Electrolytes For Solid Oxide Fuel Cells Research Articles

Elucidation of the Transport Properties of Calcium-Doped High Entropy Rare Earth Aluminates for Solid Oxide Fuel Cell Applications.

Solid oxide fuel cells (SOFCs) are paving the way to clean energy conversion, relying on efficient oxygen-ion conductors with high ionic conductivity coupled with a negligible electronic contribution. Doped rare earth aluminates are promising candidates for SOFC electrolytes due to their high ionic conductivity. However, they often suffer from p-type electronic conductivity at operating temperatures above 500°C under oxidizing conditions caused by the incorporation of oxygen into the lattice. High entropy materials are a new class of materials conceptualized to be stable at higher temperatures due to their high configurational entropy. Introducing this concept to rare earth aluminates can be a promising approach to stabilize the lattice by shifting the stoichiometric point of the oxides to higher oxygen activities, and thereby, reducing the p-type electronic conductivity in the relevant oxygen partial pressure range. In this study, the high entropy oxide (Gd,La,Nd,Pr,Sm)AlO3 is synthesized and doped with Ca. The Ca-doped (Gd,La,Nd,Pr,Sm)AlO3 compounds exhibit a higher ionic conductivity than most of the corresponding Ca-doped rare earth aluminates accompanied by a reduction of the p-type electronic conductivity contribution typically observed under oxidizing conditions. In light of these findings, this study introduces high entropy aluminates as a promising candidate for SOFC electrolytes.

Efficient statistical approach for thermo-electrical properties of gadolinia-doped ceria thin films

The thermo-electrical properties of gadolinia-doped ceria (GDC) thin films play a vital role in solid oxide fuel cell (SOFC) applications. Nonetheless, the effects of temperature, dopant concentration, and thickness on thermal expansion, and ionic conduction remain ambiguous. In the present study, we propose an efficient theoretical approach to emphasize the roles of surface layers and surface vicinity (called next-surface layers) on the thermo-electrical properties of GDC thin films. Using statistical moment method, thermal expansion coefficient, and ionic conductivity are calculated as functions of temperature, dopant concentration, and thickness. The lattice strain and ionic disorder in the surface and next-surface layers cause an increase in thermal expansion coefficient and ionic conductivity of thin films. Compared with bulk GDC, the thermal expansion coefficient is slightly larger while the ionic conductivity is more than one to two orders of magnitude enhancement and exhibits the maximum value at the higher concentration. The ionic conductivity depends non-linearly on the dopant concentration and the maximum conductivity is shifted toward a higher value as the temperature increases. The enhancement in thermal expansion coefficient and ionic conductivity offers new opportunities for SOFC electrolytes whose efficiency can be effectively controlled by tailoring the thickness. The theoretical calculations are compared to measured results from experiments.

Plasma-sprayed bulk-like yttria-stabilized zirconia coatings for solid oxide fuel cell electrolytes based on liquid-phase sintering-induced interfacial healing

To achieve a coating density meeting the solid oxide fuel cell (SOFC) electrolyte requirements of high gas tightness and ionic conductivity, in this study, a new interface healing densification process based on a liquid-phase sintering induction mechanism was conducted on plasma-sprayed 8 mol% Y2O3-stabilized ZrO2 (8YSZ) coatings. Using Fe2O3 and Bi2O3 as healing additives, metallurgical healing of unbound interfaces was achieved by impregnating the additives into the gap interfaces, followed by liquid-phase sintering at 1200 and 1050 °C. After healing, the YSZ coating exhibited a dense bulk-like microstructure with a significant reduction in the gas leakage rate by two orders of magnitude, and the oxygen ion conductivity of the coating was significantly increased. The YSZ coating healed with the Fe2O3 additive showed an oxygen ionic conductivity nearly one order of magnitude higher than that of the as-sprayed coating, reaching more than 80% of the value of the high-temperature-sintered YSZ bulk.

