Dry N2 Research Articles

CO2 Adsorption Behavior and Kinetics on Amine-Functionalized Composites Silica with Trimodal Nanoporous Structure

A trimodal porous support with special trimodal pore structure has been prepared by physically mixing the silica gel (HPS) and SBA-15 and then devoted to fabricate TEPA-functionalized adsorbent for CO2 capture. The trimodal multistage mesopores structure can promote the TEPA dispersion and mitigate the mass-transfer resistance in the adsorbent and, hence, improve capture performance, compared to the single mesoporous support. The influence of the mass ratios of HPS to SBA-15, amine loaded amount, CO2 concentration, adsorption temperatures, and water vapor were studied. The CO2-saturated adsorption amount of 5.05 mmol/g was obtained at 75 °C in dry N2 flow containing 15 vol % CO2 when the mass ratio of SBA-15 to HPS was 1:2 with 50 wt % TEPA loadings. Moreover, the CO2-saturated adsorption amount presented a 16% improvement in humid N2 flow containing 15 vol % CO2 flow at 75 °C. In addition, the S2HPS-TEPA50% also demonstrated good stability after 10 adsorption/desorption cycles. Based on in situ DRIFTS re...

The influence of atmosphere on the performance of pure-phase WZ and ZB InAs nanowire transistors

We compare the characteristics of phase-pure MOCVD grown ZB and WZ InAs nanowire transistors in several atmospheres: air, dry pure N2 and O2, and N2 bubbled through liquid H2O and alcohols to identify whether phase-related structural/surface differences affect their response. Both WZ and ZB give poor gate characteristics in dry state. Adsorption of polar species reduces off-current by 2–3 orders of magnitude, increases on–off ratio and significantly reduces sub-threshold slope. The key difference is the greater sensitivity of WZ to low adsorbate level. We attribute this to facet structure and its influence on the separation between conduction electrons and surface adsorption sites. We highlight the important role adsorbed species play in nanowire device characterisation. WZ is commonly thought superior to ZB in InAs nanowire transistors. We show this is an artefact of the moderate humidity found in ambient laboratory conditions: WZ and ZB perform equally poorly in the dry gas limit yet equally well in the wet gas limit. We also highlight the vital role density-lowering disorder has in improving gate characteristics, be it stacking faults in mixed-phase WZ or surface adsorbates in pure-phase nanowires.

Latent Porosity in Alkali-Metal M2B12F12 Salts: Structures and Rapid Room-Temperature Hydration/Dehydration Cycles.

Structures of the alkali-metal hydrates Li2(H2O)4Z, LiK(H2O)4Z, Na2(H2O)3Z, and Rb2(H2O)2Z, unit cell parameters for Rb2Z and Rb2(H2O)2Z, and the density functional theory (DFT)-optimized structures of K2Z, K2(H2O)2Z, Rb2Z, Rb2(H2O)2Z, Cs2Z, and Cs2(H2O)Z are reported (Z2- = B12F122-) and compared with previously reported X-ray structures of Na2(H2O)0,4Z, K2(H2O)0,2,4Z, and Cs2(H2O)Z. Unusually rapid room-temperature hydration/dehydration cycles of several M2Z/M2(H2O)nZ salt hydrate pairs, which were studied by isothermal gravimetry, are also reported. Finely ground samples of K2Z, Rb2Z, and Cs2Z, which are not microporous, exhibited latent porosity by undergoing hydration at 24-25 °C in the presence of 18 Torr of H2O(g) to K2(H2O)2Z, Rb2(H2O)2Z, and Cs2(H2O)Z in 18, 40, and 16 min, respectively. These hydrates were dehydrated at 24-25 °C in dry N2 to the original anhydrous M2Z compounds in 61, 25, and 76 min, respectively (the exact times varied from sample to sample depending on the particle size). The hydrate Na2(H2O)2Z also exhibited latent porosity by undergoing multiple 90 min cycles of hydration to Na2(H2O)3Z and dehydration back to Na2(H2O)2Z at 23 °C. For the K2Z, Rb2Z, and Cs2Z transformations, the maximum rate of hydration (rhmax) decreased, and the absolute value of the maximum rate of dehydration (rdmax) increased, as T increased. For K2Z ↔ K2(H2O)2Z hydration/dehydration cycles with the same sample, the ratio rhmax/rdmax decreased 26 times over 8.6 °C, from 3.7 at 23.4 °C to 0.14 at 32.0 °C. For Rb2Z ↔ Rb2(H2O)2Z cycles, rhmax/rdmax decreased from 0.88 at 23 °C to 0.23 at 27 °C. For Cs2Z ↔ Cs2(H2O)Z cycles, rhmax/rdmax decreased 20 times over 8 °C, from 6.7 at 24 °C to 0.34 at 32 °C. In addition, the reversible substitution of D2O for H2O in fully hydrated Rb2(H2O)2Z in the presence of N2/16 Torr of D2O(g) was complete in only 60 min at 23 °C.

