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The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.

Gas diffusion layer (GDL) configurations containing PUREBLACK® and VULCAN® carbons with 30 wt % polyethylene glycol as pore forming agent are evaluated under two ex-situ methods of accelerated stress testing (AST), in water and hydrogen peroxide (30%), for 1000 and 24 h, respectively. The samples are characterized via contact angle, scanning electron microscopy (SEM), porosity and pore size distribution and the fuel cell performance and durability are also evaluated, before and after the ASTs. Contact angle and SEM demonstrate extensive degradation impact on VULCAN® carbon, especially in hydrogen peroxide, with cracked surface due to carbon corrosion and wash-off, complete hydrophobicity loss, along with porosity increase. The fuel cell performance is evaluated at 60 and 100% RH at 70 °C, using O2 and air as oxidants, and the degraded VULCAN® carbon-based GDLs after the ASTs, result in significant performance loss and durability in air (~20% after 50 h) test shows non uniform gas distribution to the catalyst layer after ~30 h of continuous operation under constant current density 600 mA.cm−2, especially under high RH conditions. On the other hand, PUREBLACK®-based GDLs demonstrate superior durability in air (~12% after 50 h), possibly attributed to its graphitized carbon structure, as evident from the stable durability for 50 h.

The deconvolution of physicochemical processes in impedance spectra of SOCs with nickel/ceria fuel electrodes is challenging as gas diffusion strongly overlaps with the electrochemical processes at fuel and air electrode. To overcome this issue, symmetrical cells were applied and the gas diffusion process at the fuel electrode was quantified by altering the inert component (nitrogen/helium) in a ternary fuel gas mixture. An effective gas transport parameter considering microstructural and geometrical features was derived, enabling a precise quantification of polarization resistances related to gas diffusion and hydrogen electrooxidation. The obtained values were applied to parameterize an existing dc cell model. The model validation in fuel cell and electrolyzer mode showed an excellent agreement between measured and simulated current/voltage characteristics over a wide range of technically meaningful gas compositions and operating temperatures.

This research proposes a novel design of a millimeter-sized air-breathing proton exchange membrane fuel cell (AB-PEMFC). The producing method of the air-breathing PEMFC consisted of the sequential deposition of the elements in layers: 1) endplate of a flat polymer, 2) fuel flow channel with gas diffusion layers (GDL), 3) silicone seal with embedded micro Pt (platinum) wires, 4) membrane electrode assembly (MEA) with high platinum load, 5) GDL with micro Pt wires. Performance tests were done using an AB-PEMFC and the stack of two mono cells under different conditions. The results obtained by the computational fluid dynamics (CFD) allowed analyzing the current collector (CC) position. The performance results show 110 W L−1 for the cell power density and 2200 W kg−1 for the specific power density.

The root barrier to radial O2 loss (ROL) is a trait enabling waterlogging tolerance of plants. The ROL barrier restricts O2 diffusion to the anoxic soil so that O2 is retained inside root tissues. We hypothesised that the ROL barrier can also restrict radial diffusion of other gases (H2 and water vapour) in rice roots with a barrier to ROL. We used O2 and H2 microsensors to measure ROL and permeability of rice roots, and gravimetric measurements to assess the influence of the ROL barrier on radial water loss (RWL). The ROL barrier greatly restricted radial diffusion of O2 as well as H2 . At 60 kPa pO2 , we found no radial diffusion of O2 across the barrier, and for H2 the barrier reduced radial diffusion by 73%. Similarly, RWL was reduced by 93% in roots with a ROL barrier. Our study showed that the root barrier to ROL not only completely blocks radial O2 diffusion under steep concentration gradients but is also a diffusive barrier to H2 and to water vapour. The strong correlation between ROL and RWL presents a case in which simple measurements of RWL can be used to predict ROL in screening studies with a focus on waterlogging tolerance.

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.

Gasification reactivity and characteristics of three coal chars and two petcokes were investigated in detail. The temperature programmed reaction technique were used to test the gasification reactivity. The characteristics of the various chars were analyzed by XRD, SEM, N2 adsorption technique and FT-IR. As expect, the coal chars and petcokes showed significantly different gasification reactivity. The reactivity of the two petcokes was much poorer than that of the three coal chars. The gasification reactivity of the coal char increased with the decreasing of coal rank. The gasification reactivity was closely related to the characteristics of samples. It was found that the lower degree of graphitization, less compact surface and more developed pore structure corresponded to higher gasification reactivity of chars. These characteristics of the carbon structure was more favorable to gas diffusion, and hence resulted in high gasification reactivity. In addition, coal char contained more oxygen-containing functional groups and active components such as Ca/Mg/Fe/K/Na compounds, which all had promoting effect on gasification reaction.