Structural and Electrochemical Performance of Sr0.9La0.1WO4 Electrolyte Materials for Solid Oxide Fuel Cells

A possible component of power generation technologies, solid oxide fuel cells (SOFCs) offer a high fuel-to-power conversion efficiency and no negative environmental impact. The solid-state sintering process was used to synthesize the scheelite-structured Sr0.9La0.1WO4 (SLW1) electrolyte material, and phase stability and ionic conductivity were evaluated for their technological applicability for SOFC applications. The resulting mixture, which was a single phase in a tetragonal crystal system, produced a scheelite structure of the space group I41/a. Its symmetry, space group, and structural characteristics are confirmed by X-ray diffraction (XRD) at room temperature and the Rietveld analysis that follows. A highly dense crystal structure was revealed by SEM examination. The ionic conductivity of the SLW1 sample is higher than SBW materials and lower than the conventional BCZY perovskite structure. At 900°C in both the wet Ar and dry Ar conditions, the SLW1 sample’s ionic conductivity was 2.41 × 10−5 S cm-1 and 1.76 × 10−5 Scm−1. This scheelite-like compound showed a thick microstructure and substantial conductivity, making it a potential mixed ion-conducting electrolyte for SOFC.

An innovative perovskite oxide enabling improved efficiency for low-temperature ceramic electrochemical cells

In recent years, energy carriers for renewable sources and devices that convert chemical energy into electrical energy, such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), have made hydrogen production economically viable and have numerous industrial uses. We have designed SrFe0.3TiO3 (SFT) materials to function as SOFC and H-SOEC electrolytes at low operational temperatures of 520–420 °C. The SFT (600 °C) shows a higher fuel cell power density of 650 mW/cm2 and a reasonable current density of 1.14 A/cm2 in fuel cell and electrolysis cell mode at 520 °C. The formation of the surface layer enables high ionic and Proton conduction due to a high number of oxygen vacancies, and the core–shell type interface enables easy and quick proton transportation restricted to the surface. Energy band alignment and distribution relaxation time (DRT) were also evaluated to study ion transport in SFT materials. These results open up advanced avenues for the design of high-performance, sophisticated proton-conducting electrolytes for ceramic electrochemical cells.

High-throughput prediction of oxygen vacancy defect migration near misfit dislocations in SrTiO3/BaZrO3 heterostructures

Among their numerous technological applications, semi-coherent oxide heterostructures have emerged as promising candidates for applications in intermediate temperature solid oxide fuel cell electrolytes, wherein interfaces influence ionic transport.

Hydrothermal synthesis of zirconia doped with naturally mixed rare earths oxides and their electrochemical properties for possible applications in solid oxide fuel cells

Solid oxide fuel cells (SOFC) are electrochemical conversion devices that produces electricity directly from oxidizing a fuel and their development became of high importance to drastically reduce the greenhouse emission. Rare earth elements (REEs) are widely used as materials and dopants in controlling the ionic conductivity of solid electrolytes for SOFCs. Their criticality and high costs for separation to individual REEs lead to first studies aiming to search possible use of mixed REEs with natural occurrence as extracted from concentrates. This paper focused on obtaining sintered pellets based on zirconia doped with natural mixture of REEs extracted from monazite and study their microstructure, impedance spectra and dielectric properties vs. operating temperatures to assess their potential applications as solid electrolyte. ZrO2 doped powders with 8% natural mixture of REEs (8ZrMZ) were synthesized by hydrothermal process. ZrO2 doped with 4% Y2O3 (4ZrY) and 8%Y2O3 (8ZrY) were also obtained by the same route and used as standard materials already used in commercial SOFCs. All powders were uniaxially pressed and sintered in air, with highest densities obtained for 1400 °C. The Niquist diagrams for 8ZrMZ samples show significantly lower ionic conductivity compared to standards 4ZrY and 8 ZrY. This may be attributed to the presence of detrimental Fe and Si impurities following the mixed REE after Th and U removal from monazite concentrates and the ratio of REEs in the dopant composition affecting the ionic conductivity due to possible association of structural defects. Research works are further needed to improve the receipt for using naturally mixed REEs and asses their possible use as a competitive dopant for solid electrolytes.

