacancies and evaluation of their concentration in the material was carried out using Raman spectroscopy analysis. Electrical properties of all the samples were analyzed by impedance spectroscopy. It was found that microwave sintered co-doped ceria sample Ce0.8Sm0.1Y0.1O2−δ exhibits the highest total ionic conductivity with minimum activation energy among all the compositions and conventional sintered sample. Therefore, it can be concluded that the microwave sintered Ce0.8Sm0.1Y0.1O2−δ sample may be useful as a promising electrolyte material for the IT-SOFCs.

An efficient Sm and Ge co-doped ceria nanocomposite electrolyte for low temperature solid oxide fuel cells

In this study we present a new nanocomposite electrolyte based on samarium (Sm) and germanium (Ge) co-doped ceria Ce0.7Sm0.15Ge0.15O2-δ (SGeDC). The nanocomposite electrolyte was prepared using co-precipitation method. The crystal structure and surface morphology were determined using x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Four probe dc conductivity indicated the value of 0.074S/cm at 650°C. The Fuel cell performance was carried out using hydrogen as fuel. The maximum OCV observed was 0.95V while the peak power density came out to be 600mW/cm2 at 600°C. It is suggested that adding Ge, the conductivity as well as performance of this new nanocomposite electrolyte is comparatively enhanced and it can find potential applications in low temperature solid oxide Fuel cells (LTSOFCs).

An Efficient Ge and Sm Co-Doped Ceria Nanocomposite Electrolyte for Low Temperature Solid Oxide Fuel Cells

Electrochemical studies of Fuel cell with different composite electrolyte In this paper, three composite electrolytes (Ce0.8Sm0.2O1.9/Na2CO3) SDC, (Ce0.8Gd0.2O1.9/Na2CO3) GDC and (La0.8Sr0.2Ga0.8Mg0.2O3−δ/Na2CO3)LSGM nanocomposite electrolytes have been studied, also see the effect of Na2CO3, present as second phase, and effect of Ni support, sintering and pressure for dry pressing for fuel cell performance. The electrolytes were prepared through co-precipitation method. Different techniques were used to characterize the prepared electrolytes. The crystal structures were determined using x-ray diffraction (XRD) and structural morphologies were analyzed through scanning electron microscopy (SEM). The four probe dc conductivity and two probe AC impedance analysis were carried out in open air. The fuel cell performance was determined with and without Nickel support on anode side which resulted in a considerable difference in obtained peak power densities. It is suggested that prepared electrolytes can find potential applications in low temperatures Solid Oxide Fuel Cells (LT-SOFCs). Key words: nanocomposite, LTSOFCs, Crystal structure, SDC, Sintering

Effect of Mg doping and sintering temperature on structural and morphological properties of samarium-doped ceria for IT-SOFC electrolyte

Samples of Sm and Mg co-doped ceria electrolyte of Ce1−xSmx−yMgyO2−δ (x = 0.2; y = 0.00, 0.05, 0.1, 0.15, and 0.175) were synthesized by sol–gel process. The prepared samples were sintered at 1100 and 1400 °C for 4 h. The bulk densities were measured by Archimedes method. XRD measurements indicate that the synthesized samples were in single-phase cubic fluorite structure (space group Fm3m). The cell parameters decrease with the concentration of Mg, and 2θ values slightly shift towards right. The particle sizes obtained were between 7.14 and 17.44 nm. The sintered sample achieved 95% of theoretical density. FTIR spectra of samples sintered at 1400 °C indicates weak interactions between 3550–3400 cm−1 and 1600–1300 cm−1 are attributed to O–H stretching modes and strong bonds 850–450 cm−1 are assigned to characteristic Ce–O vibrations. The surface morphology and chemical composition were analyzed by SEM and EDS, SEM micrographs show spherical faceted grains, and the samples were crack free, dense material with some pores on surface which are inconsistent with density results. The average grain size obtained was 0.5 μm. Particle size obtained by TEM was in agreement with that obtained by XRD. The high-density ceria co-doped ceramic can be used as electrolyte in SOFC.

Zinc and platinum co-doped ceria for WGS and CO oxidation

This study presents the synthesis and application of zinc and platinum co-doped ceria for CO oxidation and water gas shift reaction (WGS). To synthesize the catalyst, novel combustion synthesis procedure at pH=10 has been employed, yielding the catalyst in single step without further purification procedures. The catalyst was found to be active under high temperature conditions (>350°C) thus asserting the functionality of the catalyst as single stage WGS catalyst. In this study, we have also developed a dual site redox mechanism to understand the intrinsic kinetics of WGS reaction. For the proposed mechanism, a plausible microkinetic model has been developed for WGS and CO oxidation reactions, respectively. In line with the application of reaction route (RR) analysis to the microkinetic models developed for single site pathway for WGS. In this study, we have extended the RR approach to dual site redox mechanism. From the above analysis, the surface dissociation of OH surface species was found to be rate determining step of the mechanism. The rate expression developed using RR analysis was validated through isothermal plug flow reactor (PFR) model. The PFR simulations predicted the experimental trend for wider range of temperature conditions thus portraying the significance of the microkinetic model developed in this study.