Thermochemical stability and microstructural evolution of Yb2Si2O7 was studied in high-temperature high-velocity water vapor at temperatures between 1200–1400 °C. Two reactions were shown to occur in the steam environment: Yb2Si2O7 reaction to form Yb2SiO5, and further Yb2SiO5 reaction to form Yb2O3. Parabolic rates of both reactions were observed, and similar reaction enthalpies were determined for each reaction; 207 kJ/mol and 205 kJ/mol, respectively. Densification of the product phase Yb2SiO5 shut off pore connectivity for gas transport to the reaction interface at gas velocities exceeding 115−125 m/s and for temperatures of 1300 °C and 1400 °C, resulting in reduced reaction rates at higher velocities. Outward gas diffusion by a silicon hydroxide species is predicted to govern ytterbium silicate reactions with high temperature water vapor. Microstructure changes at high temperatures and velocities were shown to greatly impact the long-term stability of Yb2Si2O7.

Water flooding occurs at the output region of the anode side, which is one of the main reasons for performance degradation of automotive fuel cell systems. If liquid water saturation ratio in gas diffusion layers can be observed and regulated within a suitable range, water flooding in anode channels can be avoided. For this purpose, a zero dimensional dynamic model which focuses on the internal states (such as liquid water saturation ratio in gas diffusion layer) for the anode side before water flooding is presented. A nonlinear state observer for the anode side is designed using the unscented Kalman filter algorithm. Influences of the relative humidity sensor and initial values of internal states on the observation results are analyzed. The results show (1) four key internal states (e.g., water vapor pressure, hydrogen and nitrogen pressure, average liquid water saturation ratio) can be observed using this method, and the time constant of the sensor has a smaller influence on the observer than the signal noise. (2) With a suitable sensor (noise power

A chitosan-derived nitrogen-doped carbon (NDC) with a well-designed pore structure is prepared by a novel activation process using ZnO and water vapor. The gas diffusion electrode comprising the ob...

In Nature Communications, Hu, Feng, and their colleagues present a scalable, facile method to tune the hydrophobicity of CO2 reduction gas diffusion electrodes by adding polytetrafluoroethylene (PTFE) nanopowder into the catalyst ink. For a copper catalyst CO2 reduction electrode, the additive significantly enhances CO2 reduction performance and imparts persistent hydrophobicity.

Tin foil and SnOx/C gas-diffusions electrodes (GDEs) were investigated via electrochemical impedance spectroscopy (EIS) to extract the differential double-layer capacitance (Cdl) as a measure of the wetted surface area. Time-dependent Cdl values revealed an immediate stationary wetting for tin foil electrodes while a distinct increase of Cdl – which becomes stationary with time – was observed for GDEs. The time-dependent wetting behavior of the GDEs was substantiated by physical post-mortem characterization. Since the wetted surface area determines the number of reachable active sites the performance of GDEs should be normalized to the wetted surface area for evaluation of reactivity.

For hydrogen-based polymer electrolyte fuel cells (PEFCs), water transport control in gas diffusion layers (GDLs) by wettability distribution is useful to suppress the flooding problem. In this study, the water transport of a novel GDL with hydrophilic-hydrophobic patterns was investigated. First, we clarified that the water motion in the hydrophilic GDL with microstructures could be reproduced by the enlarged scale model. The scale model experiment also showed that the same water behavior in hydrophilic GDL can be obtained from Capillary numbers (Ca) in a range of Ca ~ 10−5 to 10−3. As the computational load is inversely proportional to Ca, the computational load could be reduced by 1/100th by using Ca ~ 10−3, which is 100 times higher than PEFC operation (Ca ~ 10−5). Finally, the simulation with Ca ~ 10−3 was performed, and we showed that the GDL with straight region of contact angle 50° minimized the water accumulation.

