Electrolytes For Solid Oxide Fuel Cells Research Articles

Physical methods of YSZ film application on solid oxide fuel cell electrolyte

Today high effective and sensitive physical methods are used to deposit thin and durable YSZ films (zirconium oxide stabilized by yttrium) for a solid oxide fuel cells electrolyte. The review article is intended to analyze the advantages and disadvantages of perspective physical methods used in the papers of various authors, such as reactive magnetron and plasma sputtering, pulsed laser deposition. One of the main advantages of the pulsed laser deposition method is the choice of the background gas and the ambient pressure during the emission of the ultraviolet camera and the evaporation energy, however, the penetration of microporous particles and target particles on the substrate surface leads to structural changes caused by deformation of the film, as well as a change in the morphology of the film surface YSZ. In this paper, the advantages and disadvantages of the remaining methods are discussed in detail by comparing the articles of the authors. In particular, from the above methods, special attention is paid to the features of the reactive magnetron sputtering method, and it is shown that this method is the most effective, sensitive, expressive method for future use.

Development by Mechanochemistry of La0.8Sr0.2Ga0.8Mg0.2O2.8 Electrolyte for SOFCs.

In this work, a mechanochemical process using high-energy milling conditions was employed to synthesize La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) powders from the corresponding stoichiometric amounts of La2O3, SrO, Ga2O3, and MgO in a short time. After 60 min of milling, the desired final product was obtained without the need for any subsequent annealing treatment. A half solid oxide fuel cell (SOFC) was then developed using LSGM as an electrolyte and La0.8Sr0.2MnO3 (LSM) as an electrode, both obtained by mechanochemistry. The characterization by X-ray diffraction of as-prepared powders showed that LSGM and LSM present a perovskite structure and pseudo-cubic symmetry. The thermal and chemical stability between the electrolyte (LSGM) and the electrode (LSM) were analyzed by dynamic X-ray diffraction as a function of temperature. The electrolyte (LSGM) is thermally stable up to 800 and from 900 °C, where the secondary phases of LaSrGa3O7 and LaSrGaO4 appear. The best sintering temperature for the electrolyte is 1400 °C, since at this temperature, LaSrGaO4 disappears and the percentage of LaSrGa3O7 is minimized. The electrolyte is chemically compatible with the electrode up to 800 °C. The powder sample of the electrolyte (LSGM) at 1400 °C observed by HRTEM indicates that the cubic symmetry Pm-3m is preserved. The SOFC was constructed using the brush-painting technique; the electrode–electrolyte interface characterized by SEM presented good adhesion at 800 °C. The electrical properties of the electrolyte and the half-cell were analyzed by complex impedance spectroscopy. It was found that LSGM is a good candidate to be used as an electrolyte in SOFC, with an Ea value of 0.9 eV, and the LSM sample is a good candidate to be used as cathode.

Environmentally sustainable facile synthesis of nanocrystalline holmium hafnate (Ho2Hf2O7): Promising new oxide-ion conducting solid electrolyte

A2B2O7 oxides with defect-fluorite structure are one of the potential candidates for solid oxide fuel cell electrolyte material due to their excessive thermodynamic stability in oxygen potential gradient at elevated temperature between 500 and 900 °C. Holmium hafnate nanoparticles have been synthesised through the Leeds Alginate Process (LAP) using inorganic salts of holmium and hafnium as starting materials immobilized in alginate beads. Ion exchange with sodium alginate and its subsequent thermal treatment have been used to prepare the nanopowder of Ho2Hf2O7. Thermal decomposition of dried beads is carried out at 700 °C for 2 h and 6 h to obtain the nanoparticles of Ho2Hf2O7. This calcination temperature was determined after carrying out simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). High Temperature X-ray Diffraction (HT-XRD) was carried out to gain further insight into the thermal decomposition process in static ambient environment. HT-XRD analysis corroborated with the results obtained from TGA/DSC. Nano-crystalline powder of single phase Ho2Hf2O7 has been obtained by calcination of oven dried ion-exchanged alginate beads in relatively low temperature range of 500–700 °C. Rietveld refinement of X-ray diffraction (XRD) data confirmed the formation of single phase defect fluorite structure of Ho2Hf2O7. The crystallographic parameters calculated from TEM and XRD analysis are in excellent agreement with each other. Furthermore, TEM–EDX analysis confirms that the Ho2Hf2O7 synthesised by the facile alginate process is nearly stoichiometric. Raman spectroscopy gives evidence of the presence of oxide-ion vacancy in holmium hafnate which is supported with ac-impedance spectroscopy measurement at selected three temperatures. The present study suggests that the LAP has the capability of yielding on a large scale single phase defect-fluorite nanoparticles of electrolyte materials for solid oxide fuel cells in environmentally sustainable, economical and energy efficiently manner.