Effect of sintering temperature on the microstructure and ionic conductivity of Ce0.8Sm0.1Ba0.1O2-δ electrolyte

This study investigated the effects of sintering temperature on the microstructure and ionic conductivity of codoped ceria electrolyte with barium and samarium as dopants. The electrolyte (Ce0.8Sm0.1Ba0.1O2-δ) powder was synthesized using the citric acid-nitrate combustion method and calcined at 900°C for 5 h. The calcined electrolyte exhibited a cubic fluorite crystal structure with some impurity phases. The calcined powder was then pressed into cylindrical pellets using uniaxial die-pressing. The pellets were sintered at three different temperatures, i.e., 1200, 1300 and 1400°C for 5 h. Microstructural analysis of the pellets showed that the average grain size increased with the increase in sintering temperature. The sintered densities of the pellets were measured by Archimedes’ method, and the relative density values were within the range of 78%TD to 87%TD as the sintering temperature increased from 1200 to 1400°C. Electrochemical impedance spectroscopy analysis showed that conductivity increased with the increase in sintering temperature, but no considerable change in conductivity was observed for the pellets sintered at 1300 and 1400°C. The results revealed that the electrolyte pellet sintered at 1300°C exhibited the ionic conductivity of 0.005 S/cm with lowest activation energy of 0.7275 eV.

Ionic/Electronic Conductivity, Thermal/Chemical Expansion and Oxygen Permeation in Pr and Gd Co-Doped Ceria PrxGd0.1Ce0.9-xO1.95-δ

The oxygen permeation flux of Ce0.9Gd0.1O1.95-δ (CGO)-based oxygen transport membranes under oxidizing conditions is limited by the electronic conductivity of the material. This work aims to enhance the bulk ambipolar conductivity of CGO by partial substitution of Ce with the redox active element Pr. A series of compositions of PrxGd0.1Ce0.9-xO1.95-δ (x = 0, 0.02, 0.05, 0.08, 0.15, 0.25, 0.3 and 0.4) was prepared by solid state reaction. X-ray powder diffraction (XPD) indicates that Pr is completely dissolved in the fluorite structure up to 40 at.%. Pronounced nonlinear thermal expansion behavior was observed as a function of temperature, due to the simultaneous contributions of both thermal and chemical expansion. The electronic and ionic conductivities were measured as a function of temperature and oxygen partial pressure. Within the range from 10 to 15 at.% Pr, a drastic drop of the activation energy of the hole mobility and an abrupt increase of the hole conductivity at low temperature was observed. The behavior could be rationalized by a simple percolation model. Oxygen permeation fluxes through disk shaped samples fed with air on one side and N2 on the other side were also measured. The oxygen flux through Pr0.05Gd0.1Ce0.85O1.95-δ was higher than that for CGO by one order of magnitude owing to the enhanced electronic conductivity albeit the flux is still limited by the electronic conductivity. In terms of the electronic and ionic conductivity, the estimated maximum oxygen permeation flux of a 10 μm Pr0.4Gd0.1Ce0.9O1.95-δ -based membrane exceeds 10 Nml cm−2 min−1 at 900°C under a small oxygen potential gradient (0.21/10−3 bar) which is promising for use in oxygen production and in oxy-fuel combustion. Also the material may be well applicable to SOFC/SOEC composite electrodes where mixed conductivity is also desirable.

Enhanced Catalytic Performance of Manganese and Cobalt Co–doped CeO2 Catalysts for Diesel Soot Oxidation

AbstractNanosized manganese and cobalt codoped ceria (Ce0.8Mn0.1Co0.1O2−δ) solid solutions have been prepared through simple coprecipitation method to study the effect of Mn and Co bi‐dopants towards diesel soot oxidation. Pure ceria (CeO2), manganese doped ceria (Ce0.8Mn0.2O2−δ), and cobalt doped ceria (Ce0.8Co0.2O2−δ) solid solutions have also been prepared for comparison. XRD results revealed the formation of solid solutions in doped samples. XPS results confirmed the presence of more Ce3+ ions and surface adsorbed oxygen in codoped ceria. H2‐TPR study disclosed that the codoping of ceria exceptionally improves the redox behaviour of CeO2. The catalytic activity results demonstrate that Ce0.8Mn0.1Co0.1O2−δ shows much better activity (T50 ∼ 636 K) while compared to pure CeO2 (T50 ∼ 874 K) in tight contact conditions. A larger surface area, facile redox behaviour, and high concentration of surface adsorbed oxygen species are proposed to be the crucial factors for the enhanced catalytic activity.