Organic light emitting diodes (OLEDs) and amorphous oxide semiconductors (AOSs), which are very important technologies in high performance flexible displays, have issues related to degradation due to diffusion of water and hydrogen, respectively. To solve these issues, gas diffusion barrier properties were evaluated with aluminum oxide deposited by atomic layer deposition (ALD) and alucone deposited by molecular layer deposition (MLD) using trimethylaluminum (TMA) as a metal precursor and H2O and hydroquinone (HQ) as co-reactants, respectively. The water vapor transmission rate (WVTR) and hydrogen gas permeability (HGP) were measured for the fabricated films via electrical calcium tests and vacuum time-lag, respectively. To enhance the diffusion barrier properties, Al2O3/alucone hybrid multi-layer structures were successfully deposited through an in situ ALD/MLD process. The 4.5 dyads of the Al2O3/alucone structure showed improved barrier properties compared to the single Al2O3 film with a WVTR of 8.24 × 10-5 g m-2 day-1 and a HGP of 9.93 × 10-5 barrer, and factors related to gas diffusion in multi-layer structures were discussed. The stability to external stress was also evaluated based on the WVTR change rate after the bending test, and we confirmed that the stability of the multi-layer structures was improved due to the flexibility of inserted alucone layers. All the developed structures had a high optical transmittance of >80% in the 300-800 nm wavelength region based on UV-vis measurements.

A reduced-order model was developed to calculate the redox kinetics of oxygen carrier in chemical looping combustion. The reduced-order model can describe the major physical/chemical features of the redox steps of oxygen carrier, such as gas diffusion around and inside the particle, surface reaction, product growth, product layer diffusion, pore structure change etc. It is an analytical model simplified using the Thiele modulus method and thus is much easier for computational fluid dynamics modeling and reactor design. The accuracy of variations of redox conversion under different temperatures and gas concentrations predicted by the reduced-order model is verified by comparison with both the detailed one-dimensional model and the experimental data. The results indicate that the reduced-order model can reproduce the prediction accuracy of the detailed one-dimensional model and agrees well with the experimental data. The well observed two-stage behavior of a fast initial stage followed by a second slower stage was discussed in detail. Further, the reduced-order model was used to analyze the effect of particle structural parameters on the kinetics. The relative importance of each controlling step in the kinetics of oxygen carrier predicted by the reduced-order model was compared.

In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies (MEAs) used to achieve a high performance of direct hydrazine fuel cells (DHFCs). We have investigated the effect of water management and the electrode thickness on the performance of DHFCs, depending on the hydrophobicity of the gas diffusion layers in the cathode and the catalyst loading in the anode with the carbon-supported Ni, synthesized by a polyol process. With the optimal water management and electrode thickness, the MEA constructed using the as-prepared Ni/C anode catalyst containing the metallic and low oxidative state and ultra-low Pt loading cathode reduced the ohmic resistance and mass transfer limitation in the current-voltage curves observed for the alkaline DHFC, achieving an impressive power performance over 500 mW cm–2.

The spent cathode carbon block (SCCB) produced from the overhaul aluminum reduction cell is regarded as hazardous solid waste because it contains a large amount of soluble fluoride and small amount of cyanide. Coupling vacuum-heating method is considered an effective way to address the issues of such hazardous waste. Herein, SCCB is processed under the conditions of 3000 Pa and 1673–1973 K. The correlation between soluble fluoride content and treatment time was analyzed. The apparent activation energy of the detoxification reaction was calculated based on the Arrhenius equation. The rate-determining step of the detoxification process has also been analyzed in detail. The results show that the detoxification process is a first-order reaction. The apparent activation energy was k = 15.08 kJ mol−1, and gas diffusion was the rate-determining step of the detoxification reaction.

A novel three-dimensional CFD simulation of H2 gas permeation through dense palladium (Pd) membrane was developed. Due to discontinuity of flow in a membrane, usually, gas diffusion process is simulated by introducing source and sink terms. In a novel approach, an analogy between heat and mass transfer is considered. The most important advantage of this approach is that there is no need to define sink and source terms, and the membrane thickness is considered as a solution domain without separating the geometry adjacent to the membrane. Also, it allows the modeling of multilayer membranes with different mechanisms of diffusion, separately. The effect of membrane geometry on the hydrogen separation was investigated using the straight and helical modules by defining user-defined function (UDF) and user-defined scalars (UDS). The results showed an average flux and H2 recovery enhancement of 20% and 13% for helical configuration, respectively. The influence of the feed gas and sweep gas flow rates, helix pitch, coil diameter, pressure difference, and module temperature on hydrogen separation was also investigated. The proposed simulation model was validated using the experimental data. The results indicated that this method has a maximum error of about 10% for H2 flux.

