Investigation into the effect of molybdenum-site substitution on the performance of Sr₂Fe_1.5Mo_0.5O_6-δfor intermediate temperature solid oxide fuel cells

<p>In this paper, niobium doping is evaluated as a means of enhancing the electrochemical performance of a Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) perovskite structure cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) applications. As the radius of Nb approximates that of Mo and exhibits +4/+5 mixed valences, its substitution is expected to improve material performance. A series of Sr₂Fe_1.5Mo_0.5-xNb_xO_6-δ (x = 0.05, 0.10, 0.15, 0.20) cathode materials are prepared and the phase structure, chemical compatibility, microstructure, electrical conductivity, polarization resistance and power generation are systematically characterized. Among the series of samples, Sr₂Fe_1.5Mo_0.4Nb_0.10O_6-δ (SFMNb_0.10) exhibits the highest conductivity value of 30 S cm^-1 at 550°C, and the lowest area specific resistance of 0.068 Ω cm² at 800°C. Furthermore, an anode-supported single cell incorporating a SFMNb_0.10 cathode presents a maximum power density of 1102 mW cm^-2 at 800°C. Furthermore no obvious performance degradation is observed over 15 h at 750°C with wet H₂(3% H₂O) as fuel and ambient air as the oxidant. These results demonstrate that SFMNb shows great promise as a novel cathode material for IT-SOFCs.</p>

Investigation into the effect of Fe-site substitution on the performance of Sr₂Fe_1.5Mo_0.5O_6-δanodes for SOFCs

<p>Ni-substituted Sr₂Fe_1.5-xNi_xMo_0.5O_6-δ (SFNM) materials have been investigated as anode catalysts for intermediate temperature solid oxide fuel cells. Reduced samples (x = 0.05 and 0.1) maintained the initial perovskite structure after reduction in H₂, while metallic nickel particles were detected on the grain surface for x = 0.2 and 0.3 using transmission electron microscopy. Temperature programmed reduction results indicate that the stable temperature for SFNM samples under reduction conditions decreases with Ni content. In addition, X-ray photoelectron spectroscopy analysis suggests that the incorporation of Ni affects the conductivity of SFNM through changing the ratios of Fe³⁺/Fe²⁺ and Mo⁶⁺/Mo⁵⁺. Sr₂Fe_1.4Ni_0.1Mo_0.5O_6-δ shows the highest electrical conductivity of 20.6 S cm^-1 at 800 °C in H₂. The performance of this anode was further tested with electrolyte-supported cells, giving 380 mW cm^-2 at 750 °C in H₂, hence demonstrating that Ni doping in the B-site is beneficial for Sr₂Fe_1.5Mo_0.5O_6-δ anode performance. </p>

Evaluation of strontium-site-deficient Sr₂Fe_1.4Co_0.1Mo_0.5O_6-δ-based perovskite oxides as intermediate temperature solid oxide fuel cell cathodes

<p>In this paper strontium-site-deficient Sr₂Fe_1.4Co_0.1Mo_0.5O_6-δ-based perovskite oxides (S_xFCM) were prepared and evaluated as the cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). All samples exhibited a cubic phase structure and the lattice shrinked with increasing the Sr-deficiency as shown in XRD patterns. XPS results determined that the transition elements (Co/Fe/Mo) in S_xFCM oxides were in a mixed valence state, demonstrating the small polaron hopping conductivity mechanism existed. Among the samples, S_1.950FCM presented the lowest coefficient of thermal expansion of 15.62 × 10^-6 K^-1, the highest conductivity value of 28 S cm^-1 at 500 °C, and the lowest interfacial polarization resistance of 0.093 Ω cm² at 800 °C, respectively. Furthermore, an anode-supported single cell with a S_1.950FCM cathode was prepared, demonstrating a maximum power density of 1.16 W cm^-2 at 800 °C by using wet H₂ (3% H₂O) as the fuel and ambient air as the oxidant. These results indicate that the introduction of Sr-deficiency can dramatically improve the electrochemical performance of Sr₂Fe_1.4Co_0.1Mo_0.5O_6-δ, showing great promise as a novel cathode candidate material for IT-SOFCs.</p>

