High O2 Partial Pressure Research Articles

Effects of O2/Ar Ratio on Preparation and Dielectric Properties of CaZrO3 Films by Radio Frequency (RF) Magnetron Sputtering.

CaZrO3 (CZO) thin films were deposited on Pt/Ti/SiO2/Si substrates at 450 °C by radio-frequency magnetron sputtering technology. The microstructures and dielectric properties of CZO thin films were investigated. X-ray diffraction analysis reveals that the perovskite orthogonal CZO phase would be promoted by a higher O2 partial pressure in the flow ratio of O2/Ar after thin films were annealed at 700 °C for 3 h in air. The films prepared under the flow ratio of O2/Ar (20:40, 30:40 and 40:40) show the main perovskite crystal phase of CaZrO3 with a small amount of Ca0.2Zr0.8O1.8. The main crystal phase was Ca0.2Zr0.8O1.8 when the film was deposited under an O2/Ar ratio of 40:10. The annealed film with a 40:40 O2/Ar ratio exhibits a dielectric performance with a high dielectric constant (εr) of 25 at 1 MHz, a temperature coefficient of permittivity of not more than 122.7 ppm/°C from 0 °C to 125 °C, and a low leakage current density of about 2 × 10-7 A/cm2 at 30 V with an ohmic conduction mechanism.

Minimizing the Lag Phase of Cupriavidus necator Growth under Autotrophic, Heterotrophic, and Mixotrophic Conditions.

Cupriavidus necator has the unique metabolic capability to grow under heterotrophic, autotrophic, and mixotrophic conditions. In the current work, we examined the effect of growth conditions on the metabolic responses of C. necator. In our lab-scale experiments, autotrophic growth was rapid, with a short lag phase as the exponential growth stage was initiated in 6 to 12 h. The lag phase extended significantly (>22 h) at elevated O2 and CO2 partial pressures, while the duration of the lag phase was independent of the H2 or N2 partial pressure. Under heterotrophic conditions with acetate as the organic substrate, the lag phase length was short (<12 h), but it increased with increasing acetate concentrations. When glucose and glycerol were provided as the organic substrate, the lag phase was consistently long (>12 h) regardless of the examined substrate concentrations (up to 10.0 g/L). In the transition experiments, C. necator cells showed rapid transitions from autotrophic to heterotrophic growth in less than 12 h and vice versa. Our experimental results indicate that C. necator can rapidly grow with both autotrophic and heterotrophic substrates, while the lag time substantially increases with nonacetate organic substrates (e.g., glucose or glycerol), high acetate concentrations, and high O2 and CO2 partial pressures. IMPORTANCE The current work investigated the inhibition of organic and gaseous substrates on the microbial adaption of Cupriavidus necator under several metabolic conditions commonly employed for commercial polyhydroxyalkanoate production. We also proposed a two-stage cultivation system to minimize the lag time required to change over between the heterotrophic, autotrophic, and mixotrophic pathways.

Repair of aromatic hydrocarbon-based membranes tested under accelerated fuel cell conditions

Hydrocarbon-based materials are of interest as next-generation proton exchange membranes (PEMs) for polymer electrolyte fuel cells (PEFCs). The biggest drawback of aromatic hydrocarbon PEMs is the presence of aromatic groups contained within the polymer, which make these materials susceptible to radical induced degradation reactions. In the fuel cell community antioxidant action is usually equated with scavenging of potent radicals, i.e. HO•, by various additives. In this work, however, we report on the repair of damaged membranes. This is tested by performing in situ accelerated stress tests at open circuit voltage with high H2 and O2 partial pressures. Membranes with aromatic sulfonate groups are synthesized as these are common constituents in hydrocarbon-based membranes. Two different approaches to incorporate the repair agent, cerium(III), are explored: 1) ionic bonding of Ce(III) to sulfonate groups and 2) covalent attachment through stable complexes of crown ether and Ce(III). We report that, during fuel cell operation, polymer degradation can be significantly reduced by Ce(III) when immobilized in the membrane. Ionic attachment did not yield in the desired repair effect as a result of cerium loss from the membrane.