A freestanding vanadium nitride nanowire (VN-NW) membrane is employed as a carbon-free gas diffusion cathode (GDC) for high-performance Li–CO2 batteries. Li–CO2 cells built with the VN-NW GDC exhibit excellent electrochemical performance, achieving 100 discharge/charge cycles with an ultralow round-trip overpotential of

Ammonia is a useful energy carrier for solid oxide fuel cell (SOFC) with advantages over hydrogen. Understanding of the performance and stability of ammonia-fed SOFC operated at elevated pressure (p) is an important step towards the development of high-efficiency hybrid SOFC power system with micro gas turbine (MGT). This paper reports cell performance, electrochemical impedance spectra (EIS), and stability measurements of a pressurized ammonia-fed anode-supported SOFC at p = 1–5 atm and T = 750–850°C using a planar (50 × 50 mm2) single-full-cell (400 μm Ni-YSZ anode/3 μm YSZ electrolyte/12 μm LSC-GDC cathode). The full cell together with metallic frames and current collectors are sandwiched by a pair of rib-channel flow distributors (interconnectors) in a high-pressure testing facility. Results show that pressurization and increasing temperature enhance the ammonia-fed SOFC performance significantly having almost the same power densities as those of hydrogen/nitrogen-fed SOFC, as substantiated and explained by EIS data and an equivalence circuit model where the effects of p and T on ohmic, gas diffusion, and gas conversion impedances are shown. Moreover, the loaded short (10 h) stability tests at 700°C and 0.8 V for 1 atm/3 atm cases reveal no/little power degradation, where the microstructures without any crack within the scale of SEM observation and nearly the same element atomic percentages of Ni-YSZ anode surfaces from EDX spectra are found. These results suggest that the pressurized ammonia-fed SOFC is a promising candidate for the hybrid SOFC-MGT power generation.

The efficiency of new brands of technical carbon CH210 and C40 in the electrogeneration of Н2О2 from О2 in gas-diffusion electrodes (GDE) on their basis is studied in acidic solutions of the 0.5 М K2SO4 : 0.1 M H2SO4 (3 : 1) electrolyte. The textural characteristics of original materials and their mixtures with polytetrafluoroethylene used as the hydrophobizer are determined by low-temperature nitrogen adsorption as well as their electric double layer capacitance. For a comparison, similar studies are also carried out with technical carbon Vulcan XC-72. The rate constants for hydrogen peroxide decomposition on these materials in acidic solutions are determined. The data on the kinetics of hydrogen peroxide accumulation at the overall current density of 1500 А/m2 are as follows: the 6 h electrolysis produces the solution with Н2О2 concentration exceeding 2.5 М with the current efficiency higher than 70.0%. It is concluded that in this case, the surface area is not the determining factor. The technical carbons СН210 and С40 are comparable as regards their efficiency with the well-known technical carbon Vulcan XC-72 and can be used as electrocatalysts in GDE for electrosynthesis of Н2О2 from О2.

When a pipeline is under fire safety work construction, the stack effect of the pipeline will increase the diffusion rate of nitrogen, reduce the oxygen content, and cause asphyxia. To prove the influence of the stack effect of the pipeline on the nitrogen movement in the pipeline and put forward effective ventilation control measures, the formation mechanism, gas diffusion law, and ventilation parameters of the stack effect of the oil and gas pipelines are studied through theoretical derivation and numerical simulation. The results show that the nitrogen concentration at the height of the breathing zone in the hot zone first increases and then decreases along the axial distance. The larger the temperature difference, the faster the diffusion speed of nitrogen in the fire safety work area, and the lower the oxygen concentration. When the temperature difference increases to 30 °C, the maximum oxygen concentration in the work area is 0.177; to control the problem of low oxygen content caused by the stack effect, three ventilation schemes are put forward. Through the analysis that installing fans symmetrically on both sides, 4 m away from the pipe opening, can effectively reduce the stack effect intensity when the optimal working wind speed of the fan is 4 m/s. The findings of this study can help in better understanding the causes of the chimney effect during pipeline fire safety work and provide theoretical basis for controlling personnel suffocation caused by the chimney effect.