Improved electrochemical performance of Sr₂Fe_1.5Mo_0.4Nb_0.1O_6-δ -Sm_0.2Ce_0.8O_2-δ composite cathodes by a one-pot method for intermediate temperature solid oxide fuel cells

<p>In this paper, Sr₂Fe_1.5Mo_0.4Nb_0.1O_6-δ (SFMNb)-xSm_0.2Ce_0.8O_2-δ (SDC) (x = 0, 20, 30, 40, 50 wt%) composite cathode materials were synthesized by a one-pot combustion method to improve the electrochemical performance of SFMNb cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The fabrication of composite cathodes by adding SDC to SFMNb is conducive to providing extended electrochemical reaction zones for oxygen reduction reactions (ORR). X-ray diffraction (XRD) demonstrates that SFMNb is chemically compatible with SDC electrolytes at temperature up to 1100 °C. Scanning electron microscope (SEM) indicates that the SFMNb-SDC composite cathodes have a porous network nanostructure as well as the single phase SFMNb. The conductivity and thermal expansion coefficient of the composite cathodes decrease with the increased content of SDC, while the electrochemical impedance spectra (EIS) exhibits that SFMNb-40SDC composite cathode has optimal electrochemical performance with low polarization resistance (R_p) on the La_0.9Sr_0.1Ga_0.8Mg_0.2O₃ electrolyte. The R_p of the SFMNb-40SDC composite cathode is about 0.047 Ω cm² at 800 °C in air. A single cell with SFMNb-40SDC cathode also displays favorable discharge performance, whose maximum power density is 1.22 W cm^-2 at 800 °C. All results indicate that SFMNb-40SDC composite material is a promising cathode candidate for IT-SOFCs.</p>

Epitaxial ferroelectric Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ thin films on La_0.7Sr_0.3MnO₃ bottom electrode

<p>Epitaxial (001)-oriented 0.7Pb(Mg_0.33Nb_0.67)O₃-0.3PbTiO₃ (PMN-PT) thin films were deposited by pulsed laser deposition on vicinal SrTiO₃ (001) substrates using La_0.7Sr_0.3MnO₃ as bottom electrode. Detailed microstructural investigations of these films were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Polarization-field hysteresis curves were measured at room temperature. Spontaneous polarization P s , remnant polarization P r and coercive voltage V c were found to be 25 μC/cm², 15 μC/cm² and 0.81 V, respectively. Field dependent dielectric constant measurements exhibited butterfly shaped curves, indicating the true ferroelectric nature of these films at room temperature. The dielectric constant and the dielectric loss at 100 kHz were found to be 238 and 0.14, respectively. The local piezoelectric properties of PMN-PT films were investigated by piezoelectric force microscopy and were found to exhibit a local piezoelectric coefficient of 7.8 pm/V.</p>

Co-tape casting fabrication, field assistant sintering and evaluation of a coke resistant La_0.2Sr_0.7TiO₃-Ni/YSZ functional gradient anode supported solid oxide fuel cell

<p>The ability to directly utilize hydrocarbons and other renewable liquid fuels is one of the most important issues affecting the large scale deployment of solid oxide fuel cells (SOFCs). Herein we designed La_0.2Sr_0.7TiO₃-Ni/YSZ functional gradient anode (FGA) supported SOFCs, prepared with a co-tape casting method and sintered using the field assisted sintering technique (FAST). Through SEM observations, it was confirmed that the FGA structure was achieved and well maintained after the FAST process. Distortion and delamination which usually results after conventional sintering was successfully avoided. The La_0.2Sr_0.7TiO₃-Ni/YSZ FGA supported SOFCs showed a maximum power density of 600mWcm^-2Âat 750°C, and was stable for 70h in CH₄. No carbon deposition was detected using Raman spectroscopy. These results confirm the potential coke resistance of La_0.2Sr_0.7TiO₃-Ni/YSZ FGA supported SOFCs.</p>

One-dimensional porous La_0.5Sr_0.5CoO_2.91 nanotubes as a highly efficient electrocatalyst for rechargeable lithium-oxygen batteries

