Electrolytes For Solid Oxide Fuel Cells Research Articles

Elektrolit Dwi Lapisan bagi Sel Fuel Oksida Pepejal Bersuhu Sederhana-Rendah: Ulasan Kajian

Fuel cell is an energy converter device that generates electricity through electrochemical reaction between hydrogen and oxygen. An example of fuel cell is the solid oxide fuel cell (SOFC) which uses a ceramics based solid electrolyte. Due to the use of ceramics, SOFC normally operates at high temperatures up to 1000 °C. This high operating temperature makes SOFC known for its efficient energy conversion capability and excellent fuel flexibility. However, despite the advantages, the extreme temperatures limit the uses of SOFC. High operation temperature leads to long term operational issues in durability and cell degradation. Yttria stabilized zirconia, YSZ is a commonly used material for electrolyte in high temperature SOFCs. However, YSZ electrolyte is unable to perform well when the operating temperature is reduced to intermediate-low zones below 800 °C. Thus, development of new materials for SOFC components is needed whereby the production of electrolyte materials becomes one of the main scopes for research in intermediate-low temperature SOFCs. Apart from the synthesis of new materials, another approach in increasing the ionic conductivity of intermediate-low temperature SOFC is through the fabrication of a bilayered electrolyte. As such, this review article focuses on the potential of bilayered electrolyte for intermediate-low temperature SOFCs

The role of TiO2 on the microstructure and the electrochemical behavior of Ce0.8Gd0.2O2-δ for solid oxide fuel cell electrolyte

Ce0.8Gd0.2O2-δ (GDC) with various TiO2 contents was prepared by a conventional mixed oxide method. The effects of doping the ceramic solid electrolyte (GDC) with titanium oxide were investigated with regard to crystal structure, microstructure, electrical property and fuel cell performance. The XRD analysis revealed the existence of a phase comprising a cubic fluorite structure. Above 2 mol% TiO2 a second phase as Gd2Ti2O7 was found. TiO2 promoted grain growth of the ceria ceramics. The grain boundary (GB) conductivity of GDC-TiO2 composite was increased by a small addition of TiO2. The maximum power density was achieved by the cell with GDC-1mol%TiO2 as electrolyte.

Densification behavior of yttria-stabilized zirconia powders for solid oxide fuel cell electrolytes

Yttria-stabilized zirconia (YSZ) is the most common electrolyte material for solid oxide fuel cells. Herein, we conducted a comparative study on the densification behavior of three different kinds of commercial 8 mol% YSZ powders: (i) TZ-8Y (Tosoh, Japan), (ii) MELox 8Y (MEL Chemicals, UK), and (iii) YSZ-HT (Huatsing Power, China). The comparison was made on both the self-supporting pellets and thin-film electrolytes coated onto a NiO–YSZ anode support. For the pellets, MELox 8Y showed the highest densification at lower sintering temperatures with 93% and 96% of the theoretical density at 1250 and 1300 °C, respectively. Although YSZ-HT showed a higher sintering rate than TZ-8Y, a sintering temperature of 1350 °C was required for both the powders to reach 95% of the theoretical density. For the thin-film electrolytes, on the other hand, YSZ-HT showed the highest sintering rate with a dense microstructure at a co-sintering temperature of 1250 °C. Our results indicate that besides the average particle size, other factors such as particle size distribution and post-processing play a significant role in determining the sintering rate and densification behavior of the YSZ powders. Additionally, a close match in the sintering shrinkage of the electrolyte and anode support is important for facilitating the densification of the thin-film electrolytes.

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.”

Evolution of the residual stress in solid oxide fuel cell during creep

The evolutions of stress in the multilayer structure of solid oxide fuel cell (SOFC) working under high temperature are calculated by an analytical model. A finite element model is established to validate the results of the present model. The results show that, the present model can be used to analyze the stress relaxation of the SOFC during creep, the stresses both in anode and electrolyte drop dramatically at the first time, but the stress in cathode is first increased and then decreased. The stress relaxation rates of the anode, electrolyte, and cathode of SOFC are 97.87%, 94.91%, and 57.36%, respectively. The creep behavior of electrolyte has little effect on the stress redistribution of the single cell, while anode as well as cathode plays an important role in the evolution of the residual stress and curvature.

