Y2O3 Stabilized ZrO2 Electrolyte Research Articles

Interfacial engineering of (Ce,Zr)O2 composite barrier layers for enhancing the durability of solid oxide fuel cells

The dense GdxCe1-xO2 (GDC) barrier layer can't prevent the diffusion of small amounts of Sr through grain boundaries. Recent studies indicate that the (Ce,Zr)O2 composite, placed between GDC and YSZ (Y2O3 stabilized ZrO2) electrolyte, can effectively suppress SrZrO3 formation. In this study, we successfully designed and prepared an anode-supported solid oxide fuel cell (SOFC) with a dense GDC/IDL (interdiffusion layer) composite barrier layer, demonstrates excellent inhibition of elemental diffusion through grain boundaries. Compared with the cell with a single dense GDC barrier layer, the cell with GDC/IDL composite barrier layer exhibits largely improved durability, with a two-fold decreased degradation rate of 2.7 %/kh, operated under constant current density of 400 mA/cm2 at 720 °C. The cell with GDC/IDL barrier layer presents decreased initial performances, with lager Rohm of 0.085 Ω cm2 than 0.075 Ω cm2, and smaller initial Pmax of 0.905 W/cm2 than 1.019 W/cm2 at 750 °C. However, the cell performance surpasses the cell with single GDC barrier after 230 h. Thus, we obtain a new strategy to achieve improved cell durability by sacrificing the cell's initial performance. The in-situ constructed continuous and dense GDC/IDL composite optimizes the electrolyte/cathode interface while maintaining decent electrochemical performance, providing a new horizon to design and prepare high performance and durable SOFCs.

Anodic polarization creates an electrocatalytically active Ni anode/electrolyte interface and mitigates the coarsening of Ni phase in SOFC

An intimate Ni anode/electrolyte interface is vital for the performance and operating stability of solid oxide fuel cells, while the interface is greatly influenced under anodic polarization conditions. Here for the first time Ni anodes are directly assembled on 8 mol% Y2O3-stabilized ZrO2 (YSZ) electrolyte without high temperature sintering process, and the interface formation between Ni anode and YSZ electrolyte is studied at varied anodic polarization currents at 800 °C. The results show that an intimate anode/electrolyte interface can be created by applying anodic polarization current, leading to remarkably enhanced electrocatalytic activity and operating stability. The major reason of enhanced stability is ascribed to the mitigated microstructure coarsening of Ni anodes due to the strong interfacial bonding induced by the anodic polarization. The present findings shed lights on rational design of Ni based anode/electrolyte interface by tuning the anodic polarization.

Relationship between SiO2 content and electrical properties of 8-mol% Y2O3-stabilized ZrO2 electrolyte

Relationship between SiO2 content and electrical properties of 8-mol% Y2O3-stabilized ZrO2 electrolyte

CO2 electroreduction enhanced by transitional layer at cathode/electrolyte interface

A transitional layer is introduced between the La0.75Sr0.25Cr0.5Mn0.5O3-δ˗Gd0.1Ce0.9O1.95 (LSCM-GDC) cathode and the YSZ (8 mol% Y2O3 stabilized ZrO2) electrolyte by a calcining-stripping-calcining method to improve the cell performance for CO2 electroreduction. The effects of second calcination temperature and the LSCM/GDC weight ratio in the transitional layer are investigated to understand the role of the transitional layer. Experimental results reveal that the transitional layer is effective to decrease the cathodic polarization resistance. The cell performance increases with increasing the second calcination temperature in the temperature range of 800–1200 °C, but decreases at a higher second calcination temperature. The optimal performance is achieved at the second calcination temperature of 1200 °C and the LSCM/GDC weight ratio of 1:1 in the transitional layer. The current densities of the optimized cell with a transitional layer are improved by approximately 50% at various applied voltages compared to the cell without the transitional layer. Besides, based on the calculation results of distribution of the relaxation time and the experimental results, the performance improvement is related to the enhancement of the diffusion and exchange processes of the oxygen species at the three phase boundaries after the introduction of the transitional layer.