Scattered and linked microcracks in solid oxide fuel cell electrolyte

Scattered and linked microcracks in the electrolyte layer have been analysed in detail in anode supported planar solid oxide fuel cells. The empirical model established allowed critical characteristics of scattered and localised microcracking to be determined using electrolyte microstructural parameters. The model was verified with experimental data obtained for electron beam deposited scandia-stabilised zirconia electrolytes. Suitable annealing and deposition temperatures during fuel cell fabrication could be predicted from the critical temperature difference below which microcracking does not occur.

Comprehensive comparison of SOFCs with proton-conducting electrolyte and oxygen ion-conducting electrolyte: Thermoeconomic analysis and multi-objective optimization

A power generation system based on integrated methane fed solid oxide fuel cell (SOFC) and organic Rankin cycle (ORC) was modeled and validated against experimental results available in the literature. A comprehensive comparative analysis was conducted on the system performance based the oxygen ion-conducting electrolyte SOFC (SOFC-O2−) and proton-conducting electrolyte SOFC (SOFC-H+) electrolyte. The comparative analysis was conducted from viewpoints of energy, exergy, economic, and environmental. Current density and stack temperature were considered as the input variables. The multi-objective optimization procedure based on an evolutionary algorithm was conducted in the presence of exergy efficiency and sum of the unit cost of the products (SUCP) as the objective functions. The performance of the SOFC-O2− and the SOFC-H+ based power generation systems were compared at their optimum conditions. The system based the SOFC-O2− had a better performance compared to the system based the SOFC-H+ from the objective functions viewpoints. The system based the SOFC-O2− had a higher exergy efficiency (60.20% compared to 54.06%) and lower SUCP (48.24 $/GJ compared to 48.75 $/GJ) than the system based the SOFC-H+ at their optimum conditions. The SOFC-O2− produced 18 kW power higher than the SOFC-H+. This led to increase the system power from 147.9 kW in the case of the SOFC-H+ to 156.4 kW for the SOFC-O2−.

Ternary Alkali Carbonates Effect on Electrochemical Characterization of Nanocomposite Calcium-Doped Ceria Electrolytes (LNK-CDC) for SOFC

Abstract The entire world is facing a great shortfall in the energy supply due to the high consumption rate of fossil fuel-based energy resources. Solid oxide fuel cells (SOFCs) are the best alternative energy devices, which convert hydrogen fuel directly into electricity. Alkali carbonated calcium-doped ceria electrolytes (LNK-CDC) as (Ce0.8 Ca0.2), (Ce0.7 Ca0.3), and (Ce0.6 Ca0.4) were synthesized by the co-precipitation method. With the addition of alkali carbonate, nanocomposites of ceria are well preserved after sintering at 600–700 °C. The structural and morphological properties were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Crystallite sizes were found in the range of 50–80 nm. The maximum ionic conductivity of LNK-CDC (Ce0.8Ca0.2) was achieved to be 0.14 S/cm at 650 °C for anion vacancy migration by the dense microstructure. The minimum activation energy was determined to be 0.23 eV. The Fourier-transform infrared spectroscopy (FTIR) spectra of the prepared materials show the absorbance of IR and their behavior. The maximum power density of symmetric fuel cells LNK-CDC sandwiched with LNCZ oxide electrodes was recorded as 0.52 W cm−2 at 650 °C in the presence of hydrogen (fuel). It is suggested that coating of the equal molar ratio of ternary alkali metals on ceria doped comparatively enhance the performance of new nanocomposite electrolyte for SOFC and other energy applications.

