Samaria-doped Ceria Research Articles

Structural, morphological and conductivity properties of samaria doped ceria (SmxCe1-xO2-x/2) electrolytes synthesized by electrospinning method

Samaria doped ceria (SDC) electrolytes with theoretical Sm3+ doping concentrations (15, 20 and 25 mol%) were synthesized by electrospinning method and electrolyte performances were investigated for the first time in the literature. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), thermogravimetric/differential thermal analysis (TG/DTA) and impedance analysis. It was determined that the Sm3+ contents of the samples were 17.4, 24 and 27.8 mol% instead of the theoretical values of 15%, 20% and 25% by using SEM-EDX analysis. XRD analysis confirmed that the doping of Sm3+ into Ce4+ was successful. The relative density of the samples was 95.8%, 81.4% and 76% for SDC-17, SDC-24, and SDC-28 samples respectively. The results showed that the sintering and the grain formation of the SDC nanofibers prepared by electrospinning method were difficult at particularly high samarium concentrations. It was found that the SDC-17 exhibited the highest ionic conductivity with the value of 0.0346 S cm−1. Higher doping concentrations caused a decrease in ionic conductivity and an increase in activation energy.

Metal‐Supported Solid Oxide Electrolysis Cell with Significantly Enhanced Catalysis

High‐temperature electrolysis (HTE) using solid oxide electrolysis cells (SOECs) is a promising hydrogen production technology and has attracted substantial research attention over the last decade. While most studies are conducted on hydrogen electrode‐supported type cells, SOEC operation using metal‐supported cells has received minimal attention. The development of metal‐supported SOECs with performance similar to the best conventional SOECs is reported. These cells have stainless steel supports on both sides, 10Sc1CeSZ electrolyte and electrode backbones, and nano‐structured catalysts infiltrated on both hydrogen and oxygen electrode sides. Samarium‐doped ceria (SDC) mixed with Ni is infiltrated as a hydrogen electrode catalyst, and the effect of ceria:Ni ratio is studied. On the oxygen electrode side, catalysts including lanthanum strontium manganite (LSM), lanthanum strontium cobalt ferrite (LSCF), praseodymium oxide (Pr6O11), and their composite catalysts with SDC (i.e., LSM‐SDC, LSCF‐SDC, and Pr6O11‐SDC) are compared. Using the materials with highest catalytic activity (Pr6O11‐SDC and SDC40‐Ni60) and optimizing the catalyst infiltration processes, excellent electrolysis performance of metal‐supported cells is achieved. Current densities of −5.31, −4.09, −2.64, and −1.62 A cm−2 are achieved at 1.3 V and 50 vol% steam content at 800, 750, 700, and 650 °C, respectively.

Interplay between grain boundary diffusion and annealing temperature on the conductivity of NiO coated Samarium doped ceria

Elemental diffusion in ceramics can modulate the conductivity as well as fuel cell performance. Here, we report the effect of diffusion on NiO coated samarium doped ceria (SDC) with temperature and correlated with conductivity. NiO thin film was deposited using electron beam physical vapor deposition over the pre-sintered SDC substrate and subsequently treated at 800 °C, 1000 °C, and 1200 °C. Depth profiling analysis across NiO-SDC hetero-interface using FESEM-EDAX revealed that the width of the diffusion zone increased with temperature. All the constituent ions like Ni, Sm and Ce diffuse mutually without forming any impurity phases at the NiO-SDC interface. The estimated diffusivity values demonstrated that the nickel predominantly diffuses through the grain boundary of SDC. The constituent cations were found to diffuse several hundred nanometers through grain boundaries at a temperature of 1200 °C. An increase in the electrical conductivity was observed in proportion to the width of the diffusion layer. The diffusion of nickel predominantly along the grain boundary reduced the grain boundary resistance by altering the space charge potential at the NiO-SDC interface. Our study demonstrates that the modification of grain boundary through the controlled diffusion of metal ions reduce the resistance for oxygen ion transport in NiO-SDC electrolyte.