Pulsed constant voltage electrophoretic deposition of YSZ electrolyte coating on conducting porous Ni–YSZ cermet for SOFCs applications

In the present investigation, solid oxide fuel cells (SOFCs) electrolyte coatings of 8 mol% Y2O3 stabilized ZrO2 (YSZ) are applied on Ni-YSZ cermet fuel cell anode in ethanol by pulsed constant voltage-electrophoretic deposition (EPD). Press pressure and sintering temperature as two of the most effective parameters for NiO-YSZ composite fabrication are investigated. In order to create electrically conductive anodes, NiO-YSZ composite is reduced in H2 atmosphere while its crystallinity being studied by X-ray diffraction (XRD). Pulsed constant voltage EPD process parameters such as pulse width, applied voltage and total deposition time are examined. The YSZ electrolyte film is sintered for 4 h at two different temperatures of 1300 and 1350 C°. Optical microscope (OM) is used to study the surface quality of coating. Substrate morphology and the quality of YSZ electrolyte film are investigated by scanning electron microscope (SEM). Atomic force microscopy (AFM) is used to probe the surface roughness and the morphology of green and sintered coatings. Results show improved deposition yield by increasing applied voltage and total deposition time. Uniform and dense coating was deposited at voltage of 35 V, pulse width of 1 ms, 50% duty cycle and total deposition time of 6 min having the thickness and roughness of about 17 ± 1 μm and 166 ± 5 nm, respectively.

Biomass carbon fueled tubular solid oxide fuel cells with molten antimony anode

Cell performance and efficiency of tubular molten antimony (Sb) anode direct carbon solid oxide fuel cells (DC-SOFCs) was investigated with two different biomass carbon fuels. The 8mol.% Y2O3 stabilized ZrO2 (YSZ) supported cells with La0.6Sr0.4Co0.2Fe0.8O3-10mol.% Gd2O3 doped CeO2 (LSCF-10GDC) as the cathode were fabricated by slurry-casting, slurry-dipping and sintering processes. A relatively high power density of 196 and 304mWcm−2 was achieved at 750 and 800°C, respectively. Two biomass carbon, cocoanut active charcoal (CAC) and pyrolysed corn starch (PCS), were used as the fuels for cell running at 750 and 800°C and the exhausted gas consist was recorded. The proceedings of anode reactions were closely related to the fuel properties and working temperature and had an obvious influence on the cell running in turn. The fuel utilization and electrical efficiency of the special molten Sb anode cell was defined and calculated by the experimental data. The fuel utilization was above 50% but the electrical efficiency was below 34%, limited by the low Nernst voltage of the reaction of Sb oxidation, thick YSZ electrolyte used and significant heat generated by Sb2O3 reduction.

Tubular direct carbon solid oxide fuel cells with molten antimony anode and refueling feasibility

Tubular direct carbon SOFCs (solid oxide fuel cells) supported by YSZ (Y2O3 stabilized ZrO2) electrolyte are fabricated by slurry-casting, slurry-dipping and sintering processes with La0.6Sr0.4Co0.2Fe0.8O3-10 mol.% Gd2O3 doped CeO2 (LSCF-10GDC) as the cathode. Their electrochemical performance is examined at temperatures from 700 to 800 °C using molten antimony (Sb) anode and activated carbon fuel. The ohmic resistance of the cell is between 1.01 and 0.37 Ω cm2 mainly originated from the thick YSZ electrolyte (150 μm); the polarization resistance ranges from 0.22 to 0.06 Ω cm2. The maximum power density at 800 °C is 304 mW cm−2 and can be greatly increased by using a thinner and/or more conductive electrolyte. With 1 g activated carbon as the fuel, the cell performance is stable at 200 mW cm−2 at 800 °C for more than 6 h by chemical consumption (oxidization) of the carbon, which reduces the electrochemically formed Sb2O3 to Sb. The cell performance decreases as the fuel is used up and is recovered by refueling.

