Dense Bilayer Research Articles

(Digital Presentation) GDC/YSZ Bilayer Electrolyte Fabrication by In-situ Hydrothermal Growth

GDC (gadolinia-doped ceria) can be used as barrier layer between the high-performance LSCF (La0.6Sr0.4Co0.2Fe0.8O3-δ) cathode and YSZ (8% mol yttria stabilized zirconia) electrolyte, to prevent chemical incompatibility and elements diffusion. However, the GDC layer is difficult to achieve as high density as the YSZ electrolyte, especially under low sintering temperatures. While, increase sintering temperature over ~1200 ℃ could induce the formation of (Ce,Zr)O2 solid solution.In this work, we report a highly dense bilayer GDC/YSZ electrolyte prepared at low sintering temperature. Specifically, the as-sintered anode supported SOFC half-cell with already-dense YSZ electrolyte was immersed in solution of Gd(NO3)3·6H2O and Ce(NO3)3·6H2O, followed by a hydrothermal treatment at 180 ℃ (accounts for steam pressure of ~1 MPa) for 36 h. This yielded a dense GDC layer growth on YSZ electrolyte with thickness of ~200 nm. Then, the cells were sintered at 1100, 1150 and 1200 ℃, respectively. Afterwards, the hydrothermal treatment was repeated once, to grow an additional GDC layer. This post-grown GDC was then co-sintered with the screen printed LSCF cathode at 1075 ℃.Results show that, the GDC/YSZ bilayer electrolyte is successfully fabricated under low sintering temperature below 1200 ℃, with overall GDC layer as thick as ~540 nm and ultra-high density as the YSZ electrolyte. The single cell with 1200 ℃ sintered GDC, named as GDC-1200, shows the best output performance, i.e. maximum power density of ~0.96 W/cm2 at 780 ℃. Moreover, the cell runs stably at 720 ℃ for 300 hours, showing decent durability.Fig. 1 (a) j-V-P curves of bilayer electrolyte SOFCs with varied GDC sintering temperature; (b) operation voltage versus time for GDC-1200 cell under constant current mode; (c) SEM images and (d) EDS mapping of single cell (GDC-1200) fracture Figure 1

Synergy of selective gas transport in bilayered membranes

Dense bilayer PTMSP/PIM-1 membranes and PTMSP/PIM-1 blends were prepared and studied in order to obtain insight into the recently observed synergistic effect of increased CO2/N2 selectivity for thin-film composite (TFC) membranes consist of PIM-1 (selective layer) and PTMSP (gutter layer). It was shown that the mixing of these two polymers does not lead to a synergistic effect in gas permeance, since dense films made by blending of PIM-1 and PTMSP showed classical trade-off permeation/selectivity behavior. Analysis of gas-transport property data using a bicomponent resistance-in-series model allowed us to conclude that the increased N2 transport resistance of the layer formed on the border of the two polymers is presumably responsible for the increased ideal selectivity.

Solid oxide fuel cells with zirconia/ceria bilayer electrolytes via roll calendering process

Solid oxide fuel cell (SOFC) with yttria-stabilized zirconia (YSZ)/gadolinium-doped ceria (GDC) bilayer electrolytes has been considered one of representative types of high-performance intermediate-temperature SOFCs, because it enables to apply highly active cathode materials. However, the processing of fully dense bilayer electrolytes with good interfacial structure, which are essential for high-performance and secure operation, has not yet been successfully achieved. Here, we present a simple and cost-effective roll calendering process for fabrication of SOFCs with YSZ/GDC bilayer electrolytes. From understanding on the correlation between processing conditions of roll calendering and microstructure of bilayer electrolytes, the roll calendering process is optimized, and in turn, the bilayer electrolytes with overall thickness of 8.0 μm, relative density above 98%, and enhanced interfacial connectivity of 69% is obtained by co-sintering at reduced temperature of 1250 °C. This excellent structural enhancement in comparison with conventional uniaxial pressing process is explained by a shear force applied during roll calendering process, which presumably facilitates particle rearrangement within bilayer electrolytes. The optimized cell yields promising electrochemical performance of 1.45 W/cm2 at current density of 2 A/cm2 and low ohmic resistance of 0.046 Ω cm2 at 800 °C.

