Co-doped Ceria Electrolytes Research Articles

Improved ionic conductivity of Ca-doped and Ca-La co-doped ceria electrolytes for intermediate temperature solid oxide fuel cells

Improved ionic conductivity of electrolytes is necessary for solid oxide fuel cells, meant for the development of efficient and clean energy devices. This study is focused on the enhancement of ionic conductivity in Ca-doped and Ca-La co-doped cerium oxide (ceria) electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The co-doped ceria electrolytes, LCDC20 (Ce0.8La0.1Ca0.1O2−δ), exhibited enhanced ionic conductivity of 1.06 ×10−1 S cm−1 at 1073 K, when compared to conventional yttria-stabilized zirconia (YSZ) electrolytes, and has lower activation energy of 1.02 eV. Also, these co-doped electrolytes showed decreased sintering temperatures, which amounts to cost-effective electrolyte materials for IT-SOFCs.

Zr and Gd co-doped ceria oxide conductor with low electronic conductivity in reducing atmosphere

The Gd and Zr co-doped ceria electrolyte Gd0.1Ce0.9-xZrxO1.95 (x = 0, 0.03, 0.06, 0.09, 0.12, 0.15, labeled as GDC, Zr0.03GDC, Zr0.06GDC, Zr0.09GDC, Zr0.12GDC, Zr0.15GDC) was synthesized by solid-state reaction. The XRD and Rietveld refinements reveal that ZrxGDC is in a cubic fluorite phase with the cell parameters a decrease from 5.4186(1) to 5.3728(1) Å and cell volume V decreases 159.10(2) to 155.09(2) Å3 as the x increases from 0 to 0.15. SEM studies confirm a dense microstructure with well-defined grains in a size of 10–20 μm. The Raman spectra agree with the fact that a solid solution is formed and the blue-shift of Raman modes is observed as expected. XPS analysis shows that Ce4+ is more stable in Zr doped GDC. The conductivity of Zr0.03GDC reaches 1.2 × 10−3 S/cm at 450 °C. The bond valence of Ce4+ is constrained to a higher one as the Ce4+ is substituted by Zr4+ in the solid solution, and a higher stability in the reducing atmosphere was achieved. The electronic conductivity decreases from 14.8% of GDC to 0.1% of Zr0.03GDC at 400 °C. The oxygen ion transference number of Zr0.03GDC is improved significantly to > 0.93 in 3% H2/Ar at 700 °C.

Structural and ionic conduction study of Sm–Pr co-doped ceria electrolyte materials for LT-SOFC applications

Samarium praseodymium (Sm–Pr) co-doped ceria was synthesized by the co-precipitation technique as an electrolyte for low-temperature solid oxide fuel cell (LT-SOFC) applications. The structural, morphological, compositional, and electrical characterization of the synthesized samples were evaluated via x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX) and impedance spectroscopy. The generation of a single-phase fluorite structure of co-doped ceria without any secondary phases has been verified by XRD analysis, exhibiting the successful incorporation of Sm and Pr ions into the ceria lattice. Vegard's law is utilized for Pr redox behavior explaining the variation in lattice constant values. SEM pictures show that the co-doped ceria powder has a homogeneous and well-dispersed microstructure, and has enhanced particle size. The impedance spectroscopy results indicate that Sm–Pr co-doped ceria has much higher ionic conductivity than single-doped ceria. The highest amount of ionic conductivity (σionic) for the composition Ce0.80Sm0.10Pr0.10O2−δ recorded as 2.12×10−2S/cm at 500°C, and 6.19×10−2S/cm at 750°C with the lowest activation energy Ea=0.48eV, which has been not reported earlier. Sm and Pr are chosen as dopants because of their capacity to generate oxygen vacancies and improve ceria's ionic conductivity. This study contributes to the enhancement in the ionic conductivity of co-doped ceria by co-precipitation technique and the temperature-dependent frequency exponent factor "s" is also explored to comprehend the conduction mechanism of the prepared samples.