LaNbO4–NiO–Y2O3 Stabilized ZrO2 Anode‐Support Materials for Solid Oxide Fuel Cells

As anode‐support materials for solid oxide fuel cells, porous LaNbO4–NiO–Y2O3 stabilized ZrO2 (YSZ) composites (LNY), containing 0, 5, 10, 15, and 20 wt% of LaNbO4 and designated as 0LNO, 5LNO, 10LNO, 15LNO, and 20LNO, respectively, are prepared by tape casting and sintering. They are investigated for their microstructure and mechanical, electrical and thermal expansion properties. The porosity of as‐sintered LNY is around 30%, and that of reduced LNY cermets decreases from 47% for reduced 0LNO to 43% for reduced 20LNO. The fracture strength (σf) of LNY is higher than that of the reduced form; however, both of them are not rather sensitive to the amount of LaNbO4, depending on crack‐originating flaws in the specimens. The fracture toughness (KIC) of LNY increases with LaNbO4 content and is 1.87 MPa·m1/2 for 20LNO, which is more than 20% increase from that of 0LNO; however the KIC for reduced LNY is higher than that of LNY, and decreases with increasing LaNbO4 content due to the decreased amount of ductile metallic Ni phase. The conductivity of reduced LNY depends on Ni content and is higher than 289 S/cm at temperatures below 900°C. The coefficient of thermal expansion (CTE) of both LNY and reduced LNY is in the range between 12.4 and 11.4 × 10−6 K−1; which is closely matched with that of YSZ electrolyte.

Tubular SOFC with Hollow Fiber Ceramic Support and Inner Coating

In this work, zirconia supported segmented-in-series type single cell with inner side coating was studied. The support tube was fabricated through phase-inversion method using 3%mol Y2O3 doped ZrO2 (TZP). Then the NiO-8%mol Y2O3 stabilized ZrO2 (YSZ) anode layer, YSZ electrolyte layer and (La0.8Sr0.2)0.95Mn3O3- δ (LSM)-YSZ cathode layer and LSM layer was applied by screen printing and high-temperature sintering in proper orders. Finally, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) - Gd0.1Ce0.9O1.95 (GDC) composite layer was coated on the inner side of the support tube. Cell performance characterization was conducted using room-temperature humidified hydrogen and methane at a gas flow rate of 40mL/min inside the tube and ambient air at cathode side. Results show that, the open circuit voltage at 850 oC under H2 and CH4 was 1.04V and 1.08V separately, while the corresponding maximum power density was 96 and 106 mW/cm2 respectively. No obvious degradations were observed in the stability test under humidified H2 for 50h and CH4 for 250h.

Tubular SOFC with Hollow Fiber Ceramic Support and Inner Coating

In this work, porous ceramic supported tubular cell with inner coating was studied. The hollow fiber support tube was fabricated through phase-inversion method using 3%mol Y2O3 doped ZrO2 (TZP). Then the NiO-8%mol Y2O3 stabilized ZrO2 (YSZ) anode layer, YSZ electrolyte layer, (La0.8Sr0.2)0.95MnO3-δ(LSM)-YSZ cathode layer and LSM current collected layer were applied by screen printing and high-temperature sintering in proper orders. Finally, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ-Gd0.1Ce0.9O1.95 composite layer was coated on the inner side of the support tube. Cell performance characterization was conducted using room-temperature humidified hydrogen and methane at a gas flow rate of 40 mL min-1 inside the tube and ambient air at cathode side. Results show that, the maximum power density was 96 and 106 mW cm-2 at 850 oC under H2 and CH4, respectively. No obvious degradations were observed in the stability test under humidified H2 for 50 h and CH4 for 250 h.