Structural and electrochemical studies of microwave sintered nanocomposite electrolytes for solid oxide fuel cells

In this study, a nanocomposite electrolyte is synthesized using a microwave sintering technique, providing an alternative method and improving the conventional sintering technique. In this paper, samarium doped ceria (SDC) materials are synthesized by the co-precipitation method using carbonates as precipitating agents. The precursor of SDC-carbonate is sintered in a microwave (MW) oven and conventionally heated in a digital furnace at 900 °C. X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques are applied for structural studies. For electrochemical characterization, four probe conductivity and fuel cell performances are completed. The materials prepared using MW improved the densification and exhibited excellent sintering during compared to the conventional method of preparation for the same material. Excellent fuel cell performance (0.65 W cm−2) is achieved with microwave sintering. This method of sintering proves that the microwave process can save time and energy when compared to conventional sintering. This method can provide significant economic benefits compared to conventional sintered materials for applications in fuel cell technology.

Comparative Characterization on Structural Properties of Calcined Sm0.5Sr0.5CoO3−δ - Sm0.2Ce0.8O1.9 Carbonate as Potential Composite Cathode for SOFC

In this research work, Samarium Strontium Cobalt Oxide, Sm0.5Sr0.5CoO3−δ (SSC) and Samarium Doped Ceria, Sm0.2Ce0.8O1.9 (SDC) carbonate or (SDCc) were used as the new composite cathode powder materials. This composite cathode powder was prepared via high energy ball milling (HEBM) method for SOFC application. The composition of 50 wt.% of SSC was chosen to be added with 50 wt.% of SDCc powder. The prepared powders of composite cathode SSC:SDCc were then undergone calcination process at different operating temperatures which has been varied from 600 °C, 650 °C, 700 °C and 750 °C. Characterizations of the SSC-SDCC composite cathode powders were performed through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). However from the XRD analysis, there was an appearance of new secondary peaks which corresponded to strontium carbonate (strontianite), SrCO3 of SSC-SDCc composite cathode powders. The result obtained from FTIR analysis verified the existence of carbonates elements in all SSC-SDCc composite cathodes. Based on FTIR studies, the selection for operating temperatures of calcination did not give significant impact on the thermal and structural properties of calcined SSC-SDCc carbonate composite cathodes. Additionally, the presence of secondary phase revealed from the XRD study might result in different microstructural that could influence the electrochemical behavior.

Effect of bismuth oxide on crystallization and sealing behavior of barium borosilicate glass sealant for SOFCs

Barium borosilicate glasses (BaO–SiO2–B2O3) with the addition of 5–25 wt% bismuth oxide as additive (equivalent to 1.23–5.88 mol% of Bi2O3 in glasses) were prepared for using as a sealant for planar solid oxide fuel cells. The effect of Bi2O3 addition on thermal properties, structure, crystallization and joining interface of the BaO–SiO2–B2O3 glasses was investigated. IR spectra showed a significant effect of Bi2O3 addition in the BaO–SiO2–B2O3 glass structure, causing a progressive conversion of [BO3] to [BO4] unit in the glasses. The Bi2O3 addition made the BaO–SiO2–B2O3 glass network less rigid resulting in a decrease of a glass transition temperature and a softening point but still maintains the thermal expansion match between the Bi2O3-containing glasses and samaria-doped ceria solid electrolyte as well as an iron‑chromium metallic interconnect. 5-wt% Bi2O3 obviously decelerated the crystallization of the Bi2O3-containing glasses. Good adhesion of the 5-wt% Bi2O3-containing glass sealant with samaria-doped ceria electrolyte and iron-chromium metallic interconnect without any gaps was achieved at prolong test for 30 h at 800 °C.

A New Sodium-ion-conducting Layered Perovskite Oxide as Highly Active and Sulfur Tolerant Electrocatalyst for Solid Oxide Fuel Cells

In this paper, a layered perovskite oxide NaLaTiO4 with sodium-ion conductivity is proposed as a highly active, sulfur tolerant and stable anode for solid oxide fuel cells (SOFCs). The cell with NaLaTiO4-infiltrated samaria-doped ceria (SDC) anode shows high power outputs and favorable stability over 200-hour operation with 1000 ppm H2S-H2 as fuel at 800 oC. The excellent sulfur tolerance of NaLaTiO4 is attributed to its polarity, high surface basicity, oxygen vacancy concentrations and water storage capability. These results may open up new avenues for the design of high-performance, sulfur-tolerant anodes for SOFCs.