Lowering the sintering temperature of solid oxide fuel cell electrolytes by infiltration

A dense electrolyte with a relative density of over 95% is vital to prevent gas leakage and thus the achievement of high open circuit voltage in solid oxide fuel cells (SOFCs). The densification process of ceria based electrolyte requires high temperatures heat treatment (i.e. 1400–1500 °C). Thus, the minimum co-sintering temperatures of the anode-electrode bilayers are fixed at these values, resulting in coarse anode microstructures and consequently poor performance. The main purpose of this study is to densify gadolinia doped ceria (GDC), a common SOFC electrolyte, at temperatures lower than 1400 °C. By this aim, an approach involving the infiltration of polymeric precursors into porous electrolyte scaffolds, a method commonly used for composite SOFC electrodes, is proposed. By infiltrating polymeric precursors of GDC into porous GDC scaffolds, a reduction in the sintering temperature by at least 200 °C is achieved with no additives that might affect the electrical properties. Energy dispersive x-ray spectroscopy line scan analyses performed on porous GDC scaffolds infiltrated by a marker solution (polymeric FeOx precursor in this case) reveals a homogeneous infiltrated phase distribution, demonstrating the effectiveness of polymeric precursors.

Chemical solution deposition and characterization of the La1-хSrxScO3-α thin films on La1-xSrxMnO3-α substrate

The development of solid oxide fuel cells (SOFC) is one of the priority directions for the creation of alternative energy sources. High operating temperatures of these devices are lead to the complexity of the constructions and active diffusion processes between the functional materials. The use of thin-film proton electrolytes is a promising way to reduce the operating temperature of SOFC, while the conductivity level and, as a result, the effective power, may be maintained due to the smaller thickness of the film.Based on LaScO3 proton-conducting oxides with a perovskite structure, having high chemical stability to water vapor, are promising proton electrolytes for SOFC, but they are poorly studied in the form of thin films. Lanthanum-strontium manganite is one of the most common materials for the SOFC cathode. The aim of this work is to study the effect of the La0.6Sr0.4MnO3-α cathode substrate composition on the properties, including the electrical conductivity of La1-xSrxScO3 (0.01, 0.05 and 0.10) thin-film proton electrolytes, obtained by simple centrifugation of the film-forming solution. The properties of La1-xSrxScO3 in the form of ceramic and thin-film samples are compared.The experiment showed that the films La1-xSrxScO3 at 5 ÷ 30-fold deposition on cathode substrates form continuous coatings with a grain size of 50–200 nm, which do not contain transverse pore. These results have a fundamental importance for the development of SOFC with ultra-thin film electrolyte on a supporting electrode. It is established that under dry and wet air the electrical conductivity of La0.6Sr0.4MnO3-α/La1-xSrxScO3/Pt cells is bulk conductivity and it rises with increasing atmospheric humidity, which indicates an increase in the contribution of proton conductivity. In this case, the grain-boundary resistance of the material and the polarization resistance of the electrodes are practically not realized. The conductivity of LSS films is 1–2 orders of magnitude higher than the bulk conductivity of ceramic samples of similar composition and has a low activation energy. The observed differences in the conductive properties of films are explained by the interaction of related perovskites of the scan date and lanthanum manganite.The data obtained may be of interest to specialists in the fields of hydrogen energy, electrochemistry, materials science, the development of electrochemical devices: sensors, fuel cells.

Barium (Zinc) Borosilicate Sealing Glass and Joining Interface with YSZ Electrolyte and Crofer22APU Interconnect in SOFCs