Infiltrated porous YSZ as a cathode active layer for cathode-supported solid oxide fuel cells

A novel active cathode structure of La0.6Sr0.4Fe0.9Sc0.1O3−δ (LSFSc) infiltrated porous 8mol% Y2O3-stabilized ZrO2 (YSZ) was fabricated by tape casting, co-sintering and infiltration techniques. The infiltrated porous-YSZ layer worked as a cathode active layer (CAL) between a YSZ electrolyte layer and (La0.8Sr0.2)0.95MnO3 (LSM95) cathode substrate. The obtained fuel cells with Ni/SDC anode showed the maximum power densities of 0.574, 0.733 and 0.835W·cm−2 at 750, 800 and 850°C, respectively, with H2 as fuel and air as the oxidant.

Plasma-Sprayed Y2O3-Stabilized ZrO2 Electrolyte With Improved Interlamellar Bonding for Direct Application to Solid Oxide Fuel Cells

Atmospheric plasma spraying was employed to prepare anode, cathode, and Y2O3-stabilized ZrO2 (YSZ) electrolyte to aim at reducing manufacturing cost. YSZ electrolytes were deposited on the anode at different deposition temperatures of 200 °C, 400 °C and 600 °C to optimize the gas tightness of plasma-sprayed YSZ electrolyte. The influences of the deposition temperature on the microstructure and gas-tightness of plasma-sprayed YSZ electrolyte were investigated. The effect of microstructure and the gas-tightness of YSZ electrolyte on the open circuit voltage and the output performance of solid oxide fuel cells (SOFCs) were examined. The results showed with the increase of deposition temperature, the porosity of YSZ electrolytes almost decreased by about 80% and the microstructure of YSZ electrolytes changed from the typical lamellar structure to the continuous columnar crystal structure. At a deposition temperature of 600 °C the gas permeability decreased to 1.5 × 10−7 cm4gf−1s−1, and the highest open circuit voltage can reach 1.026 V, indicating the applicability of the as-sprayed YSZ directly to the SOFC electrolyte.

Synthesis and electrochemical characterization of Sr2Fe1.5Mo0.5O6–Sm0.2Ce0.8O1.9 composite cathode for intermediate-temperature solid oxide fuel cells

Nanoporous composite oxides Sr2Fe1.5Mo0.5O6–Sm0.2Ce0.8O1.9 (SFM–SDC) have been prepared by a facile one-step method as cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The SFM–SDC composite materials have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and electrochemical impedance spectroscopy (EIS). The EIS results exhibit that SFM–SDC40 (wt% 60:40) cathode has encouraging electrochemical performance with low polarization resistance (Rp) on YSZ (Y2O3-stabilized ZrO2) electrolyte. Subsequently, bi-layer cathodes SDC/SFM–SDC are fabricated, and excellent electrochemical performance of such composite cathodes are observed. We demonstrate that the SDC interlayer significantly decreases the Rp of cathode and accelerates the charge transfer process. As a result, the Rp of the SDC/SFM–SDC40 bi-layer cathodes is almost 50% less than that of SFM–SDC40 cathode on YSZ electrolyte at 800 °C, and Rp is only 0.11 Ω cm2. Compared with single cells without an interlayer, the anode-supported single cells with SDC interlayer exhibit enhancement in overall power performance.

One-step synthesis of high performance Sr2Fe1.5Mo0.5O6–Sm0.2Ce0.8O1.9 composite cathode for intermediate-temperature solid oxide fuel cells using a self-combustion technique

A Sr2Fe1.5Mo0.5O6–Sm0.2Ce0.8O1.9 (SFMO–SDC) nanocomposite material has been prepared by the self-combustion method. The phase structure and morphology of the material have been characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). These results show the coexistence of perovskite and fluorite structures within the porous microstructure which are uniformly distributed throughout the prepared samples. The electrochemical performance of the material has been investigated by electrochemical impedance spectroscopy (EIS) measurements. Using an SDC interlayer SFMO–SDC composite cathode is prepared and applied onto a standard YSZ (8% Y2O3-stabilized ZrO2) electrolyte. A low polarization resistance of the prepared sample is obtained and remarkable performance of the SFMO–SDC based IT-SOFCs is achieved. It is demonstrated that the SFMO–SDC/SDC/YSZ/NiO–YSZ fuel cell reached power densities of 2.21, 1.66, 1.16 and 0.71 W cm−2 at 800, 750, 700 and 650 °C, respectively, in humidified H2 (3 vol% H2O).