Effect of test atmosphere on the tribological behaviour of the tetrahedral amorphous carbon (ta-C) and fluorinated ta-C (ta-C-F) coatings against steel

Tetrahedral amorphous carbon based coatings generally exhibit a low coefficient of friction (COF) while sliding against steel and aluminum, but their tribological properties are sensitive to the test environment. In this study, tribological behaviour of tetrahedral amorphous carbon (ta-C) and fluorinated ta-C (ta-C-F) coatings were investigated under different atmospheres including ambient air (53% relative humidity, RH) and dry N2 (3% RH) against a steel counterface. The ta-C showed a period of low COF of 0.27 in ambient air and a C transfer layer was formed on the counterface, but the COF increased with sliding duration to ~0.4 due to transfer of Fe2O3 debris to ta-C surface. A high COF of ~0.60 with high fluctuations occurred in dry N2 as no carbon transfer layers were formed on the counterface. The ta-C-F coating exhibited a steady-state behaviour with low COF (μs) values under both ambient (μs=0.25) and dry N2 (μs=0.23) atmospheres. Formation of an F containing carbonaceous transfer layer on the counterface provided low COF for ta-C-F.

Temperature dependence of partial conductivities of the BaZr0.7Ce0.2Y0.1O3-δ proton conductor

Partial conductivities are presented for BaZr0.7Ce0.2Y0.1O3-δ, an important proton conductor for protonic-ceramic fuel cells and membrane reactors. Atmospheric dependencies of impedance performed in humidified and dry O2, air, N2 and H2(10%)/N2(90%) in the temperature range 300–900 °C, supported by the modified emf method, confirm significant electron-hole and protonic contributions to transport. For very reducing and wet atmospheres, the conductivity is predominantly ionic, with a higher participation of protons with decreasing temperature and increasing water-vapour partial pressure (pH2O). From moderately reducing conditions of wet N2 to wet O2, however, the conductivity is considerably influenced by electron holes as revealed by a significant dependence of total conductivity on oxygen partial pressure (pO2). With higher pH2O, proton transport increases, with a concomitant decrease of holes and oxygen vacancies. However, the effect of pH2O is also influenced by temperature, with a greater protonic contribution at both lower temperature and pO2. Values of proton transport number tH ≈ 0.63 and electronic transport number th ≈ 0.37 are obtained at 600 °C for pH2O = 0.022 atm and pO2 = 0.2 atm, whereas tH ≈ 0.95 and th ≈ 0.05 for pO2 = 10−5 atm. A hydration enthalpy of −109 kJ mol−1 is obtained in the range 600–900 °C.

Properties of Concentrated Aqueous Electrolyte Solution in a Vicinal Region of Coexisting Solid Surface

Numerous electrochemical devices are expected to operate in higher output using large amount of active materials and concentrated electrolyte solution in limited volume of each device. Therefore, little amount of concentrated electrolyte solution is penetrated in active materials for electrode. Although a lot of researchers have been investigating for electrolyte solution, the properties of electrolyte solution coexisting with solid materials are not studied very much. It is well-known that the solid surface affects the properties of water nearby the solid/liquid interface1. We have been studying the properties of the coexisting system consisting of an aqueous electrolyte solution and an inorganic powder, and confirmed that various kinds of solutions change its properties depending on a distance from solid surface2. In the present study, we focused on zinc aqueous solution because strong interaction of Zn2+ makes large hydration sphere, therefore interaction from solid surface might be much observable. While almost all 2:2 electrolytes are slightly soluble due to their strong interaction, ZnSO4 can dissolve up to 3 mol L-1 at ambient temperature. As Rudolph et. al reported using Raman spectroscopy, Zn2+ and SO4 2- forms a 1:1 inner-sphere contact ion pair even in a dilute solution3. Dehydration occurred by forming contact ion pair is supposed to affect water activity and this behavior might change in a solid/liquid coexisting system by the effect from solid surface. We measured liquid properties of ZnSO4aqueous solution coexisting with silica nanoparticles in order to discuss the change in liquid property caused by silica surface in the vicinal region of solid phase. Aqueous solutions containing prescribed concentration were prepared by stirring commercial salts in deionized water, and mixed with fumed silica as 85 – 100 vol% of liquid phase using agate mortar. We carried out DSC, Raman spectroscopy, 1H NMR, and proton relaxation measurement. The employed scanning temperature range in the DSC measurement was between -70 and 50°C and a scan rate was 5°C per minute. Cooling and heating processes were repeated three times in dry N2 atmosphere. Raman spectroscopy and the proton relaxation measurement were carried out at 25oC. From results of DSC measurement, H2O-ZnSO4 system exhibited binary phase diagram which have eutectic composition at 0.050 mole fraction of ZnSO4, therefore this suggests 19 water molecules and one ZnSO4 salt exhibit phase transition at once. This ratio of salt to water molecule at eutectic composition is very low value compared with other eutectic system. This indicates a combination of zinc cation and sulfonate anion have strong influence on water molecules. Because it is known that Zn2+ have 6 water molecules as first hydration sphere and 12 water molecules as second hydration sphere4, phase transition at the eutectic composition was supposed to take along almost all water molecules of first and second hydration sphere. In the coexisting system with silica nanoparticles, single endothermic peak of eutectic mixture exhibited splitting into some endothermic peaks, suggesting heterogeneous phase transitions were occurred. From Raman spectroscopy in solid/liquid coexisting system shown as Fig. 1, the ν1-SO4 2- band of 1 mol L-1 (ZnSO4 · 55.2H2O) shifted to higher wavenumber with liquid phase volume fraction decrease, and closed to the value of 3 mol L-1 (ZnSO4 · 7.7H2O) which have much less water molecules per 1 salt than eutectic composition or sum of the first and second hydration sphere. In the vicinity of silica nanoparticle, Zn2+ was not supposed to make hydration sphere sufficiently due to sharing water molecules with solid surface. This result agrees with the previous study for the α-Al2O3 powder/ZnCl2 aqueous solution coexisting system2, and it suggests that the structural change of the ionic species affect ionic conduction behavior. Consequently, the tendency of zinc cation and sulfate anion to form contact ion pair was enhanced in the vicinity region of silica solid surface, while that in higher concentration was negligible. This behavior was similar to the liquid phase volume fraction dependences of 1H spin-spin relaxation time which asymptotically closed to a constant value with decrease of liquid phase volume fraction, regardless of the bulk concentration. 【References】 [1] W. Drost-Hansen, Ind. Eng. Chem., 61(11), 10 (1969). [2] M. Mizuhata, et al., Phys. Chem. Chem. Phys., 6, 1944 (2004). [3] W. W. Rudolph, et al., Z. Phys. Chem., 209, 181 (1999). [4] W. W. Rudolph, et al., Journal of Solution Chemistry, 28, 9 (1999). Figure 1