This work describes the performance of two glass-ceramic compositions, BaO-SiO2-B2O3 (Barium borosilicate glass: BaBS) and BaO-ZnO-SiO2-B2O3 (Barium zinc borosilicate glass: BaBS−Zn), used for joining YSZ ceramic electrolytes and Crofer22APU metallic interconnects in solid oxide fuel cells (SOFCs) working at 800°C for 50 h. ZnO had a negative effect on the thermal expansion coefficient (TEC) value of the BaBS-Zn glass-ceramic. XRD and SEM results revealed the formation of rod-shaped barium zinc silicate crystalline phases in the BaBS-Zn glass, which was accompanied by cracks and poor adherence at the YSZ/BaBS-Zn joint interface after working at 800°C for 50 h. The formation of cracks parallel to the interface between the Crofer22APU interconnect and the BaBS-Zn glass-ceramic sealant was observed due to the severe TEC mismatch. The BaBS glass–ceramic adhered well to the YSZ electrolyte as well as the pre-oxidized Crofer22APU without cracks. Chromium oxide scale developed between the pre-oxidized Crofer22APU/BaBS glass-ceramic joint interface with increasing the pre-oxidation temperature. This study shows that BaBS glass-ceramic is more effective than BaBS-Zn as a sealant for joining YSZ electrolytes and Crofer22APU metallic interconnects in SOFCs working at 800°C for 50 h.

Hydrothermal Synthesis and Characterization of an Apatite‐Type Lanthanum Silicate Ceramic for Solid Oxide Fuel Cell Electrolyte Applications

AbstractApatite‐type lanthanum silicate (La10Si6O27; LS) nanopowders are synthesized using a hydrothermal process and used for the electrolyte applications in solid oxide fuel cells (SOFCs). The synthesized nanopowders are characterized by Rietveld refinement of the X‐ray diffraction (XRD) data, SEM–energy‐dispersive X‐ray spectroscopy (EDS), TEM, and dialotometry. The prepared nanopowders can be sintered to near theoretical density at sintering temperature of 1500 °C. Reactivity studies between the synthesized La10Si6O27 material and cathode materials such as La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), Nd2NiO4 (NNO), and Pr2NiO4 (PNO), are carried out by XRD analysis revealing that they do not react. Symmetric cells are fabricated and characterized electrochemically. The area specific resistances for LSCF, NNO, PNO, and PNO‐LS (1:1 (wt %)) measured at 900 οC, are 100, 2.2, 1.8, and 0.5 Ω cm2, respectively. EDS analysis shows that interdiffusion of cations at the cathode–electrolyte interface is not detected for LS/PNO, which is attributed to the low area‐specific resistance values. The results demonstrate that Pr2NiO4 and the composites are promising cathode materials for the apatite‐type lanthanum silicate electrolyte for SOFC applications.

Electrical properties of nanocube CeO2 in advanced solid oxide fuel cells

Search for electrolyte materials with a high ionic conductivity at low temperatures has always been a key challenge for the development of solid oxide fuel cells (SOFCs). In present work, we found un-doped CeO2 nanocubes used as an electrolyte for advanced fuel cell showed remarkable performances. The CeO2 nanocubes were synthesized by a simple hydrothermal approach. The synthesized CeO2 nanocubes were used as an electrolyte sandwiched between two layers of semiconducting Ni0.8Co0.15Al0.05LiO2-δ to fabricate the fuel cell. Such device has achieved an excellent maximum power density of 406 mW cm−2 at 600 °C. These results demonstrate CeO2/CeO2-δ heterogeneous interfaces could provide a high ionic conductive path conductor for the electrolyte in SOFCs, which widen the selecting range of the electrolyte candidates for advanced SOFCs.

The Effect of Chromium Oxide on the Conductivity of Ce0.9Gd0.1O2, a Solid-Oxide Fuel Cell Electrolyte

To study the effect of chromium oxide on the electric properties of Ce0.9Gd0.1O2, a solid-oxide fuel cell electrolyte, two approaches were used: (a) the studying of electrochemical properties of the Ce0.9Gd0.1O2- electrolyte after the spontaneous adsorption of chromium-containing molecules from a gas phase and (b) the analyzing of transport properties of the Ce0.9Gd0.1O2-based chromium-containing compositions obtained by the mixing of solid-oxide electrolyte with chromium(III) oxide. It was found that the chromium reduction at the electrolyte surface dominates when chromium is adsorbed from gas phase. Both approaches allow concluding that the chromium presence in Ce0.9Gd0.1O2 deteriorates the electrolyte transport properties at temperatures above 735°С. This is caused by the chromium incorporation into the electrolyte’s fluorite structure, as well as surface microheterogeneity induced by the chromium presence at the Ce0.9Gd0.1O2 surface and the cerium and gadolinium cation redistribution between the grains’ bulk and surface. At intermediate temperatures (below 735°С) the electric conductivity of the Ce0.9Gd0.1O2-based chromium-containing composition exceeds that of the initial solid-oxide electrolyte, which can be due to changes in transport properties of the chromium-containing phases formed at the Ce0.9Gd0.1O2 surface and grain boundaries.

