Scandia-stabilized Zirconia Research Articles

Highly Efficient CuCo2O4 Decorated Er0.4Bi1.6O3 Nanostructured Cathode for Intermediate Temperature Solid Oxide Fuel Cells

AbstractThe cathode efficiency for intermediate temperature solid oxide fuel cells is largely limited by the catalytic activity for oxygen reduction reaction. Here by, we design and synthesize CuCo2O4 decorated Er0.4Bi1.6O3 cathode by means of a simple gelation method and then screen‐print it on scandium‐stabilized zirconia electrolyte cell followed by a relatively lower temperature sintering process. The decoration of CuCo2O4 adequately enhances the electro‐catalytic activity of the composite cathode for the ORR. In addition, Er0.4Bi1.6O3 matrix also reduces the sintering temperature (from 1000 °C to 850 °C) compared to the pristine CuCo2O4 electrode. The CuCo2O4‐decorated‐Er0.4Bi1.6O3 composite cathode demonstrates a lower polarization resistance (0.016 Ω cm2 at 800 °C) in air, exhibiting an 87% decrease in comparison to the primary CuCo2O4 cathode.

Fabrication of an anode functional layer for an electrolyte-supported solid oxide fuel cell using electrohydrodynamic jet printing**Report presented at 9th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2018), 7–11 November 2018, Ninh Binh City, Vietnam

Electrohydrodynamic jet (E-jet) printing is an advanced printing technique using an electric field to create the flow of inks from a nozzle via electrohydrodynamics. This technique can deliver very small droplets or flows of inks for high resolution printing. Here, we describe the fabrication of an anode functional layer for an electrolyte-supported solid oxide fuel cells using E-jet printing technique. An ink containing nickel oxide and 10% scandia-stabilized zirconia (10ScSZ) was used to print on an electrolyte plate. Different printing parameters were investigated to vary the structure and morphology of the printed layer. A multiple anode functional layer was fabricated following the optimal printing parameters. The results showed that the thickness of the lines of the printed grid-structured layer could be altered by changing the printing speed. In addition, the grid interval could be easily adjusted. Moreover, multiple overlapped grid layers could be quickly fabricated by printing another layer on a printed dried layer. This anode structure is very beneficial for fuel cell since it possesses a high porosity for quick diffusion of fuel gas and an increased active surface area for enhancing electrochemical reactions. The results showed that the open-circuit voltage (OCV) values of both cells were approximately 1.1 V although the anode functional layer fabricated by using E-jet printing was 7–10 times thinner than that using screen printing.

Influence of the Solid-Electrolyte Ionic Material in a Potentiometric Sensor for Ethylene Detection

Potentiometric sensors based on metal oxides as electrodes and 8YSZ as electrolyte at 550°C can provide selective response to C2H4 with low cross-sensitivity toward CO, H2O, C14H10 and C11H10. The target of the present work is to evaluate the influence of the material used as electrolyte, the electrolyte thickness and the working temperature to check the effect of these parameters on the response to C2H4. After surface functionalization via Ni nanoparticle deposition onto the working electrode to improve the sensor performance, the effect of 8YSZ electrolyte thickness (from 0.1 to 1.2 mm) on the sensor response was studied. The best performance was achieved with the thinner electrolyte (0.1 mm) in terms of selectivity to C2H4 and low cross-sensitivity toward CO. In second place, Ce0.8Gd0.202-δ (CGO) and scandium-stabilized zirconia (ScSZ) oxide-ion conductors were tested as an alternative to 8YSZ to operate at lower temperatures. ScSZ and CGO based-devices provided promising sensing performance at 450°C and C2H4 concentrations below 100 ppm in dry conditions upon functionalization of the working electrode with Ni nanoparticles. At 550°C, both electrolyte materials show a selective response to C2H4 with low cross-sensitivity toward CO even in wet conditions or in presence of polyaromatics.