Phase Transformation of YSZ Electrolyte in Anode-Supported SOFCs

Cubic-stabilized zirconia doped with 8 mol% Y2O3 (8YSZ) is a highly popular electrolyte material for solid oxide fuel cells (SOFCs) due to its exceptional oxide ionic conductivity, which remains consistent across a broad range of oxygen partial pressures. However, previous studies [1,2] have shown that the addition of nickel oxide (NiO) to 8YSZ can expedite the phase transformation process (from cubic to tetragonal) when exposed to a reducing atmosphere at relatively high temperature as 900℃. This phase transformation is closely related to the degradation of 8YSZ's conductivity. Therefore, it is crucial to investigate whether NiO, which should dissolve into the YSZ electrolyte during the co-sintering process with the NiO-YSZ anode at high temperatures, can lead to a similar phenomenon in anode-supported cells (ASCs). Hence, investigating the NiO solid solution phenomenon and its effect on the phase transformation in the YSZ electrolyte of ASCs can offer insights into its degradation behavior.In this study, NiO-YSZ anode support and YSZ electrolyte were co-sintered at 1370℃, 1450℃, and 1550℃, respectively, for 2 hours to fabricate the half-cell samples. Subsequently, these samples were reduced at 900℃ and 700℃, respectively, with a flow of 50ccm dry H2. High-resolution secondary ion mass spectrometry (SIMS) was used to detect the presence of NiO in YSZ, and Raman spectroscopy was used to detect the phase transformation (cubic to tetragonal) occurring in the YSZ.The SIMS results showed that the amount of NiO in the YSZ electrolyte increased with higher sintering temperatures. Moreover, after reducing the cells at 900℃, phase transformation was detected in all samples. However, there was no significant difference among those cells in terms of the degree of phase transformation, which indicated that phase transformation was not accelerated by the increase of dissolved NiO in YSZ. On the other hand, no phase transformation was observed for the cells reduced at 700℃. The mechanism of phase transformation of YSZ in anode-supported SOFCs and its related conductivity degradation will be discussed in the presentation.

The Evolution of Solid Oxide Fuel Cell Materials

Solid oxide fuel cells (SOFCs) are a key component of the future energy landscape. Although there is considerable research on the physical properties and technology of classic oxide materials for electrode and electrolytes in SOFCs, the field is very active as new experimental and theoretical techniques are now available that can improve these systems. In the present review, we consider key systems such as perovskite-related materials, the impact of strain and interfaces and advanced concepts that can improve the properties of SOFC materials. In particular, we consider the oxygen diffusion properties of perovskite-related materials and focus on La2NiO4+δ and the double perovskites such as GdBaCo2O5.5. Then, we review the importance of interfaces and strain as a way to engineer defect processes. Finally, we consider advanced concepts to form designed structures that explore the effect of local high entropy on lattice stabilization.

Structural and Electrical Characterization of LaSrAl1-xMgxO4-δ Layered Perovskites Obtained by Mechanical Synthesis.

This work presents the structural and electrical characterization of K2NiF4-type layered perovskites of LaSrAl1-xMgxO4-δ composition to be used as oxide-ion electrolytes for a solid-oxide fuel cell (SOFC). These perovskites were prepared by mechano-chemical synthesis (ball milling), an alternative to traditional synthesis methods such as citrate-nitrates and solid-state reaction. With these methods, two things are avoided: first, the use of nitrate salts, which are more environmentally harmful than oxide precursors, and second, it saves the series of long thermal treatments associated with solid-state reactions. After grinding the precursors, nanometric particles were obtained with a combination of crystalline regions and amorphous regions; this effect was determined by XRD and TEM, showing that Mg has a positive effect on the phase formation by only mechanical synthesis. R2C4: After sintering, it was found by XRD that the sample x = 0.1 only presents the diffraction peaks corresponding to the desired phase, which shows a phase purity greater than 97%, even higher than that of the standard undoped sample. For x = 0.2 and 0.3, there was a segregation of impurities, possibly by the local migration of La and Sr heavy cations; this was determined by SEM and EDS. The electrical characterization of the sintered pellets was carried out by electrochemical impedance spectroscopy, which determined that the incorporation of Mg in the structure improves the ionic conductivity by three orders of magnitude, obtaining conductivities of 1.6 mS/cm at 900 °C for x = 0.2. Although the improvement in conductivity is considerable, many challenges such as densification, the segregation of impurities, and the study of mechanical and thermal properties must be carried out on these materials to endorse them as solid electrolytes in SOFC.