Recent Advances in the Quest for a New Insulation Gas with a Low Impact on the Environment to Replace Sulfur Hexafluoride (SF6) Gas in High-Voltage Power Network Applications

The growing environmental challenge of electrical energy systems has prompted a substantial increase in renewable energy generation. Such generation systems allow for significant reduction of CO2 emissions compared with a traditional fossil fuel plant. Furthermore, several improvements in power systems network configuration and operation combined with new technologies have enabled reduction of losses and energy demand, thus contributing to reduction of CO2 emissions. Another environmental threat identified in electrical networks is the leaking of insulating sulfur hexafluoride (SF6) gas used in electrical gas insulated substations (GIS) and equipment. Because of its Global Warming Potential (GWP) of nearly 24,000 and its long life in the atmosphere (over 3000 years), SF6 gas was recognized as a greenhouse gas at the 1997 COP3; since then its use and emissions in the atmosphere have been regulated by international treaties. It is expected that as soon as an alternative insulating gas is found, SF6 use in high-voltage (HV) equipment will be banned. This paper presents an overview of the key research advances made in recent years in the quest to find eco-friendly gases to replace SF6. The review reports the main properties of candidate gases that are being investigated; in particular, natural gases (dry air, N2 or CO2) and polyfluorinated gases especially Trifluoroiodomethane (CF3I), Perfluorinated Ketones, Octafluorotetra-hydrofuran, Hydrofluoroolefin (HFOs), and Fluoronitriles are presented and their strengths and weaknesses are discussed with an emphasis on their dielectric properties (especially their dielectric strength), GWP, and boiling point with respect to the minimum operating temperature for HV power network applications.

Structure and Electrical-Transport Relations in Ba(Zr,Pr)O3-δ Perovskites.

Members of the perovskite solid solution BaZr1-xPrxO3-δ (0.2 ≤ x ≤ 0.8) with potential high-temperature electrochemical applications were synthesized via mechanical activation and high-temperature annealing at 1250 °C. Structural properties were examined by Rietveld analysis of neutron powder diffraction and Raman spectroscopy at room temperature, indicating rhombohedral symmetry (space group R3̅c) for members x = 0.2 and 0.4 and orthorhombic symmetry (Imma) for x = 0.6 and 0.8. The sequence of phase transitions for the complete solid solution from BaZrO3 to BaPrO3 is Pm3̅m → R3̅c → Imma → Pnma. The structural data indicate that Pr principally exists as Pr4+ on the B site and that oxygen content increases with higher Pr content. Electrical-conductivity measurements in the temperature range of 250-900 °C in dry and humidified (pH2O ≈ 0.03 atm) N2 and O2 atmospheres revealed an increase of total conductivity by over 2 orders of magnitude in dry conditions from x = 0.2 to x = 0.8 (σ ≈ 0.08 S cm-1 at 920 °C in dry O2 for x = 0.8). The conductivity for Pr contents x > 0.2 is attributable to positively charged electronic carriers, whereas for x = 0.2 transport in dry conditions is n-type. The change in conduction mechanism with composition is proposed to arise from the compensation regime for minor amounts of BaO loss changing from predominantly partitioning of Pr on the A site to vacancy formation with increasing Pr content. Conductivity is lower in wet conditions for x > 0.2 indicating that the positive defects are, to a large extent, charge compensated by less mobile protonic species. In contrast, the transport mechanism of the Zr-rich composition (x = 0.2), with much lower electronic conductivity, is essentially independent of moisture content.