Hydrogen is usually locked in energy-rich organic compounds and there is almost no pure hydrogen in nature. Organic compounds produced in reservoirs of hydrogen and carbon are an important source of hydrogen production. Understanding the productivity characteristics reservoirs of hydrogen and carbon is the important step to ensure adequate hydrogen energy. This study analyzes the production of hydraulically fractured organic reservoir of hydrogen and carbon. First, based on the diffusion mechanism in reservoir matrix, a multi-scale dual-porosity medium model of reservoir of hydrogen and carbon is established. Then, the mathematical model is solved and verified through a historical matching of field gas production data. Finally, parameter analysis was performed to determine the key parameters to improve the recovery efficiency in organic reservoir of hydrogen and carbon. Results show that improving fracture permeability can improve gas recovery efficiency of hydrocarbon reservoirs. The matrix desorption can develop natural gas production for a long period. Long sizes of hydraulic fractures have large contact surfaces for gas diffusion and increase gas generation and cumulative gas production. The proposed model can predict and analyze the production performance of reservoirs of hydrogen and carbon.

The incorporation of highly active but also highly sensitive catalysts (e.g. the [FeFe] hydrogenase from Desulfovibrio desulfuricans) in biofuel cells is still one of the major challenges in sustainable energy conversion. We report the fabrication of a dual-gas diffusion electrode H2 /O2 biofuel cell equipped with a [FeFe] hydrogenase/redox polymer-based high-current-density H2 -oxidation bioanode. The bioanodes show benchmark current densities of around 14 mA cm-2 and the corresponding fuel cell tests exhibit a benchmark for a hydrogenase/redox polymer-based biofuel cell with outstanding power densities of 5.4 mW cm-2 at 0.7 V cell voltage. Furthermore, the highly sensitive [FeFe] hydrogenase is protected against oxygen damage by the redox polymer and can function under 5 % O2 .

In order to improve the performance of proton exchange membrane fuel cell (PEMFC), the compressed nickel foam as flow field structure was applied to the fuel cell. The fuel cell test system was built and the performance of fuel cells with nickel foam flow field with different thicknesses were tested and analyzed by electrochemical active surface area (EASA), electrochemical impedance and polarization curve. And its operating parameters were optimized to improve the performance of PEMFC. Our results show that the membrane electrode assembly (MEA) can show a larger catalytic active area and uniformity of gas diffusion can be improved by using the nickel foam flow field instead of the conventional graphite serpentine flow field, and the impedance characteristic of 110PPI nickel foam can be improved by increasing the compression ratio of the original material. What's more, the polarization characteristic and power output performance of PEMFC with nickel foam flow field were improved by optimizing the operating parameters. Using the optimized operating parameters (cell temperature = 80 °C; humidification temperature = 75 °C; stoichiometric ratio = 2; back pressure = 0.23 Map), a peak power density of 1.89 W cm−2 was obtained with an output voltage of 0.46 V.

In this study, the mechanism of reduction of hematite-magnetite concentrate (HMC) by graphite-calcium carbonate reductant mixture at about 1000 °C was investigated. The initial and middle stages of the reduction process (up to 63 pct) were mainly affected by the heat transfer inside the crucible. It was concluded that in the middle to final stages of the reduction process, the gaseous diffusion of reducing gas to the FeO-Fe reaction interface and the carbon gasification are the mixed controlling mechanism. The reduction rate was relatively slow below the carbon gasification temperature. According to X-ray diffractometer (XRD) analysis, the formation of the metallic iron was not observed before the carbon gasification. The scanning electron micrographs showed the formation of iron whiskers in the outer layer of the sample, which resulted in swelling of the sample. The observation of the reduced samples’ sections showed that the reduction progress was topochemical. The progress of the reduction from the inner surface of the sample was insignificant compared to the reduction from the outer.

Clathrate hydrates are ubiquitous in deep-sea sediments and the permafrost on earth, as well as abundant in interstellar environments. Despite many potential applications of gas hydrates for gas storage/transportation, carbon sequestration, and water treatment, the fundamental mechanism for gas hydrate nucleation and growth are still poorly understood due to the difficulty in spatial and temporal measurements that can probe specific structural properties. Here, high resolution measurements for xenon hydrate formation from ice spheres by X-ray computed tomography are reported. For the first time, the nucleation and growth of hydrates can be accurately and directly quantified from microscale measurements, resulting in new estimates for the intrinsic reaction rate constant of xenon hydrate formation, and the effective diffusion coefficient of xenon in the hydrate. The measured activation energy of hydrate formation is 71.11 kJ/mol and the diffusivity of xenon in hydrate ranges from 2.8 × 10–15 to 4.3 × 10–14 m2/s. These results are of fundamental value in developing a comprehensive understanding on the mechanism of gas hydrate formation, which is essential in their application for energy solutions and increasingly important in astrophysical science.

