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Study of novel proton conductors for high temperature Solid Oxide Cells

Author Anastasia Iakovleva
Source
Time of Publication: 2015
Abstract The main objective of the present work was the systematic study of several groups of materials: Gd3-xMexGaO6-δ (Me = Ca2+, Sr2+), Ba2Y1+xNb1-xO6-δ , and BaZr0.85Y0.15O3-δ (BZY15) as proton conductors. We developed a synthesis route for each group of materials such as microwave- assisted citric acid combustion method, freezedrying synthesis and modified citrate-EDTA complexing method. Pure nanopowders and dense ceramics were obtained after these syntheses plus a classical sintering process. The structure and composition of the obtained products were characterized by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The temperature dependences of the conductivity were investigated by impedance spectroscopy as a function of pO2 and pH2O. For the family of Gd3-xMexGaO6-δ (Me = Ca2+, Sr2+), we studied the influence of dopant nature and content on the structural and electrical properties. Results indicate that the substitution possible till 10 % of doping content. According to the SEM observations, the grain size is increased with increasing dopant content. Concerning electrical properties, we found an increase of conduction with increasing dopant content. All compounds present a good stability in humid, hydrogen and CO2 containing atmosphere. In case of Ba2Y1+xNb1-xO6-δ materials, the physico-chemical properties of synthesized materials have been characterized by the XRD and SEM techniques. The average grain size increased significantly with increasing amount of Y3+. Conduction properties were slightly improved with the partial substitution of niobium by yttrium. The stability of Ba2Y1+xNb1-xO6-δ compounds was investigated under different atmospheres and conditions. The ionic conduction in this case is quite low, which has been explained by futher molecular dynamics simulations. Finally, we studied the influence of an ZnO and NiO additives on the sintering of BZY15, being these sintering aids used to lower the sintering temperature. Zinc oxide as a sintering aid lowers the sintering temperature by 300 C and slightly increases the bulk and total conductivity of BZY15.
Remark THESE DE DOCTORAT

Advanced low-temperature ceramic nanocomposite fuel cells using ultra high ionic conductivity electrolytes synthesized through freeze-dried method and solid-route

Authors Muhammad Imran Asghar, Mikko Heikkil, Peter D.Lund
Source
Materials Today Energy
Volume: 5, Pages: 338-346
Time of Publication: 2017
Abstract Low ionic conductivity and slow reaction kinetics often limit the performance of a ceramic nanocomposite fuel cell (CNFC). Here, we report a novel synthesis method, freeze-dried method, to achieve a record high ionic conductivity for nanocomposite electrolytes (>0.5 S/cm) based on Ce0.85Sm0.15O2 (SDC) and a eutectic mixture of Na2CO3, Li2CO3, K2CO3 (NLK). The highest ionic conductivity (0.55 S/cm) was reached by increasing the carbonate content of the electrolyte to 35 wt%. For the sake of comparison, the nanocomposite electrolytes were also prepared through solid-route. Composite anodes and cathodes for complete fuels were prepared from NiO and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), respectively using both solid-route and freeze-dried nanocomposite electrolytes. Complete fuel cells manufactured from these nanocomposite materials produced ∼1.1 W/cm2 at 550 C. The EIS measurements revealed low ohmic losses (0.18 Ω cm2) and even lower charge transfer resistance (0.05 Ω cm2). In addition, it was found that the open-circuit-voltage (OCV) of the CNFCs improved from 1.1 V to 1.2 V when a mixture of air and CO2 was supplied as compared to the case when only air was supplied at the cathode. Finally, high temperature X-ray diffraction (HT-XRD) revealed stable structures of SDC, NiO and LSCF up to 600 C, which shows the thermal stability of these fuel cell materials.
Keywords Fuel cells, Ceramic, Nanocomposite, Carbonate, Ionic conductivity, Perovskite
Remark https://doi.org/10.1016/j.mtener.2017.07.017
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Stability and range of the type II Bi1 − xWxO1.5 + 1.5x solid solution

Authors Julia Wind, Paula Kayser, Zhaoming Zhang, Ivana Radosavljevic Evansc, Chris D.Ling
Source
Solid State Ionics
Volume: 308, Pages: 173-180
Time of Publication: 2017
Abstract We have established the stability and range of the cubic type II phase of Bi1 − xWxO1.5 + 1.5x using a combination of X-ray diffraction, neutron diffraction and X-ray absorption spectroscopy. Type II is a high temperature modification that can be obtained by quenching/rapid cooling of samples with compositions between x = 0.148 to x = 0.185. Slower cooling rates yield the stable low temperature polymorph, the tetragonal type Ib phase (Bi rich samples), and mixtures of type Ib and Aurivillius phase (W-rich samples). Throughout the entire solid solution range, type II exhibits a (3 + 3) dimensional incommensurate modulation with modulation vectors slightly smaller than 1/3 based on a cubic fluorite type subcell (δ-Bi2O3). The main structural motifs are well-defined tetrahedra of WO6 octahedra in a δ-Bi2O3-matrix, with additional W being incorporated on corners and face centers of the approximate commensurate 3 3 3 supercell in octahedral coordination, confirmed by XANES analysis of the W L3-edge. Impedance measurements reveal oxide ionic conductivities comparable to those of yttria-stabilised zirconia even after a decrease in ionic conductivity of about half an order of magnitude on thermal cycling due to transition to the tetragonal type Ib phase.
Keywords Oxide ionic conductors, Solid solution, Bismuth oxide, Incommensurately modulated structures, Neutron diffraction, XANES
Remark https://doi.org/10.1016/j.ssi.2017.07.015
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High performance novel gadolinium doped ceria/yttria stabilized zirconia/nickel layered and hybrid thin film anodes for application in solid oxide fuel cells