Flash Sintering Samaria-Doped Ceria–Carbon Nanotube Composites

Composite ceramic green pellets were prepared by attrition milling a mixture of (CeO2)0.8(Sm2O3)0.2 (samaria-doped ceria, SDC) ceramic powder and carbon nanotubes (CNTs), followed by uniaxial and isostatic pressing. The pellets were sintered inside a dilatometer by applying AC electric fields at 850 °C and limiting the electric current to 1 A, achieving 20.2% final shrinkage. The SDC samples reached 13.3% shrinkage under the same conditions. Higher average grain sizes were measured in specimens flash sintered with CNTs. Impedance spectroscopy analyses show that the specimens flash sintered with addition of CNTs have higher electrical conductivity. Higher delivered Joule heating at the interfaces due to the presence of the electronic conductors (CNTs) are proposed as the main reason for that improvement of the electrical behavior.

Sb3+ and Gd3+ co-doped Cerium oxide Nanocrystalline Ceramic system: Structural and Dielectric Studies

Nanostructured ceramic materials have high conductivity compared to bulk materials. Ceria based systems, with fluorite structure, [samarium doped ceria (SDC) and gadolinium doped ceria (GDC)] are found to be the best electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFC). In the present study, Ce0.8Gd0.1Sb0.1O2-δ nanostructured materials were synthesized by wet co-precipitation method. X ray diffraction pattern confirms the crystallization of the sample in the most conducting cubic fluorite phase. The presence of Ce, Gd, and Sb in the sample is qualitatively confirmed by Fourier transform infrared spectroscopy. Scanning electron spectroscopy image shows mesoporous nature of the sample. The addition of Sb3+ to the GDC system reduces the sintering temperature by 33.33%. The dielectric studies show that the prepared sample is an ionic material with two types of conduction mechanisms – grain interior and grain boundary. Hence, two different activation energies for ionic conduction are obtained for the sample at low and high temperature region.

Electrical properties of rare earth doped ceria electrolyte for solid oxide fuel cell applications

This paper attempt to investigate the structural and electrical properties of the boron doped Samarium doped Ceria (SDC) electrolyte prepared by simple solid state reaction method. The prepared sample was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and impedance Spectroscopy for their composition, size, and electrical conductivity. In this present work, we are evaluating the electrical conductivity of the prepared electrolyte. The sintered pellet exhibits good surface morphology. The frequency dependence of dielectric properties is obtained from impedance spectroscopy studies. Results of analysis reveal that nanocrystalline codoped sample was successfully prepared at low processing temperature with good ionic conductivity suitable for solid oxide fuel cell applications

Low Ni-Containing Cermet Anodes of Solid Oxide Fuel Cells with Size-Controlled Samarium-Doped Ceria Particles

Ni-based cermet materials are typically used for anodes of solid oxide fuel cells. However, the Ni phase in such anodes can cause durability problems. One possible solution to the durability problems is to reduce the amount of Ni in the anode, although decreased Ni amount in turn reduces conductivity and electrochemical activity of the anode. In this study, Ni-SDC (samarium-doped ceria) cermet anodes were prepared with different SDC particle sizes and Ni contents, and it was investigated how particle size ratio of the SDC and Ni affected the performance at low Ni contents. AC impedance analyses revealed that ohmic resistance was the primary factor affecting the current-voltage characteristics in the tested system, and it was found that large SDC particles were effective in reducing the ohmic resistance even with low Ni contents. The behavior of measured ohmic resistances of the anodes was well described by percolation theory, indicating that the electrical conductivity of the anodes was governed by the formation of connected Ni clusters.

Kinetics of CO2 electrolysis on composite electrodes consisting of Cu and samaria-doped ceria

Oxygen vacancies at interfaces play a vital role in CO2 electrolysis which is demonstrated by AC impedance and current–voltage analysis.

Sr2Fe1.4Mn0.1Mo0.5O6−δ perovskite cathode for highly efficient CO2 electrolysis

An all-ceramic cermet cathode based on perovskite-oxide Sr2Fe1.4Mn0.1Mo0.5O6−δ and samaria-doped ceria shows unprecedented performance in solid oxide electrolysis of pure CO2.