Facile fabrication strategy of highly dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolyte via cold isostatic pressing for low temperature solid oxide fuel cells

Gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolytes have received significant attention for use in solid oxide fuel cells since this electrolyte enables the use of a cobalt-containing cathode, which show a high performance at low temperature. However, the low sintering temperature of the bilayer electrolyte, which is required to avoid side reactions, results in low density, limiting its practical applications. In this study, we report a facile and cost-effective method for the fabrication of dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolytes at low temperatures. Even at a low sintering temperature of 1250 °C, a thin and dense bilayer electrolyte structure was achieved using an isostatic pressure process on the dip-coated electrolyte layers and anode support substrate. Solid oxide fuel cells adopting this dense gadolinium-doped ceria/yttria-stabilized zirconia bilayer electrolyte exhibited high power density of 1.251 W cm−2 at 650 °C and high stability for 100 h. These significant improvements in performances is attributed to the greatly reduced porosity (<2.5%) of the bilayer electrolyte when there are no side reactions between the gadolinium-doped ceria and yttria-stabilized zirconia layers. The strategies presented here provide general guidelines on electrolyte design and processing for the fabrication of high-performance solid oxide fuel cells with low operation temperature, low cost and mass-producibility.

Surface Properties of Alkoxysilane Layers Grafted in Supercritical Carbon Dioxide

Silicon oxide surface properties can be easily modified by grafting alkoxysilane molecules. Here, we studied the structure and the morphology of ultrathin layers prepared by the grafting of alkoxysilanes having different head groups (thiol, amine, and iodo) in supercritical carbon dioxide (CO2) on model plane silicon oxide surfaces. Several characterization techniques (X-ray reflectivity, water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM)) were used to determine the physicochemical properties of the layers prepared at different temperatures. Moreover, for the first time, AFM peak force measurements were used to delve deeper into the determination of the structure of these ultrathin alkoxysilane layers. The results show that the grafting temperature and the nature of the head group strongly affect the morphology and structure of the grafted layers. Dense monolayers are obtained with 3-(mercaptopropyl)trimethoxysilane at 60 °C, polycondensed layers are always prepared with [3-(aminoethylamino)propyl]trimethoxysilane, and a dense bilayer is synthesized with 3-(iodopropyl)triethoxysilane at 120 °C.

Low-temperature co-sintering for fabrication of zirconia/ceria bi-layer electrolyte via tape casting using a Fe2O3 sintering aid

Abstracts Bilayer electrolytes have potential in solid oxide cells to improve ionic conduction whilst blocking electronic conduction. GDC/YSZ bilayer electrolyte processing has proven problematic due to thermochemical instability at high sintering temperatures. We first match the shrinkage profile of the two bulk materials using a Fe 2 O 3 sintering additive. Additions of 5 mol% of Fe 2 O 3 in the GDC layer and 2 mol% of Fe 2 O 3 in the YSZ layer prevents delamination during co-sintering. The addition of Fe 2 O 3 promotes densification, enabling achievement of a dense bilayer at a reduced sintering temperature of 1300 °C; ∼150 °C below conventional sintering temperatures. Elemental analysis showed the compositional distribution curves across the bilayer interface to be asymmetric when Fe 2 O 3 is employed. The Fe 2 O 3 increases the total conductivity of the bilayer electrolyte by an order of magnitude; this is explained by the effect of Fe 2 O 3 on reducing the resistive solid solution interlayer at YSZ/GDC interface from ∼15 to ∼5 μm.

High Resistivity Lipid Bilayers Assembled on Polyelectrolyte Multilayer Cushions: An Impedance Study.