High performance La3Ni2O7 cathode prepared by a facile sol–gel method for intermediate temperature solid oxide fuel cells

La3Ni2O7 oxide has been synthesized by a facile sol–gel method using a nonionic surfactant (EO)106(PO)70(EO)106 tri-block copolymer (Pluronic F127) as the chelating agent. The pure phase of La3Ni2O7 has been obtained by sintering at temperatures of 1100°C for 12h. La3Ni2O7 oxide as a cathode presents no visible reaction with an Y2O3-stabilized ZrO2 (YSZ) electrolyte. The electrochemical performance of the prepared oxide as a cathode has been investigated. Area specific resistance of La3Ni2O7 material on YSZ electrolyte is as low as 0.39Ωcm2 at 750°C. Furthermore, an anode-supported single-cell configuration of NiO–YSZ/YSZ/La3Ni2O7 has been achieved a maximum power density of 848mWcm−2 at 750°C. The cell performance was stable under a constant current of 0.6Acm−2 for over 30h at 750°C. These results therefore suggest that La3Ni2O7 synthesized by this sol–gel method is a highly promising cathode material for applications in IT-SOFCs.

Performance degradation of impregnated La0.6Sr0.4Co0.2Fe0.8O3+Y2O3 stabilized ZrO2 composite cathodes of intermediate temperature solid oxide fuel cells

Composite cathodes of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and Y2O3 stabilized ZrO2 (YSZ) are fabricated by impregnating the porous YSZ scaffold pre-formed on YSZ electrolyte substrate with a solution containing La, Sr, Co and Fe in desired composition. The performance stability of the cathodes is evaluated in air at 750 °C for up to 120 h by electrochemical impedance spectroscopy under the condition of open circuit. An insignificant small amount of resistive phase SrZrO3 is formed at 800 °C during cathode preparation; however, its volume is not further increased at 750 °C for 120 h, as indicated by the XRD results. The cathode polarization resistance (Rp) increases from 0.17 to 0.30 Ωcm2 after the 120 h test mainly due to the increase of the low frequency polarization resistance (Rp2), which characterizes the low frequency processes in the reaction of oxygen reduction. The morphology change of the well connected LSCF particles to dispersive and flattened configuration accounts for the increase of the Rp2 and in turn the degradation of cathode performance.

Performance of Ni/Y2O3-Stabilized ZrO2 Cermet Cathode Prepared by Mechanical Alloying for High-Temperature Electrolysis of Water Vapor

A Ni/Y2O3-stabilized ZrO2 composite cathode was fabricated by high-energy ball milling of Ni and Y2O3-stabilized ZrO2 powders for high-temperature electrolysis (HTE) of water vapor. The composite powder composition, time and rotation speed of ball milling were optimized by trial and error for suitable performance with the maximum efficiency of the fabricated cathode in high-temperature electrolysis of water vapor (steam) at 800 °C. Thus-synthesized composite powders were characterized using various analytical tools, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size analysis (PSA), and a self-supporting planar unit cell was prepared with a Ni/Y2O3-stabilized ZrO2 composite cathode and a Pt paste anode screen-printed on each side of a Y2O3-stabilized ZrO2 electrolyte disc (30 mm in diameter) and then sintered at 1450 °C for high-temperature electrolysis. XRD and PSA results showed that ball milling parameters, such as ball milling time and rotation speed, affect the crystallinity, average particle size, and particle size distribution of ball-milled Ni/Y2O3-stabilized ZrO2 composites. The effects of cathode and Y2O3-stabilized ZrO2 electrolyte thicknesses on the efficiency of hydrogen production were investigated using a self-supporting planar HTE unit cell operating at 800 °C. The engineering significance of high-energy ball milling (HEBM) is evident: HEBM is approximately equivalent to 60 µm screen printing over the Y2O3-stabilized ZrO2 electrolyte and could obviate a tedious and time-consuming screen-printing process in the fabrication of a cathode.