Modified and Novel Lorrca Oxygenscan Measurement Parameters with Physiological Relevance

BACKROUND: Despite arising from a single-point hemoglobin (Hb) mutation (βGlu6 replaced by valine), patients with sickle cell disease (SCD) display wide phenotype variation. This likely arises from sickling and its resulting pathology having multiple physiologic triggers, many of which are red blood cell (RBC) related, i.e., sickle hemoglobin (HbS) and fetal hemoglobin (HbF) concentration, membrane permeability, cell hydration, etc. These triggers are inadequately captured by single measurement parameters and require a more holistic functional RBC assessment (reflecting their composite effects). To provide such, oxygen (O2) gradient ektacytometry (LORRCA oxygenscan RR Mechatronics) was designed as a commercial, rapid, reproducible, and automated laboratory assay, which mimics in vivo physiology, quantifying RBC deformability across the physiological O2 gradient. This assay captures the process of sickling/unsickling of a RBC population when challenged with deoxygenation and reoxygenation. Significant variance in the oxygenscan point of sickling measurement was observed (POS - defined as the pO2at which EImax declined 5% - representing the initiation of sickling), despite following all guidelines for sample handling. EI fluctuation at higher O2 partial pressure (pO2) was noted as the cause for this. We consequently modified the POS determination, centering our analysis on EI rate of change (i.e., the first derivative of the EI trace), rather than the single point software determination. We further identified two new analyses parameters which reflect aspects of RBC physiology of potential physiologic benefit in SCD. Firstly, we used the rate of change in EI (a first derivative-based analysis) on the reoxygenation arm of the LORRCA trace, to identify the pO2 at which EI was observed to significantly increase from EImin, defining this as the point of unsickling (POU). Lastly, we set about quantifying the hysteresis between the O2 unloading and O2 loading EI curves, calling this the area between curves. METHODS: RBCs from SCD patients were incubated with the Hb allosteric effector 5-hydroxymethylfurfural (5HMF; 20% Hct, 37C, HMF: 0-5mM, 0-3 hrs); 5HMF binds to Hb NH2 terminal αValine1, increasing oxyHbS abundance, thereby inhibiting the mechanistic trigger for deoxygenation induced HbS polymerization.Oxygenscans were performed with elongation index (EI) determined by laser light diffraction, across the physiologic O2 gradient (pO2 ~150-10 mmHg; sample gassed with nitrogen ~1300 seconds followed by swift re-oxygenation in room air ~280 seconds). Samples were analyzed utilizing standard parameters offered by the LORRCA software in addition to our modified POS determination and analysis of POU and area between curves. RESULTS: Little change in mean POS was observed in baseline measurements (minus 5HMF) between the standard LORRCA software analysis and our modified analysis (POS pO2 = 55.1 ± 20.4 vs 56.9 ± 10.1mmHg mean±SD, respectively), however the coefficient of variance (COV) of our modified analysis was ~20% lower. The same trend was observed in samples across all doses of 5HMF. No significant difference in POS was detected with the standard analysis between any of the 5HMF doses. However, a significant reduction in POS between 0 and 5mM 5HMF final was determined with our modified analysis (POS pO2 = 56.9 ± 10.1 vs 39.8 ±11.6mmHg, respectively). A significant difference was also observed in the POU between 0 and 5mM HMF (POU pO2 = 38.3 ± 9.1 vs 21.3 ± 5.7mmHg, respectively) with HMF resulting in a lower pO2 at which unsickling was observed. This has obvious patient benefit implications, with SRBCs regaining deformability at lower pO2. Finally, a significant difference was also observed in the area between the deoxygenation and reoxygenation EI curves between 0 and 5mM HMF (area between curve = 8.9 ± 4.6 vs 4.6 ± 1.6AU, respectively). This smaller area between curves implies less change in deformability behavior between oxygenation states in the presence of 5HMF. SUMMARY: We have developed a more robust analysis methodology for the determination of POS by oxygenscan. This appears to work well even on sub-optimal scans and can detect a change in sickling characteristics for the allosteric modifier 5HMF. In addition, we suggest two further analyses parameters for oxygenscan (POU and area between curves) which reflect aspects of RBC physiology of potential physiologic benefit in SCD.