Authors F.J.Garcia-Garcia, A.M. Beltrn, F. Yubero, A.R. Gonzlez-Elipe, R.M. Lambert
Source
Journal of Power Sources
Volume: 363, Pages: 251-259
Time of Publication: 2017
Abstract Magnetron sputtering under oblique angle deposition was used to produce Ni-containing ultra thin film anodes comprising alternating layers of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) of either 200 nm or 1000 nm thickness. The evolution of film structure from initial deposition, through calcination and final reduction was examined by XRD, SEM, TEM and TOF-SIMS. After subsequent fuel cell usage, the porous columnar architecture of the two-component layered thin film anodes was maintained and their resistance to delamination from the underlying YSZ electrolyte was superior to that of corresponding single component Ni-YSZ and Ni-GDC thin films. Moreover, the fuel cell performance of the 200 nm layered anodes compared favorably with conventional commercially available thick anodes. The observed dependence of fuel cell performance on individual layer thicknesses prompted study of equivalent but more easily fabricated hybrid anodes consisting of simultaneously deposited Ni-GDC and Ni-YSZ, which procedure resulted in exceptionally intimate mixing and interaction of the components. The hybrids exhibited very unusual and favorable IV characteristics, along with exceptionally high power densities at high currents. Their discovery is the principal contribution of the present work.
Keywords Magnetron sputtering, Oblique angle deposition, Thin film anodes, Layered and hybrid structures, SOFC
Remark https://doi.org/10.1016/j.jpowsour.2017.07.085
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Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

Authors Einar Vllestad, Matthias Schrade, Julie Segalini, Ragnar Strandbakke, and Truls Norby
Source
Journal of Materials Chemistry A
Volume: 5, Pages: 15743-15751
Time of Publication: 2017
Abstract Rare earth double perovskites comprise a class of functional oxides with interesting physiochemical properties both for low- and high-temperature applications. However, little can be found relating electrical properties with equilibrium thermodynamics of non-stoichiometry and defects. In the present work, a comprehensive and generally applicable defect chemical model is developed to form the link between the defect chemistry and electronic structure of partially substituted BGLC (Ba1−xGd0.8La0.2+xCo2O6−δ, 0 ≤ x ≤ 0.5). The equilibrium oxygen content of 4 different compositions is determined as a function of pO2 and temperature by thermogravimetric analysis, and combined with defect chemical modelling to obtain defect concentrations and thermodynamic parameters. Oxidation enthalpies determined by TG-DSC become increasingly exothermic (−50 to −120 kJ mol−1) with increased temperature and oxygen non-stoichiometry for all compositions, in excellent agreement with the thermodynamic parameters obtained from the defect chemical model. All compositions display high electrical conductivities (500 to 1000 S cm−1) with shallow pO2-dependencies and small and positive Seebeck coefficients (3 to 15 μV K−1), indicating high degree of degeneracy of the electronic charge carriers. The complex electrical properties of BGLC at elevated temperatures is rationalized by a two-band conduction model where highly mobile p-type charge carriers are transported within the valence band, whereas less mobile “n-type” charge carriers are located in narrow Co 3d band.
Remark DOI: 10.1039/C7TA02659E
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Formation of NiO/YSZ functional anode layers of solid oxide fuel cells by magnetron sputtering

Authors I.V. Ionov, A.A. Solov’ev, A.M. Lebedinskii, A.V. Shipilova, E.A. Smolyanskii, A N. Koval’chuk, A.L. Lauk
Source
Russian Journal of Electrochemistry
Volume: 53, Issue: 6, Pages: 670–676
Time of Publication: 2017
Abstract The decrease in the polarization resistance of the anode of solid-oxide fuel cells (SOFCs) due to the formation of an additional NiO/(ZrO2 + 10 mol % Y2O3) (YSZ) functional layer was studied. NiO/YSZ films with different NiO contents were deposited by reactive magnetron sputtering of Ni and Zr–Y targets. The elemental and phase composition of the films was adjusted by regulating oxygen flow rate during the sputtering. The resulting films were studied by scanning electron microscopy and X-ray diffractometry. Comparative tests of planar SOFCs with a NiO/YSZ anode support, NiO/YSZ functional nanostructured anode layer, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode were performed. It was shown that the formation of a NiO/YSZ functional nanostructured anode leads to a 15–25% increase in the maximum power density of fuel cells in the working temperature range 500–800C. The NiO/YSZ nanostructured anode layers lead not only to a reduction of the polarization resistance of the anode, but also to the formation of denser electrolyte films during subsequent magnetron sputtering of electrolyte.
Keywords SOFC, magnetron sputtering, nanostructured electrode, thin-film anode, polarization resistance
Remark Link