Revealing Nanoscale Passivation and Corrosion Mechanisms of Reactive Battery Materials in Gas Environments

Lithium (Li) metal is a high-capacity anode material (3860 mAh g-1) that can enable high-energy batteries for electric vehicles and grid-storage applications. However, Li metal is highly reactive and repeatedly consumed when exposed to liquid electrolyte (during battery operation) or the ambient environment (throughout battery manufacturing). Studying these corrosion reactions on the nanoscale is especially difficult due to the high chemical reactivity of both Li metal and its surface corrosion films. Here, we directly generate pure Li metal inside an environmental transmission electron microscope (TEM), revealing the nanoscale passivation and corrosion process of Li metal in oxygen (O2), nitrogen (N2), and water vapor (H2O). We find that while dry O2 and N2 (99.9999 vol %) form uniform passivation layers on Li, trace water vapor (∼1 mol %) disrupts this passivation and forms a porous film on Li metal that allows gas to penetrate and continuously react with Li. To exploit the self-passivating behavior of Li in dry conditions, we introduce a simple dry-N2 pretreatment of Li metal to form a protective layer of Li nitride prior to battery assembly. The fast ionic conductivity and stable interface of Li nitride results in improved battery performance with dendrite-free cycling and low voltage hysteresis. Our work reveals the detailed process of Li metal passivation/corrosion and demonstrates how this mechanistic insight can guide engineering solutions for Li metal batteries.

Functional Electro-materials Based on Ferricyanide Redox-active Ionic Liquids

The unique physical and chemical properties of conventional room temperature ionic liquids (RTILs) render them highly deployable materials in electrochemical devices performing functions such as solvent-free electrolytes in capacitors, batteries and sensors. However, these non-faradaic applications can be complimented by incorporating faradaic redox functionality into the ionic liquid structure which facilitates access to a large array of new electrochemical applications such as dye sensitised solar cells, redox batteries, hydrid capacitors and selective amperometric sensor applications which are all reliant on heterogeneous or homogenous electron-transfer processes. This paper presents and discuses some examples of redox active ionic liquids base on the ferri-/ferro- functionality. These functional electro-materials which are already known [Ref. [18]] exhibit simple reversible one-electron electrochemistry at very negative potentials (by at least −1V relative to aqueous systems) in anhydrous media. Glass transition temperatures lower than −50°C were also observed along with an overall thermal stability up to at least 400°C under dry N2 atmosphere conditions. Opportunities and challenges for these types of electro-materials are discussed.

Hydrogen sensing ability of Cu particles coated with ferromagnetic Pd–Co layer

A new hydrogen sensor utilizing a ferromagnetic hydrogen absorbing alloy was developed. An optimum sensing element, Cu particles coated with Pd–Co hydrogen absorbing alloy was prepared by the barrel sputtering technique. The surface of prepared Cu particle was covered uniformly by Pd–Co thin layer constituted of aggregated nanoparticles. The sensitivity of the sensing element to H2 concentrations under flowing dry N2 and dry air gases was examined. The element has a reasonable sensitivity to the H2 concentration of the range from 3.8% to 0.2%, and the lower limit of detectable H2 concentration was estimated to be less than 0.1%. In dry air, the water formation on the Pd–Co surface affected its sensing ability, because the temperature of the sensing element increased by the exothermic reaction. The effect of moisture on the H2 sensing ability was also investigated. The moisture slightly degraded the output signal under flowing air. It could be ascribed to an additional consumption of hydrogen atoms by water molecules and oxygen atoms on the Pd–Co surface. This sensor takes advantage of magnetic susceptibility measurement, which requires no electrical wire between the sensing element and an electric circuit, leading to a safe evaluation system of H2 concentration in air.

High temperature polymer degradation: Rapid IR flow-through method for volatile quantification

Accelerated aging of polymers at elevated temperatures often involves the generation of volatiles. These can be formed as the products of oxidative degradation reactions or intrinsic pyrolytic decomposition as part of polymer scission reactions. A simple analytical method for the quantification of water, CO2, and CO as fundamental signatures of degradation kinetics is required. This study describes an analytical framework and develops a rapid mid-IR based gas analysis methodology to quantify volatiles that are contained in small ampoules after aging exposures. The approach requires identification of unique spectral signatures, systematic calibration with known concentrations of volatiles, and a rapid acquisition FTIR spectrometer for time resolved successive spectra. The volatiles are flushed out from the ampoule with dry N2 carrier gas and are then quantified through spectral and time integration. This method is sufficiently sensitive to determine absolute yields of ∼50 μg water or CO2, which relates to probing mass losses of less than 0.01% for a 1 g sample, i.e. the early stages in the degradation process. Such quantitative gas analysis is not easily achieved with other approaches. This approach opens up the possibility of quantitative monitoring of volatile evolution as an avenue to explore polymer degradation kinetics and its dependence on time and temperature.