<p>The electrochemical performance of one-dimensional porous La_0.5Sr_0.5CoO_2.91 nanotubes as a cathode catalyst for rechargeable nonaqueous lithium-oxygen (Li-O₂) batteries is reported here for the first time. In this study, one-dimensional porous La_0.5Sr_0.5CoO_2.91 nanotubes were prepared by a simple and efficient electrospinning technique. These materials displayed an initial discharge capacity of 7205 mAh g^-1 with a plateau at around 2.66 V at a current density of 100 mA g^-1. It was found that the La_0.5Sr_0.5CoO_2.91 nanotubes promoted both oxygen reduction and oxygen evolution reactions in alkaline media and a nonaqueous electrolyte, thereby improving the energy and coulombic efficiency of the Li-O₂ batteries. The cyclability was maintained for 85 cycles without any sharp decay under a limited discharge depth of 1000 mAh g^-1, suggesting that such a bifunctional electrocatalyst is a promising candidate for the oxygen electrode in Li-O₂ batteries.</p>

Flash-Sintering and Characterization of La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ Electrolytes for Solid Oxide Fuel Cells

<p>La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM), a promising electrolyte material for intermediate temperature solid oxide fuel cells, can be sintered to a fully dense state by a flash-sintering technique. In this work, LSGM is sintered by the current-limiting flash-sintering process at 690°C under an electric field of 100 V cm^-1, in comparison with up to 1400°C or even higher temperature in conventional furnace sintering. The resultant LSGM samples are investigated by scanning electron microscopy, X-ray diffraction, and electrochemical impedance spectroscopy. The SEM images exhibit well-densified microstructures while XRD results show that the perovskite structure after flash-sintering does not changed. EIS results show that the conductivity of LSGM sintered by the current-limiting flash-sintering process increases with sintering current density value. The conductivity of samples sintered at 120 mA mm^-2 reaches 0.049 σ cm^-1 at 800°C, which is approximate to the value of conventional sintered LSGM samples at 1400°C. Additionally, the flash-sintering process is interpreted by Joule heating theory. Therefore, the current-limiting flash-sintering technique is proved to be an energy-efficient and eligible approach for the densification of LSGM and other materials requiring high sintering temperature.</p>

Preparation and characterization of Pr_0.6Sr_0.4FeO_3-δ-Ce_0.9Pr_0.1O_2-δ nanofiber structured composite cathode for IT-SOFCs

<p>In this work, Pr_0.6Sr_0.4FeO_3-δ-Ce_0.9Pr_0.1O_2-δ (PSFO-CPO) nanofibers were synthesized by a one-step electrospin technique for use in intermediate-temperature solid oxide fuel cell (IT-SOFC) applications. PSFO-CPO nanofibers were produced with a diameter of about 100nm and lengths exceeding tens of microns. The thermal expansion coefficient (TEC) matches with standard GDC electrolytes and the resulting conductivity also satisfies the needs of IT-SOFCs cathodes. EIS analysis of the nanofiber structured electrode gives a polarization resistance of 0.072Ωcm² at 800°C, smaller than that from the powdered cathode with the same composition. The excellent electrochemical performance can be attributed to the well-constructed microstructure of the nanofiber structured cathode, which promotes surface oxygen diffusion and charge transfer processes. All the results imply that the one-step electrospin method is a facile and practical way of improving the cathode properties and that PSFO-CPO is a promising cathode material for IT-SOFCs.</p>

Synthesis of Pr_0.6Sr_0.4FeO_3-δ-xCe_0.9Pr_0.1O_2-δ cobalt-free composite cathodes by a one-pot method for intermediate-temperature solid oxide fuel cells