Structural and proton conductivity study of BaZr1-xRExO3-δ(RE = Dy, Sm) ceramics for intermediate temperature solid oxide fuel cell electrolyte

Proton-conducting BaZr1-xRExO3-δ (RE = Dy, Sm) (x = 0.05, 0.10, 0.15, 0.20) ceramics were synthesized via a conventional mixed oxide reaction route. The X-ray diffraction patterns indicated that the studied compositions crystallized as a single phase in the cubic space group $$ Pm\overline{3}m $$. The site preference of the rare earth dopant has been proved by Rietveld analysis of the XRD profile, and the site occupancies have been derived for the studied compositions. Thermogravimetric study of the pre-hydrated samples showed a substantial mass loss, proving the oxygen vacancy filling by H2O after hydration of the samples. Dense microstructures of sintered ceramics are observed, with the Dy-doped compositions showing fairly larger grains (2–3 μm) as compared to Sm-doped barium zirconate. The electrical conductivity under wet N2 ($$ {P}_{{\mathrm{H}}_2\mathrm{O}} $$ = 0.031 atm) environment has been calculated using electrochemical impedance spectroscopy. The conductivity improved gradually with the increase in doping proportions, in case of both the dopants. However, the conductivity of Dy-doped BaZrO3 is found one order higher as compared to Sm-doped BaZrO3, for any fixed doping concentration. The total conductivity of 20% Dy-doped barium zirconate is found to be 4.15 × 10−3 S/cm at 600 °C which is the highest among the studied compositions. The high proton conductivity suggests the material suitable for solid oxide fuel cell electrolyte at intermediate temperatures.

Characterization of Calcia Stabilized Zirconia as a solid E lectrolyte M ade through a sol gel M ethod in Solid Oxide Fuel Cell

Solid Oxide Fuel Cell (SOFC) is a solid-state energy conversion device which produces electricity through the conversion of chemical energy directly to electrical energy. The research was carried out to characterize Calcia Stabilized Zirconia (CSZ) that was made using sol gel method. In this study, the production of CSZ pellets consisted of three steps. First step was the extraction of ZOC (ZrOCl28H2O) and second step was the production of Zr(OH)4 and the last step was dissolution of ZrOH4 into HCl and then adding CaO to get CSZ powder. The CSZ powder was then pressed to form pellets, followed by sintering at 1200 oC for 3 hours. The characterization was conducted using X ray diffraction to analyze the presence of impurities as well as the formation of cubic phase and scanning electron microscope was used to observe the pores in the microstructure. From the XRD data and SEM analysis, it can be concluded that the Calcia Stabilized Zirconia as a solid electrolyte in SOFC using sol gel method gave promising results.

Synthesis and Characterization Studies of Ca2+ and Y3+ Co-Doped Ceria-Na2CO3 Nanocomposite Electrolytes for Low Temperature SOFCs

Doped ceria-carbonate composites have been developed for low temperature (300-600 °C) solid oxide fuel cells (SOFCs) due to its enhanced performance compared to single phase doped ceria electrolytes and the possibility to avoid the Ce4+ reduction. In this study, Y3+ and Ca2+ doped and co-doped ceria Ce0.8Y0.2-xCaxO2-δ (x = 0 and 0.1) samples were synthesized through a simple and cost-effective molten salt method. Nanocomposites based on doped and co-doped ceria-Na2CO3 were then synthesized through mechanical milling. The prepared materials were characterized by X-ray diffraction, thermal analysis, scanning electron microscopy and electrochemical impedance spectroscopy. XRD result shows a single cubic fluorite phase of ceria with carbonate exist as amorphous phase. SEM micrographs also exhibited the homogeneous distribution of ceria and amorphous carbonate phase. Electrical conductivity analysis at different sintering temperatures shows high conductivity value is obtained for co-doped ceria-carbonate nanocomposite sample sintered at 700°C.

Reducing sintering temperature while maintaining high conductivity for SOFC electrolyte: Copper as sintering aid for Samarium Doped Ceria

High sintering temperature (up to 1400 °C), a requirement for near complete density of common solid oxide fuel cell (SOFC) electrolytes, leads to physical strain on porous electrode structures when co-sintered with electrolyte, and to high manufacturing cost. Lowering sintering temperature can hence be another step towards commercialization of SOFC technology. The efficacy of copper as sintering additive for Samarium Doped Ceria (SDC) was evaluated by characterizing the crystal structure and microstructure of sintered samples, the shrinkage behavior during sintering, and the electrical conductivity of SDC samples with and without copper. Copper contents of 0.1, 0.5, 1.0, 3.0, and 5.0 mol % were studied, among which 0.5 mol% copper and above led to segregation of a copper oxide phase on the surface and grain boundaries of SDC. Copper content as low as 0.5 mol% led to significant reduction in sintering temperature, approximately 300 °C from conventional sintering temperature of 1400 °C. If copper content is too low, e.g. 0.1 mol%, it has minimum effect in lowering the sintering temperature. In addition, 0.5 mol% copper led to the smallest decrease in total conductivity; for example, at 800 °C it reduced by 17% from 0.077 to 0.0642 S/cm. Finally, addition of copper up to 5.0 mole% does not affect the thermal expansion coefficient of the electrolyte.