Effects of particle size of 8mol% Y2O3 stabilized ZrO2 (YSZ) and additive Ta2O5 on the phase composition and the microstructure of sintered YSZ electrolyte

Abstract The chemical stability and sinterability of nano- and micro-sized yttria stabilized zirconia (YSZ) powders were investigated, and the effect of Ta 2 O 5 additive on the sinterability of YSZ electrolyte was also studied. Addition of Ta 2 O 5 easily causes phase transformation of YSZ from cubic to monoclinic, and thus unfavorable for the improvement of ionic conductivity of YSZ electrolyte. Nano-sized YSZ easily causes abnormal grain growth and hence readily results in inhomogeneous microstructure of YSZ matrix, while micro-sized YSZ displays relatively low sinterability. Comparatively, mixture with 50 wt.% nano-sized and 50 wt.% micro-sized YSZ powders exhibits high sinterability and could be sintered to homogeneous microstructure, which can be used as starting materials to prepare dense YSZ electrolyte at low temperatures.

Electrochemical Performance and Microstructure of The LNF-SDC Composite Cathode for SOFC

Symmetric cells consisting of the LaNi0.6Fe0.4O3 (LNF)- Sm0.2Ce0.8O1.9 (SDC) composite cathodes and 8 mol%Y2O3- stabilized ZrO2 (YSZ) electrolyte have been investigated in order to evaluate the oxygen reduction performance of the composite cathode by AC impedance analysis. Cell performance and cathodic overvoltage were examined for cells consisting of the Ni-YSZ cermet anode, YSZ electrolyte, and composite cathode. The addition of 50 wt% SDC to LNF resulted in the lowest polarization resistance. A cell using the 50 wt% LNF + 50 wt% SDC composite cathode showed the maximum power density and the cathodic overvoltage for this cell showed as half as lower than that for a cell using the LNF cathode under the same condition. Enhancement of the electrochemical performance in the LNF-SDC composite cathode is most likely to be caused by the SDC particles connecting LNF particles with the electrolyte surface.

Characterization of YSZ Solid Oxide Fuel Cells Electrolyte Deposited by Atmospheric Plasma Spraying and Low Pressure Plasma Spraying

Yttria doped zirconia has been widely used as electrolyte materials for solid oxide fuel cells (SOFC). Plasma spraying is a cost-effective process to deposit YSZ electrolyte. In this study, the 8 mol% Y2O3 stabilized ZrO2 (YSZ) layer was deposited by low pressure plasma spraying (LPPS) and atmospheric plasma spraying (APS) with fused-crushed and agglomerated powders to examine the effect of spray method and particle size on the electrical conductivity and gas permeability of YSZ coating. The microstructure of YSZ coating was characterized by scanning electron microscopy and x-ray diffraction analysis. The results showed that the gas permeability was significantly influenced by powder structure. The gas permeability of YSZ coating deposited by fused-crushed powder is one order lower in magnitude than that by agglomerated powder. Moreover, the gas permeability of YSZ deposited by LPPS is lower than that of APS YSZ. The electrical conductivity of the deposits through thickness direction was measured by potentiostat/galvanostat based on three-electrode assembly approach. The electrical conductivity of YSZ coating deposited by low pressure plasma spraying with fused-crushed powder of small particle size was 0.043 S cm−1 at 100 °C, which is about 20% higher than that of atmospheric plasma spraying YSZ with the same powder.