Tailoring the electrode-electrolyte interface of Solid Oxide Fuel Cells (SOFC) by laser micro-patterning to improve their electrochemical performance

Authors J.A.Cebollero, R.Lahoz, M.A.Laguna-Bercero, A.Larrea
Source
Journal of Power Sources
Volume: 360, Pages: 336-344
Time of Publication: 2017
Abstract Cathode activation polarisation is one of the main contributions to the losses of a Solid Oxide Fuel Cell. To reduce this loss we use a pulsed laser to modify the surface of yttria stabilized zirconia (YSZ) electrolytes to make a corrugated micro-patterning in the mesoscale. The beam of the laser source, 5 ns pulse width and emitting at λ = 532 nm (green region), is computer-controlled to engrave the selected micro-pattern on the electrolyte surface. Several laser scanning procedures and geometries have been tested. Finally, we engrave a square array with 28 μm of lattice parameter and 7 μm in depth on YSZ plates. With these plates we prepare LSM-YSZ/YSZ/LSM-YSZ symmetrical cells (LSM: La1-xSrxMnO3) and determine their activation polarisation by Electrochemical Impedance Spectroscopy (EIS). To get good electrode-electrolyte contact after sintering it is necessary to use pressure-assisted sintering with low loads (about 5 kPa), which do not modify the electrode microstructure. The decrease in polarisation with respect to an unprocessed cell is about 30%. EIS analysis confirms that the reason for this decrease is an improvement in the activation processes at the electrode-electrolyte interface.
Keywords SOFC, Laser machining, Corrugated surface, Electrode polarisation, Cathode activation, Electrode/electrolyte interface
Remark https://doi.org/10.1016/j.jpowsour.2017.05.106
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Suppression of electrical conductivity and switching of conduction mechanisms in ‘stoichiometric’ (Na0.5Bi0.5TiO3)1−x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions

Authors Fan Yang, Patrick Wu and Derek C. Sinclair
Source
Journal of Materials Chemistry C
Volume: 5, Pages: 7243-7252
Time of Publication: 2017
Abstract (Na0.5Bi0.5TiO3)1−x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions were prepared by a solid state reaction and their electrical properties were established by ac impedance spectroscopy and electromotive force transport number measurements. Incorporation of BiAlO3 (BA) decreases the electrical conductivity of Na0.5Bi0.5TiO3 (NBT) and sequentially changes the conduction mechanism with increasing x from predominant oxide-ion conduction to mixed ionic–electronic conduction and finally to predominant electronic conduction. The suppressed oxide-ion conduction by BA incorporation significantly reduces the dielectric loss at elevated temperatures and produces excellent high-temperature dielectric materials for high BA contents. The possible reasons for the suppressed oxide-ion conduction in the NBT–BA solid solutions have been discussed and we propose that the local structure, especially trapping of oxygen vacancies by Al3+ on the B-site, plays a key role in oxide-ion conduction in these apparently ‘stoichiometric’ NBT-based solid-solution perovskite materials.
Remark DOI: 10.1039/C7TC02519J
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High conductive (LiNaK)2CO3Ce0.85Sm0.15O2 electrolyte compositions for IT-SOFC applications

Authors Ieeba Khan, Muhammad Imran Asghar, Peter D.Lund, Suddhasatwa Basu
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 32, Pages: 20904-20909
Time of Publication: 2017
Abstract Composite electrolytes of lithium, sodium, and potassium carbonate ((LiNaK)2CO3), and samarium doped ceria (SDC) have been synthesized and the carbonate content optimized to study conductivity and its performance in intermediate-temperature solid oxide fuel cell (IT-SOFC). Electrolyte compositions of 20, 25, 30, 35, 45 wt% (LiNaK)2CO3–SDC are fabricated and the physical and electrochemical characterization is carried out using X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscope, and current–voltage measurements. The ionic conductivity of (LiNaK)2CO3–SDC electrolytes increases with increasing carbonate content. The best ionic conductivity is obtained for 45 wt% (LiNaK)2CO3–SDC composite electrolyte (0.72 S cm−1 at 600 C) followed by the 35 wt% (LiNaK)2CO3–SDC composite electrolyte (0.55 S cm−1 at 600 C). The symmetrical cell of the 35 wt% (LiNaK)2CO3–SDC composite electrolyte with lanthanum strontium cobalt ferrite (LSCF) electrode in air gives an area specific resistance of 0.155 Ω cm2 at 500 C. The maximum power density of the fuel cell using 35 wt% (LiNaK)2CO3–SDC composite electrolyte, composite NiO anode and composite LSCF cathode is found to be 801 mW cm−2 at 550 C.
Keywords IT-SOFC, Ternary carbonate–SDC electrolyte, Carbonate loading, Composite electrolytes
Remark https://doi.org/10.1016/j.ijhydene.2017.05.152
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Mixed ionic–electronic conduction in K1/2Bi1/2TiO3