Modification of Oxygen-Ionic Transport Barrier of BaCo0.4Zr0.1Fe0.4Y0.1O3 Steam (Air) Electrode by Impregnating Samarium-Doped Ceria Nanoparticles for Proton-Conducting Reversible Solid Oxide Cells

A reliable and high performance proton-conducting reversible solid oxide cell (P-RSOCs) is developed to generate electricity in a protonic ceramic fuel cell (PCFC) mode and to generate hydrogen gas in a protonic ceramic electrolysis (PCEC) mode in a single electrochemical device. Herein we propose a modified triple conducting (H+/O2−/e−) steam (air) electrode through the infiltration of an Sm0.2Ce0.8O2-δ (SDC) oxygen-ionic conductor, because the polarization resistance (Rp) of P-RSOCs mainly comes from the steam (air) electrode in both the operational modes. The SDC-infiltrated nanoparticles on the composite BaCo0.4Zr0.1Fe0.4Y0.1O3+δ (BCZFY)-BaCe0.7Zr0.1Y0.2-xYbxO3-δ (BCZYYb) electrode result in a considerable improvement in the oxygen reduction reaction and oxygen evolution reaction catalytic activity at 600–700°C due to the extension of electrochemical active sites with the increasing of surface area. In addition, the enhanced ionic conduction of a triple conducting composite using infiltrated oxygen-ionic SDC conductors leads to an effective decrease in the Rp (1.388→1.079 Ω·cm2 at 600°C symmetric cell) with improved cell performance in both the PCFC and PCEC modes. Furthermore, the NiO-BCZYYb anode-supported cell with the SDC-infiltrated composite BCZFY-BCZYYb air electrode shows excellent durability in the PCFC and PCEC modes without any degradation during 250 h each at 650°C.

Effect of Milling Process and Calcination Temperature on the Properties of BSCF-SDC Composite Cathode

The ionic conductivity, super conductivity, ferroelectricity, and magnetic resistance of barium strontium cobalt ferrite (BSCF) make it a good solid cathode material. This study aims to investigate the influence of milling process and calcination temperature on the behaviour of nanocomposite cathode BSCF–samarium-doped ceria (SDC). The BSCF–SDC composite powders were mixed using two milling processes, namely, wet milling and dry milling. The composite cathode powders were mixed through wet milling by high-energy ball milling at 550 rpm for 2 hours. For dry milling, the powders were milled at 150 rpm for 30 minutes. The powders then underwent calcination at 900 °C, 950 °C, 1050 °C, and 1150 °C for 2 hours. The composite cathodes were examined on the basis of phase and microstructure through field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD), respectively. In conclusion, the selection of suitable milling process and calcination temperature is important in eliminating secondary phases in BSCF–SDC composite cathodes and in enhancing their properties.

Influence of Heat Treatment and Milling Speed on Phase Stability of Ba<sub>0.5</sub>Sr<sub>0.5</sub>Co<sub>0.8</sub>Fe<sub>0.2</sub>O<sub>3-δ</sub> Composite Cathode Solid Oxide Fuel Cell

This study presents the preparation of barium strontium cobalt ferrite (BSCF)–samarium doped ceria (SDC) added samarium doped ceria carbonate (SDCC) cathode for solid oxide fuel cell (SOFC). The aim of this study is to investigate the effect of heat treatment on compatibility and characterization of BSCF composite. Calcined BSCF was mixed with SDCC and SDC by ball milling at 150 and 200 rpm respectively. Subsequently, both were uniaxially pressed to form pellets and sintered at 600°C for 2 hours. The BSCF behavior of composite samples was characterized via X-ray diffraction to determine the crystalline phase of BSCF composite. Fourier transform infrared spectroscopy was used to determine the existence of carbonate bond. Field emission scanning electron microscopy was used to examine the grain morphology. The crystalline BSCF phase percentage increased and secondary phases reduced when the milling speed decreased. After milling, BSCF composites still displayed uniform elemental distribution. Heat treatment has an impaired crystalline phase of perovskite BSCF. Without heat treatment, the BSCF composites showed agglomerate and unmolded particles.