Proton Conduction and Electrochemical Performance of La/Pr co-Doped Ceria Electrolyte in Ceramic Fuel Cell

Proton Conduction and Electrochemical Performance of La/Pr co-Doped Ceria Electrolyte in Ceramic Fuel Cell

The structures, morphologies and intermediate-temperature electrochemical properties of CuO aided sintering Gd3+ and Ho3+ co-doped ceria electrolytes

In this study, a CuO-assisted sintering Ho3+ and Gd3+ co-doped CeO2 (Gd0.1Ho0.1Ce0.8O2-α-CuO, GHDC-CuO) electrolyte has been successfully synthesized using a citric acid and glycine combustion technique. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe and characterize the morphologies and structures of the produced samples. The XRD results showed that the doped samples' primary diffraction peaks were consistent with those of conventional cerium dioxide. The SEM findings demonstrated that adding the right quantity of CuO aided in the densification of the electrolytes. The total resistance was significantly impacted by the addition of CuO in the following order: R (1400-GHDC) > R (1450-GHDC) > R (1450-GHDC-CuO) > R (1400-GHDC-CuO). After being assembled into a thin film fuel cell, the maximum output power densities of 1400-GHDC-CuO (18 µm) using Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) as the cathode were 396 mW·cm-2 and 490 mW·cm-2 at 700 °C and 750 °C, respectively.

Development and electrochemical performance of co-doped ceria (Sm0.10Ga0.10Ce0.80O2-δ) electrolyte material for low-temperature solid oxide fuel cell (LT-SOFC)

Developing an electrolyte material for using in the low-temperature fuel cell (LT-SOFC) is a highly challenging issue. In this study, Samarium (Sm) and Gallium (Ga) doped ceria CeO2 (Sm0.10Ga0.10Ce0.80O2-δ) named as SGDC electrolyte material have been prepared by co-precipitation method and its ionic conductivity and electrical performance have been evaluated in the 400–700 °C temperature range. The crystallographic condition and phase formation of the material was analysed and observed a single-phase cubic fluorite crystal structure with a mean value of 39 nm in the prepared SGDC. The electrolyte materials showed a comparatively lower activation energy of 0.49 eV; however, they exhibited remarkably high ionic conductivity, current density and power density at a significantly lower operating temperature of 400 °C. The electrochemical results demonstrate the potentiality of the prepared Sm0.10Ga0.10Ce0.80O2-δ material to be used as the electrolyte for LT-SOFC.

The influence of sintering additive on the structure and intermediate-temperature electrochemical properties of Gd3+ and Er3+ co-doped ceria electrolyte

The influence of sintering additive on the structure and intermediate-temperature electrochemical properties of Gd3+ and Er3+ co-doped ceria electrolyte

Electrical properties of praseodymium and samarium co-doped ceria electrolyte for low-temperature solid oxide fuel cell application

Electrical properties of praseodymium and samarium co-doped ceria electrolyte for low-temperature solid oxide fuel cell application

Structural and electrical properties of Sm and Er co-doped ceria electrolytes

The aim of this study is to prepare Er and Sm co-doped CeO2 electrolytes via the Pechini method and investigate the effects of simultaneous addition of Sm and Er on the structural and electrical features of CeO2. The structural, functional group analysis, microstructures, and electrical properties of the electrolyte samples are conducted by X–ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and impedance spectroscopy (IS). All the calcined and sintered electrolytes were obtained with cubic fluorite crystal structure without secondary oxide phases. After sintering at 1400 °C, highly dense electrolytes were achieved (> 90%). The IS measurements indicated that the highest ionic conductivity was observed for the singly doped Ce0.80Sm0.20O1.90 (σ750 °C = 3.86 x 10−2 S/cm) electrolyte. σ750°C was found to be 3.82 x 10−2, 1.73 x 10−2, 0.61 x 10−2 S/cm for Ce0.80Er0.05Sm0.15O1.90, Ce0.80Er0.10Sm0.10O1.90 and Ce0.90Er0.10O1.95, respectively.