Chemical Stability Enhancement of Aromatic Proton Exchange Membranes Using a Damage Repair Mechanism

Harmful radical species (HO•, HOO•) are formed during fuel cell operation. Out of these species, the highly electrophilic hydroxyl radical is the most reactive (1.8 – 2.7 V vs. NHE). Consequently, the most electron-rich constituents, aromatic rings, are preferentially attacked and undergo rapid degradation. Hydroxyl radical formation rates depend on operating conditions and cell parameters, but even with low formation rates the damage accumulates over time and can lead to thinning or embrittlement of the membrane, and will cause irreversible damage to the cell. Due to these effects, long-term operation becomes challenging. Therefore, membranes with enhanced radical stability are increasingly desirable. In our previous work, we have shown, using kinetics measurements, that it should be possible for Ce(III) to act as a repair agent for formed damaged intermediates (cf. Figure).[1] In our follow-up work we demonstrate that Ce(III) can indeed reduce degradation rates.[2] These experiments were performed in a fuel cell setup using accelerated stress tests at open circuit voltage (OCV), a cell temperature of 80 °C, 100% RH and high H2 and O2 partial pressures of 2 bar. In-situ measurements and post-test analyses unequivocally show that bound Ce(III) can mitigate degradation of poly(α-methylstyrene sulfonate)-based membranes. We believe that this approach could also be applicable for other aromatic-based polymers if a sufficiently long-lived intermediate is formed upon radical attack.

Growth behavior of Ir metal formed by atomic layer deposition in the nanopores of anodic aluminum oxide.

The conformal coating or surface modification in high aspect ratio nanostructures is a tough challenge using traditional physical/chemical vapor deposition, especially for metal deposition. In this work, the growth behavior of iridium (Ir) metal formed by atomic layer deposition (ALD) in anodic aluminum oxide (AAO) templates was explored deeply. It is found that the surface hydrophilicity is crucial for the nucleation of ALD Ir. An in situ ALD Al2O3 layer with an ultra-hydrophilic surface can greatly promote the nucleation of ALD Ir in AAO nanopores. The effect of the Ir precursor pulse time, diameter, and length of AAO nanopores on the infiltration depth of ALD Ir was investigated systematically. The results show that the infiltration depth of ALD Ir in AAO nanopores is in proportion to the pore diameter and the square root of the Ir precursor pulse time, which follows a diffusion-limited model. Furthermore, the Ir precursor pulse time to obtain conformal Ir coating throughout all the AAO channels is in proportion to the square of the aspect ratio of AAO templates. In addition, the conformal Ir deposition in AAO nanopores is also related to the Ir precursor purge time and the O2 partial pressure. Insufficient Ir purge time could cause a CVD-like reaction, leading to the reduction of the infiltration depth in AAO. Higher O2 partial pressure can facilitate Ir nucleation with more Ir precursor consumption at the entrance of nanopores, decreasing the infiltration depth in AAO nanopores, so appropriate O2 partial pressure should be chosen for ALD Ir in high aspect ratio materials. Above all, our research is valuable for surface modification or coating of metal by ALD in high aspect ratio nanostructures for 3D microelectronics, nano-fabrication, catalysis and energy fields.

Corrosion risk assessment of geothermal reinjection wellbore in Xining Basin, China

A potential corrosion risk exists during the re-injection of geothermal water in Xining Basin of China due to air entering the well caused by it being open. In this paper, a series of corrosion experiments using metal coupons and geothermal waters was conducted to evaluate the corrosion risk for steels in different typical geothermal waters by dissolved air. A novel and comprehensive prediction model for O2 corrosion rate in reinjection wellbores was established, and a sensitivity analysis of factors influencing air corrosion risk in reinjection wellbores was carried out. The results show that the main corrosive components in the geothermal water from the Xining Basin are Cl−, SO42−, H+ and the O2 added, which can cause a uniform corrosion and a small amount of local corrosion on the surface of carbon steel. The main corrosion products are FeO(OH) and Fe3O4. A high O2 partial pressure and flow velocity, a moderate temperature and salinity, and low pH promote a high corrosion rate for carbon steel. When the geothermal water is injected with a small amount of air, only the deeper part of the wellbore with a high temperature and pressure will suffer a serious corrosion risk, while when a large amount of air is mixed with geothermal water and injected, a huge corrosion risk will be imposed on the entire wellbore. Anti-corrosion measures should be taken if air is added to a wellbore. Removing the O2 from the geothermal water is the most effective solution for carbon steel. In addition, the established corrosion rate prediction model can consider more influencing factors and specializes in the situation of a low O2 partial pressure, which can be used as an effective tool to assess the corrosion risk in reinjection wells.