Role of Divalent Co-Dopant as Structure Stabilizer in Scandia-Stabilized Zirconia Electrolyte for SOFC

The present investigation reports the role of divalent binary co-dopant (Ca2+) in 11 mol% scandia stabilized zirconia (11SSZ) electrolytes to resolve its severe long-term aging issue for application in solid oxide fuel cells (SOFC). Dense electrolytes were formulated via the solid-state reaction method and their crystal structure was identified by X-ray diffractometer (XRD). To examine total electrical conductivity and its stability in oxidizing and reducing atmosphere DC four-point probe measurement was used. Among all the compositions, 0.2Ca11SSZ demonstrates the highest conductivity of 0.075 S cm−1 at 800 °C, with excellent stability of 6.7%/100 h in a reducing (97 vol% H2/3 vol% H2O) atmosphere. However, the presence of 0.5 mol% calcium in 11SSZ results in more than threefold suppression of aging rate compared to undoped11SSZ i.e. 2.19%/200 h in air atmosphere at 800 °C. Additionally, the doping of divalent Ca2+ widens the electrolytic domain up to pO2 ∼ 10−26 atm at 1000 °C compared to state-of-art 8YSZ (pO2 ∼ 10−22 atm), with 0.024% linear expansion on phase transition and 172 MPa flexural strength. Convincingly, the excellent structure stability and ionic conductivity of calcium co-doped 11SSZ compared to state-of-the-art electrolytes make them potential candidates to be used as an electrolyte for SOFC application.

Nanocrystal Engineering of Thin-Film Yttria-Stabilized Zirconia Electrolytes for Low-Temperature Solid-Oxide Fuel Cells.

To overcome significantly sluggish oxygen-ion conduction in the electrolytes of low-temperature solid-oxide fuel cells (SOFCs), numerous researchers have devoted considerable effort to fabricating the electrolytes as thin as possible. However, thickness is not the only factor that affects the electrolyte performance; roughness, grain size, and internal film stress also play a role. In this study, yttria-stabilized zirconia (YSZ) was deposited via a reactive sputtering process to fabricate high-performance thin-film electrolytes. Various sputtering chamber pressures (5, 10, and 15 mTorr) were investigated to improve the electrolytes. As a result, high surface area, large grain size, and residual tensile stress were successfully obtained by increasing the sputtering pressure. To clarify the correlation between the microstructure and electrolyte performance, a YSZ thin-film electrolyte was applied to anodized aluminum oxide-supported SOFCs composed of conventional electrode materials which are Ni and Pt as the anode and the cathode, respectively. The thin-film SOFC with YSZ deposited at 15 mTorr exhibited the lowest ohmic resistance and, consequently, the highest maximum power density (493 mW/cm2) at 500 °C whose performance is more than five times higher than that of the cell with YSZ deposited at 5 mTorr (94.1 mW/cm2). Despite the basic electrode materials, exceptionally high performance at low operating temperature was achieved via controlling the single fabrication condition for the electrolyte.

Electrochemical Study of Zinc Adsorption on Yttria-Stabilized Zirconia-Water Interfaces