Microscopic origin of ultra-low friction coefficient between the wear track formed on carbon nitride coating and transfer layer on sliding ball in friction tests under dry N2

Carbon nitride (CNx) coatings have been found to exhibit an ultra-low friction coefficient (less than 0.01) after repeated sliding against a silicon nitride (Si3N4) ball in a dry nitrogen gas (N2) atmosphere. However, the mechanism for this has not yet been fully elucidated with respect to analyzing changes in the space structure of CNx. In the present study, we examined the microscopic structural changes in the near-surface structural transition layers of the wear track in the CNx coating and the transfer layer of the Si3N4 ball, using scanning transmission electron microscopy and electron energy-loss spectroscopy. We investigated the nitrogen concentration, density, and curvature of fragmented graphitic planes in the structural transition layers of both the CNx coating and the transfer layer of the Si3N4 ball by analyzing the plasmon peak and carbon K-edge. In addition, we theoretically examined the chemical bonding states of nitrogen doping in various model clusters using an ab initio molecular orbital method to clarify the role of nitrogen in the ultra-low friction behavior. The mechanism behind the ultra-low friction behavior is explained by nano-graphitization of the fragmented carbon structure with optimal nitrogen concentration passivating the contacting counter surfaces of the coating and ball formed during sliding.

Unique dielectric features of a ceramic-semiconductor nanocomposite MgNb2O6 + 0.25Zn0.5Cd0.5S

The present communication deals with the optical/dielectric characteristics of MgNb2O6+0.25Zn0.5Cd0.5S nanocomposite (10–30nm) mixture. Zn0.5Cd0.5S (size ∼10nm) was synthesized by microwave assisted solvo-thermal method. Monophase magnesium niobate (MN) nanoparticles (10–20nm) were synthesized in a single step by mechanochemical treatment of MgO+Nb2O5 under dry N2 atmosphere. The nanocomposite, MgNb2O6+0.25Zn0.5Cd0.5S, was prepared by mechanical admixing of MgNb2O6 and Zn0.5Cd0.5S taken in 4:1 molar ratio. The photoluminescence study shows violet, yellow and orange-red emissions by the MgNb2O6+0.25Zn0.5Cd0.5S composite. The observed dielectric constant value (ε) for MgNb2O6+0.25Zn0.5Cd0.5S is only 4.7, which is ∼5 times smaller than the ε value of MgNb2O6 while a dielectric loss for the composite being closer to zero ensures promising commercial applications.

Biosolids differently affect seed yield, nodule growth, nodule-specific activity, and symbiotic nitrogen fixation of field bean

The main aim of this research was to verify whether mineral nitrogen (N) continuously released by organic fertilisers during the field bean growth cycle may be sufficiently high to enhance plant growth and seed yield but sufficiently low that it does not negatively affect nodulation and symbiotic N2 fixation. Plants were grown without N fertilisation, and with mineral and organic N (biosolids) fertilisation. All plant parts were collected and dry matter, N content, %Ndfa, and N2 fixed were measured at 8th node, flowering, and maturity stages. Nodule specific activity, N derived from soil, and N remobilisation were estimated. The nitrate concentration of soil was also determined. Biosolids reduced nodule growth, nodule fixation activity, and N2 fixation during the vegetative but not the reproductive phase. During seed filling, nodule fixation activity increased and N2 fixation was roughly twice that of the Control plants. Biosolids increased seed yield by removing the imbalance between N demand and N supply for pod growth. This may be related to an increase in nodule-specific activity due to the reduction in mineral N in the soil.

Evaluation of techniques for sampling volatile arsenic on volcanoes

Volatile arsenic (As) species, like arsine, mono-, di-, and trimethylarsine (AsH3, MeAsH2, Me2AsH, Me3As) are reported to be released from volcanoes but their determination is difficult because of low concentrations, low boiling points, and high reactivity, especially in the presence of volcanic gases like H2S and SO2. We tested needle trap devices (NTDs), cryotrapping, and Tedlar® bags for quantitative and species-preserving sampling. NTDs did not trap AsH3, MeAsH2, Me2AsH, did not release sorbed Me3As quantitatively, and lead to artifact formation of dimethylchloroarsine, which also questions the reliability of previous reports from solid phase micro extraction fibers using the same sorption materials. Cryotrapping in dry ice was insufficient to trap AsH3 and MeAsH2; Me2AsH and Me3As were only partially retained. Sampling in Tedlar® bags remained the best alternative. Stability of all four arsines was confirmed for dark storage at 5°C for 19days in a matrix of dry N2, 11days in 20% O2, and 19days in 3800ppmv CO2 (>80% recovery for all species), while in the presence of H2S, Me3As recovery was only 67% and in the presence of SO2, Me2AsH and Me3As recovery was 40 and 11%, respectively. Removing interfering reactive gases by a NaOH trap, we sampled natural volcanic emissions at fumaroles of Vulcano and Solfatara (Italy). Detected total arsine concentrations of 0.5–77ng·m−3 were 1–2 orders of magnitude higher than the calculated background. Inorganic arsine was the dominant species suggesting that secondary microbially catalyzed methylation is a process of minor importance in the fumarolic gases.