PLD growth and characteristics of lead-free NKLNST ferroelectric nanotubes

Lead-free (Na0.5358K0.4042Li0.06)(Nb0.893Sb0.057Ta0.05)O3 (NKLNST) nanotubes were successfully grown on Pt(111)/Ti/SiO2/Si(001) substrates by using pulsed laser deposition (PLD) with home-made ceramic target under relatively high O2 partial pressures. The as-grown NKLNST nanotubes exhibited a perovskite phase and grew along (001) direction. The nanotubes’ outer diameters are ranging between 100 and 200 nm, their typical length is around 1 µm with a wall thickness of 10−20 nm. The films composed of NKLNST nanotubes show well-defined P–E hysteresis loops, with Pr of 3.77 μC/cm2 and Ec of 37.6 kV/cm. While under low electric field, the charge transport is dominated by ohmic conduction, at high electric fields, space charge-limited current turns out to be the governing leakage mechanism in these films. The work shows the potential of PLD in the synthesis of nanostructures of complex oxides under proper conditions.

U-loss associated with laser-heating of hematite and goethite in vacuum during (U–Th)/He dating and prevention using high O2 partial pressure

Single-aliquot (U–Th)/He dating of hematite has been used to study iron-oxide precipitation in various environments, but we show there is an important challenge to the method: highly retentive hematite samples require temperatures of >1000°C to be completely degassed, whereas the temperature for major U-loss is ∼980°C. This leads to erroneously high (U–Th)/He ages. Through the analysis of U, Th, and Sm of hematite and goethite samples, we establish the degree of U-loss at this temperature and demonstrate that prolonged heating at temperatures of 950°C can lead to U-loss. We show that loss of U in goethite and hematite samples is associated with phase change from hematite to magnetite as Fe is reduced. The onset temperature of vacuum reduction of hematite can be increased from about 800–900°C in vacuum to approximately 1250°C in an oxygen partial pressure of 100mbar. We demonstrate that samples can be outgassed to extract helium at 1150°C without U-loss in an O2-rich atmosphere during heating, which does not increase the analytical blanks. We describe our implementation and automation of the procedure. An average age calculated on a reference hematite sample from replicate aliquots (n=12), which were analyzed using this procedure, has a relative uncertainty of 2% (1σ), and is within uncertainty of the previously measured two-aliquot age. We suggest this O2 degassing procedure as a way to precisely and reproducibly determine single-aliquot hematite and goethite (U–Th)/He ages.

Improved Transparent Gas Sensor Properties of Cu-Doped SnO2 Films using O2 Plasma Treatment

Cu-doped SnO2 films were deposited on glass slide substrate using an RF magnetron sputtering method. The effects of O2 partial pressures in the deposition process and post O2 plasma treatment were assessed for optical and sensing properties. O2 partial pressures from 2% to 10% were assessed. Post-plasma treatment used a 15 mL/min O2 flow, 450 °C annealing temperature and 30 min treatment time. Optical transmission spectra showed that the films deposited at higher O2 partial pressures had higher transparency and increased band gaps from 3.08 to 3.78 eV. After O2 plasma treatment, the films showed better than optical transmission. However, when the O2 partial pressure increased to 10%, the optical transmission declined slightly because the film had higher surface roughness, smaller crystals and fewer oxygens in the parent rutile tetragonal cells, enhanced the sensor response at room temperature.

Water Enables Efficient CO2 Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework.

Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO2 emissions. However, the separation of CO2 from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO2 partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO2 strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO2. High partial pressures of O2 (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO2 capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg2(dobpdc) (dobpdc4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO2 by a cooperative mechanism that enables access to a large CO2 cycling capacity with a small temperature swing (2.4 mmol CO2/g with ΔT = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO2 capture in 2-ampd-Mg2(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO2 adsorption, thereby increasing the thermodynamic driving force for CO2 binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg2(dobpdc), its high CO2 adsorption capacity, and its high CO2 capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.

Metabolic effects of vitamin B12 on physiology, stress resistance, growth rate and biomass productivity of Cyanobacterium stanieri planktonic and biofilm cultures