Rapid surface kinetics enhancement via flash light sintering for low-temperature solid oxide fuel cells

“Samaria-doped ceria (SDC), with exceptional electrochemical catalyzing characteristics, is a promising material for the operating temperature of solid oxide fuel cells (SOFC). Despite its extraordinary electrochemical reactivity, its chemical unstable behavior in terms of reduction phenomenon has made its application to SOFC electrolyte challenging. In regard to the defect chemistry, however, this instability can enhance the oxygen incorporation rate at the surface of the electrolyte. Here, we report a rapid surface treating method for SDC thin films via flash light sintering, which revealed an outstanding crystallinity development with nano-grains and increment of mobile dopant cation-induced oxygen vacancies within few milliseconds. We demonstrated that the flash light sintering-induced rapid development of crystallinity and reduction of ceria increases oxygen reducing surface kinetics, leading to an improvement in the oxygen incorporation rate of the cathodic reaction in SOFCs. The performance of SOFC sintered by flash light indicated more than two-folds enhancement comparing the pristine cell.”

Rational Design of Perovskite-Based Anode with Decent Activity for Hydrogen Electro-Oxidation and Beneficial Effect of Sulfur for Promoting Power Generation in Solid Oxide Fuel Cells.

The poor sulfur tolerance of conventional nickel cermet anodes is particularly concerning for solid oxide fuel cell technology. Herein, we report an innovative anode composed of a samaria-doped ceria (SDC) scaffold and a perovskite La0.35Ca0.50TiO3-δ thin film with a surface modified with strongly coupled and in situ-formed Ni nanoparticles; the anode was prepared via an infiltration-calcination-reduction method. The rational design of such an anode transforms the detrimental effect of sulfur on the cell performance (poisoning) of state-of-the-art Ni cermet anodes into a beneficial effect promoting power generation from H2. A cell with a Ni + SDC cermet anode and a Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode showed an 18.3% reduction in the power output at 800 °C when the fuel gas was switched from pure H2 to H2-1000 ppm H2S, while a similar cell with this innovative anode showed a power output enhancement of 6.6%. Furthermore, the operational stability was significantly improved. The perovskite phase was found to account for the improved cell power output in the presence of sulfur impurity. The introduction of the nickel nanoparticles further significantly enhanced the electrode activity, while the strong coupling effect of exsolved nickel nanoparticles with the perovskite thin film improved the sulfur tolerance of the nickel phase. As a result, the anode showed both high activity and stability while operating on H2 fuel with high concentration of H2S (1000 ppm). The promoting effect of sulfur on the power generation over the perovskite anode is also discussed.

Li effects on layer-structured oxide LixNi0.8Co0.15Al0.05O2-δ: Improving cell performance via on-line reaction

Li+ plays a critically important role in layer-structured LiNiO2 family oxides in that it affects the oxidant state of Ni and catalyst's function. Layer-structured LixNi0.8Co0.15Al0.05O2-δ (LxNCA, x = 1, 1.2, 1.4) with different lithium content was prepared and applicated as both cathode and anode catalysts in symmetrical solid oxide fuel cell (SSOFC) that using samarium doped ceria (SDC) as electrolyte. Excess Li precursor resulted in the formation of Li2CO3 in L1.2NCA and L1.4NCA materials, whose influence on the performance of LxNCA was studied. Oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) of LxNCA as well as its catalytic stability were investigated by impedance spectroscopy. Its ORR process was found to be greatly influenced by the amount of Li in LxNCA while HOR was less related to Li content. Accompanying the on-line reduction and oxidation of LxNCA, fuel cells tested under reverse operation condition revealed enormous improvement in Pmax, which was due to the significant improvement of ORR process and the reduction of interface resistance.

Thermally stable current-collecting silver grid coated with ceramic-capping layer for low-temperature solid oxide fuel cells

In an effort to decrease the operating temperature of solid oxide fuel cells (SOFCs), nano-porous thin Pt layers have been used as a cathode material with catalytic activity. Because of porous and thin characteristic of the Pt cathode, however, a large cathode area results in a significant performance deterioration because of the increased sheet resistance of the Pt cathode. In this study, we developed a Ag-patterned grid as a current-collecting layer and a samaria-doped ceria (SDC) oxide-capping layer on the porous Pt cathode to decrease sheet resistance and enhance electrochemical performance. Enhanced electron transportation and thermo-stable behavior of fabricated fuel cells indicated three-fold enhanced peak power density and more than two-fold thermomechanical stability, as per scanning electron microscopy (SEM) and electrochemical analysis results.