A series of novel negative temperature coefficient thermistor materials based on SrCexNbxWO4+4x (0.1 ≤ x ≤ 0.8) ceramics was synthesized by the solid-state route. X-ray diffraction, scanning electron ...microscopy, and X-ray photoelectron spectroscopy revealed that the SrCexNbxWO4+4x ceramics were composed of scheelite structural solid solution based on the SrWO4 phase and a CeNbO4.08 secondary phase that exhibited a fergusonite structure. The resistance-temperature analysis demonstrated that the resistivity ρ800 of the SrCexNbxWO4+4x ceramics decreased from 8.25 ± 0.08 × 106 to 2.52 ± 0.11 × 102 with the increase of x value, along with a decrease in the thermal constant B from 11,102 ± 97–4137 ± 37 K. It was observed that the SrCexNbxWO4+4x ceramics exhibited high resistivity and excellent aging characteristics as well as suitable B values at elevated temperatures, making it a promising candidate that can be used for the fabrication of high-temperature NTC thermistors with a wide operating temperature range.
This study presents a nanofiber-derived functional anode consisting of proton-conducting SrCe0·8Y0·2O3-δ nanofibers and electro-catalytic Ni for proton-conducting solid oxide fuel cells. Fuel cell ...testing with the nano-fibrous SrCe0·8Y0·2O3-δ-Ni anode exhibits a maximum power density of 201.0 mW/cm2 at 800 °C, which is significantly higher than those of cells with a powder-derived Ba0·8Sr0·2Ce0·6Zr0·2Y0·2O3-δ-Ni anode or a nano-fibrous SrCe0·8Y0·2O3-δ anode. Its relatively lower ohmic resistance can be explained in terms of protonic and electronic “highways” throughout the nano-fibrous SrCe0·8Y0·2O3-δ-Ni anode. The significantly lower polarization resistance elements, R1and R2, further indicate that the nano-fibrous SrCe0·8Y0·2O3-δ-Ni anode has superior catalytic activity for the hydrogen oxidation reaction and thus generates more protons that can participate in the cathode reactions. The results show that the performance enhancement in the fuel cell with the nano-fibrous SrCe0·8Y0·2O3-δ-Ni anode can be attributed to its low ohmic resistance, excellent electrode catalytic activity, and good gas transport property.
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•Nano-fibrous SCY-Ni anode has been fabricated to boost P-SOFCs for the first time.•The fuel cell exhibits a significantly enhanced peak power density.•The lower ohmic resistance can be attributed to “highways” throughout the anode.•Nano-fibrous SCY-Ni anode has sufficient catalytic activity for HOR.•Both polarization resistance elements, R1 and R2, are the lowest among all cells.
Hydrogen permeation through SrCe
1−
x
Tb
x
O
3−
δ
(
x
=
0.025, 0.05 and 0.10) membranes using various gas streams as the sweep was investigated. Hydrogen impermeable SrCe
1−
x
Tb
x
O
3−
δ
membranes ...with air or inert gas in the downstream become hydrogen permeable when there is a reducing gas, such carbon monoxide or hydrogen, existing in the downstream. The membrane remains hydrogen permeable after the downstream sweep gas is changed from the reducing gas to the inert gas. This phenomenon is explained by the electronic conductivity of the materials. These results further confirm that SrCe
1−
x
Tb
x
O
3−
δ
(0.025
<
x
<
0.1) is a mixed proton–electron conducting material in a hydrogen containing atmosphere. The activation energy of hydrogen permeation is close to the activation energy of electronic conduction of the materials, confirming that the hydrogen permeation is determined by the electronic conductivity of the material. For SrCe
0.95Tb
0.05O
3−
δ
, increasing the downstream CO partial pressure from 0.001 to 0.1
atm leads to a small increase in hydrogen flux from 1.4
×
10
−2 to 1.6
×
10
−2
ml/cm
2
min. The hydrogen flux of SrCe
1−
x
Tb
x
O
3−
δ
increases with upstream hydrogen partial pressure.
U radu se ukazuje na važnost biblijskog leksika povezanog s abdominalnim organima, kako u izvorniku, tako i u hrvatskim prijevodima. Hebrejske riječi za bubrege i jetru u Bibliji na hrvatski se ne ...prevode uvijek doslovno, kao što se to ne čini ni u prijevodima na druge jezike, nego se katkad prevedu figurativno, zbog čega je provedena semantička i traduktološka analiza tih izraza. Abdominalni organi imaju u Bibliji značajnu ulogu, kako u fiziološkoj funkciji, tako i kao sjedište najdubljih osjećaja, pri čemu se s bubrezima, jetrom i žuči povezuju srdžba i gnjev. Bubrezi i jetra tako govore o psihosomatskim aspektima emocionalnih stanja biblijskih pisaca, zbog čega se na raznim mjestima ne prevode doslovno, nego se shvaćaju kao metonimije osjećaja. Budući da se unutar ove teme znakovito javlja par srce/bubreg, uočljiva je tendencija da se taj izraz shvati figurativno, kao merizam koji obuhvaća cjelokupnost čovjekova razmišljanja i osjećanja.