Although synthesized only by bacteria and archaea, cobalamin (vitamin B12) is essential for virtually all living cells. One major function is its role in methionine synthesis, as a co-factor for the B12-dependent methionine synthase MetH. However, a large number of microbes avoid requirements for B12 by encoding cobalamin-independent enzymes, such as the B12-independent methionine synthase MetE. Interestingly, many such microbes retain transporters for exogenous B12, produced by neighboring microbes. We hypothesize that selection for retention of B12 transport suggests preservation of unrevealed but critical roles for cobalamin in photoautotroph fitness. To identify the impacts of B12 on photoautotrophic metabolism, we studied the physiological and transcriptional adaptation of Cyanobacterium stanieri HL-69 to varying irradiance and oxidative stress in the presence and absence of B12. The metabolic flexibility of C. stanieri, which possesses both MetH and MetE, allows comparative analysis of cobalamin impacts on its global metabolism. As anticipated, B12 availability governed transcription of cobalamin transporter btuB, metH and a number of genes involved in the methionine-folate cycle. Surprisingly, however, B12 impacted the cell integrity, growth rate and biomass productivity of C. stanieri under conditions of likely oxidative stress due to biofilm growth or under high partial pressures of O2. Furthermore, C. stanieri response to B12 globally rewired cellular metabolic networks, including nitrogen metabolism, energy metabolism, redox homeostasis and oxidative stress response. These findings demonstrate previously-unappreciated roles for B12 metabolism beyond methionine synthesis and reveal how interactions with cobalamin-producing heterotrophs may affect phytoplankton function and dynamics in natural microbial communities. Further comprehension and mastering of the natural oxidative stress resistance mechanisms modulated by cobalamin could be used for the design and implementation of more robust algal bioprocesses retaining high biomass productivities especially under stress conditions.

Load Cycle Durability of Pt/Nb-SnO2 in Polymer Electrolyte Fuel Cells Under Potentiostatic/Galvanostatic Operation

Polymer electrolyte fuel cells (PEFCs) used in fuel cell vehicles (FCVs) are still faced with the challenge of increasing the stack durability. It is essential to resolve the degradation of the cathode catalyst layer due to carbon corrosion, dissolution and particle growth of Pt, and decomposition of membranes under various types of FCV operating conditions such as startup/shutdown, load cycling, and idling. In particular, it is difficult to suppress the degradation of Pt, because the speed of the FCV is controlled by the driver, leading to load cycling, which is known to decrease the durability of carbon black-supported Pt cathode catalysts. In particular, the degradation of Pt is accelerated at high relative humidity and long holding times at open circuit voltage (OCV) due to Pt oxide growth [1]. The dissolved Pt2+ ions are likely to diffuse into the ionomer and membrane during load cycling due to the limited ability of the carbon black support to trap these ions. In contrast, Pt on an Nb-SnO2 support might be expected to be slower to diffuse into the ionomer and membrane due to strong metal-substrate interactions [2]. In fact, we reported that the durability of a Pt/Nb-SnO2 cathode catalyst was superior to that of a Pt/GCB cathode catalyst during potentiostatic simulated load cycling [3]. In this research, we evaluated the load cycle durability for membrane electrode assemblies using a Pt/Nb-SnO2 cathode catalyst in PEFCs under galvanostatic and potentiostatic cycling operation. The Pt loading amount for both the Pt/Nb-SnO2 cathode catalyst and the Pt/CB anode catalyst was 0.1 mg cm-2. The cell performances were evaluated under H2/O2 at 80 °C and 100% RH before and after the durability evaluation. Figure 1a shows the protocol for the durability evaluation involving OCV and load holding times at a low current density of 0.33 A cm-2 (sample A1), at a high current density of 0.55 A cm-2 (sample A2), and, in the case of Fig. 1b, the load cycles between the upper cell voltage at 0.94 V and the lower cell voltage at 0.6 V were operated by a potentiostat under H2/N2 (sample A3). A1, A2 and A3 conditions were performed with H2; utilizations of the reactant gases were H2 (70%)/air (40%), H2 (70%)/O2 (20%) and H2 (100 mL min-1)/N2 (100 mL min-1) at 80 °C and 80% RH in Fig. 2. These durability evaluations can be characterized as follows: A1, A2, with the OCV/load holding times of 60 s/3 s; and A3, with upper/lower cell voltage holding times of 60 s/3 s; the sweep rate of 165 mV s-1 from the lower to upper cell voltage, simulates the durability test of A1. Figures 3 and 4 show the cell performances and mass activities under H2/O2 at 80 °C and 100% RH before and after the durability evaluation. After the durability evaluation, the cell performances for both A1 (H2/air condition) and A2 (H2/O2 condition) were nearly the same as their initial performances, but that for A3 (H2/N2 condition) decreased. The mass activity change decreased with the higher O2 partial pressure in the cathode after the durability evaluation. The mass activity of A2 (H2/O2 condition) was the highest of all conditions after the durability evaluation, in spite of the upper cell voltage being the highest. The behavior was in contrast to the case of a carbon-supported Pt catalyst (not shown here). These results suggest that the durability of the Pt/Nb-SnO2 cathode catalyst could correlate with the thickness of the electron depletion layer between the surface of the Nb-SnO2 and Pt. We reported that the electron depletion layer was induced by adsorption of oxygen species on the surface of SnO2 [4]. Therefore, we consider that the degradation from Pt dissolution in the electrochemical oxidation reaction (Pt → Pt2+ + 2e-) could be suppressed by increasing the thickness of the electron depletion layer due to an increase in the amount of adsorbed oxygen species as a function of O2 partial pressure. We will discuss in detail the degradation mechanisms of the Pt/Nb-SnO2 cathode catalyst in comparison with Pt/GCB during the load cycle durability evaluation. C. Takei, K. Kakinuma, K. Kawashima, K. Tashiro, M. Watanabe, and M. Uchida, J. Power Sources, 324, 729-737 (2016).Y. Chino, K. Taniguchi, Y. Senoo, K. Kakinuma, M. Hara, M. Watanabe, and M. Uchida, J. Electrochem. Soc., 162, F736-F743 (2015).R. Kobayashi, K. Kakinuma, A. Iiyama, and M. Uchida, 232nd ECS Meeting, 1388 (2017).Y. Senoo, K. Kakinuma, M. Uchida, H. Uchida, S. Deki, and M. Watanabe, RSC Adv., 4, 32180-32188 (2014). Figure 1