Macroscale Superlubricity of Multilayer Polyethylenimine/Graphene Oxide Coatings in Different Gas Environments.

Friction and wear decrease the efficiency and lifetimes of mechanical devices. Solving this problem will potentially lead to a significant reduction in global energy consumption. We show that multilayer polyethylenimine/graphene oxide thin films, prepared via a highly scalable layer-by-layer (LbL) deposition technique, can be used as solid lubricants. The tribological properties are investigated in air, under vacuum, in hydrogen, and in nitrogen gas environments. In all cases the coefficient of friction (COF) significantly decreased after application of the coating, and the wear life was enhanced by increasing the film thickness. The COF was lower in dry environments than in more humid environments, in contrast to traditional graphite and diamond-like carbon films. Superlubricity (COF < 0.01) was achieved for the thickest films in dry N2. Microstructural analysis of the wear debris revealed that carbon nanoparticles were formed exclusively in dry conditions (i.e., N2, vacuum), and it is postulated that these act as rolling asperities, decreasing the contact area and the COF. Density functional theory (DFT) simulations were performed on graphene oxide sheets under pressure, showing that strong hydrogen bonding occurs in the presence of intercalated water molecules compared with weak repulsion in the absence of water. It is suggested that this mechanism prevents the separation graphene oxide layers and subsequent formation of nanostructures in humid conditions.

(Invited) Design of Highly Sensitive and Selective Diode-Type H2 Sensors

Numerous efforts have been directed to developing highly sensitive and selective H2 sensors, because H2, which is the most promising alternative to fossil fuels, is highly flammable and explosive in a wide concentration range (4–75% in air). However, general gas sensors (e.g., semiconductor-type and catalytic combustion-type sensors) cannot operate under O2-free atmosphere, because the effective reaction of H2 with negatively-charged oxygen adsorbates on the oxide surface is essential for the large H2 response. We have thus far demonstrated that diode-type gas sensors using noble-metal (N) sensing electrodes and an anodized titania film (N/TiO2 sensors) show quite large H2 response under oxygen-free atmosphere as well as relatively excellent H2 selectivity to other inflammable gases, in comparison with other gas sensors. Use of Pd as the sensing-electrode material especially resulted in quite large H2 response1 , 2 ), and alloying of Pd with Pt (Pd-Pt) effectively improved the H2 response and the long-term stability3). However, the H2 response of these sensors abruptly decreased with an increase in oxygen concentration in target gas. On the other hand, a Pt/TiO2 sensor showed lower H2 response than the Pd/TiO2 and Pd-Pt/TiO2 sensors, but the coating of the Pt-sensing electrode with a slight amount of Au drastically enhanced the magnitude of H2 response in air, probably due to a decrease in the amount of oxygen adsorbates on the Pt electrode4,5). Therefore, effects of the Au coating of the Pt-sensing electrode on the H2-sensing properties have been investigated in this study. A polished Ti plate (10 mm × 5 mm × 0.5 mm) was annealed at 600°C for 1 h in air, and the half part was anodized at 20°C for 30 min at a current density of 50 mA cm-2 in 0.5 M H2SO4 aqueous solution. A pair of Pt electrodes (3 mm × 3 mm) was fabricated on the surface of both the TiO2 thin film and the Ti plate by magnetron sputtering for 6 min at 300 W in Ar. Subsequently, Au was coated on the Pt electrodes by magnetron sputtering at 40 W in Ar (sputtering time (n): 10–120 s) and Au wires were attached on both the electrodes by using Au paste. The sensing properties of the obtained sensors (Au(n)/Pt/TiO2 sensors, after annealing at 600°C for 1 h in air) to 5–8000 ppm H2 balanced with air or N2 under dry or wet atmosphere were measured at 250°C, while applying a dc voltage of 100 mV to the sensors under forward bias condition (Au(n)/Pt(+)–TiO2–Ti(−)). The response of a Pt/TiO2 sensor to 8000 ppm H2 in dry air was three orders of magnitude smaller than that in dry N2, but Au coating on the Pt electrode drastically enhanced the forward current of the Pt/TiO2 sensor in air. The Au(20)/Pt/TiO2 sensor showed the largest H2 response in dry air among all Au(n)/Pt/TiO2 sensors, but the magnitude of H2 response in dry air was still smaller than that in dry N2. The addition of moisture to the atmosphere further enhanced the H2 response of the Au(20)/Pt/TiO2 sensor in air, while it decreased the H2 response in N2. Consequently, the response of the Au(20)/Pt/TiO2 sensor to 8000 ppm H2 in air was comparable to that in N2 under the most humidified atmosphere (AH: 12.8 g m-3). The Au(20)/Pt/TiO2 sensor showed linear relationship between the H2 response and the logarithmic H2 concentration, and the sensor could respond to 50 ppm H2 in dry and wet air, while the sensor easily responded to even 5 ppm H2 in dry and wet N2. In addition, the Au(20)/Pt/TiO2 sensor showed quite excellent H2 selectivity against propane and propene. These results indicate that the optimal Au coating on the Pt electrode was quite effective in improving both the H2 response and H2 selectivity in air as well as reducing oxygen-concentration dependence of the H2response, especially under wet atmosphere. 1) Y. Shimizu, N. Kuwano, T. Hyodo, M. Egashira, Sens. Actuators B 83(2002) 195. 2) Y. Shimizu, K. Sakamoto, M. Nakaoka, T. Hyodo, M. Egashira, Adv. Mater. Res. 47-50(2008) 1510. 3) T. Hyodo, M. Nakaoka, Y. Shimizu, M. Egashira, Sens. Lett. 9(2011) 641. 4) T. Hyodo, T. Yamashita, Y. Shimizu, ECS Transactions 50(12) (2012) 171. 5) T. Hyodo, T. Yamashita, Y. Shimizu, Sens. Actuators B 207 (2015) 105.