Research has shown that zinc ions can mitigate the corrosion of the alloy materials in nuclear power plants in addition to reducing radiation contaminations. Understanding how zinc ions alter the interfacial structure of the alloy surface is therefore important in improving the life cycle of the materials and achieving higher burnups of the nuclear fuels. While the corrosion mitigation of zinc on nickel and stainless-steel alloys has been widely studied and reported, its effect on zirconium oxide surfaces, i.e. the oxide layer of zirconium alloys exposed to the aqueous solution, has rarely been reported. Meanwhile, zirconium oxide also serves as the solid oxide fuel cell electrolyte in energy storage. The study of the corrosion mitigation mechanism on zirconia could also contribute to the successful commercialization of SOFC technologies as cleaner and more efficient energy conversion electrochemical systems. In this work, we utilize the electrochemical techniques to study the interfacial structure changes under the influence of zinc ions on the yttria-stabilized zirconia (YSZ) surfaces on the (100), (110), and (111) orientations in contact with aqueous solution with and without externally applied electric potentials. The experimental measurements indicated the modification of the interfacial structures by zinc on (100) and (111) surfaces is strongly influenced by the applied external electric fields, while the modification of surface structure by zinc ions is not as evident on the (110) surface. Our study also showed that the Zn2+ adsorption layers on the oxide surfaces could be better preserved by tuning the electric potential on the oxide substrates towards the negative potentials.

Advanced Manufacturing of Unique Solid Oxide Fuel Cell Electrode and Electrolyte Microstructures through Aerosol Deposition

Development of various additive manufacturing technologies over the years has given an opportunity for highly customizable and unique structures to be fabricated with applications towards several different industries. For ceramic manufacturing, techniques such as direct ink writing (DIW), stereolithography (SLA), and fused deposition modeling (FDM) have been utilized to construct very complex structures. These technologies have also been developed for use towards solid oxide fuel cells (SOFCs) where they have been utilized to manufacture components greater than 200 µm in thickness. Some components of the SOFC such as the electrodes, electrolyte, and barrier layer are much smaller and consist of thicknesses from 1 µm to 50 µm. Along with the reduced thickness, the electrodes of a SOFC are often comprised of a composite material where the previously mentioned technologies struggle with achieving both the required high resolution and compositional change needed to manufacture these specific components. This project’s goal is to develop an additive manufacturing technique that suits both requirements for manufacturing the electrodes, electrolyte, and barrier layer of a SOFC.The technology that has been developed to complete the manufacturing of highly customizable electrodes along with the electrolyte and barrier layer is Aerosol Deposition. The Aerosol Deposition system contains several different elements that lead to consistently tailored microstructures for the various 3-D printed parts including the use of syringe pumps, an ultrasonic atomizing nozzle from Sonaer Ultrasonics, an infrared heater, and a flexible automation system. The ultrasonic atomizing nozzle is used to convert a stream of liquid into a fine mist via mechanical vibrations. The liquid that is supplied to our ultrasonic atomizing nozzle is low solids loading solvent-based suspension containing approximately 1 - 5 vol% of solids and polymer pore formers. Suspensions are supplied to the nozzle by mechanical pressure provided from a programmable syringe pump. This technology accompanied with a flexible automation system gives the potential for highly customizable and repeatable microstructures that can aid in evaluating variables associated with the different components of the SOFC.Development of the additive manufacturing system to fabricate the anode functional layer, electrolyte, barrier layer, and cathode active and current collector layers through an automated process have been studied. For the electrodes, a microstructure that contains approximately 30% - 40% porosity is suitable to enhance the electrochemical performance of the electrode. Sintering temperatures for the electrodes typically range from 1000 °C to 1300 °C which can typically densify the microstructure and restrict the amount of porosity present. To implement porosity within the microstructure poly(methyl methacrylate) was incorporated into electrode suspensions due to their ability to diffuse out of the electrode microstructure at temperatures of ~450 °C. The electrical and mechanical properties of the separate components have been characterized accordingly utilizing electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Acknowledgements: This work was performed in support of the US Department of Energy’s Solid Oxide Fuel Cell Program. The authors would like to acknowledge the WVU Shared Research Facilities (SRF) and thank Dr. Thomas Kalapos from Leidos Research Support Team for his assistance.