Evaluating thermodynamic performance limits of thermochemical energy storage subsystems using reactive perovskite oxide particles for concentrating solar power

Concentrating solar power with cost effective and efficient thermal energy storage (TES) has the potential to achieve high dispatchability and enable high penetration of other renewable energy sources. However, levelized cost of electricity of integrated CSP systems remains prohibitively high, and new storage subsystems with higher specific energy storage (kJ kg-1) and overall solar-to-electric efficiencies are needed to lower the costs of dispatchable electricity from CSP. This paper explores the potential for increased specific energy storage and solar-to-electric efficiencies of a TES subsystem that combines sensible and chemical energy storage (i.e., thermochemical energy storage – TCES) using a redox cycle of reducible perovskite oxide particles. The TCES subsystem stores energy through sensible heating and endothermic perovskite reduction in a concentrated solar particle receiver at high temperature (Thot from 700 to 1100 °C) and low O2 partial pressure (pO2 from 10-2 to 10-4 bar). Stored energy is recovered as needed in a particle reoxidation reactor/heat exchanger fed by air. Energy parasitics to lower pO2 for perovskite reduction in the receiver by vacuum pumping or inert sweep gas generation depend on system design and operating conditions. In this work, TCES with the perovskite strontium-doped calcium manganite (Ca0.9Sr0.1MnO3-δ) is evaluated for specific storage and overall solar-to-electric efficiency in a subsystem using vacuum pumping or N2 sweep gas for the reducing environment in the receiver. Vacuum pumping parasitics increase proportionally to changes in oxygen non-stoichiometry (Δδ) and are prohibitively high for Δδ>0.1. Sweep-gas parasitics to separate N2 from air asymptote to smaller constant values at large Δδ. Thus, a sweep gas subsystem has lower balance-of-plant parasitics at Δδ needed for high specific TCES. Improvements in vacuum pump efficiencies from current commercially available values to >10% could reduce pumping parasitics and achieve solar-to-electric efficiencies approaching 35%. Various combinations of reducing pO2 and increasing Thot can achieve the same energy storage for either inert sweep gas or reversible vacuum-pump systems with solar-to-electric efficiencies above 35%.