Characterization of Cerium Dioxide Thin Films Prepared By Plasma-Enhanced Atomic Layer Deposition for Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are considered to be the next generation of energy conversion devices because of their environmental friendliness and high efficiency. Particularly due to its high operating temperature, it has high fuel flexibility and does not require water management. However, the high operating temperature that causes these advantages accelerates the degradation of fuel cell components, thereby reducing the durability and limiting the usable materials. Therefore, in recent years, a lot of research has been conducted to lower the operating temperature of the SOFCs. One method of lowering the operating temperature of SOFCs is to apply an electrolyte having good ionic conductivity at low temperatures(400-600℃). Potential examples are doped ceria materials. One of the well-known ceria-based electrolytes is Gd-doped ceria (GDC), which exhibits ion conductivity 1-2 times higher than yttria stabilized zirconia, YSZ, which is the most commonly used electrolyte in SOFC. GDC has good ionic conductivity, but when exposed to a reducing environment, Ce4+ is reduced to Ce3+ and begins to have electronic conductivity, which causes a decrease of open circuit voltage (OCV). Therefore, in order to apply GDC as an electrolyte, an additional blocking layer must be added so that it is not exposed to the hydrogen environment of the anode. This additional layer increases not only the thickness of the electrolyte but also the interfacial resistance between the layers, thereby increasing the ohmic resistance. Therefore, the fabrication of GDCs with thinner and better surface properties is critical to improving the performance of low temperature SOFCs. In this study, CeO2 thin film was fabricated using atomic layer deposition (ALD) as a preceding step for the fabrication of GDC thin films. Oxygen plasma was used to oxidize the precursor to widen the ALD window and to produce the highly crystalline CeO2. The growth rate of CeO2 was determined by controlling precursor and oxidizer exposure time, and the thickness of thin film per cycle was confirmed. The surface morphology was observed by scanning electron microscope (SEM), and dense and pinhole-free thin film surface was confirmed. In addition, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses were performed and the characteristic crystalline peaks and chemical compositions were compared with those of the thermal ALD CeO2 thin films.

Electrical properties of gadolinia doped ceria electrolytes fabricated by infiltration aided sintering

Common solid oxide fuel cell (SOFC) electrolyte materials (e.g., gadolinia doped ceria – GDC) demand temperatures exceeding 1400 °C for densification by conventional solid state sintering. It is very desirable to reduce the densification of the SOFC electroltytes to i) avoid microstructural coarsening of the composite anode layers, which are co-sintered with the electolyte layer in the anode supported SOFC fabrication scheme and ii) reduce energy consumption during SOFC manufacturing. We have recently demostrated a novel infiltration-aided sintering route to densify GDC ceramics at 1200 °C. In the present work, we present the electrical properties of GDC ceramics fabricated thusly. Comparison of high density (≥95%) samples fabricated by conventional or infiltration-aided sintering reveal that at 700 °C, similar total electrical conductivities are obtained, while at 300 °C, specific grain boundary resistivity is smaller in the latter. Bulk (grain) conductivity is higher in porous GDC ceramics (relative density ≤ 90%) fabricated by infiltration-aided sintering than the conventionally sintered ones with similar porosities. Finally, open circuit voltage of 0.84 V at 700 °C, obtained under dilute hydrogen and stagnant air conditions suggests that GDC ceramics densified by infiltration-aided sintering are suitable for use as SOFC electrolytes.

Hole conductivity in the electrolyte of proton-conducting SOFC: Mathematical model and experimental investigation

Proton-conducting solid oxide fuel cell (SOFC) is promising for the intermediate and low temperature applications. The hole conductivity within the electrolyte has noticeable impact on the cell performance. In this article, a new model is proposed to evaluate the hole conductivity of the electrolyte directly. Single cells with different electrolyte thicknesses are fabricated to validate our model. The BaCe0.7Zr0.1Y0.2O3−δ electrolyte and Sm0.5Sr0.5CoO3−δ-Ce0.8Sm0.2O2−δ cathode is employed in our experiments. The predicted cell output capacities are in accord with both our experiments and the reported results, confirming that our proposed method is valid and effective. There are several distinct features of our model compared with previous reports: 1) Hole conductivity could be evaluated directly from the measured output voltages of the full cell, thus it simplifies the relevant experiment; 2) in order to make the cathode reaction model transferable among samples with diverse micro-structures, new parameters named TPB-specific exchange current density is proposed; and 3) for proton-conducting SOFC, an equivalent circuit model with the consideration of both electrolyte hole conductivity and various overpotentials is firstly proposed. Our model points out that the influence of the hole conductivity on the cell capacity could not be neglected in cases of relatively low output current, high temperature and thin membrane. Therefore the hole conductivity of the electrolyte must be taken into consideration in the related simulations.