High-temperature steam electrolysis combined with methane partial oxidation by solid oxide electrolyzer cells

Solid oxide electrolyzer cells consisting of scandia-stabilized zirconia (ScSZ) electrolyte, Ni-yttria-stabilized zirconia (YSZ), and lanthanum strontium ferrite (LSCF)-gadolinia-doped ceria (GDC) were fabricated, and their performance in high-temperature steam electrolysis combined with methane partial oxidation was investigated. The voltage of the electrolyzer cell operated with methane/steam input was significantly reduced compared to that of the cell with air/steam input. The hydrogen production rates at 1.3 V (850 °C) were 4.53 and 1.74 sccm for the electrolyzer cell with methane/steam and air/steam inputs, respectively. On-line gas chromatography analysis confirmed the production of hydrogen and carbon monoxide in the anode side, indicating that methane partial oxidation occurred at the anode side.

Plasma-spray derived, corrosion-resistive electrolyte for liquid antimony anode direct carbon fuel cell

Direct carbon fuel cells (DCFC) that employ solid oxide electrolytes and liquid antimony (Sb) anodes are efficient electrochemical cells for converting various types of solid carbon fuels directly into power. Though the liquid Sb anode exhibits decent performance, electrolyte corrosion by molten Sb2O3 during fuel cell operation has long been an issue. The present study investigates the behavior of scandia stabilized zirconia (ScSZ) electrolytes fabricated through different approaches in liquid antimony anode DCFCs. As for conventional sintered ScSZ electrolyte, we observed severe electrolyte corrosion by molten Sb2O3, which agrees with previous reports. In contrast, corrosion or thinning by the oxide was not detected in ScSZ electrolyte prepared with atmospheric plasma spray (APS) technology. Both electrochemical testing and microscopic characterization results suggest that plasma spray is a promising method to prepare robust electrolytes for liquid antimony anode based DCFCs.

Inert substrate-supported microtubular solid oxide fuel cells based on highly porous ceramic by low-temperature co-sintering

Inert substrate-supported microtubular solid oxide fuel cells (MT-SOFCs) are attractive due to their advantages, including high reduction–oxidation (redox) cycling stability and thermal cycling tolerance. A method involving sequential dip-coating, leaching, and co-sintering was developed and applied to fabricate inert substrate-supported MT-SOFCs through acid leaching nickel from the conventional Ni–yttria-stabilized zirconia (YSZ) anode. A thin current collector was deposited onto the support surface to minimize the current collection losses by collecting current from the entire surface area of the anode. A dense electrolyte could be obtained at a co-sintering temperature of 1250 °C. The produced MT-SOFC with the configuration of porous zirconia support/Ni–Scandia-stabilized zirconia (SSZ) anode current collector/Ni-SSZ anode/SSZ electrolyte/strontium-doped lanthanum manganite (LSM)-SSZ cathode/LSM cathode current collector was evaluated by electrochemical characterization tests. The inert substrate-supported MT-SOFC exhibited the maximum power densities of 616, 542, 440, and 300 mW cm−2 at 800, 750, 700, and 650 °C, respectively using dry hydrogen and air. In addition, the thermal cycling stability of the MT-SOFC was evaluated. The cell survived from thermal cycling tests and came out intact after 50 thermal cycles between 700 °C and 400 °C during an operation time of 50 h.

Influence of codoping on the conductivity of Sc-doped zirconia by first-principles calculations and experiments

Doped zirconia is a promising electrolyte candidate for Solid Oxide Fuel Cells (SOFCs). The effects of dopants and their interactions with oxygen vacancies on the conduction properties have been systematically investigated by density functional theory (DFT) calculations and experiments. The influences of dopants' valences and radii on the defect formation energies and defect binding energies are discussed. Our results show that, for Scandia stabilized zirconia (ScSZ) co-doped with In3+, Yb3+, or Bi3+, the defect formation energy differences and binding energy differences of different sites are low, which indicates that for these co-doping cases the oxygen vacancies distribute more randomly, and are more beneficial for improving the oxygen vacancy diffusing efficiency. The inner influence mechanisms of the co-dopants are discussed from the aspects of elastic and electrostatic effects. Oxygen diffusion barriers in ScSZ co-doped with various elements are also calculated by the saddle point method. The calculated results indicate that the diffusion barrier orders for different edges are ESc-Zr < EZr-Zr < ESc-M for RM > RZr and ESc-Zr ≈ ESc-M < EZr-Zr for RM < RZr. Furthermore, relative experiments are carried out to verify the theoretical results.