This work emphasizes the importance of human abdominal organs in biblical vocabulary of the source texts, and in Croatian Bible translations. Hebrew words for kidneys and liver as found in the original biblical texts, Croatian translations, and other languages rarely translate literally. Often they would be paraphrased figuratively which may cause semantic and translational debates over these terms. Clearly, abdominal organs play an important role in the biblical texts, whether in their physiological functions, but also as the seat of the deepest emotions. Kidneys, liver and gall-bladder have been frequently linked with the emotions of anger and wrath. Kidneys and liver particularly reflect the psychosomatic emotional states of the biblical author. Therefore, many biblical texts where we find those organs are not translated literally but rather as metonymy for those emotions. The original texts often bring the pair kidneys/liver together and in its figurative translations they become a merism which covers the entire emotional and mental state of a human being.
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•CH4 reactor/H2 separator recycle system is studied for non-oxidative CH4 conversion.•CH4 reactor/H2 separator recycle circumvents thermodynamic limit in CH4 reaction.•High purity of ...H2 product and high performance membrane separator are achieved.•>90 % selectivity and >50 % yield in aromatic product are achieved in recycle system.•Economic feasibility of CH4 reactor/H2 separator recycle system is simulated.
Direct non-oxidative methane conversion (DNMC) is one of the most promising options to convert methane (CH4) in natural gas in remote extraction sites to liquid aromatics, which is easier to transport compared to CH4 gas. The main constraint of the DNMC is low CH4 conversion, and thus aromatics product yield due to thermodynamic limitation. This work reports a gas recycle CH4 reactor/hydrogen (H2) membrane separator to achieve high CH4 conversion and aromatics yield by circumventing the thermodynamic limitation. The DNMC took place over an iron/silica (Fe/SiO2) catalyst in a packed-bed reactor to produce C2 (i.e. ethane, ethylene and acetylene) and aromatics, along with reaction product H2. The product stream passed through a condenser to collect aromatic products and then a H2-permeable membrane separator to remove H2. The unreacted CH4, C2 products and H2 residual in the product stream were sent to the recycle loop for the next round of DNMC reaction and H2 removal. The results demonstrated that >90 % product selectivity toward aromatics and >50 % aromatics yield are achieved in the gas recycle CH4 reactor/ H2 membrane separator system.
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•Dual-phase SCY-SDC laminated membrane was prepared and characterized.•Laminated membrane shows a maximum H2 flux of 0.163 mL min−1 cm−2 at 900 °C.•This flux was higher than that for ...the conventional SCY-SDC dual-phase membrane.•Such discrepancy was due to shorter transport paths and less phase interfaces.
This work characterizes the hydrogen permeation fluxes of dual-phase SrCe0.9Y0.1O3-Ce0.8Sm0.2O2 (SCY-SDC) laminated membrane that contains regular and independent transport channels made of alternating films of SCY and SDC phases. Such membrane was synthesized via combined tape casting, co-pressing, and sintering route. The hydrogen flux of the dual-phase SCY-SDC laminated membrane reached 0.163 mL min−1 cm−2 at 900 °C when 100 mL min−1 of 20 vol% H2 in He and 100 mL min−1 of N2 were passed in the feed side and the permeate side, respectively. Such flux is significantly larger than the flux of the conventional SCY-SDC dual-phase membrane made by mixing SCY-SDC powder mixture and subsequent sintering at the same operation condition. The enhanced flux for the dual-phase laminated membrane relative to the conventional dual-phase membrane is attributed to the shorter diffusion paths for protons and electrons and the lower amount of the phase interfaces. The dual-phase SCY-SDC laminated membrane also displayed stable hydrogen permeation flux of around 0.15 mL min−1 cm−2 during 166-hour continuous operation at 850 °C in the presence of carbon dioxide in the permeate gas stream. Such stable performance highlights its chemical stability. Another attractive advantage of the dual-phase SCY-SDC laminated membrane lies in the minor discrepancy of the thermal expansion coefficient of SCY (α = 1.12·10−5 K−1) to that of SDC (α = 1.28·10−5 K−1) as obtained by dilatometry from room temperature to 1500 °C, which ensures its mechanical integrity during repeated thermal cycles.