Semiconductor electrolyte for low-operating-temperature solid oxide fuel cell: Li-doped ZnO

Semiconductors have been successfully demonstrated as the electrolytes for solid oxide fuel cells (SOFCs) in recent years. Many such semiconductors have shown their potentials as a competent ionic conductor for fuel cell operation, indicated by the appreciable ionic conduction and electrochemical performance. In the present study, we depart from traditional electrolyte concept to introduce a new semiconductor electrolyte, Li-doped ZnO to low-operating-temperature SOFCs. The used material was synthesized via a co-precipitation method and investigated from phase structure, morphology and UV–vis absorption perspectives. Utilizing Li-doped ZnO as electrolyte layer, we found the corresponding fuel cell exhibited a remarkable maximum power density of 443 mW cm−2 along with open circuit voltage (OCV) of 1.07 V at 550 °C, and represented a lower-temperature operation feasibility with power outputs of 138–165 mW cm−2 at 425–450 °C. Besides, high ionic conductivities of 0.028–0.087 S cm−1 and low activation energy of 0.5 eV were also found in the synthesized Li-doped ZnO at 425–550 °C. Our investigation in terms of electrochemical impedance spectra (EIS) analysis manifested that Li-doped ZnO as the electrolyte layer boosted the electrode reactions of the device, which resulted in rather small polarization resistances and eventually realized good low-temperature performances. Further study based on the rectification characteristic of Ni/Li-doped ZnO contact verified the Schottky junction formation of Li-doped ZnO with anodic Ni, which can avoid the underlying electronic short-circuiting problem. These findings show a profound significance of using doped semiconductor for the future exploitation of SOFC electrolytes.

Structure Evolution and Reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.0) System.

Solid oxide fuel cells (SOFCs) are solid-state electrochemical devices that directly convert chemical energy of fuels into electricity with high efficiency. Because of their fuel flexibility, low emissions, high conversion efficiency, no moving parts, and quiet operation, they are considered as a promising energy conversion technology for low carbon future needs. Solid-state oxide and proton conducting electrolytes play a crucial role in improving the performance and market acceptability of SOFCs. Defect fluorite phases are some of the most promising fast oxide ion conductors for use as electrolytes in SOFCs. We report the synthesis, structure, phase diagram, and high-temperature reactivity of the Sc(2- x)V xO3+δ (0 ≤ x ≤ 2.00) oxide defect model system. For all Sc(2- x)V xO3.0 phases with x ≤ 1.08 phase-pure bixbyite-type structures are found, whereas for x ≥ 1.68 phase-pure corundum structures are reported, with a miscibility gap found for 1.08 < x < 1.68. Structural details obtained from the simultaneous Rietveld refinements using powder neutron and X-ray diffraction data are reported for the bixbyite phases, demonstrating a slight V3+ preference toward the 8b site. In situ X-ray diffraction experiments were used to explore the oxidation of the Sc(2- x)V xO3.0 phases. In all cases ScVO4 was found as a final product, accompanied by Sc2O3 for x < 1.0 and V2O5 when x > 1.0; however, the oxidative pathway varied greatly throughout the series. Comments are made on different synthesis strategies, including the effect on crystallinity, reaction times, rate-limiting steps, and reaction pathways. This work provides insight into the mechanisms of solid-state reactions and strategic guidelines for targeted materials synthesis.