Влияние стабилизирующих добавок на электропроводность керамики на основе ZrO2

The creation of solid oxide fuel cells (SOFC) is one of the promising solutions to the problem of electricity supply. It is advantageous to use stabilized zirconium dioxide (ZrO2) as solid electrolytes in SOFC. In this paper, zirconium dioxide powders with additives of yttrium and scandium oxides (ZrO2–Y2O3, ZrO2–Sc2O3 and ZrO2–Y2O3–Sc2O3) were synthesized. Ceramic samples were obtained from the powders to study the effect of stabilizing additives on the conductive properties of zirconium dioxide. The addition of yttrium oxide Y2O3 in an amount of 8 mol. % contributed to the formation of a solid cubic solution of zirconium dioxide, and scandium oxide Sc2O3 increased the strength and conductive characteristics of the material. The definition of the conductive characteristics was carried out by impedance spectroscopy. Platinum paste was preliminarily applied by printing, which, when measured, ensured contact with the entire surface of the sample under study. It is shown that the addition of yttrium oxide contributes to the formation of a solid cubic solution of zirconium dioxide, and scandium oxide increases the strength (microhardness) and conductive characteristics of the material. Of interest is the simultaneous alloying of zirconium dioxide with scandium and yttrium oxides. The results of determining the properties of ceramic samples showed that the increase in electrical conductivity is more influenced by the addition of Sc2O3 compared with the addition of Y2O3. Stabilization without yttrium oxide leads to unstable conductivity values over time. A sample of ZrO2 – 1 mol%. – Y2O3 – 8 % mol. Sc2O3 has the potential to be used as an electrolyte in solid oxide fuel cells.

PHASE RELATION STUDIES IN THE ZrO2-CeO2-Dy2O3 SYSTEM AT 1500 °С

The systems containing ceria, dysprosium and zirconia are perspective for the development of energy saving technological solutions and solid oxide fuel cells (SOFC). Ceramics based on ZrO 2 is used as a high temperature electrolyte for SOFC. The solid solutions based on CeО 2 are the most perspective electrolytes, operating at moderate temperatures, because of their ionic conductivity and high sensitivity to changes of oxygen partial pressure is much higher than ones of ZrO 2 stabilized with Y 2 O 3 (YSZ). In the present work, first the phase equilibria and physicochemical properties for solid solutions in the ternary ZrО 2 -CeО 2 -Dy 2 O 3 system at temperature 1500 °С (150 h) in air were studied by X-ray diffraction in the overall concentration range of compositions. Cerium oxide nitrate Ce(NO 3 ) 3 ∙6H 2 O and zirconium oxide nitrate ZrO(NO 3 ) 2 ×2Н 2 О of grade «ch» (above 98%, dysprosium oxide (99.99 % produced by Merck Corp.) and analytical-grade nitric acid were used as the starting materials. Samples were prepared with a concentration step of 1-5 mol % from nitrate solutions with subsequent evaporation and decomposіtion of nitrates into oxides through annealing at 1200 °С for 2 h. Powders were pressed in pellets (diameter 5 mm, height 4 mm) under a pressure of 10-30 MPа. XRD analysis of samples was performed by powder procedure on a DRON-3 apparatus at ambient temperature under CuКa radiation. Scanning step was 0.05-0.1 degrees in the range 2θ = 15–90°. Lattice parameters were calculated by the least square method using the LATTIC computer code with an error of not lower than 0.0001 nm for the cubic phase. Any new phase in the ternary system was revealed at 1500 °С. The structure of the boundary binary systems defines the phase equilibria in the ZrО 2 -CeО 2 -Dy 2 O 3 system. Solid solutions based on tetragonal (Т) modification ZrО 2 , cubic (С) modification Dy 2 O 3 and cubic with fluorite-type structure (F) modifications СеО 2 (ZrО 2 ) were determined.