Authors Linhao Li, Ming Li, Ian M. Reaney and Derek C. Sinclair
Source
J. Mater. Chem. C
Volume: 5, Pages: 6300-6310
Time of Publication: 2017
Abstract Recently, it has been reported that the Pb-free piezoelectric perovskite Na1/2Bi1/2TiO3 (NBT) can be compositionally tuned by close control of the A-site starting stoichiometry to exhibit high levels of oxide-ion conduction. The related K1/2Bi1/2TiO3 (KBT) perovskite has also drawn considerable interest as a promising Pb-free piezoelectric material; however, its conduction properties have been less extensively investigated. Here we report on the influence of the K/Bi ratio in the starting composition on the electrical properties using a combination of impedance spectroscopy and ion-transport property measurements. KBT ceramics exhibit mixed ionic–electronic (oxide-ion) conduction with tion ∼ 0.5 at 600–800 C and although variations in the A-site starting stoichiometry can create a ∼1 order of magnitude difference in the bulk conductivity at >500 C, the conductivity is low (ca. 0.1 to 1 mS cm−1 at 700 C) and the activation energy for bulk conduction remains in the range ∼1.2 to 1.5 eV. The high temperature electrical transport properties of KBT are therefore much less sensitive to the starting A-site stoichiometry as compared to NBT. However, KBT ceramics exhibit non-negligible proton conduction at lower temperatures (<300 C). For K/Bi ≥ 1 the total conductivity of KBT ceramics at room temperature can be as high as ∼0.1 mS cm−1 under wet atmospheric conditions. This study demonstrates ionic conduction to be a common feature in A1/2Bi1/2TiO3 perovskites, where A = Na, K.
Remark DOI: 10.1039/C7TC01786C
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Effect of plasma spraying power on LSGM electrolyte of metal-supported solid oxide fuel cells

Authors Chang-Sing Hwang, Te-Jung Hwang, Chun-Huang Tsai, Chun-Liang Chang, Sheng-Fu Yang, Ming-Hsiu Wu, Cheng-Yun Fu
Source
Ceramics International
Volume: 43, Issue: 1, Pages: S591-S597
Time of Publication: 2017
Abstract Four nickel-iron metal-supported solid oxide fuel cells with a diameter of 2.4 cm and a cathode active area of 1.76 cm2 are fabricated by atmospheric plasma spraying (APS) and heat-treated in air at 850 C and 500 g cm−2 pressure for 4 h. These cells with the same functional layer materials have electrolyte layers produced by different APS torch powers, but the APS fabrication parameters for other functional layers of these cells are kept the same. XRD data show that there is a LaSrGaO4 impurity phase in the prepared dense LSGM electrolyte produced at 54 kW torch power. According to experimental data on the current-voltage-power and AC impedance measurements at temperatures ranging from 550 to 800 C, the cell with dense LSGM electrolyte produced at 52 kW torch power has the best power performance and the lowest electrolyte resistance and the corresponding delivered power densities at 0.7 V for 550, 600, 650, 700, 750 and 800 C temperatures are 0.147, 0.271, 0.426, 0.585, 0.716 and 0.796 W cm−2, respectively.
Keywords Metal-supported, Solid oxide fuel cell, Atmospheric plasma spraying, LSGM electrolyte
Remark Link

Composite mixed ionic-electronic conducting ceramic for intermediate temperature oxygen transport membrane

Authors Ming Wei Liao, Tai Nan Lin, Wei Xin Kao, Chun Yen Yeh, Yu Ming Chen, Hong Yi Kuo
Source
Ceramics International
Volume: 43, Issue: 1, Pages: S628-S632
Time of Publication: 2017
Abstract The dense ceramic substrate formed by a mixed ionic-electronic conducting (MIEC) material can be used as an oxygen transport membrane (OTM), enabling the transport of high flux oxygen with certain selectivity and gas separation at high temperatures (800 ~ 900 C). In recent years, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) has been reported to be a promising MIEC material for oxygen permeation due to its relatively high oxygen ion conductivity at high temperatures. However, the catalytic efficiency of BSCF is relatively low among the MIEC materials, resulting in the dramatic decrease of oxygen permeation at temperatures below 800 C. In the present study, a composite MIEC ceramic consisting of a BSCF substrate and the catalytic La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) layer has been proposed. A simple method of laser surface melting is executed to fabricate the composite oxygen transport membrane. The scanning electron microscope (SEM) investigations show that LSCF powders can be well-adherent to the BSCF surface after laser scanning melting process. The oxygen permeation flux reaches 0.5 ml min−1 cm−2 for pure BSCF membrane with thickness of 420 m, while the BSCF membrane substrate with laser scanning LSCF exhibits substantial improvement on oxygen permeation up to 60% at 700 C. The result suggests that the composite MIEC ceramic has significant potential for intermediate temperature oxygen transport membrane.
Keywords Membranes, Composites, Laser surface melting
Remark https://doi.org/10.1016/j.ceramint.2017.05.222
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The Effect of Metallic Co-Coating Thickness on Ferritic Stainless Steels Intended for Use as Interconnect Material in Intermediate Temperature Solid Oxide Fuel Cells