Stability and Oer Activity of IrOx in PEM Water Electrolysis

Renewable H2 production is a prerequisite for successfully establishing fuel cell-based electromobility and hydrogen infrastructure. In this respect, proton exchange membrane water electrolysis (PEM-WE) has attracted much interest, not least due to the enormous power densities possible in these devices (1). Research is mainly focused on the anode side, where the oxygen evolution reaction (OER) takes place, causing the vast majority of kinetic losses. OER catalysts of choice are usually iridium oxide (IrOx) based, owing to its decent activity and acceptable stability (2,3). Recent studies showed a strong dependence of the OER activity and dissolution resistance of IrOx on its surface morphology and hydration state, which were controlled by the calcination temperature during the synthesis. They found that crystalline, thermal IrO2is the most stable but least active species (4,5). TGA-analysis from our lab reveals that IrOx can easily be reduced to metallic Ir in dilute H2 at a typical PEM-WE operation temperature of 80 °C. This is also observed for IrOx based membrane electrode assemblies (MEAs) held at OCV in a PEM-WE, where crossover H2 from the cathode side reduces the surface of the IrOx catalyst at the anode within hours, as evident from the formation of H-UPD features in the cyclic voltammogram (see Figure 1b, red vs. blue CV). At the same time, polarization curves after this reduction show significantly decreased cell voltage at slightly reduced Tafel slopes (Figure 1a, red vs. blue curves), corresponding to an increased OER activity. However, a subsequent CV following these polarization curves (see Figure 1b, black CV) reveals that the H-UPD features have disappeared again and that the catalyst surface properties have transformed to a state closer to the less crystalline, hydrous IrOx reported in ref. 4. This suggests that partial IrOx reduction and re-oxidation into (hydrous) IrOx can occur during cycles of extended OCV periods and electrolyzer operation. In analogy to voltage cycling degradation observed in fuel cells, the here described reduction/oxidation cycles might also lead to iridium dissolution. Therefore, we will study the effect of transient operation conditions in PEM-WEs on the OER activity, surface properties, and stability of IrOx based anodes. We will also provide a systematic analysis of OER kinetic parameters such as exchange current density and activation energy as well as their dependence on relative humidity for a commercial iridium oxide catalyst. References (1) K. A. Lewinski, D. F. van der Vliet, and S. M. Luopa, ECS Transactions, 69, 893 (2015). (2) C. Rozain, E. Mayousse, N. Guillet, and P. Millet, Appl. Catal. B, 182, 123 (2016). (3) E. Fabbri, A. Habereder, K. Waltar, R. Kötz, and T. J. Schmidt, Catal. Sci. Technol., 4, 3800 (2014). (4) T. Reier, D. Teschner, T. Lunkenbein, A. Bergmann, S. Selve, R. Kraehnert, R. Schlögl, and P. Strasser, J. Electrochem. Soc., 161, F876 (2014). (5) S. Cherevko, T. Reier, A. R. Zeradjanin, Z. Pawolek, P. Strasser, and K. J. J. Mayrhofer, Electrochem. Commun., 48, 81 (2014). Figure 1a. PEM-WE polarization curves recorded at 80 °C under dynamic O2 (anode)/H2 (cathode) at 147 kPaabs and 200 % RH (inlet). Blue curves were taken after a 12 h conditioning at 1 Acm-2 while red curves signify the status after a 15 h in-situ reduction of the anode catalyst in an H2 atmosphere. Hollow circles and crosses are subsequent repetitions. Figure 1b. Anode CVs recorded under dry N2 at 100mVs-1. Blue CV: before the polarization curves in blue, red and black CVs: before and after the polarization curves in red. The anode was loaded with 0.66 mgIrcm-2 of a commercial IrOx/TiO2 using 12 wt-% of ionomer in the catalyst layer, cathode was loaded with Pt/C at 0.35 mgPtcm-2 and a Nafion® XL membrane was used. MEAs with 5 cm2 active area were tested in a house-made single cell hardware with gold-plated titanium flowfields using porous Ti sheets and carbon fiber paper as GDLs on the anode and cathode side, respectively. Acknowledgements: P. J. Rheinländer would like to acknowledge financial support from Greenerity GmbH. M. Bernt would like to acknowledge funding from the Bavarian Ministry of Economic Affairs and Media, Energy and Technology through the project ZAE-ST (storage technologies). Figure 1

