Micro-tubular solid oxide fuel cells fabricated by phase-inversion method

A novel structured micro-tubular solid oxide fuel cell (MT-SOFC) has been fabricated by combining a phase-inversion, dip-coating and high temperature co-sintering process with impregnation of the electrode catalyst into a porous electrode matrix. The asymmetric porous anode made by phase-inversion is divided into two different layers, a thick fuel delivery layer with large finger-like pores and a thin function layer with small finger-like pores. The MT-SOFC demonstrates maximum power densities of 0.44, 0.54, 0.65 and 0.78 W/cm² at 650, 700, 750 and 800 °C, respectively with H₂–15%H₂O as fuel and ambient air as oxidant. Combining the power output with the quick start-up behavior, novel structured MT-SOFC offers a potential solution for rapid start-up high performance power devices.     

Electrophoretic Deposition of Thin-Film Coatings of Solid Electrolyte Based on Microsize BaCeO<Subscript>3</Subscript> Powders

Results are presented of an electrophoretic deposition of thin-film coatings based on doped barium cerate BaCeO₃ on a cathode substrate La₂NiO₄ (LNO), which are of interest for the technology of medium-temperature solid-oxide fuel cells. Suspensions for electrophoretic deposition in a mixed dispersion medium isopropanol/acetylacetone = 70/30 vol %, prepared from microsized powders BaCe_0.8Sm_0.2O_3–δ (BCSO) and BaCe_0.89Gd_0.1Cu_0.01O_3–δ (BCGCuO) synthesized by the citrate-nitrate method, demonstrated a high positive ζ-potential (+25 mV) suitable for deposition. A combination of the ultrasonic treatment and centrifugation made it possible to diminish the hydrodynamic diameter of BCSO and BCGCuO particles to 880 and 294 nm, respectively. It was shown that the BCGCuO film deposited onto an LNO cathode substrate has a higher density as compared with the BCSO film, which is due to the properties of the suspensions obtained. Upon a cyclic electrophoretic deposition in six stages, the total mass and thickness of the BCGCuO coating were 3.2 mg cm^–2 and 5 μm, which is sufficient for a unit solid-oxide cell to be formed. According to SEM data, the BCGCuO film is dense and has fully formed grains with sizes of 1 to 7 μm. Methods are discussed for eliminating the loss of Ba in sintering of a thin film based on BaCeO₃.     

Effect of the Copper Oxide Sintering Additive on the Electrical and Electrochemical Properties of Anode Materials Based on Sr<Subscript>2</Subscript>Fe<Subscript>1.5</Subscript>Mo<Subscript>0.5</Subscript>O<Subscript>6–δ</Subscript>

The effect of introducing 1–3 wt % copper oxide sintering additive on the electrical and electrochemical characteristics of promising anode materials for solid oxide fuel cells based on Sr₂Fe_1.5Mo_0.5O_6–δ was studied. The total conductivity increases with increasing amount of copper oxide. The maximum conductivity in humid hydrogen at 800°C, 45 S cm^–1, was reached on introducing 3 wt % CuO. The sintering additive enhances the electrochemical activity of Sr₂Fe_1.5Mo_0.5O_6–δ and Sr₂Fe_1.5Mo_0.5O_6–δCe_0.8Sm_0.2O_1.9 anodes. A decrease in the sintering temperature of the anodes containing CuO with the electrolyte based on lanthanum gallate directly correlates with the electrochemical activity of the anodes. The minimum value of the polarization resistivity, 0.15 Ω cm² at 800°С in a humid hydrogen atmosphere, was obtained for the composite anode with 3 wt % CuO sintered at a temperature of 1050°С.     

LSM-infiltrated LSCF cathodes for solid oxide fuel cells

Mixed ionic-electronic conductors in the family of La_xSr_1–xCo_yFe_1–yO_3–δ have been widely studied as cathode materials for solid oxide fuel cells (SOFCs). However, the long-term stability was a concern. Here we report our findings on the effect of a thin film coating of La_0.85Sr_0.15MnO_3–δ (LSM) on the performance of a porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) cathode. When the thicknesses of the LSM coatings are appropriate, an LSM-coated LSCF electrode showed better stability and lower polarization (or higher activity) than the blank LSCF cathode without LSM infiltration. An anode-supported cell with an LSM-infiltrated LSCF cathode demonstrated at 825 °C a peak power density of ～1.07 W/cm², about 24% higher than that of the same cell without LSM infiltration (～0.86 W/cm²). Further, the LSM coating enhanced the stability of the electrode; there was little degradation in performance for the cell with an LSM-infiltrated LSCF cathode during 100 h operation.     