<p>Cobalt-free composite cathodes consisting of Pr_0.6Sr_0.4FeO_3-δ-xCe_0.9Pr_0.1O_2-δ (PSFO-xCPO, x = 0-50 wt%) have been synthesized using a one-pot method. X-ray diffraction, scanning electron microscopy, thermal expansion coefficient, conductivity, and polarization resistance (R _P) have been used to characterize the PSFO-xCPO cathodes. Furthermore the discharge performance of the Ni-SSZ/SSZ/GDC/PSFO-xCPO cells has been measured. The experimental results indicate that the PSFO-xCPO composite materials fully consist of PSFO and CPO phases and posses a porous microstructure. The conductivity of PSFO-xCPO decreases with the increase of CPO content, but R _P of PSFO-40CPO shows the smallest value amongst all the samples. The power density of single cells with a PSFO-40CPO composite cathode is significantly improved compared with that of the PSFO cathode, exhibiting 0.43, 0.75, 1.08 and 1.30 W cm^-2 at 650, 700, 750 and 800 °C, respectively. In addition, single cells with the PSFO-40CPO composite cathode show a stable performance with no obvious degradation over 100 h when operating at 750 °C.</p>

Ca(2+)-sparks constitute elementary building blocks for global Ca(2+)-signals in myocytes of retinal arterioles.

<p>Spontaneous Ca2+-events were imaged in myocytes within intact retinal arterioles (diameter &lt; 40 mu m) freshly isolated from rat eyes. Ca2+-sparks were often observed to spread across the width of these small cells, and could summate to produce prolonged Ca2+-oscillations and contraction. Application of cyclopiazonic acid (20 mu M) transiently increased spark frequency and oscillation amplitude, but inhibited both sparks and oscillations within 60 s. Both ryanodine (100 mu M) and tetracaine (100 mu M) reduced the frequency of sparks and oscillations, while tetracaine also reduced oscillation amplitude. None of these interventions affected spark amplitude. Nifedipine, which blocks store filling independently of any action on L-type Ca2+-channels in these cells, reduced the frequency and amplitude of both sparks and oscillations. Removal of external [Ca2+] (1 mM EGTA) also reduced the frequency of sparks and oscillations but these reductions were slower in onset than those in the presence of tetracaine or cyclopiazonic acid. Cyclopiazonic acid, nifedipine and low external [Ca2+] all reduced SR loading, as indicated by the amplitude of caffeine evoked Ca2+-transients. This study demonstrates for the first time that spontaneous Ca2+-events in small arterioles of the eye result from activation of ryanodine receptors in the SR and suggests that this activation is not tightly coupled to Ca2+-influx. The data also supports a model in which Ca2+-sparks act as building blocks for more prolonged, global Ca2+-signals. (c) 2006 Elsevier Ltd. All rights reserved.</p>

cAMP/PKA-dependent increases in Ca Sparks, oscillations and SR Ca stores in retinal arteriolar myocytes after exposure to vasopressin.

PURPOSE: To investigate the effects of arginine vasopressin (AVP) on Ca(2+) sparks and oscillations and on sarcoplasmic reticulum (SR) Ca(2+) content in retinal arteriolar myocytes. METHODS: Fluo-4-loaded smooth muscle in intact segments of freshly isolated porcine retinal arteriole was imaged by confocal laser microscopy. SR Ca(2+) store content was assessed by recording caffeine-induced Ca(2+) transients with microfluorimetry and fura-2. RESULTS: The frequencies of Ca(2+) sparks and oscillations were increased both during exposure to, and 10 minutes after washout of AVP (10 nM). Caffeine transients were increased in amplitude 10 and 90 minutes after a 3-minute application of AVP. Both AVP-induced Ca(2+) transients and the enhancement of caffeine responses after AVP washout were inhibited by SR 49059, a V(1a) receptor blocker. Forskolin, an activator of adenylyl cyclase, also persistently enhanced caffeine transients. Rp-8-HA-cAMPS, a membrane-permeant PKA inhibitor, prevented enhancement of caffeine transients by both AVP and forskolin. Forskolin, but not AVP, produced a reversible, Rp-8-HA-cAMPS insensitive reduction in basal [Ca(2+)](i). CONCLUSIONS: AVP activates a cAMP/PKA-dependent pathway via V(1a) receptors in retinal arteriolar smooth muscle. This effect persistently increases SR Ca(2+) loading, upregulating Ca(2+) sparks and oscillations, and may favor prolonged agonist activity despite receptor desensitization.