Computational and Experimental Investigations of Defect Interaction and Ionic Conductivity in Doped Zirconia

Yttria- and scandia-stabilized zirconia are the most promising electrolytes for solid-oxide fuel cells, but a key drawback hindering their wide application is low ionic conductivity at low operating temperatures. As ionic conductivity is closely associated with the dopants and defect interactions in an electrolyte material, the authors theoretically and experimentally investigate the influences of these structural perturbations in Y- and Sc-doped ZrO${}_{2}$. The atomistic insight obtained should help in engineering solutions to the ionic-conductivity problem at the desired operating temperatures.

Hydrogen production of nickel–scandia-stabilized zirconia and copper/nickel–scandia-stabilized zirconia catalysts through steam methane reforming for solid oxide fuel cell operation

In this study, the catalytic activities of the steam methane reforming (SMR) reactions with two catalysts, including nickel–scandia-stabilized zirconia (Ni–SSZ) and copper/nickel–scandia-stabilized zirconia (Cu/Ni–SSZ), were examined and compared. The microstructure and crystallinity of the as-prepared catalysts were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray diffraction. Mass spectrometer was applied in the outlet streams, in order to simultaneously monitor the time-dependent kinetics in the reactor for an activity test and conversion examination. Finally, thermogravimetric analysis (TGA) and Raman spectrometer were implemented for further verification of carbon residuals on the catalysts. It was found that the incorporation of Cu on Ni–SSZ imposed significant constraints on the growth of nickel crystallites from NiO during the annealing process in reducing atmospheres. The methane conversion of Ni–SSZ and Cu/Ni–SSZ catalysts (annealed at 300 °C for 2 h) was 36.2 and 26.0%, respectively. However, the amount of carbon residuals on Cu/Ni–SSZ catalyst (300 °C for 2 h) was 18.6%, which is lower than that of the Ni–SSZ catalysts (33.2%) from TGA results. Further Raman experiments revealed that more graphite-like carbon residuals and less defects or amorphous carbons (IG/ID = 2.0) were found in the case of Cu/Ni–SSZ catalysts (300 °C for 2 h). Among the catalysts in this study, the Cu/Ni–SSZ catalyst (300 °C for 2 h) is considered as a promising catalyst for SMR reaction, since it has a fair methane conversion, and characterized higher CO2 selectivity and lower CO selectivity without compromising the hydrogen purity. More importantly, the least amount of carbon residuals was found in Cu/Ni–SSZ catalyst (300 °C for 2 h), which assured a better lifetime.

Porous Scandia-Stabilized Zirconia Layer for Enhanced Performance of Reversible Solid Oxide Cells.

Reversible solid oxide cells (RSOCs) developed so far display short-term stability during solid oxide electrolysis cell (SOEC) mode. This is due to thedelamination of the strontium-doped lanthanum manganite (LSM) air electrode when tested for a long time. Here, we report a highly stable RSOC operation of LSM for 5 cycles using half and full cells. A scandia-stabilized zirconia (SSZ) porous layer was applied between the dense SSZ electrolyte and the porous LSM electrode. The half-cells were tested under ±0.5 A cm-2, whereas the full cells were tested at +0.5 and -0.25 A cm-2 at 800 °C. It was found that the cells with a porous SSZ layer are stable and show a performance increase after five RSOC cycles. The ohmic and polarization resistance of both the half and full cells decreased after each cycle. Also, the maximum power density of the full cell increased from 425 to 550 mW cm-2, whereas the electrolysis current density increased from 294 to 407 mA cm-2 after 5 cycles at 1.3 V in 10% H2O/90% H2, at 800 °C. This performance enhancement can be ascribed to the creation of oxygen vacancies in LSM under applied current, the alleviation of oxygen partial pressure from the interface and the introduction of electronic conductivity in the electrolyte near the interface. The cell without the SSZ porous layer experienced the zirconate formation, high oxygen partial pressure at the interface as well as the silver deposition at the electrode-electrolyte interface. Therefore, an increase in the polarization resistance for the half-cell and a decrease in the electrolysis current density for the full cell were observed.