A strategy for improving sinterability and electrical properties of gadolinium-doped ceria electrolyte using calcium oxide additive

In this study, Gd and Ca co-doped ceria electrolytes with the compositions of Ce0.8Gd0.2–xCaxO2–δ (x = 0–0.08) were prepared by a novel gel-casting method. The effects of the addition of Ca on the phase compositions, sintering behavior, and electrical properties of samples were investigated. According to the scanning electron microscope results and relative density measurement results, it is found that the addition of particular quantity of CaO can promote the sintering densification with a uniform grain growth. When the sintering temperature is 1400 °C, the sample with 6 mol% addition of Ca has the highest relative density, which reaches 98.5% of the theoretical density. The electrical properties testing results confirm that the electrical conductivity of the samples can be improved significantly by doping appropriate CaO content. The maximum conductivity of 0.082 S/cm can be obtained at 800 °C in the Ce0.8Gd0.12-Ca0.06O1.87 sample. It suggests that CaO can be used as an effective sintering aid and a co-dopant on the optimization of electrical properties for ceria-based electrolytes.

Morphology and Structural Stability of Bismuth-Gadolinium Co-Doped Ceria Electrolyte Nanopowders

The reduction of the sintering temperature of doped ceria ceramics remains an open challenge for their real exploitation as electrolytes for intermediate temperature solid oxide fuel cell (IT-SOFCs) at the industrial level. In this work, we have used Bi (0.5 and 2 mol %) as the sintering aid for Gd (20 mol %)-doped ceria. Nano-sized powders of Bi/Gd co-doped ceria were easily synthesized via a simple and cheap sol-gel combustion synthesis. The obtained powders showed high sinterability and very good electrochemical properties. More importantly, even after prolonged annealing at 700 °C, both of the powders and of the sintered pellets, no trace of structural modifications, phase instabilities, or Bi segregation appeared. Therefore, the use of a small amount of Bi can be taken into account for preparing ceria-based ceramic electrolytes at low sintering temperatures.

Interface dominated conductivity change in Ce0.8Sm0.1Nd0.1O2−δ/La9.33Si6O26 composite electrolyte

Samarium and neodymium co-doped ceria (Ce0.8Sm0.1Nd0.1O2−δ abbreviated SNDC) and lanthanum silicate (La9.33Si6O26 abbreviated LSO) composite electrolytes with different mixing ratio were prepared at 1500 and 1550 °C. The composite obtained were all with high density, and no chemical reaction between two phases was observed during sintering according to the XRD result. The addition of LSO has a great influence on the suppression of grain growth of SNDC, and brought about the change in conduction behavior of composite. High distortion at hetero interface has been observed by TEM. The composite with 30 wt% LSO exhibits the highest conductivity (0.0036 S/cm at 500 °C) with an improvement of 37% compared with SNDC. The measurement at low oxygen partial pressure demonstrated the high chemical stability of composite electrolyte, making it a promising candidate for intermediate temperature SOFCs or oxygen sensors.

Electro-morphological, structural, thermal and ionic conduction properties of Gd/Pr co-doped ceria electrolytes exhibiting mixed Pr3+/Pr4+ cations

Gd0.2-xPrxCe0.8O1.90, (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) has been synthesized by means of a simple co-precipitation route based on ammonium carbonate as the precipitating agent. The as-synthesized precursors are cerium-gadolinium-praseodymium amorphous hydroxycarbonates, which are nanometric in size with highly homogeneous morphology, leading to reactive doped and co-doped nanocrystalline (≈13 nm) ceria after a mild thermal treatment (2 h at 600 °C). The obtained results highlight the very positive effect of Pr on the powders’ sintering behaviour, which favour a better densification of the final pellets, thus improving both their microstructure (with relative densities of 97–99% after sintering at 1250 °C for 3 h) and electrochemical properties (up to 1.25·10–1 S cm−1 at 800 °C for sample 6Pr) compared to the state-of-art ceria-based electrolytes. Through a comprehensive characterization, a relation was formed between the Pr content and the microstructural features of the sintered pellets and their electrical behaviour. The amount of Pr doping was investigated over a wide range and 6 mol% has been established to be optimal (possessing the lowest electronic conductivity contribution). Definitely, these results indicate that Gd0.2-xPrxCe0.8O1.90 has an excellent set of characteristics, both microstructural and electrical, and a convenient fabrication process, thus making it perfectly suitable for IT-SOFC practical applications.