Supported membranes on top of polymer cushions are interesting models of biomembranes as cell membranes are supported on a polymer network of proteins and sugars. In this work lipid vesicles formed by a mixture of 30% 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 70% 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) are assembled on top of a polyelectrolyte multilayer (PEM) cushion of poly(allylamine hydrochloride) (PAH) and poly(styrene sodium sulfonate) (PSS). The assembly results in the formation of a bilayer on top of the PEM as proven by means of the quartz crystal microbalance with dissipation technique (QCM-D) and by cryo-transmission electron microscopy (cryo-TEM). The electrical properties of the bilayer are studied by electrochemical impedance spectroscopy (EIS). The bilayer supported on the PEMs shows a high resistance, on the order of 10(7) Ω cm(2), which is indicative of a continuous, dense bilayer. Such resistance is comparable with the resistance of black lipid membranes. This is the first time that such values are obtained for lipid bilayers supported on PEMs. The assembly of polyelectrolytes on top of a lipid bilayer decreases the resistance of the bilayer up to 2 orders of magnitude. The assembly of the polyelectrolytes on the lipids induces defects or pores in the bilayer which in turn prompts a decrease in the measured resistance.

Effects of Cholesterol on the Thermodynamics and Kinetics of Passive Transport of Water through Lipid Membranes.

While it has long been known that cholesterol reduces the permeability of biological membranes to water, the exact mechanism by which cholesterol influences transmembrane permeation is still unclear. The thermodynamic and kinetic contributions to the transport of water across mixed DPPC/cholesterol bilayers of different composition are thus examined by molecular dynamics simulations. Our analyses show that cholesterol decreases transmembrane permeability to water mainly by altering the thermodynamics of water transport. In particular, the free-energy barrier to permeation is magnified in the dense bilayer interior and the partitioning of water is significantly lowered. The changes are observed to correlate quantitatively well with the cholesterol-dependent density and thickness of the bilayers. In contrast, diffusion coefficients are relatively insensitive to cholesterol concentration, except in the sparsely populated center of the bilayer. Diffusion of water in cholesterol-containing bilayers appears to be related to changes in the free area in the middle of the bilayer and to the solute cross-sectional area in the denser hydrophobic regions. Overall, cholesterol is found to have an inhibitory effect on the permeation of water at all concentrations investigated, although bilayers containing cholesterol concentrations up to 20 mol % display a more dramatic dependence on cholesterol content than at higher concentrations. Our results show that it is possible to quantitatively reproduce the relative effects of cholesterol on lipid bilayer permeability from molecular dynamics simulations.

Gd0.1Ce0.9O1.95/Er0.4Bi1.6O3 bilayered electrolytes fabricated by a simple colloidal route using nano-sized Er0.4Bi1.6O3 powders for high performance low temperature solid oxide fuel cells

Thin and dense bilayer electrolytes consisting of erbium stabilized bismuth oxide (ESB) and gadolinium-doped ceria (GDC) were fabricated on tape-cast porous Ni–GDC anode-supports using a scalable and cost-effective colloidal deposition process. Nano-sized ESB particles were successfully synthesized at temperatures as low as ∼500°C using wet chemical co-precipitation. Due to the high sinterability of this powder, dense ESB layers were obtained at a sintering temperature of 800°C. Scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis of a full button cell with an ESB/GDC bilayer sintered at 800°C showed no visible interfacial diffusion between each layer. A systematic study on the sintering behavior of ESB revealed that at higher sintering temperatures, bismuth oxide can sublime or penetrate into the GDC sublayer. The effect of both the ESB layer and the GDC layer thickness on increasing open circuit potential (OCP) was demonstrated. The current–voltage measurement of the cell showed high power density (∼1.5Wcm−2) at 650°C due to the increase in OCP and a significant reduction in area specific resistance when compared to solid oxide fuel cells (SOFCs) with a single GDC layer. These results demonstrate that ESB/GDC bilayer electrolytes have significant potential for high performance SOFCs at low operational temperature.