Authors Hannes Falk-Windisch, Julien Claquesin, Jan-Erik Svensson, Jan Froitzheim
Source
Oxidation of Metals
Pages: 1–18
Time of Publication: 2017
Abstract The effect of metallic Co-coating thickness on ferritic stainless steels is investigated. This material is suggested to be used as interconnect material in intermediate temperature solid oxide fuel cells. Uncoated, 200-, 600-, 1000-, and 1500-nm Co-coated Sanergy HT is isothermally exposed for up to 500 h in air at 650 C. Mass gain is recorded to follow oxidation kinetics, and area-specific resistance (ASR) measurements are conducted on samples exposed for 168 and 500 h. The microstructure of the thermally grown oxide scales is characterized utilizing scanning electron microscopy and energy-dispersive X-ray analysis on broad ion beam-milled cross sections. A clear increase in ASR as a function of Co-coating thickness is observed. However, the increase in ASR, as an effect of a thicker Co-coating, is correlated with thicker (Cr,Fe)2O3 scales formed on these materials and not to an increase in Co spinel top layer thickness.
Keywords Solid oxide fuel cell, Interconnect, Coating, Area-specific resistance, Corrosion
Remark DOI 10.1007/s11085-017-9782-9
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Porous Ca3Co4O9 with enhanced thermoelectric properties derived from Sol–Gel synthesis

Authors Michael Bittner, Lailah Helmich, Frederik Nietschke, Benjamin Geppert, Oliver Oeckler, Armin Feldhoff
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Highly porous Ca3Co4O9 thermoelectric oxide ceramics for high-temperature application were fabricated by sol–gel synthesis and subsequent conventional sintering. Growth mechanism of misfit-layered Ca3Co4O9 phase, from sol–gel synthesis educts and upcoming intermediates, was characterized by in-situ X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations. The Ca3Co4O9 ceramic exhibits a relative density of 67.7%. Thermoelectric properties were measured from 373 K to 1073 K. At 1073 K a power factor of 2.46 μW cm−1 K−2, a very low heat conductivity of 0.63 W m−1 K−1 and entropy conductivity of 0.61 mW m−1 K−2 were achieved. The maintained figure of merit ZT of 0.4 from sol–gel synthesized Ca3Co4O9 is the highest obtained from conventional, non-doped Ca3Co4O9. The high porosity and consequently reduced thermal conductivity leads to a high ZT value.
Keywords Thermoelectricity; Thermal conductivity; Porosity; Oxide; Ca3Co4O9
Remark https://doi.org/10.1016/j.jeurceramsoc.2017.04.059
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Electrochemical performance of Co3O4/CeO2 electrodes in H2S/H2O atmospheres in a proton-conducting ceramic symmetrical cell with BaZr0.7Ce0.2Y0.1O3 solid electrolyte

Authors Tz. Kraia, S. Wachowski, E. Vllestad, R. Strandbakke, M. Konsolakis, T. Norby, G.E. Marnellos
Source
Solid State Ionics
Time of Publication: 2017
Abstract The electrochemical performance of Co3O4/CeO2 mixed oxide materials as electrodes, when exposed to H2S/H2O atmospheres, was examined employing a proton conducting symmetrical cell, with BaZr0.7Ce0.2Y0.1O3 (BZCY72) as the solid electrolyte. The impact of temperature (700–850 C) and H2S concentration (0–1 v/v%) in steam-rich atmospheres (90 v/v% H2O) on the overall cell performance was thoroughly assessed by means of electrochemical impedance spectroscopy (EIS) studies. The performance of the Co3O4/CeO2 electrode was significantly enhanced by increasing the H2S concentration and temperature. The obtained results were interpreted on the basis of EIS results and physicochemical characterization (XRD, SEM) studies of fresh and used electrodes. Notably, it was found that the mass transport processes, mainly associated with the adsorption and diffusion of the intermediate species resulting by the chemical and half-cell reactions taking place during cell operation, dominate the electrode polarization resistance compared with the charge transfer processes. Upon increasing temperature and H2S concentration, the electrode resistance is substantially lowered, due to the in situ activation and morphological modifications of the electrode, induced by its interaction with the reactants (H2S/H2O) and products (H2/SO2) mixtures.
Keywords H2S-tolerant electrodes; Cobalt-ceria oxides; BZCY72
Remark https://doi.org/10.1016/j.ssi.2017.04.010
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Thermal stability and enhanced thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47 (0 < x < 5)