Ammonia Synthesis at Intermediate Temperatures from N2 and Steam in Solid-State Electrochemical Cells Using Cesium Hydrogen Phosphate Based Electrolytes

Solid-state electrochemical synthesis of ammonia is promising to overcome the limited conversion of the conventional catalytic reactors [1] and to enable ammonia synthesis in more mild conditions. Several electrochemical reactors based on the following electrolytes: polymers, perovskites, fluorites, pyrochlores, and composite electrolytes, were investigated to synthesize ammonia from N2 and H2. The highest NH3 formation rate reported so far for an electrochemical system was found to be 1.13×10-8 mol cm-2 s-1 using a Nafion membrane, wet H2 and dry N2 at 80 °C and atmospheric pressure [2]. For N2-H2O ammonia synthesis Amer et al. reported 4.0×10-10 mol cm-2 s-1 at375ºC [3]. In this research ammonia synthesis was performed using solid-state electrochemical cells, for the first time, at an intermediate temperature of 220 °C and atmospheric pressure. Composites composed of CsH2PO4 and SiP2O7 were used as the electrolyte and various noble metals as the anode and cathode catalysts. The effects of the applied voltage and electrode catalysts on the NH3 formation rate and Faradaic efficiency were investigated.CsH2PO4 was prepared by dissolving stoichiometric quantities of Cs2CO3 and H3PO4 in distilled water and drying overnight at 120 °C. SiP2O7 was prepared from mesoporous SiO2 and H3PO4 as reported previously [4]. As electrode catalysts Pt/C-loaded carbon paper (Pt loading 1 mg cm-2, ElectroChem Inc.), Ru-loaded carbon paper, and Ag/Pd paste (TR-4865, Tanaka Kikinzoku Kogyo K.K.) were used. The Ru-loaded carbon paper was prepared by liquid phase reduction of RuCl3 by NaBH4, followed by filtration of the metallic Ru particles using a carbon paper. The membrane electrode assembly (MEA) was prepared by uniaxial pressing. The molar ratio of CsH2PO4 and SiP2O7 in the mixture was 2:1. The anode, electrolyte, and cathode were placed in a die, layer by layer, and then uniaxially pressed at pressure of 250 MPa for 10 min. When the Ag/Pd paste was used as the electrode catalyst, a thin layer (~0.1 mm in thickness) of the catalyst paste was pasted onto the surface of the electrolyte pellet. In ammonia synthesis, humidified N2 was supplied to the cathode chamber, and humidified H2 or humidified Ar to the anode chamber. The feed gas flow rates were 50 cm3 min-1. A water concentration of 30 % was obtained by bubbling the gas flow through water at 70 °C.Figure 1 summarizes ammonia synthesis rate from N2 and H2 for different applied voltages. The largest ammonia synthesis rate was 2.4×10-10 mol cm-2 s-1 at 0.3 V when the Pt/C was used as the cathode. Over the Ru and Ag-Pd cathodes the ammonia synthesis rate decreased monotonically for the increase in the applied voltages. A similar trend in the Faradaic efficiency, which designates the ratio of the current used for ammonia synthesis, was observed for the increase in the applied voltage. This means that H2 is preferentially formed at the cathode for the high applied voltages. The current density increased at the high applied voltages and it is probable that the coverage of the cathode surface by protons becomes high, leading to suppression of N2 adsorption to the cathode surface and preferential formation of H2. This is partially evidenced by the low NH3 formation rate over the Ag/Pd cathode which is less active for dissociation of N2.N2-H2O ammonia synthesis was carried out by feeding water vapor to the anode. The ammonia synthesis rate at 1.2 V was decreased to the order of 10-11 mol cm-2 s-1, compared with the N2-H2 synthesis. The anode might be inefficient for water electrolysis. The ammonia synthesis rate normalized to electrochemically active surface area of each cathode was compared. It was found that the Ru cathode is most active for ammonia synthesis. This result indicates that the catalyst active for dissociation of N-N bond is also requisite in electrochemical ammonia synthesis when the adsorption sites at the cathode surface are available for N2 adsorption.[1] I.A. Amar, R. Lan, C.T.G. Petit, S.W. Tao, J. Solid State Electrochem., 15 (2011) 1845-1860.[2] G.C. Xu, R.Q. Liu, J. Wang, Science in China Series B-Chemistry, 52 (2009) 1171-1175.[3] I.A. Amar, R. Lan, S.W. Tao, RSC Adv., 5 (2015) 38977-38983.[4] T. Matsui, T. Kukino, R. Kikuchi, K. Eguchi, Electrochem. Solid State Lett. 8 (2005) A256-A258. Figure 1