Synthesis,microstructure, and electric properties of CaZr<Subscript>0.9</Subscript>Y<Subscript>0.1</Subscript>O<Subscript>3 – δ</Subscript> films obtained on porous SrTi<Subscript>0.8</Subscript>Fe<Subscript>0.2</Subscript>O<Subscript>3 – δ</Subscript> supports

Compact CaZr_0.9Y_0.1O_3–δ (CZY) film on a porous SrTi_0.8Fe_0.2O_3–δ (STF) support is obtained using the technique of deposition from solutions of inorganic salts in ethanol. According to the data of scanning electron microscopy (SEM), the film has a nanoporous granular structure with the grain size of 0.2 to 1 μm. The thickness of the CZY film on the STF support is about 3 μm after 15-fold solution application. The results of studying the elemental composition showed that elements of the support diffuse into the film in the course of synthesis. Analysis of the data of impedance spectroscopy shows that conductivity of the CZY film is limited the grain bulk. It is assumed that the comparatively low conductivity activation energy of the film (50.3 kJ/mol) is due to diffusion of elements of the STF support that results in variation of the film composition and properties.     

Improvement of Performance of Oxygen-Conducting Membranes by Electric Heating

Alternating current heating of microtubular oxygen-conducting membranes was studied for the first time. In this case, oxygen–electron mixed-conduction membranes simultaneously act as a heater and an oxygen separator. The efficiency of the alternative heating method was tested on microtubular Ba_0.5Sr_0.5Co_0.78W_0.02Fe_0.2O_3–δ membranes produced by phase inversion. Alternating current heating of microtubular membranes ensures higher membrane performance in oxygen separation at T < 900°C and noticeably decreases the starting period and the lag in varying temperature conditions.     

Electrophysical and thermomechanical properties of perovskites La<Subscript>0.5</Subscript>A<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>O<Subscript>3–δ</Subscript> (A = Ca,Sr, Ba) used as fuel cell anodes: the effect of radius of alkali-earth cation

The effect of the radius of the alkali-earth cation substituted into the A sublattice of La_0.5A_0.5Mn_0.5Ti_0.5O_3–δ (А = Са, Sr, Ba) perovskites on their stability and transport and thermomechanical properties is considered. The increase in the cation radius is shown to improve the phase stability and decrease the conductivity under both oxidative and reductive conditions. The thermal and chemical expansion of La_0.5A_0.5Mn_0.5Ti_0.5O_3–δ ceramics is studied by dilatometry in controlled atmospheres and a wide temperature range at p(O₂)=10^–21–0.21 atm. The coefficients of thermal expansion of La_0.5A_0.5Mn_0.5Ti_0.5O_3–δ are in the interval of (10.7–14.3)× 10^–6 K^–1, i.e., compatible with those of standard solid electrolytes of solid-oxide fuel cells. The maximum chemical expansion does not exceed 0.2% at isothermal reduction in the CO?CO₂ mixture.     

Symmetrical solid oxide fuel cell with strontium ferrite-molybdenum electrodes

The work contains the results of studies of a promising composite material of Sr₂Fe_1.5Mo_0.5O₆ + Ce_0.8Sm_0.2O_1.9 for electrodes of symmetrical solid oxide fuel cells. It is shown that conductivity of the composite at 800°C is about 10 and 15 S/cm, for air and humid hydrogen, respectively, and polarization resistance of the electrodes in contact with the electrolyte based on doped lanthanum gallate under the same conditions is about 0.26 and 0.12 Ohm cm². Tests of a symmetrical fuel cell with a planar design and the supporting gallate electrolyte with the thickness of 300 μm show that the cell can develop the power of about 0.5 W/cm² at 800°C when air is supplied to the cathode and humid hydrogen is supplied to the anode. Analysis of polarization losses shows that the polarization of the oxygen electrode considerably exceeds the polarization of the anode.     