Ionic Conductivity of Ce0.9-xGd0.1SmxO2-δ co-doped Ceria Electrolytes

Ionic Conductivity of Ce_0.9-xGd_0.1Sm_xO_2-δ co-doped Ceria Electrolytes

Structural, optical and electrical properties of Ce0.8Sm0.2-xErxO2-δ (x = 0–0.2) Co-doped ceria electrolytes

This study examined the effects of samarium and erbium co-doping on the structural, optical, and electrical properties of ceria (CeO2). Ceramic (Ce0.8Sm0.2-xErxO2-δ; x = 0, 0.05, 0.10, 0.15, 0.20) electrolytes were synthesized via sol-gel assisted citric acid–nitrate combustion and calcined at 850 °C for 5 h. The calcined electrolytes possessed a cubic fluorite crystal structure without impure phases. The direct band gap of the calcined electrolytes increased as the erbium content increased and the lowest band gap was obtained for Ce0.8Sm0.2O2-δ (SDC) electrolyte. The calcined electrolyte powders were subsequently pressed into cylindrical pellets by uniaxial die pressing, and the pellets were sintered at 1400 °C for 5 h. The sintered densities of the pellets were measured with Archimedes’ method. The relative density of Ce0.8Sm0.1Er0.1O2-δ co-doped ceria electrolyte was higher than those of singly doped ones, and these findings were further confirmed through field emission scanning electron microscopy. Electrochemical impedance spectroscopy indicated that the conductivity of erbium-doped ceria increased as the samarium content increased. The maximum total ionic conductivity was observed in Ce0.8Sm0.1Er0.1O2-δ co-doped electrolyte. However, the singly doped SDC electrolyte exhibited the highest ionic conductivity of 13.12 mS/cm and the lowest activation energy of 0.580 eV at 600 °C among all other Ce0.8Sm0.2-xErxO2-δ co-doped ceria electrolytes.

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].

Thermal characterization of Er-doped and Er–Gd co-doped ceria-based electrolyte materials for SOFC

Ce1−xErxO2 and Ce1−2xErxGdxO2 co-doped ceria electrolyte nanopowder materials were successfully prepared by sol–gel method. Depending on the temperature, the crystal structure changes were analyzed by X-ray diffraction. It was observed that the crystal size of the electrolytes decreased depending on the temperature and the time. X-ray diffraction results confirmed cubic fluorite structure in the samples. The microstructural properties of the samples were analyzed by scanning electron microscopy, and thermal stability measurement was performed by thermogravimetric and differential thermal analyses. The total electrical conductivity of the nanopowder electrolytes was determined by the dc four-point probe technique in air at temperatures ranging from room temperature to 1373 K. The four-probe conductivity results revealed that Ce0.8Er0.1Gd0.1O2 has a higher ionic conductivity compared to Ce0.83Er0.17O2 at 1123 K. The four-probe conductivity results show that both Ce1−xErxO2 and Ce1−2xErxGdxO2 solid electrolytes have potential application to oxide ionic conductor for solid oxide fuel cells.

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.

Electrochemical and thermal characterization of doped ceria electrolyte with lanthanum and zirconium

Nanocomposites electrolytes consisting of La3+ and Zr4+ doped with ceria labelled as La0.2 Ce0.8 O2-δ (LDC), Zr0.2Ce0.8O2-δ (ZDC) and Zr0.2La0.2Ce0.6O2-δ (ZLDC) have been synthesized via a co-precipitation route. DC conductivity was studied with a four-probe method in the range of temperature 450–650°C and maximum conductivity was found to be 0.81 × 10−2S.cm−1 (LDC) > 0.32 × 10−2S.cm−1 (ZLDC) > 0.15 × 10−2S.cm−1 (ZDC) at a temperature of 650°C, respectively. Further, electric behavior of doped and co-doped ceria electrolytes was investigated by A.C electrochemical impedance spectroscopy (frequency range ~ 0.1Hz‒4MHz). The phase/structural identification of the material prepared was studied using X-ray diffraction and found ceria to possess a cubic fluorite structure. Scanning electron microscopy (SEM) was carried out to study its morphology and particle size (~ 90–120nm). Thermal behavior on its change in weight and length with the temperature were studied by thermogravimetric analysis (TGA) and dilatometry respectively. Furthermore, thermal expansion coefficients (TECs) of prepared electrolytes are calculated and found as follows: 13.4 × 10−6°C−1, 13.6 × 10−6°C−1and 15.3 × 10−6°C−1 for LDC, ZDC and ZLDC, respectively, in the temperature range 150–1150°C.

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