Ionic and Electronic Transport in Nanocrystalline La0.9Sr0.1Ga0.9Mg0.1O3-Δ

A major limitation for the development of reversible solid oxide cells (R-SOCs) is the delamination between the oxygen electrode and electrolyte in electrolysis mode. Previously, Virkar reported that higher electronic conductivity within the predominantly ionically conducting electrolyte led to a lower tendency for the formation of high internal pressure [1]. Therefore an electrolyte having a small amount of electronic conduction may be beneficial for relieving the delamination between the oxygen electrode and electrolyte in R-SOCs. Strontium- and magnesium-doped lanthanum gallate (LSGM) has been widely investigated as an electrolyte for medium-low temperature (400-650 ºC) R-SOCs due to its high ionic conductivity and compatibility with some perovskite electrodes. Compared to well-established yttria stabilized zirconia electrolytes, which have ionic transference numbers close to 1 across a wide range of oxygen partial pressures, LSGM can exhibit non-negligible p-type electronic conductivity under oxidizing conditions [2, 3]. Furthermore, limited studies have demonstrated enhanced electronic transference numbers at grain boundaries compared to the bulk, attributed to space charge effects [3, 4]. Therefore, it is of interest to understand the impact of nanostructuring and grain boundaries on the ionic and electronic transport properties of LSGM for relieving the delamination issue in R-SOCs. In this work, two methods - field assisted sintering technique/spark plasma sintering (FAST/SPS) and traditional pressureless sintering were employed to prepare dense La0.9Sr0.1Ga0.9Mg0.1O3-δ (LSGM9191) pellets from nanopowders synthesized by the Pechini method. Post-sintering anneals were applied to the FAST/SPS pellets to oxidize them and control grain size. Microstructure was evaluated by scanning and transmission electron microscopy with EELS/EDS line scans at grain boundaries, and transport properties were measured by 2-point ac-impedance spectroscopy over the temperature range using porous Pt/Ag electrodes. Equivalent circuit fitting with application of microstructural models was applied to evaluate local conductivities. The impact of grain size on grain core (gc), grain boundary (gb) and total conductivity were studied. Grain size did not affect the gc conductivity, and the gb and total conductivity increased with grain growth. Specific gb conductivity decreased with increasing grain size. Additionally, the dependence of the conductivities on oxygen partial pressure (pO2) and applied dc bias was measured to assess any electronic contribution to the conductivity. We found that the gb conductivities of LSGM9191 pellets prepared by FAST/SPS with different grain sizes (ranging from ~100nm to 800 nm) did not exhibit pO2 dependence, showing different behavior than some previous research [5]. The dependence of gb conductivity on dc bias (both in N2 or 21% O2) was also smaller than previous reports [6, 7]. Therefore, the electronic conductivity and space charge effect was limited, which might be caused by the high dopant content in the present work compared to previous studies and/or by impurities/ amorphous material/ organic residue trapped at the GBs as a result of the FAST/SPS process. However, the gb conductivity of a LSGM9191 pellet prepared by pressureless sintering did show a small pO2 dependence, indicating some p-type conductivity, albeit lower than in previous reports. The results suggest that factors such as grain size, doping level, grain boundary chemistry, and processing routes could be modified to tailor mixed conduction in LSGM for R-SOC applications. Acknowledgements Support from WPI-I2CNER to NHP and a JSPS Fellowship (201702103) to TC are gratefully acknowledged. Reference [1] Anil V. Virkar, Mechanism of oxygen electrode delamination in solid oxide electrolyzer cells, International of Hydrogen Energy, 35 (2010) 9527-9543 [2] V.V. Kharton et al., Electron-hole transport in (La0.9Sr0.1)0.98Ga0.8Mg0.2O3- δ electrolyte: effects of ceramic microstructure, Electrochimica Acta 48 (2003) 1817-1828 [3] H.J. Park et al., Space Charge Effects on the Interfacial Conduction in Sr-Doped Lanthanum Gallates: A Quantitative Analysis. Phys. Chem. C 2007, 111, 14903-14910 [4] N.H. Perry, Local electrical and dielectric properties of nanocrystalline solid oxide fuel cell electrolytes, Northwestern University, Ph.D. thesis, 2009 [5] H.J. Park et al., Mixed conduction behavior in nanostructured lanthanum gallate, Electrochemistry Communications 11(2009) 962-964 [6] C.T. Chen et al., Current–voltage characteristics of grain boundaries in polycrystalline Sr-doped LaGaO3 Phys. Chem. Chem. Phys., 2012, 14, 9047–9049 [7] Raghvendra • R. K. Singh • P. Singh, Influence of small DC bias field on the electrical behaviour of Sr- and Mg-doped lanthanum gallate, Appl. Phys. A (2014) 116:1793–1800