Direct nonoxidative methane conversion (DNMC) transforms CH4 to higher (C2+) hydrocarbons and H2 in a single step, but its utility is challenged by low CH4 equilibrium conversion, carbon deposition ...(coking), and its endothermic reaction energy requirement. This work reports a heat‐exchanged autothermal H2‐permeable tubular membrane reactor composed of a thin mixed ionic‐electronic conducting SrCe0.7Zr0.2Eu0.1O3–δ membrane supported on a porous SrCe0.8Zr0.2O3–δ tube in which a Fe/SiO2 DNMC catalyst is packed, that concurrently tackles all of these challenges. The H2‐permeation flux drives CH4 conversion. O2 from an air simulant (O2/He mixture) sweep outside the membrane reacts with permeated H2 to provide heat for the endothermic DNMC reaction. The energy balance between the endothermic DNMC and exothermic H2 combustion on opposite sides of the membrane is achieved, demonstrating the feasibility for autothermal operation using a simple air sweep gas. Moreover, the back diffusion of O2 from the sweep side to the catalyst side oxidizes any deposited carbon into CO. Thus, for the first time demonstrating all the desired attributes, a heat‐exchanged H2‐permeable membrane reactor capable of achieving single‐step auto‐thermal DNMC catalysis while simultaneously improving CH4 conversion and preventing coking is achieved.
Modular gas‐to‐liquid (GTL) technology enables the utilization of immense stranded natural gas resources with major environmental benefits. By converting gaseous CH4 into liquid C2+ hydrocarbons, transportation of these liquid hydrocarbons becomes economically viable. In this paper, the first‐ever autothermal direct nonoxidative methane conversion (DNMC) to value added C2+ hydrocarbons in an integrated DNMC‐catalyst/H2‐permeable‐membrane modular reactor is presented.
As a candidate material for hydrogen separation, Yb-doped SrCeO3 has attracted increasing attention in recent decades. In the present study, Yb-doped SrCe0.9Yb0.1O3-α ceramics were prepared by the ...dry pressing and sintering approach, with the microstructure evolution and the micro morphology investigated. It was indicated that the ceramics sintered in air were of a pure perovskite structure, and that the sintering temperature had a significant effect on the growth of ceramic grains. The average grain size increased from 1 μm to 10 μm with an increase in sintering temperature from 1300 to 1500 °C. Further investigation of the thermodynamics and kinetics of grain growth revealed that the grain boundary diffusion was the main driving force of grain growth during solid phase sintering, with a grain growth index of 4 and an activation energy of approximately 61.23 kJ mol−1. These results illustrate an obvious tendency of grain size growth. By electrochemical workstation with different atmospheres the effects of sintering temperature on the conductivity were characterized in the temperature range of 700–900 °C. The electrical conductivities σ of SrCe0.9Yb0.1O3-α ceramics in different atmospheres were as follows: σ(wet hydrogen) > σ(dry hydrogen) > σ(dry air) > σ(wet air). In the test atmosphere containing water and hydrogen the conductivity of protons increased with increasing temperature because of the protons jump between lattices in the form of interstitial hydrogen ions or bare protons.
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•After sintering, Yb was completely dissolved in SrCeO3, and the Yb doped SrCeO3 had a pure perovskite structure. Cell parameters of Yb doped SrCeO3 were increased compared with SrCeO3.•The radial shrinkage of 10% Yb doped SrCeO3 ceramics increased from 7.29% at 1300 °C to 11.95% at 1500 °C. The results of sintering kinetics illustrated that the grain growth index of ceramics was 4, which indicated that the grain growth is mainly from the grain boundary diffusion. The activation energy of grain growth was about 61.23 kJ mol−1.•At 700–900 °C, the electrical conductivity of SrCe0.9Yb0.1O3-α ceramics in different atmospheres was as follows: σ(wet hydrogen) > σ(dry hydrogen) > σ(dry air) > σ(wet air).
Hydrogen permeation through SrCe₀.₇Zr₀.₂Eu₀.₁O₃₋δ membranes was investigated as a function of temperature, feed H₂O partial pressure, feed H₂ partial pressure and flow rate. Hydrogen permeation flux ...was proportional to the transmembrane H₂ partial pressure gradient with a 1/4 dependence. A maximum H₂ permeation flux of 0.23 and 0.21cm³/cm²min was obtained at 900°C for 100% H₂ and 97vol% H₂/3vol% H₂O conditions, respectively. The activation energy decreased with increasing H₂ partial pressure and/or decreasing steam partial pressure. Permeation flux through the SrCe₀.₇Zr₀.₂Eu₀.₁O₃₋δ membrane was stable under wet H₂, water gas shift reaction and steam reforming of methane conditions.
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