Authors G. Cerretti, M. Schrade, X. Song, B. Balke, H. Lu, T. Weidner, I. Lieberwirth, M. Panthfer, T. Norby and W. Tremel
Source
Journal of Materials Chemistry A
Time of Publication: 2017
Abstract Thermoelectric materials are believed to play a fundamental role in the energy field over the next years thanks to their ability of directly converting heat into usable electric energy. To increase their integration in the commercial markets, improvements of the efficiencies are needed. At the same time, cheap and non-toxic materials are required along with easily upscalable production cycles. Compounds of the tetragonal tungsten bronze (TTB) series Nb8−xW9+xO47 fulfill all these requirements and are promising materials. Their adaptive structure ensures glass-like values of the thermal conductivity, and the substitution on the cation side allows a controlled manipulation of the electronic properties. In this contribution we report the stability study of the two highly substituted samples of the series, Nb5W12O47 (x = 3) and Nb4W13O47 (x = 4), when subjected to thermal cycling. Moreover, we show the results of the thermoelectric characterization of these samples. The two compounds have not been affected by the thermal treatment and showed an improvement of the thermoelectric performances up to a zT = 0.2 above 1000 K.
Remark Link

Influence of (Zn,Co)O/ZnO) interface amounts on ionic conduction performance of (Zn1-x,Cox)O (x=0.01, 0.05 and 0.10)

Authors Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Glgn, Satoru Kaneko, Endo Tamio
Source
Composites Part B: Engineering
Time of Publication: 2017
Abstract We investigated the effect of dopant Co atoms into ZnO lattice, on ionic conduction at internal grain and/or through the grain boundary. Influence of dopant Co amount on resistivity was associated with enhanced activation energies of ionic conductivity through the grain boundaries. The change in the activation energy indicated that the mechanism of ionic conduction through the boundaries can be manipulated with Co amount in the lattice. Three conductance mechanisms were identified from the Cole-Cole Plots in order to understand the relaxation mechanism and activation energies of ionic transportations. Formed activation energy, 395 meV, by increasing Co dopant amount up to 10 mol% was attributed to enhanced ionic conductivity through enhancing (Zn,Co)O/ZnO) interface amounts at the grain boundaries. Furthermore, increased activation energy were also enhanced the electronic stability at high temperatures due to decrease in electronic conductivity compared to undoped ZnO.
Keywords Ionic activation energy; Oxide semiconductors; Impedance spectroscopy
Remark https://doi.org/10.1016/j.compositesb.2017.04.020
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Development of novel metal-supported proton ceramic electrolyser cell with thin film BZY15–Ni electrode and BZY15 electrolyte

Authors M. Stange, E. Stefan, C. Denonville, Y. Larring, P.M. Rrvik, R. Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 19, Pages: 13454–13462
Time of Publication: 2017
Abstract Metal supports for planar MS-PCEC were manufactured using tape-casting of low-cost ferritic stainless steel. A coating protecting the metal support against oxidation was applied by vacuum infiltration and a buffer layer of La0.5Sr0.5Ti0.75Ni0.25O3–δ (LSTN) was further deposited to smoothen the surface. The BaZr0.85Y0.15O3–δ–NiO (BZY15–NiO) cathode and the BaZr0.85Y0.15O3–δ (BZY15) electrolyte were applied by pulsed laser deposition (PLD) at elevated substrate temperatures (at 700 C and 600 C, respectively). The main challenges are related to the restrictions in sintering temperature and atmosphere induced by the metal support, as well as strict demands on the roughness of substrates used for PLD. Reduction treatment of the half cells confirmed that NiO in the BZY15–NiO layer was reduced to Ni, resulting in increased porosity of the BZY15–Ni cathode, while keeping the columnar and dense microstructure of the BZY15 electrolyte. Initial electrochemical testing with a Pt anode showed a total resistance of 40 Ωcm2 at 600 C. Through this work important advances in using metal supports and thin films in planar PCEC assemblies have been made.
Keywords Proton ceramic electrolyser cell (PCEC); Tape casting; Thin film deposition; Metal supports
Remark https://doi.org/10.1016/j.ijhydene.2017.03.028
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Energetically benign synthesis of lanthanum silicate through “silica garden” route and its characterization

Authors Kavita Parmar, Santanu Bhattacharjee
Source
Materials Chemistry and Physics
Volume: 194, Pages: 147–152
Time of Publication: 2017
Abstract Lanthanum silicate synthesis through “silica garden” route has been reported as an alternative to energy intensive milling procedure. Under optimum conditions lanthanum chloride crystals react with water glass (sodium silicate) to produce self generating hollow lanthanum silicate precipitation tube(s) (LaSPT). The micro tubes are irregular, thick, white coloured and amorphous but are hierarchically built from smaller tubules of 10–20 nm diameters. They retain their amorphous nature on being heated up to 600 C beyond which crystallization starts. The major phase in the LaSPT heated at 900 C is La2Si2O7. “As synthesized” LaSPT is heterogeneous and comprises non stoichiometric phases. The exterior and interior surfaces of these tubes are remarkably different in their morphology and chemical composition. LaSPT sintered at 1200 and 1300 C show fair amount of ionic conductivity.
Keywords Silica garden; Lanthanum silicate; Synthesis; Characterization
Remark https://doi.org/10.1016/j.matchemphys.2017.03.021
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Effect of Pt catalyst and external circuit on the hydrogen permeation of Mo and Nb co-doped lanthanum tungstate