Optimizing Bilayer Electrolyte Thickness Ratios for High Performing Low-Temperature Solid Oxide Fuel Cells

Over the last several years, significant developments have been made in bilayer electrolytes (e.g. GDC(Ce0.9Gd0.1O2-δ)/ESB((Er0.20Bi0.80O1.5)) suitable for low-temperature operating solid oxide fuel cells (SOFCs). Such bilayer electrolytes offer the potential for developing high performing LT-SOFCs by lowering the ohmic area specific resistance (ASR), and by improving the open circuit voltage (OCV) of mixed ionic/electronic conducting (MIEC) type electrolyte (e.g., GDC). However, optimizing the thickness ratio of the bilayer electrolyte is essential to achieve high power densities at low-temperatures (650-500 ℃). Here, we made a systematic study by varying the thickness ratios between GDC and YCSB((Bi0.75Y0.25)1.86Ce0.14O3±δ) bilayer electrolytes on an anode-supported LT-SOFCs, in all cases, the maximum power density (MPD) of the bilayer electrolyte cells is higher than pristine GDC based cells with reduced ohmic ASR values. Specifically, a high MPD of ~1 W/cm2 at 650 ℃ was achieved on a GDC(20μm) / YCSB(12μm) bilayer electrolyte based SOFC, which is 62% higher than pristine GDC based SOFC (0.64 W/cm2) operating on humidified H2 as fuel. Such enhancement is due to the 9.3% improvement in OCV (from 0.791 to 0.865 V) and a considerable 36% reduction in ohmic ASR values (from 0.094 to 0.069 Ω.cm2). Such reduction in ohmic ASR of the GDC/YCSB bilayer electrolyte SOFCs is due to the increase of GDC electrical conductivity as a result of lower pO2 at the interface of YCSB and GDC, and hence, must be considered in optimizing the thickness ratio of the bilayer electrolyte for achieving higher power density SOFCs. Figure 1

In Situ Formation of Ba3CoNb2O9/Ba5Nb4O15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance.

The in situ formation of a heterostructure delivers superior electrochemical properties as compared to the mechanical mixing, which shows great promise for developing new electrolytes for solid oxide fuel cells (SOFCs). Herein, in an SOFC constructed by the Ba5Nb4O15 electrolyte and Ni0.8Co0.15Al0.05LiO2-δ anode, an in situ formation of Ba3CoNb2O9/Ba5Nb4O15 heterostructure is designed by Co-ion diffusion from the anode to the electrolyte during cell operation, resulting in improved ion conductivity and fuel cell performance. An abnormal phenomenon is observed that the SOFC based on the Ba3CoNb2O9/Ba5Nb4O15 electrolyte delivered a peak power density of 703 mW/cm2 at 510 °C, which is higher than that at 550 °C. Characterization in terms of X-ray photoelectron spectroscopy and X-ray diffraction verifies that the operating temperature affected the Co doping concentrations, leading to different conducting behaviors of the heterostructure. Furthermore, it is found that the heterojunction of Ba3CoNb2O9 and Ba5Nb4O15 can restrict the electron migration to avoid current leakage of the cell and simultaneously enhance the proton conductivity. These findings manifest the developed in situ Ba3CoNb2O9/Ba5Nb4O15 heterostructure as a promising electrolyte for SOFCs.

Revolutionizing hydrogen production with LSGM-based solid oxide electrolysis cells: An innovative approach by sonic spray

Solid oxide electrolysis cells (SOECs) are considered promising systems for generating green hydrogen, which is an alternative new energy source. Yttria-stabilized zirconia (YSZ), the most common electrolyte in SOFC (solid oxide fuel cell) and SOEC (solid oxide electrolysis cell) has pure ionic conductivity, but it is limited in high temperatures. Instead, La1-xSrxGa1-yMgyO3-δ (LSGM) has emerged as an important candidate electrolyte in such cells because of its superior ionic conductivity with a value of 0.1 S/cm at 1073 K. Therefore, electrolysis cells supported by LSGM may exhibit high durability and efficiency compared to YSZ-supported cells. In this study, an LSGM electrolyte-supported SOEC was successfully fabricated using a sonic spray method, which is presented as a new manufacturing approach. The cell was optimized by controlling the spray frequency and particle size, and its performance was then characterized and electrochemically analyzed. The results showed that the LSGM-based SOEC presents high performance for H2 production. During electrochemical electrolysis at 1073 K, a current density as high as 1.15 A·cm−2 was achieved when 1.3 V was applied. This superior electrolysis performance is attributed to the high ionic conductivity of LSGM. The performance and efficiency obtained with the use of LSGM demonstrate that this electrolyte could be successfully used in SOEC applications.