Sr-Nd-Pb Isotope Evidence for Ice-Sheet Presence on Southern Greenland During the Last Interglacial

To ascertain the response of the southern Greenland Ice Sheet (GIS) to a boreal summer climate warmer than at present, we explored whether southern Greenland was deglaciated during the Last Interglacial (LIG), using the Sr-Nd-Pb isotope ratios of silt-sized sediment discharged from southern Greenland. Our isotope data indicate that no single southern Greenland geologic terrane was completely deglaciated during the LIG, similar to the Holocene. Differences in sediment sources during the LIG relative to the early Holocene denote, however, greater southern GIS retreat during the LIG. These results allow the evaluation of a suite of GIS models and are consistent with a GIS contribution of 1.6 to 2.2 meters to the =4-meter LIG sea-level highstand, requiring a significant sea-level contribution from the Antarctic Ice Sheet.

Anxiolytic-like effects observed in rats exposed to the elevated zero-maze following treatment with 5-HT₂/5-HT₃/5-HT₄ ligands

<p>The present study examined the effects of administering selective 5-HT antagonists and agonists to rats tested in the elevated zero-maze (EZM) model of anxiety. The EZM paradigm has advantages over the elevated plus-maze (EPM) paradigm with respect to measuring anxiety, yet has been utilized less frequently. Three experiments were conducted each with a diazepam control (0.25, 0.5 and 0.75 mg/kg). In the first experiment, we administered the 5-HT_2C antagonist RS 102221 (0.5, 1.0, and 2.0 mg/kg) and 5-HT_2C agonist MK-212 (0.25, 0.5 and 0.75 mg/kg); in the second experiment, we administered the 5-HT₃ antagonist Y-25130 (0.1, 1.0 and 3.0 mg/kg) and 5-HT₃ agonist SR 57227A (0.1, 1.0 and 3.0 mg/kg), and in the third experiment, we administered the 5-HT₄ antagonist RS 39604 (0.01, 0.1, 1.0 mg/kg) and 5-HT₄ agonist RS 67333 (0.01, 0.1 and 0.5 mg/kg). The administration of 5-HT_2/3/4 subtype antagonists all generated behavioral profiles indicative of anxiolytic-like effects in the EZM, which was apparent from examination of both traditional and ethological measures. While little effect was observed from 5-HT₂ and 5-HT₃ agonists, the 5-HT₄ agonist RS 67333 was found to produce a paradoxical anxiolytic-like effect similar to that produced by the 5-HT₄ antagonist RS 39604. We conclude by discussing the implications of these findings.</p>

Photodissociation and chemistry of N₂in the circumstellar envelope of carbon-rich AGB stars

The envelopes of AGB stars are irradiated externally by ultraviolet photons; hence, the chemistry is sensitive to the photodissociation of N$_2$ and CO, which are major reservoirs of nitrogen and carbon, respectively. The photodissociation of N$_2$ has recently been quantified by laboratory and theoretical studies. Improvements have also been made for CO photodissociation. For the first time, we use accurate N$_2$ and CO photodissociation rates and shielding functions in a model of the circumstellar envelope of the carbon-rich AGB star, IRC +10216. We use a state-of-the-art chemical model of an AGB envelope, the latest CO and N$_2$ photodissociation data, and a new method for implementing molecular shielding functions in full spherical geometry with isotropic incident radiation. We compare computed column densities and radial distributions of molecules with observations. The transition of N$_2$ $\to$ N (also, CO $\to$ C $\to$ C$^+$) is shifted towards the outer envelope relative to previous models. This leads to different column densities and radial distributions of N-bearing species, especially those species whose formation/destruction processes largely depend on the availability of atomic or molecular nitrogen, for example, C$_n$N ($n$=1, 3, 5), C$_n$N$^-$ ($n$=1, 3, 5), HC$_n$N ($n$=1, 3, 5, 7, 9), H$_2$CN and CH$_2$CN. The chemistry of many species is directly or indirectly affected by the photodissociation of N$_2$ and CO, especially in the outer shell of AGB stars where photodissociation is important. Thus, it is important to include N$_2$ and CO shielding in astrochemical models of AGB envelopes and other irradiated environments. In general, while differences remain between our model of IRC +10216 and the observed molecular column densities, better agreement is found between the calculated and observed radii of peak abundance.