Optimization of ScSZ/GDC bilayer thin film electrolyte for anodic aluminum oxide supported low temperature solid oxide fuel cells

Due to the poor chemical stability of CeO2-based materials, doped CeO2 electrolytes are generally used as a stabilized ZrO2 protection layer/doped CeO2 electrolyte bilayer structure. Since the ionic conductivity of stabilized ZrO2 materials is lower than that of doped CeO2 materials, the thickness of the ZrO2 protective layer needs to be optimized. Thus, in this study, nano-porous anodic aluminum oxide template based scandia stabilized zirconia (ScSZ)/gadolinia doped ceria (GDC) bilayer electrolyte low temperature solid oxide fuel cells (LT-SOFCs) are successfully fabricated and investigated. The optimized thickness of the ScSZ protection layer is revealed by physical and electrochemical characterizations to maximize the performance of LT-SOFCs. The 160 nm ScSZ/400 nm GDC bilayer electrolyte LT-SOFC achieves a maximum power density of 252 mW · cm−2 and an open circuit voltage of 1.02 V OCV at 450 °C.

Chromium poisoning and degradation at LaNi0.6Fe0.4O3 cathode with LaNi0.6Fe0.4O3–Gd0.2Ce0.8O2 functional layer for SOFC under open circuit condition

We fabricate symmetrical cells adopting LaNi0.6Fe0.4O3–δ (LNF) cathode with LNF–Gd0.2Ce0.8O2 (GDC) functional layer on scandia-stabilized zirconia electrolyte by screen printing. Degradation of cathode performances by Cr poisoning is studied. Specific polarization resistance (Rp) increases with time to power of 1/4 and 1/3 in LNF cathode with and without functional layer under exposure of Cr vapors at 750 °C for 900 and 500 h, respectively. Electrochemical impedance spectra illustrate LNF exhibits greater Rp than that of LNF with functional layer under exposure of Cr vapors due to strong Cr deposition at LNF/ scandia stabilized zirconia (ScSZ) interface. No significant degradation in performance has been observed after 900 h of operating under the same condition due to very little Cr deposition at LNF-GDC/ScSZ interface, suggesting little poisoning effect for O2 reduction on LNF cathode with functional layer. These demonstrate LNF cathode with functional layer has high resistance towards Cr deposition and high tolerance towards Cr poisoning.

A homogeneous grain-controlled ScSZ functional layer for high performance low-temperature solid oxide fuel cells

Scandia-stabilized zirconia (ScSZ) is employed as a cathodic functional layer onto yttria-stabilized zirconia based fuel cell systems for low-temperature solid oxide fuel cells.

Joint Impedance Spectroscopy and Fractography Data Analysis of Ceria Doped Scandia Stabilized Zirconia Solid Electrolyte modified by powder types and sintering temperature

Parameters of the non-Debye relaxation in the 10Sc1CeSZ solid electrolyte made of various types of ZrO2 powder stabilized with 10-mol.% Sc2O3 and 1-mol.% CeO2 were studied. The influence of powder properties and their sintering temperatures on the impedance spectra is analyzed. In regard to electrical response, the polycrystalline ceramic electrolytes may be considered as a single-phase or a two-phase material consisting of a grain bulk and a boundary. In many cases, the boundary resistance is independent practically on dopants and their distribution across the powders and sintering temperatures. The powder compositions suitable for an electrolyte and electrodes are specified.