Long-Term Conductivity Stability of Electrolytic Membranes of Scandia Stabilized Zirconia Co-Doped with Ytterbia.

The effect of high-temperature aging for 4800 h at a temperature of 1123 K on the crystal structure and the conductivity of (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 and (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 single-crystal membranes were studied. Such membrane lifetime testing is critical to the operation of solid oxide fuel cells (SOFCs). The crystals were obtained by the method of directional crystallization of the melt in a cold crucible. The phase composition and structure of the membranes before and after aging were studied using X-ray diffraction and Raman spectroscopy. The conductivities of the samples were measured using the impedance spectroscopy technique. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition showed long-term conductivity stability (conductivity degradation not more than 4%). Long-term high-temperature aging of the (ZrO2)0.90(Sc2O3)0.08(Yb2O3)0.02 composition initiates the t″ → t' phase transformation. In this case, a sharp decrease in conductivity of up to 55% was observed. The data obtained demonstrate a clear correlation between the specific conductivity and the change in the phase composition. The (ZrO2)0.90(Sc2O3)0.09(Yb2O3)0.01 composition can be considered a promising material for practical use as a solid electrolyte in SOFCs.

A Novel Lanthanum-based Solid Oxide Fuel Cell Electrolyte Composite with Enhanced Thermochemical Stability toward Perovskite Cathode

Lanthanum-based electrolytes for Solid Oxide Fuel Cells (SOFCs) gain extensive attention due to their lower activation energy and low-cost preparation to convert the energy stored in gaseous chemicals into electricity. In this context, a La9.33Si6O26-La0.8Sr0.2Ga0.8Mg0.2O2.55 (LSO-LSGM) SOFC electrolyte composite with various mass ratio LSO:LSGM (w/w) (5:0, 4:1, 3:2, 2:2, 2:3, 1:4) are successfully prepared for the first time using different LSO precursors with various mass target of 3g (LSO-LSGMA) and 5g (LSO-LSGMB), respectively. The result shows that the lower mass target in the synthesis of LSO induced formation of protoenstatite and coesite secondary phases on the composite of LSO-LSGM based on XRD, FTIR, and XPS analysis. The SEM micrograph suggests that agglomeration occurred more in LSO-LSGMA than in LSO-LSGMB. Generally, the composites signified high chemical stability on La0.8Sr0.2Co0.6Fe0.4O2.55 (LSCF) cathode based on the XRD analysis. The LSO-LSGMA composites which contained a high percentage of protoenstatite and coesite resulted in an additional peak of MgSi2Sr, especially for the sample with the mass ratio of 41 (LSO-LSGM41) suggesting that the chemical stability of LSO-LSGMA on LSCF cathode is much lower than LSO-LSGMB.

Efficient ion conductivity enhancement mechanism induced by metal ion diffusion of SOFCs based on Fe-doped Gd2O3 electrolyte

Considerable efforts have been made in the past several decades to search for electrolytes that can work at low temperatures for solid oxide fuel cells (SOFCs). The rare-earth oxide Gd2O3 is a thermodynamically stable semiconductor material, but it has not yet been thoroughly explored for use in SOFC devices. In this study, a series of Fe-doped Gd2O3 with varying compositions were successfully synthesized to function as electrolytes for SOFCs. The as-prepared material, 10% Fe-doped Gd2O3 (Fe0.1Gd1.9O3), exhibited an excellent peak power density of 1352 mW/cm2 at 550 ℃, while the ionic conductivity reached 0.25 S cm−1. Various spectroscopic measurements, such as X-ray photoelectron spectroscopy, ultraviolet-visible (UV–vis) spectroscopy, and density functional theory calculations, were employed to understand the enhanced ion transportation mechanism and the improved performance of Fe-doped Gd2O3. The results showed that the Fe-doped Gd2O3 and energy bandgap tuning of electrolytes can significantly improve fuel cell performance at low temperatures, which is of great significance for the future development of low-temperature ceramic fuel cells.