Transport and Electrochemical Properties of SrFe(Al,Mo)O<Subscript>3–δ</Subscript>

In this work, effects of molybdenum doping on the crystal structure, stability, electrical conductivity, oxygen permeability and thermomechanical properties of Sr(Fe,Al)O_3–δ-based perovskites, were studied. The electrochemical performance of model anodes of solid oxide fuel cells (SOFCs), made of SrFe_0.7Mo_0.3O_3–δ, was assessed. Whilst the introduction of Mo cations improves structural stability with respect to the oxygen vacancy ordering processes, excessive molybdenum content leads to a worse phase and mechanical stability under oxidizing conditions. Mo-doping was shown to decrease the thermal and chemical expansivity, to reduce p-type electronic conductivity and to increase n-type electronic conduction. The oxygen permeation fluxes through gas-tight Sr_0.97Fe_0.75Al_0.2Mo_0.05O_3–δ membranes are determined by both the bulk oxygen diffusion and surface exchange kinetics. The role of the latter factor increases on decreasing temperature and reducing oxygen partial pressure. Due to a relatively high electrical conductivity and moderate thermal expansion coefficients in reducing conditions, SrFe_0.7Mo_0.3O_3–δ-based anodes show a substantially high electrochemical activity.     

Electrotransport properties of SOFC cathode materials based on lanthanum cuprate doped with praseodymium and strontium oxides

A complex study of thermal, conducting, and electrocatalytic properties of cuprates La_1.8?xPr_xSr_0.2CuO_4–δ (х = 0.2; 0.4) with the K₂NiF₄ structure is carried out in order to assess their prospects as the cathode materials for solid-oxide fuel cells. The thermal analysis reveals stability of samples heated up to 950°С in air. The conductivity of cuprates measured in the temperature range of 100–900°С and the partial oxygen pressure from 10^–3 to 1 atm is of the metallic nature and varies from 70 to 40 S/cm in the temperature interval of 500–900°С in air. The studies of chemical stability of cuprates with respect to solid electrolytes demonstrate the absence of their chemical interaction with Ce_0.9Gd_0.1O_1.95 (GDC) at 900°С and with La_0.8Sr_0.2Ga_0.85Mg_0.15O_3–δ (LSGM) at 1000°C after 25 h annealing. For La_1.6Pr_0.2Sr_0.2CuO_4–δ electrodes deposited on the surface of GDC or LSGM solid electrolytes, the studies of electrocatalytic activity in the oxygen reduction reaction demonstrate that the smallest polarization resistance is typical of electrodes deposited on the GDC surface.     

Ceramic membranes based on scandium-stabilized ZrO2 obtained by tape casting technique

Results of studies of solid-electrolyte membranes with the composition of 89 mol % ZrO₂-10 mol % Sc₂O₃-1 mol % CeO₂ obtained using the technique of slip casting on a moving tape are presented. Optimization of technological parameters of membrane casting and sintering allowed manufacturing parallel plane gastight plates with the thickness of 200–250 μm that were tested in model solid oxide fuel cells (SOFC) of planar design with standard electrodes based on nickel-containing cermets and lanthanum-strontium manganite. It is shown that though conductivity of such membranes is lower as compared to that of compacted and sintered compacted samples due to diffusion of the aluminum oxide admixture in the course of the manufacturing process, power density of SOFC is sufficiently high and reaches 430 mW/cm² at 850°C.     

Development of an Osmium Redox Polymer Mediated Bioanode and Examination of its Performance in Gluconobacter oxydans Based Microbial Fuel Cell

Gluconobacter oxydans (G. oxydans ) cells together with an osmium redox polymer (ORP) [Osmium (2,2’‐bipyridine)2(poly‐vinylimidazole)10Cl]Cl were combined with a glassy carbon paste electrode (GCPE) to form a bioanode for a microbial fuel cell (MFC) based on G. oxydans . Although there are G.oxydans / ORP combined bioanode in the literature, as far as it is known, this system is the first one where G.oxydans /ORP bioanode is combined with a cathode and a MFC is formed. After the optimization of experimental parameters, analytical characteristics of ORP/G. oxydans /GCPE bioanode were investigated. ORP/G. oxydans /GCPE showed two linear ranges for ethanol substrate as 1.0–30 mM (R²=0.902) and 30–500 mM (R²=0.997) and analytical range as 1.0–1000 mM. Limit of detection (3.0 s/m) and limit of quantification (10 s/m) values were calculated as 1.29 mM and 4.30 mM respectively where the RSD value was 1.16 % for n=5. Combining the developed bioanode in the presence of 5.0 mM K₃Fe(CN)₆ mediator with a Pt wire cathode a double compartment MFC was obtained via a salt bridge. G. oxydans /GCPE bioanode based MFC had maximum power density of 0.133 μW cm⁻² (at 33.5 mV), maximum current density as 8.73 μA cm⁻² and OCP value of 156 mV. On the other hand, ORP/G. oxydans /GCPE based MFC showed maximum power density as 0.26 μW cm⁻² (at 46.8 mV), maximum current density as 15.079 μA cm^‐2 and OCP value of 176 mV.     