Production of syngas from H2O/CO2 by high-pressure coelectrolysis in tubular solid oxide cells

The conversion of CO2 and steam into syngas in a pressurized solid oxide coelectrolysis (SOC) cell is considered one of the most promising pathways towards the production of sustainable fuels. In this study, a high pressure tubular SOC system was designed and developed that can efficiently convert a mixture of steam and CO2 into valuable syngas fuel. Tubular SOC cells based on a Ni-yttria stabilized zirconia (Ni-YSZ) fuel electrode, scandia stabilized zirconia (ScSZ) electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Ce0.8Gd0.2O1.9−δ (GDC) composite air electrode were fabricated and tested at various high pressure conditions to determine the electrochemical and syngas production characteristics. The pressurized tubular SOC cell was first operated at the ambient pressure for various inlet gas conditions and the electrochemical performance of the tubular SOC was studied by current-voltage curves combined with electrochemical impedance spectroscopy at different H2O and CO2 mole% in the inlet gas. The pressurized SOC cell was then operated between 1 and 8 bar pressure at 800 °C in both fuel cell and coelectrolysis modes. In the fuel cell mode, the SOC showed a 44.2% increase in the maximum power density to with a pressure increase of 1–8 bar. The increase in the performance of the cell in the fuel cell mode was attributed to the higher open circuit voltage (OCV) and reduced polarization resistance of the electrodes at higher pressures. In the coelectrolysis mode, the pressure dependency of the electrochemical characteristics on the tubular SOC cell was studied and the relation between different parameters of the system and the pressure conditions was derived. It was found that the higher open circuit voltage (OCV) and the reduced polarization resistance resulted in a significant improvement in the performance of the pressurized tubular SOC cell for the production of syngas. A post-test material characterization by electron microscopy did not show any significant degradation in the tubular SOC cell microstructure during the high pressure operation at 8 bar.

Stabilizing Nanocrystalline Oxide Nanofibers at Elevated Temperatures by Coating Nanoscale Surface Amorphous Films.

Nanocrystalline materials often exhibit extraordinary mechanical and physical properties but their applications at elevated temperatures are impaired by the rapid grain growth. Moreover, the grain growth in nanocrystalline oxide nanofibers at high temperatures can occur at hundreds of degrees lower than that would occur in corresponding bulk nanocrystalline materials, which would eventually break the fibers. Herein, by characterizing a model system of scandia-stabilized zirconia using hot-stage in situ scanning transmission electron microscopy, we discover that the enhanced grain growth in nanofibers is initiated at the surface. Subsequently, we demonstrate that coating the fibers with nanometer-thick amorphous alumina layer can enhance their temperature stability by nearly 400 °C via suppressing the surface-initiated grain growth. Such a strategy can be effectively applied to other oxide nanofibers, such as samarium-doped ceria, yttrium-stabilized zirconia, and lanthanum molybdate. The nanocoatings also increase the flexibility of the oxide nanofibers and stabilize the high-temperature phases that have 10 times higher ionic conductivity. This study provides new insights into the surface-initiated grain growth in nanocrystalline oxide nanofibers and develops a facile yet innovative strategy to improve the high-temperature stability of nanofibers for a broad range of applications.

Fabrication of anode-supported microtubular solid oxide fuel cells by sequential dip-coating and reduced sintering steps

The expensive and time-consuming fabrication of microtubular solid oxide fuel cells (MT-SOFCs) is one of the main barriers for their commercialization. In this study, a sequential dip-coating coupled with co-firing process was developed to fabricate anode-supported MT-SOFCs using carbon rods as a sacrificial template. Both anode and electrolyte layers underwent co-firing at 1400 °C rather than conventional pre-sintering and co-sintering steps. The whole cell structure was fabricated through sequential dip-coating and drying cycles that are flexible to various tube sizes and fast in turnaround time. The fabricated MT-SOFCs were comprised of Ni–yttria-stabilized zirconia (3YSZ) anode support, scandia-stabilized zirconia (ScSZ) electrolyte, Ni-ScSZ anode functional layer, strontium-doped lanthanum manganite (LSM)–ScSZ cathode functional layer, and LSM cathode current collector layer, respectively. The electrochemical performance of the fuel cell was measured at temperatures between 650 and 800 °C. The MT-SOFC delivered stable performance for more than 50 h operation at 700 °C. The fabricated fuel cell also exhibited excellent thermal cycling stability. The results demonstrated that the sequential dip-coating coupled with co-firing is a simple, flexible and cost-effective fabrication process to produce reliable and robust MT-SOFCs.