Ni-SDC Based Cermets for Direct Dry Reforming of Methane on SOFC Anode

Solid oxide fuel cells operated with direct internal reforming of carbon-containing fuels (DIR-SOFC) can achieve high energy conversion efficiency because heat generated with electrochemical reaction can be effectively used with endothermic reforming reaction [1]. Up to now, many researchers have studied DIR-SOFC with steam reforming of hydrocarbons, but recently it was reported that a DIR-SOFC system with dry reforming of methane (CH4 + CO2 → 2H2 + 2CO) showed higher electric efficiency than conventional one with direct steam reforming of methane [2]. Moreover, DIR-SOFC with dry reforming of methane enables us to utilize biogas, mixture of methane and carbon dioxide, as fuel, contributing to reducing greenhouse gas emissions. However, when applying dry reforming reaction, carbon formation, which can cause significant deterioration of nickel in the anode, is more prone to occur than when operating on steam and methane fuel. Therefore, developing new anode materials with high coking resistance is desirable for practical use of DIR-SOFC with dry reforming of methane. Ceria-based oxides are widely used as anode components for DIR-SOFC due to their high O2- and e- conductivity in reducing atmosphere. This mixed ionic electronic conduction can expand the reaction sites over the surface of electrode, and it is also expected that carbon removal reaction is more likely to proceed. So in this study, Ni-Ce0.8Sm0.2O2- δ (samarium doped ceria; abbreviated as SDC) was applied as anode material for DIR-SOFC with dry reforming of methane. In addition, CaO addition to Ni-SDC anode was examined, aiming at enhancing coking resistance and CO2 reactivity by basicity of the additive. SDC powder was prepared by co-precipitation method, and then it was mixed with NiO at a volumetric ratio of Ni-metal:SDC = 60:40, followed by calcination at 1300°C for 5 h in air. The obtained cermet was screen-printed with polyethylene glycol on YSZ disk (20 mm in diameter, 0.5 mm in thickness), and then calcined in air to form porous Ni-SDC electrode. CaO-modified Ni-SDC anode was fabricated by infiltrating Ca(NO3)2 solution on the Ni-SDC anode, followed by calcination at 1200°C for 2 h in air. Power generation performance of the cells was evaluated by current-voltage characteristics at 1000, 900, 800, 700°C with VersaSTAT3 (Ametek Inc.), feeding 0.3% humidified H2 or the mixture of CH4 and CO2 on anode side and pure O2 on cathode side. In addition, stability tests on direct dry reforming operation were conducted under a constant current load. Also, alternative current impedance spectroscopy in humidified H2 flow was conducted under open circuit condition before and after the power generation tests to evaluate the durability of the cells. Figure 1 shows I-V characteristics of the cells with Ni-SDC, CaO-modified Ni-SDC and Ni-YSZ anode, in hydrogen operation and direct dry reforming operation at 1000°C. Ni-SDC based anodes showed higher performance than conventional Ni-YSZ, with both hydrogen and dry reforming fuel. CaO-modified Ni-SDC showed slightly lower performance than pristine Ni-SDC possibly because CaO is an insulator and may have lowered the conductivity of the anode. In Figure 1(b), Ni-YSZ displayed lower open circuit voltage and steep I-V curve, which indicates catalytic activity of Ni-YSZ was insufficient to promote dry reforming and thus leading to low H2 partial pressure and high O2 partial pressure in the anode. On the other hand, for Ni-SDC based anodes, the open circuit voltage was higher and the slope of I-V curve was as small as that with hydrogen fuel. For Ni-SDC and CaO-modified Ni-SDC anodes, overvoltages were separated into ohmic resistance, electrode reaction overvoltage and gas diffusion overvoltage from AC impedance spectra. Although CaO-modified anode showed almost no difference before and after power generation test, pristine Ni-SDC anode, on the other hand, showed larger ohmic resistance and gas diffusion overvoltage after power generation, which probably due to carbon deposition on anode.

Characterization of a novel gas sensor using sintered ceria nanoparticles for hydrogen detection in vacuum conditions

Detection of trace amounts of hydrogen in vacuum conditions is essential in reusable space transportation systems and for safety control in manned space exploration. We evaluated the H2 detection in vacuum conditions by a novel gas sensor using sintered ceria (cerium oxide) nanoparticles. The results show that sensor resistance depended on H2 and O2 partial pressure ratios at any pressure from 10−5Pa to atmospheric pressure. We conclude that the ceria resistance does not depend on total pressure but on H2 and O2 adsorption. The increase in sensor resistance resulted from a decrease in oxygen vacancies dependent on the O2 storage of ceria at a high O2 partial pressure. On the other hand, H2 dissociated and formed a cluster with ceria oxygen atoms when the H2 partial pressure was higher than the O2 partial pressure. Sensor resistance markedly decreased in these conditions because Ce3+ with free electrons were generated. The sensor could also detect other reducing gases such as CH4 and C4H10. In summary, the proposed sensor can convert gas adsorption into an electrical signal even in vacuum conditions, and has the potential to be a highly durable device with high sensitivity.