Authors Yong Cao, Bo Chi, Jian Pu, Li Jian
Source
Journal of Membrane Science
Volume: 553, Pages: 336–341
Time of Publication: 2017
Abstract In this contribution, the hydrogen permeation properties of 30% Mo and 15% Nb co-doped La5.4WO11.1-δ (LWNM30) with/without Pt catalyst and external circuit were investigated. It was found that the surface reaction was the limiting factor in the hydrogen permeation process of LWNM30, and could be improved by using Pt as catalyst. The applied external circuit could also increase the hydrogen flux of LWNM30, and two followed effects might be responsible: the external circuit could transfer the electrons and promote the diffusion process; the external circuit could remove the charge layer on the surface and enhance the surface reaction rate.
Keywords Lanthanum tungstate; Hydrogen permeation; Pt catalyst; Mo and Nb; External circuit
Remark Link

Magnetron-sputtered La0.6Sr0.4Co0.2Fe0.8O3 nanocomposite interlayer for solid oxide fuel cells

Authors A. A. Solovyev, I. V. Ionov, A. V. Shipilova, A. N. Kovalchuk, M. S. Syrtanov
Source
Journal of Nanoparticle Research
Time of Publication: 2017
Abstract A thin layer of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) is deposited between the electrolyte and the La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode layer of a solid oxide fuel cell (SOFC) by pulsed magnetron sputtering using an oxide target of LSCF. The films were completely dense and well adherent to the substrate. The effects of annealing in temperature range from 200 to 1000 C on the crystalline structure of the LSCF films have been studied. The films of nominal thickness, 250–500 nm, are crystalline when annealed at temperatures above 600 C. The crystalline structure, surface topology, and morphology of the films were determined using X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. To study the electrochemical characteristics of the deposited-film, solid oxide fuel cells using 325-nm LSCF films as interlayer between the electrolyte and the cathode have been fabricated. The LSCF interlayer improves the overall performance of the SOFC by increasing the interfacial area between the electrolyte and cathode. The electrolyte-supported cells with the interlayer have 30% greater, overall power output compared to that achieved with the cells without interlayer. The LSCF interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte. Our results demonstrate that pulsed magnetron sputtering provides a low-temperature synthesis route for realizing ultrathin nanocrystalline LSCF film layers for intermediate- or low-temperature solid oxide fuel cells.
Keywords (La,Sr)(Co,Fe)O3 Magnetron sputtering Nanocomposite Interlayer Solid oxide fuel cells Nanostructured thin films Energy conversion
Remark DOI: 10.1007/s11051-017-3791-0
Link

Ferroelectric crystal Ca9Yb(VO4)7 in the series of Ca9R(VO4)7 non-linear optical materials (R = REE, Bi, Y)

Authors Bogdan I. Lazoryak, Sergey M. Aksenov, Sergey Yu. Stefanovich, Nikolai G. Dorbakov, Dmitriy A. Belov, Oksana V. Baryshnikova, Vladimir A. Morozov, Mikhail S. Manylov and Zhoubin Lin
Source
Journal of Materials Chemistry C
Time of Publication: 2017
Abstract The crystal structure, thermal, dielectric and second harmonic generation (SHG), and nonlinear optical activity data for whitlockite-type Ca9Yb(VO4)7 single crystals were obtained on one and the same sample produced by means of the Czochralski method. The crystal structure refinement has revealed that Yb3+ cations substitute for Ca2+ ions only in the M1, M2 and M5 positions of the whitlockite-type structure. Dielectric, differential thermal analysis and SHG data have shown that Ca9Yb(VO4)7 belongs to the family of high-temperature Ca3(VO4)2 ferroelectrics with Curie temperature Tc = 1221 K, where the symmetry changes from R3c to R[3 with combining macron]c. At higher temperatures a previously unknown complementary phase transition is discovered at T2 = 1276 K and is associated with the symmetry change during heating from R[3 with combining macron]c to R[3 with combining macron]m. Unlike other whitlockites, two phase transitions in Ca9Yb(VO4)7 are separated by a broad interval (ΔT = 55 K) which allows one to register two phase transitions by DSC and dielectric measurements. According to the thermal type both transitions are classified as first-order transformations and their structural mechanisms are considered. Inhomogeneity in the cation distribution is argued to have a crucial influence on the optical quality and ferroelectric domain structures of Ca9Yb(VO4)7 and other whitlockite-type laser crystals.
Remark Link