Evaluation of Sc2O3–CeO2–ZrO2 electrolyte-based tubular fuel cells using activated charcoal and hydrogen fuels

Solid oxide fuel cells (SOFCs), as energy conversion devices, can use a variety of gaseous (hydrogen, methane, ammonia, carbon monoxide) and solid carbon fuels derived from coal and biomass. A critical component of SOFCs is the oxygen-ion conducting electrolyte material. Yttria-stabilised zirconia (YSZ) is a state-of-the-art electrolyte material often used in SOFCs; it has excellent stability in both reducing and oxidising atmospheres, good mechanical strength and compatibility with electrodes. However, YSZ electrolyte has low ionic conductivity, which leads to high voltage losses in electrolyte-supported SOFCs. Scandia-stabilised zirconia has much higher conductivity, but the phase assemblage is complex, with many phases having detrimental effect on the conductivity. Additions of a small quantity of dopants, such as ceria, appear to stabilise the cubic structure. In this work, we investigate the electrochemical performance of ceria-stabilised scandia–zirconia electrolyte supported tubular fuel cells using hydrogen fuel, and directly compare its electrochemical performance with YSZ-electrolyte supported cells using Ce0.9Gd0.1O2–Ag composite electrodes for both types of cells. The electrolyte conductivity and phase assemblage of ceria stabilised scandia-zirconia have been investigated. We also analysed the electrochemical performance of a tubular cell using activated charcoal as a fuel, and nitrogen and carbon dioxide as purge gases. Electrochemical impedance spectroscopy was used to investigate rate-limiting processes and other factors affecting the fuel oxidation reaction.

Syngas production in high performing tubular solid oxide cells by using high-temperature H2O/CO2 co-electrolysis

By using electricity from renewable sources, high-temperature solid oxide co-electrolysis cells (SOCs) can perform advantageous conversion of H2O/CO2 to high-value syngas. In this work, we investigated the performance of tubular solid oxide co-electrolysis cells for the production of syngas by electrochemical conversion of H2O/CO2. The tubular solid-oxide electrolysis cells comprise Ni-yttria stabilized zirconia (Ni-YSZ) based fuel-electrode supported cells, a yttria or scandia-stabilized zirconia (YSZ and ScSZ) electrolyte, and a composite air-electrode of (La0.85Sr0.15)0.9MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). The electrochemical performance of the tubular SOCs for various operating conditions was analyzed using I-V curves, EIS analysis, and gas chromatography. From the results, we confirm the correlation between the operating conditions and the electrochemical performance of the co-electrolysis process in the tubular SOCs. Furthermore, we found that the syngas yield of the ScSZ electrolyte-based SOC cell was better than that of the YSZ electrolyte-based SOC. The results show that using a tubular SOC offered highly efficient conversion of H2O/CO2, with high yield and good-quality syngas.

Oxide composite of La0.3Sr0.7Ti0.3Fe0.7O3-δ and CeO2 as an active fuel electrode for reversible solid oxide cells

In this paper, La0.3Sr0.7Ti0.3Fe0.7O3-δ (LSTF0.7) composite with CeO2 is successfully prepared by infiltration method as a thin porous electrode and examined in detail as a fuel electrode for efficient reversible solid oxide cells (RSOCs) at different ratios of CO/CO2 at the temperatures of 700–850 °C. XRD analysis indicates that the cubic perovskite LSTF0.7 is stable in CO or CO2 at high temperature and compatible with CeO2 and scandia-stabilized zirconia (ScSZ) electrolyte. In electrolysis mode, the current density of 3.56 A cm−2 is obtained from the I–V curve at 2.0 V in 50% CO+ 50% CO2 at the temperature of 850 °C. The polarization resistance (Rp) of the whole cell at 800 °C is 0.28 Ω cm2 when 1.4 V is applied in the same gas composition. The corresponding activation energy of the fuel electrode under open circuit is calculated to be 81.37 kJ mol−1. In fuel cell mode, the maximal power density of 437 mW cm−2 is obtained at 800 °C in 70% CO+ 30% CO2 as well. The reversible operation at 800 °C indicates that a slow degradation phenomenon in both SOFC and SOEC modes is observed, due to the particle agglomeration of the infiltrated fuel electrode.