Further optimization of barium cerate properties via co-doping strategy for potential application as proton-conducting solid oxide fuel cell electrolyte

Yttrium-doped BaCeO3 is one of the most promising electrolyte candidates for solid oxide fuel cells because of its high ionic conductivity. Nd and Y co-doped BaCeO3 strategy is adopted for the further optimization of Y-doped BaCeO3 electrolyte properties. X-ray diffraction results indicate that the structure of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) with orthorhombic perovskite phase becomes more symmetric with increasing Nd concentration. The scanning electron microscope observation demonstrates that the densification and grain size of the sintered pellets significantly enhance with the increase of Nd doping level. Whether in dry and humid hydrogen or air, the increase of Nd dopant firstly increases the conductivities of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) and then decrease them after reaching the peak value at x = 0.05. Electrochemical impedance spectra at 350 °C can distinguish clearly the contribution of grain and grain boundary to total conductivity and the highest conductivity of BaCe0.8Y0.15Nd0.05O3-δ ascribes to the decrease in bulk and grain boundary resistances due to the synergistic effect of Nd and Y doping. The anode-supported single cell with BaCe0.8Y0.15Nd0.05O3-δ electrolyte shows an encouraging peak power density of 660 mW cm−2 at 700 °C, suggesting that BaCe0.8Y0.15Nd0.05O3-δ is a potential electrolyte material for the highly-efficient proton-conducting solid oxide fuel cell.

Enhancing oxygen iron conductivity of 8YSZ electrolytes in SOFC by doping with Fe2O3

The present work investigates Fe2O3 doping as a method of improving the oxygen ion conductivity (OIC) of electrolytes in solid oxide fuel cells (SOFCs) working in a temperature range between 773 K and 973 K. Yttria-stabilised zirconia (YSZ), which alone does not have an OIC sufficiently high for working in the specified temperature range, is used as the electrolyte in the present work. A molecular dynamics (MD) modelling approach is employed to simulate the electrolyte, and the oxygen ion conductivity is characterised and examined for a range of doping proportions and working temperatures. Modelling results indicate that there exists an upper limit of oxygen vacancy concentration for doped 8YSZ electrolytes, and that the optimum OIC is achieved by an 8YSZ electrolyte doped with approximately 4% Fe2O3. Also reported are several other findings that might be of interest to future studies on the performance of electrolytes.

Correlation between structural and electrochemical properties of potassium doped strontium silicates for electrolyte application in intermediate temperature solid oxide fuel cells

Electrolyte is the heart of the solid oxide fuel cell (SOFC), which can determine the working temperature. Currently, Yttria stabilized zirconia is used as electrolyte in commercial SOFCs, due to its high conductivity. The high working temperature (1073 K–1273 K) causes severe problems during SOFC design and operation. To reduce the working temperature of SOFCs to intermediate temperature (873 K–1073 K), here Sr1−XKXSiO3−δ (X = 0.00–0.20) solid solutions are synthesized by solid state reactions, characterized by different techniques. XRD patterns of Sr1−XKXSiO3−δ solid solutions can be indexed to monoclinic c2/c space group (15) structure. 29Si solid state NMR spectra of SrSiO3 and Sr0.95K0.05O3−δ shows a sharp single peak at −83.5 ppm. In 10–20 mol% K-doped samples, the additional broad peak at −89.0 ppm, is due to the presence of amorphous K2Si2O5 phase. FE-SEM and WDS mapping of SrSiO3−δ and Sr0.80K0.20SiO3−δ shows the segregation of amorphous K2Si2O5 along the grain boundaries. High temperature impedance study of Sr0.80K0.20SiO3−δ exhibits the conductivity, which is comparable to other solid electrolytes in the literature, which makes it as promising solid electrolyte for intermediate temperature SOFCs.