Status report on high temperature fuel cells in Poland – Recent advances and achievements

Authors J. Molenda, J. Kupecki, R. Baron, M. Blesznowski, G. Brus, T. Brylewski, M. Bucko, J. Chmielowiec, K. Cwieka, M. Gazda, A. Gil, P. Jasinski, Z. Jaworski, J. Karczewski, M. Kawalec, R. Kluczowski, M. Krauz, F. Krok, B. Lukasik, M. Malys, A. Mazur, A. Miele
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 7, Pages: 4366–4403
Time of Publication: 2017
Abstract The paper presents recent advances in Poland in the field of high temperature fuel cells. The achievements in the materials development, manufacturing of advanced cells, new fabrication techniques, modified electrodes and electrolytes and applications are presented. The work of the Polish teams active in the field of solid oxide fuel cells (SOFC) and molten carbonate fuel cell (MCFC) is presented and discussed. The review is oriented towards presenting key achievements in the technology at the scale from microstructure up to a complete power system based on electrochemical fuel oxidation. National efforts are covering wide range of aspects both in the fundamental research and the applied research. The review present the areas of (i) novel materials for SOFC including ZrO2-based electrolytes, CeO2-based electrolytes, Bi2O3 based electrolytes and proton conducting electrolytes, (ii) cathode materials including thermal shock resistant composite cathode material and silver-containing composites, (iii) anode materials, (iv) metallic interconnects for SOFC, (v) novel fabrication techniques, (vi) pilot scale SOFC, including electrolyte supported SOFC (ES-SOFC) and anode supported SOFC (AS-SOFC), (vii) metallic supported SOFC (MS-SOFC), (viii) direct carbon SOFC (DC-SOFC), (ix) selected application of SOFC, (x) advances in MCFC and their applications, (xi) advances in numerical methods for simulation and optimization of electrochemical systems.
Keywords SOFC; MCFC; Experiments; Simulations; Fabrication techniques
Remark https://doi.org/10.1016/j.ijhydene.2016.12.087
Link

Surface Protonics Promotes Catalysis

Authors R. Manabe, S. Okada, R. Inagaki, K. Oshima, S. Ogo & Y. Sekine
Source
Nature Scientific Reports
Volume: 6, Pages: Article number: 38007
Time of Publication: 2016
Abstract Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics.
Keywords Catalytic mechanisms, Energy, Heterogeneous catalysis, Surface spectroscopy
Remark doi:10.1038/srep38007
Link

Sm6-xMoO12-δ (x = 0, 0.5) and Sm6WO12 – Mixed electron-proton conducting materials

Authors A.V. Shlyakhtina, S.N. Savvin, N.V. Lyskov, D.A. Belov, A.N. Shchegolikhin, I.V. Kolbanev, O.K. Karyagina, S.A. Chernyak, L.G. Shcherbakova, P. Nez
Source
Solid State Ionics
Time of Publication: 2017
Abstract Samarium molybdates Sm6-xMoO12-δ (x = 0, 0.5) and samarium tungstate Sm6WO12 – potential mixed electron-proton conductors have been studied by X-ray diffraction, Raman spectroscopy, SEM and impedance spectroscopy (in ambient air and in dry and wet air). Solid solutions differing in structure have been obtained in the Sm2O3-MoO3 system at 1600 C. The samarium molybdate Sm6MoO12 has the fluorite structure (Fm3m). The less samarium rich solid solution Sm5.5MoO11.25 crystallizes in a rhombohedral (View the MathML sourceR3) structure. The morphotropic transformation is due to the change in the chemical composition of the solid solution with decreasing Sm3 + concentration. The total conductivity of the cubic fluorite phase Sm6MoO12 at 750 C in air (1.48 10− 3 S/cm, Ea = 1.22 eV) is an order of magnitude higher than that of rhombohedral Sm5.5MoO11.25 (2.34 10− 4 S/cm, Ea = 1.11 eV). At low temperatures (T < 500 C), the Arrhenius plot of total conductivity for Sm6MoO12 and Sm5.5MoO11.25 in air deviates from linearity, suggesting that there is a proton contribution to its conductivity at these temperatures, like in the case of the Sm5.4Zr0.6MoO12.3 zirconium-doped molybdate. Below ~ 500 C, Sm6MoO12 fluorite and fluorite-like Sm6WO12 have identical Arrhenius plots of conductivity in ambient air. The region of dominant proton conductivity is wider for Sm6WO12 than Sm6MoO12, reaching temperatures as high as 750 С for the former. The absolute values of total conductivity obtained for samarium tungstate and molybdate at 400 С in wet air are virtually identical and close to 3 10− 6 S/cm, which suggests the conductivity of both compounds is dominated by protons at low temperatures and the proton transport numbers are similar.
Keywords Phase transition; Fluorite; Fluorite-like phase; Proton-conducting membranes; Proton conductivity; Electron conductivity
Remark http://dx.doi.org/10.1016/j.ssi.2017.01.020
Link
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