Nanostructures from Self-Assembled Porphyrin Bilayers

The porphyrin triad bearing flexible carbazole linkers was synthesized via a MacDonald-type [2+2] condensation followed by Suzuki coupling, reductive ring closure and substitution using carbazole nitrogen as nucleophile. The carbazole linker allows the triad to form a ”U" shape that is capable of forming dense bilayer structures upon self-assembly in dichloro­methane-methanol solutions. The bilayer structures are capable of forming vesicles, which can build higher-dimensional structures upon heating.

Nanostructure of supported lipid bilayers in water

Biologically functional supported lipid bilayers (SLBs) used in the rising field of nanobiotechnology require fine tuning of the SLB interface with the substrate, e.g., a sensor surface. Depending on the application, membrane functionality implies a homogeneous and dense bilayer and a certain degree of diffusivity in order to allow for a rearrangement in response to, e.g., protein binding. Here, progress in the preparation, characterization, and application of SLBs obtained in the past three to five years are highlighted. Synchrotron techniques, which allow to reveal structural features within the membrane on a length scale of approximately 0.5 nm are discussed in more detail, as well as the relation of structural features to dynamical membrane properties obtained by complementary optical techniques.

Fabrication and characterization of thin film electrolytes deposited by RF magnetron sputtering for low temperature solid oxide fuel cells

Thin film solid electrolytes of La 0.9Sr 0.1Ga 0.8Mg 0.2O 3− δ (LSGM), Sm 0.2Ce 0.8O 1.9 (SDC), and Sc 0.11Zr 0.89O 2− δ (ScSZ) were deposited by RF magnetron sputtering onto single crystal sapphire substrates as well as onto porous NiO–SDC anodes at deposition temperatures of RT ≤ T ≤ 500 °C. The electrical conductivities, phase analyses as deposited and after annealing and microstructures of the deposited thin film electrolytes were examined. In addition, the electrochemical performance of single cells composed of Sm 0.5Sr 0.5O 3− δ (SSC) + SDC//SDC/ScSZ//NiO + SDC was demonstrated. Impervious and highly dense bilayer thin films of SDC and ScSZ have been successfully prepared on porous NiO–SDC anodes. Maximum power densities of 360 and 240 mW cm −2 from single cells of Sm 0.5Sr 0.5O 3− δ (SSC) + SDC//SDC/ScSZ//NiO + SDC were obtained at 600 and 550 °C, respectively, under humid 20% H 2 in Ar (3% H 2O) and air. RF magnetron sputtering can be applied for depositing high performance thin film electrolytes in low temperature SOFCs.

Influence of the Chemical Surface State of Silica on Adsorption Process of Conventional Cationic and Gemini Surfactants: Thermodynamic Investigations

The aim of this investigation was to study the effect of molecular structure on the adsorption of cationic surfactants onto silica. Thus, the thermodynamics of adsorption of DTAB (dodecyltrimethylammonium bromide) and of the gemini surfactant 12–2–12 (ethanediyl-1,2-bis(dodecyldimethylammonium bromide)) on raw silica (SiNa) and HCl-washed silica (SiH) has been investigated mainly by the microcalorimetric technique. The determination of differential molar enthalpies of adsorption first requires accurate knowledge of the dilution enthalpy of each surfactant under the same experimental conditions as those used during adsorption. The values of the adsorption enthalpies, corrected by the dilution effect, give information on adsorption processes. Moreover, the amount of surfactant adsorbed, the sodium ion concentration, the pH in equilibrated supernatants, and the electrophoretic mobility data complete the calorimetric results. Analysis of the experimental results allows estimation of the number of the surface sites and building up, in both cases, a picture of the adsorption process. The different steps of the adsorption process (by electrostatic and hydrophobic interactions) are described, as are also the different shapes of aggregates at the end of the adsorption. These depend on the state of the surface and the surfactant. A high density of SiNa sites leads to a dense bilayer. A spread density of SiH sites gives rise to pinned micelles.