Comparison of the in- and across-plane ionic conductivity of highly oriented neodymium doped ceria thin films

To determine the effect of grain boundaries and grain orientation on the electrical properties of solid oxide fuel cell electrolytes, a comparison of the in-plane and across-plane ionic conductivity of both strongly and poorly textured, columnar-grained doped ceria thin films was performed within equivalent temperature ranges (150–300 °C). Additionally, the in-plane conductivity of partially amorphous films, polycrystalline films with randomly oriented grains, and single crystal, epitaxial films with no grain boundaries was determined. Pulsed laser deposition permitted the growth of all these types of films and the ability to grow columnar-grained doped ceria on both conducting and insulating surfaces enabled testing of the films both in-plane and across-plane. Compared to the columnar-grained samples, partially amorphous films exhibited a lower conductivity, while epitaxial doped ceria exhibited an enhancement in conductivity of 2 orders of magnitude. Between 300 and 400 °C, the in-plane conductivity of the strongly textured film was higher than the poorly textured one. The conductivity and activation energy in-plane and across-plane for the strongly textured film was similar (2.75 × 10−5 S/cm, 0.70 eV vs. 5.50 × 10−5 S/cm, 0.68 eV at 250 °C). In contrast, for the poorly textured films, the in-plane and across-plane conductivity values differed by almost an order of magnitude (2.86 × 10−5 S/cm, 0.55 eV vs. 1.99 × 10−4 S/cm, 0.78 eV at 250 °C) suggesting that the boundaries between oriented grains were less resistive. These results further strengthen the argument that grain orientation affects ionic transport through grain boundaries.

Synthesis of Ceria Zirconia Oxides using Solvothermal Treatment

Ceria oxide (CeO2) is widely used as catalyst with high oxygen storage capacity at low temperature. The addition of zirconia oxide (ZrO2) to CeO2 can enhance oxygen storage capacity as well as thermal stability. In this work, ceria zirconia oxides has been synthesized via a low temperature solvothermal treatment in order to produce ceria zirconia oxides composite with high oxygen storage capacity as electrolyte of solid oxide fuel cells (SOFC). Under solvothermal conditions, solvent may control the direction of crystal growth, morphology, particle size and size distribution, because of the controllability of thermodynamics and transport properties by pressure and temperature. Water, mixed of water and ethanol (70/30 vol/vol), and mixed of water and ethylene glycol (70/30 vol/vol) were used as solvent, while Ce(NO3)3 and ZrO(NO3)2 with 0.06 M concentration were used as precursor. The experiments were conducted at temperature of 150 °C and pressure for 2 h in a Teflon-lined autoclave of 100 mL volume. The synthesized products were dried at 60 °C for 6 and 12 h and then calcined at 900 °C for 6 h. The particle products were characterized using SEM, XRD, TG/DTA, and Potentiostat. The results showed that the morphology of particles formed were affected by the solvent. Solid plate shaped particles were produced in water, and tend to be pore with the addition of ethylene glycol. The addition of ethanol decreased the size of particles with sphere shaped. The XRD pattern indicated that ceria-zirconia oxides particles are uniformly distributed in the structure to form a homogeneous solid solution. Based on the electrochemical analysis, ceria zirconia oxides produced via solvothermal synthesis had high conductivity ion of 0.5594 S/cm, which is higher than minimum conductivity ion requirement of 0.01 S/cm for SOFC electrolyte. It indicated that ceria zirconia oxides produced via solvothermal synthesis is suitable for SOFC electrolyte.

Enhancement of ion conductivity for doped electrolytes in SOFC by MD modeling

The objective of this paper is to search for new electrolyte materials with high conductivity to work in a middle working temperature range between 673 K and 1073 K for SOFC in order to lower down industrials manufacturing cost (Tucker, 2010). Since Yttria-stabilized zirconia (YSZ) is known as an electrolyte material for Solid Oxide Fuel Cell (SOFC) at high temperature and is relatively low in the middle temperature range, in view of the circumstance, there is a need to search for new electrolyte materials for doping to enhance the Oxygen Ion Conductivity (OIC). In this study Molecular Dynamics (MD) simulation is employed as a tool to search for great doped electrolytes that can enhance the OIC for higher performance numerically. Several new findings are obtained and reported in the context that can be used as standards to be concurrently used for YSZ electrolytes efficiency enhancement. By employing different dopants in combination of Fe2O3, ZnO, MgO, CuO and BaO with YSZ to enhance the ion conductivity of YSZ electrolytes for the middle as well as full-range working temperature for the SOFC. Subsequently, this study is able to conclude with some suitable dopants of Fe2O3 with 8YSZ in the middle working temperature range, which the best OIC is also pointed out.