Synthesis and Properties of La<Subscript>0.95</Subscript>Sr<Subscript>0.05</Subscript>ScO<Subscript>3–δ</Subscript> Protic Electrolyte Films on Porous Cathode Material

Fundamental aspects of the phase formation and morphology of films of the proton-conducting solid electrolyte La_0.95Sr_0.05ScO_3–δ, produced by wet deposition from inorganic salts on a porous cathode substrate La_0.6Sr_0.4MnO_3–δ. The conditions in which gas-tight films are deposited onto substrates with porosity of up to 25% were determined. The electrical conductivity of La_0.95Sr_0.05ScO_3–δ films was examined in relation to temperature and gas-phase composition (рН₂О, рО₂). The effect of the architecture of the electrolyte membrane on its transport properties was analyzed. The results of the study are of fundamental importance for development of proton-ceramic fuel cells with a supporting electrode.     

Aggregatively stable suspensions of micrometer powders of doped barium cerate for electrophoretic deposition of thin-film coatings of solid-oxide fuel cells

Potentialities of the method of electrophoretic deposition of thin-film coatings based on micrometer powders of multidoped barium cerate BaCe_0.8Sm_0.19Cu_0.01O_3–δ (BCSCuO) and BaCe_0.89Gd_0.1Cu_0.01O_3–δ (BCGCuO) were considered. Micrometer powders of BCSCuO and BCGCuO were produced by the methods of solid-phase and citrate-nitrate syntheses, respectively. The dispersity, fraction composition, and electrokinetic potential of nonaqueous suspensions of these powders and the electrokinetic parameters of the electrophoretic deposition process were examined. An ultrasonic treatment and ultracentrifugation produced aggregatively stable suspensions of BCGCuO and BCSCuO micrometer particles in a mixed (70/30 vol %) isopropanol–acetyl acetone medium. These suspensions are characterized by high positive values of the zeta potential (+24 and +28 mV, respectively). Thin film coatings of the electrolyte materials BCSCuO and BCGCuO, which are of interest for the technology of medium-temperature solid-oxide fuel cells, were produced by the electrophoretic deposition onto a dense model cathode.     

Electronic and ionic zeebeck coefficients in mixed conductors of Ag<Subscript>0.25–δ</Subscript>Cu<Subscript>1.75</Subscript>Se,Ag<Subscript>1.2–δ</Subscript>Cu<Subscript>0.8</Subscript>Se

The paper presents the studies of ionic and electronic Zeebeck coefficients and electronic conductivity in nonstoichiometric Ag_0.25–δCu_1.75Se, Ag_1.2–δCu_0.8Se solid solutions existing on the basis of the cubic phase of copper selenide. It is shown that Ag_1.2–δCu_0.8Se is a bilateral variable composition phase manifesting inversion of the sign of predominant charge carriers under variation of the chemical composition by silver within the homogeneity region. Mobilities of electrons and electron holes are estimated on the basis of the concentration dependences.     

Synthesis and electrocatalytic performance of La0.3Ce0.1Sr0.5Ba0.1TiO3 anode catalyst for solid oxide fuel cells

Ce-doped La_0.4Sr_0.5Ba_0.1TiO_3–δ (LCSBT) perovskite anode catalysts in solid oxide fuel cells were successfully synthesized by a modified rheological phase reaction for the first time. Pure LCSBT could be obtained under a reducing atmosphere and nano-CeO₂ particles could be exsoluted from LCSBT after being sintered in air. The catalytic activity and electrochemical performance of LCSBT anodes for the H₂ oxidation were obviously improved comparing with the pure La_0.4Sr_0.5Ba_0.1TiO_3–δ (LSBT) and LSBT&CeO₂ admixture anodes. The improved performance could be attributed to the nanostructure of LCSBT and the exsoluted nano-CeO₂ particles.     