고체산화물 전해질의 원자층 증착 공정시 플라즈마 인가를 통한 공정 전력 감소

The energy saving effect of reactant plasma in Atomic Layer Deposition (ALD) of ultrathin solid oxide fuel cell electrolyte was examined by measuring electrical current in real time. Actuating a plasma generator led to a remarkable change in electric current and therefore a Plasma Enhanced ALD (PE-ALD) Yttria-Stabilized Zirconia (YSZ) supercycle demanded ~12% higher process energy than a Thermal ALD (T-ALD) YSZ supercycle. Nonetheless, because PE-ALD YSZ electrolyte providing higher growth rate and higher gas tightness needed 2 times smaller cycle number compared to T-ALD YSZ electrolyte, applying oxygen plasma in ALD of YSZ electrolyte resultantly reduced total process energy by ~44%.

Shaping triple-conducting semiconductor BaCo0.4Fe0.4Zr0.1Y0.1O3-\u03b4 into an electrolyte for low-temperature solid oxide fuel cells

Interest in low-temperature operation of solid oxide fuel cells is growing. Recent advances in perovskite phases have resulted in an efficient H+/O2-/e- triple-conducting electrode BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for low-temperature fuel cells. Here, we further develop BaCo0.4Fe0.4Zr0.1Y0.1O3-δ for electrolyte applications by taking advantage of its high ionic conduction while suppressing its electronic conduction through constructing a BaCo0.4Fe0.4Zr0.1Y0.1O3-δ-ZnO p-n heterostructure. With this approach, it has been demonstrated that BaCo0.4Fe0.4Zr0.1Y0.1O3-δ can be applied in a fuel cell with good electrolyte functionality, achieving attractive ionic conductivity and cell performance. Further investigation confirms the hybrid H+/O2- conducting capability of BaCo0.4Fe0.4Zr0.1Y0.1O3-δ-ZnO. An energy band alignment mechanism based on a p-n heterojunction is proposed to explain the suppression of electronic conductivity and promotion of ionic conductivity in the heterostructure. Our findings demonstrate that BaCo0.4Fe0.4Zr0.1Y0.1O3-δ is not only a good electrode but also a highly promising electrolyte. The approach reveals insight for developing advanced low-temperature solid oxide fuel cell electrolytes.

Synthesis and Performance Tuning of Sm0.2Ce0.8O2−δ Electrolyte for Low Temperature Solid Oxide Fuel Cell Application

The charge transportation in the solid oxide fuel cell electrolyte, Sm0.2Ce0.8O2−δ (SDC); has been elucidated by using DC and AC measurements as a function of grain size at temperature 500°C. Initially, chemically homogeneous pellets of SDC were prepared using its powder synthesized by oxalate co-precipitation method and then mean crystallite-size of the SDC samples was varied by adjusting the sintering temperature. The mean crystallite-size was calculated from x-ray diffraction data by using the Debye–Scherrer equation. Further, the samples were examined for their crystal structure, crystallite-size and chemical homogeneity. Electrochemical impedance spectroscopy was used to understand electrical properties of the samples and its correlation with crystallite-size was revealed. SDC samples having larger crystallites exhibited higher electrical conductivity by providing a number of mobile oxygen ions for conduction. However, a lesser number of oxygen ion vacancies across crystallite-boundaries become a hurdle for oxygen migration through samples having small crystallite-size.

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

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

Optimizing rhombohedral Bi2O3 conductivity for low temperature SOFC electrolytes

Rhombohedral Bi2O3 has not been extensively evaluated as an electrolyte material for solid oxide fuel cells (SOFCs) due to the greater potential of the more highly conductive cubic phase. Due to the higher structural stability of rhombohedral Bi2O3, improving the conductivity of the material was undertaken to improve the performance of the electrolyte. Since the rhombohedral phase is generally only assessed in Bi2O3 with high total dopant concentrations, the phase stability window was mapped out in the lower dopant regime. Reported herein is a phase diagram of the rhombohedral Bi2O3 at a total dopant concentration below 10%. Within the phase stability window, the rhombohedral phase was also optimized in terms of the dopant cation and the total cation substitution rate. It was found that increasing the size of the cation dopant and decreasing the total dopant concentration required to stabilize the rhombohedral phase, ultimately maximized the conductivity. Overall, the La and Y double-doped Bi2O3 exhibited a conductivity of 3 × 10−2 S/cm at 500 °C, which is over three times higher than the conductivity of the more traditional SOFC electrolyte GDC.