UV absorption and fluorescence properties of gas-phase p-difluorobenzene

1,4-Difluorobenzene (p-DFB) is a promising aromatic tracer for determining concentration, temperature, and O2 partial pressure in mixing gas flows based on laser-induced fluorescence (LIF). Signal quantification requires the knowledge of absorption and fluorescence properties as a function of environmental conditions. We report absorption and fluorescence spectra as well as fluorescence lifetimes of p-DFB in the temperature, pressure, and oxygen partial pressure range that is relevant for many applications including internal combustion engines. The UV absorption cross section, investigated between 296 and 675 K, has a peak value close to 266 nm and decreases with temperature, while still exceeding other single-ring aromatics. Time-resolved fluorescence spectra were recorded after picosecond laser excitation at 266 nm as a function of temperature (296–1180 K), pressure (1–10 bar), and O2 partial pressure (0–210 mbar) using a streak camera (temporal resolution 50 ps) coupled to a spectrometer. The fluorescence spectra red-shift (~2 nm/100 K) and broaden (increase in full width at half maximum by 58% in the investigated temperature range) with temperature. In N2 as bath gas (1 bar), the fluorescence lifetime τ eff decreases with temperature by a factor of about 20 (from 7 ns at 298 K down to 0.32 ns at 1180 K), while at 8 bar the shortest lifetime at 975 K is 0.4 ns. A noticeable pressure dependence (i.e., reduced τ eff) is only visible at 675 K and above. Quenching of p-DFB LIF by O2 (for partial pressures up to 210 mbar) shortens the fluorescence lifetime significantly at room temperature (by a factor of 8), but much less at higher temperatures (by a factor of 1.8 at 970 K). For fixed O2 partial pressures (52 mbar and above), τ eff shows a plateau region with temperature which shifts toward higher temperatures at the higher O2 partial pressures. O2 quenching is less prominent for p-DFB compared to other aromatic compounds investigated so far. The temperature dependence of O2 quenching can be approximately expressed by an exponential function. The influence of temperature, total pressure, and O2 partial pressure on absorption cross sections and fluorescence quantum yields are given as empirical functions that allow for interpolation. For typical applications, p-DFB LIF provides up to three orders of magnitude stronger signal compared to toluene LIF.

Finite element analysis of the damage and healing behavior of self-healing ceramic materials

Self-healing of crack-damaged brittle ceramics is a valuable phenomenon that counteracts the reliability decrease caused by undesired cracking during service. In this study, we developed a constitutive model to analyze the behavior of self-healing ceramic materials within the framework of a finite element method (FEM), which can describe not only an isotropic damage process under specific boundary conditions, but also self-healing at high temperatures and O2 partial pressures. The damage process was formulated based on the fracture mechanics, while self-healing was described using oxidation kinetics modeling of self-healing time. In addition, the proposed constitutive model was applied to a FE analysis of alumina/15vol.% SiC nanocomposite materials.

Induction thermal plasma synthesis of lithium oxide composite nanoparticles with a spinel structure

Li–Mn composite oxide nanoparticles are synthesized using an induction thermal plasma, and the formation mechanism is investigated on the basis of the homogenous nucleation rate and thermodynamic considerations. Under a high O2 partial pressure, MnO crystals nucleate and Li oxide condenses on MnO nuclei at a relatively high rate, forming LiMn2O4 in a single phase. On the other hand, under a low partial pressure of O2, LiMnO2 is obtained owing to the low condensation rate of Li oxide. This study presents the successful selective synthesis of LiMn2O4 nanoparticles by controlling the partial pressure of O2.

Transcriptional and metabolic regulation of denitrification in Paracoccus denitrificans allows low but significant activity of nitrous oxide reductase under oxic conditions

Oxygen is known to repress denitrification at the transcriptional and metabolic levels. It has been a common notion that nitrous oxide reductase (N2 OR) is the most sensitive enzyme among the four N-oxide reductases involved in denitrification, potentially leading to increased N2 O production under suboxic or fluctuating oxygen conditions. We present detailed gas kinetics and transcription patterns from batch culture experiments with Paracoccus denitrificans, allowing in vivo estimation of e(-) -flow to O2 and N2 O under various O2 regimes. Transcription of nosZ took place concomitantly with that of narG under suboxic conditions, whereas transcription of nirS and norB was inhibited until O2 levels approached 0 μM in the liquid. Catalytically functional N2 OR was synthesized and active in aerobically raised cells transferred to vials with 7 vol% O2 in headspace, but N2 O reduction rates were 10 times higher when anaerobic pre-cultures were subjected to the same conditions. Upon oxygen exposure, there was an incomplete and transient inactivation of N2 OR that could be ascribed to its lower ability to compete for electrons compared with terminal oxidases. The demonstrated reduction of N2 O at high O2 partial pressure and low N2 O concentrations by a bacterium not known as a typical aerobic denitrifier may provide one clue to the understanding of why some soils appear to act as sinks rather than sources for atmospheric N2 O.