Neolignans from the Fruits of Magnolia obovata Inhibit NO Production and Have Neuroprotective Effects

One new sesquineolignan, obovatalignan A ( 1 ), and one new neolignan, obovatalignan B ( 2 ), were isolated from the Magnolia obovata fruits. Their chemical structure, including absolute configuration, was determined based on various spectroscopic methods, such as HR‐EI‐MS, 1D‐NMR (¹H, ¹³C, DEPT), 2D‐NMR (gCOSY, gHSQC, gHMBC, NOESY), and CD spectroscopy. The compounds were evaluated for protective effects against glutamate‐induced oxidative stress in HT22‐immortalized hippocampal cells and inhibitory activity against NO production in LPS‐induced RAW 264.7 cells. Compounds 1 and 2 exhibited protective effects against glutamate‐induced oxidative stress with EC₅₀ values of 18.1 ± 1.23 and 7.10 ± 0.78 μm , respectively, as well as inhibitory effects on NO production with IC₅₀ values of > 30.0 and 8.22 ± 2.01 μm , respectively.     

A Carbon–Air Battery for High Power Generation

We report a carbon–air battery for power generation based on a solid‐oxide fuel cell (SOFC) integrated with a ceramic CO₂‐permeable membrane. An anode‐supported tubular SOFC functioned as a carbon fuel container as well as an electrochemical device for power generation, while a high‐temperature CO₂‐permeable membrane composed of a CO₃^2? mixture and an O^2? conducting phase (Sm_0.2Ce_0.8O_1.9) was integrated for in situ separation of CO₂ (electrochemical product) from the anode chamber, delivering high fuel‐utilization efficiency. After modifying the carbon fuel with a reverse Boudouard reaction catalyst to promote the in situ gasification of carbon to CO, an attractive peak power density of 279.3 mW cm^?2 was achieved for the battery at 850 °C, and a small stack composed of two batteries can be operated continuously for 200 min. This work provides a novel type of electrochemical energy device that has a wide range of application potentials.     

Properties of Poly(sodium 4‐styrenesulfonate)‐Ionic Liquid Composite Film and Its Application in the Determination of Trace Metals Combined with Bismuth Film Electrode

A new kind of bismuth film modified electrode to sensitively detect trace metal ions based on incorporating highly conductive ionic liquids 1‐butyl‐3‐methyl‐imidazolium hexafluorophosphate (BMIMPF₆) in solid matrices at glassy carbon (GC) was investigated. Poly(sodium 4‐styrenesulfonate) (PSS), silica, and Nafion were selected as the solid matrices. The electrochemical properties of the mixed films modified GC were evaluated. The electron transfer rate of Fe(CN)₆^4?/Fe(CN)₆^3? can be effectively improved at the PSS‐BMIMPF₆ modified GC. The bismuth modified PSS‐BMIMPF₆ composite film electrodes (GC/PSS‐BMIMPF₆/BiFEs) displayed high mechanical stability and sensitive stripping voltammetric performances for the determination of trace metal cations. The GC/PSS‐BMIMPF₆/BiFE exhibited well linear response to both Cd(II) and Pb(II) over a concentration range from 1.0 to 50 μg L^?1. And the detection limits were 0.07 μg L^?1 for Cd(II) and 0.09 μg L^?1 for Pb(II) based on three times the standard deviation of the baseline with a preconcentration time of 120 s, respectively. Finally, the GC/PSS‐BMIMPF₆/BiFEs were successfully applied to the determination of Cd(II) and Pb(II) in real sample, and the results of present method agreed well with those of atomic absorption spectroscopy.     

Electrical Conductivity,Thermal Expansion and Electrochemical Properties of Perovskites PrBaFe<Subscript>2–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>5 + δ</Subscript>

In order to evaluate applicability of mixed-conducting PrBaFe_2–xNi _x О_{5 + δ} perovskites for cathodes of solid oxide fuel cells (SOFCs), their crystal structure, thermal and chemical expansion, electrical conductivity and electrochemical behavior were studied. The solubility limit of nickel in PrBaFe₂O_{5 + δ} corresponds to x = 0.8. At x > 0.2, the disordered cubic phase transformed into the tetragonal phase. The maximum level of conductivity (50–120 S/cm) at the operating temperatures of SOFC was found for the composition with the maximum nickel content, PrBaFe_1.2Ni_0.8О_{5 + δ}. This material is also characterized by moderate thermal and chemical expansion relative to other ferrite-nickelates. The polarization resistance of a porous PrBaFe_1.2Ni_0.8О_{5 + δ} cathode in a cell with a protective Ce_0.6La_0.4O_2–δ layer and a solid electrolyte (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ was ~0.9 Ohm cm² at a temperature of 1073 K, atmospheric oxygen pressure, and current density of–120 mA cm^–2.