This chapter provides an overview of gas diffusion layers (GDLs) used for proton exchange membrane fuel cells. The materials, properties, modifications, and durability issues are addressed here. Both carbon and metal-based substrates are covered. GDL properties, including porosity, thickness, pore size, transport properties, thermal and electrical conductivity, and compressibility, are covered. Finally, GDL modifications are briefly discussed, including hydrophobization, the addition of microporous layer, and structural modifications of the substrate to improve the proton exchange membrane fuel cell performance.

The chemical characterization of volcanic gas emissions gives insights into the interior of volcanoes. Monitoring of BrO/SO2-ratios has recently been correlated with changes in the activity of a volcano. BrO and SO2 can both be measured autonomously and simultaneously with the same instruments from a safe distance, making their ratio potentially a strong monitoring tool. However, BrO is not a primary emitted volcanic volatile and there exist still uncertainties about the formation of BrO in volcanic plumes, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. This study describes a new method for the determination of the BrO precursor, the gaseous hydrogen bromide (HBr), by quantitative collection in denuder samplers. Gas diffusion denuders use the difference in diffusion coefficients to separate gaseous from particle-phase compounds. Gaseous HBr molecules are immobilized with an organic coating at the inner walls of the denuder tubes when pumped through the denuders. Five different coatings using 1,2-epoxycyclooctane, trans-oxirane-2,3-dicarboxylic acid, 2,3-epoxy-3-phenylpropanoic acid, 9,10-epoxystearic acid, 5,6-epoxy-5,6-dihydro-[1,10]-phenanthroline (EP) were tested as denuder coatings. EP proved to be a suitable coating reagent, which at the same time, transfers the analyte into an appropriate derivate to be analyzed by high-performance liquid chromatography coupled to electrospray ionization mass spectrometry (in situ derivatization). Coating amount, breakthrough, matrix effects and the storage behavior have been characterized. No considerable cross-sensitivity with hydrogen chloride or other bromine species such as molecular bromine was observed. The comparison of HBr determination using EP-coated denuders and Raschig Tubes as alkaline traps in the laboratory showed a deviation of 2 ± 11 % for gaseous HBr between the two methods. This allows considering HBr determined by denuders as a fraction of total bromine determined by Raschig Tubes. Since other bromine species (e.g. elemental bromine, bromine oxides) are also collected and determined as bromide by Raschig Tubes, but exclusively HBr in EP-coated denuders, the method presented here allows more accurate speciation of gaseous bromine compounds and their application in volcanic plumes. The denuder sampling setup was applied with complementary denuder systems and alkaline traps in the plume of Masaya (Nicaragua) in 2016. HBr concentrations in the range between 0.44 and 2.27 ppb were measured with limits of detection and quantification below 0.1 and 0.3 ppb respectively at typical ground-based sampling conditions. The relative contribution of HBr as a fraction of total bromine decreased from 75 ± 11 % at Santiago rim (214 m distance to the volcanic emission source) to 36 ± 8 % on Nindiri rim (740 m distance). Our findings are in good agreement with previous estimations of the HBr conversion from the chemistry box model (CAABA/MECCA).

International audience; The use of a dual-layer cathode catalyst layer improves the performance of proton exchange membrane fuel cells. To generate single and dual-layer catalyst layers between the gas diffusion media and proton exchange membrane electrolyte, two commercial carbon-supported platinum catalysts with either a high microporosity carbon (Ketjen Black EC-300J) or a low porosity carbon (XC-72 Vulcan carbon) are utilized. We discovered that dual-layer cathode catalyst layers boost maximum power of fuel cells regardless of carbon porosity directionality, with either high surface area carbon at the proton exchange membrane electrolyte or gas diffusion media interface. At 25% relative humidity, a condition that generally inhibits fuel cell performance, a 20% performance boost is realized when using dual-layer cathode CLs. The electrochemical impedance spectroscopy results indicate that cathodes with dual-layer catalyst layer aid in water management due to lower kinetic activity losses of the Pt and improved hydration of the proton exchange membrane electrolyte.

Boron was introduced into carbon papers (CPs) to catalyze their graphitization in this paper. The results showed the graphitization of CPs was moved from 2400 °C to 2100 °C. At 2100 °C, boron substituted carbon atoms in the hexagonal carbon lattices to form a solid solution, and the catalytic mechanism was dissolution and precipitation. CPs with excellent electrical conductivity and good permeability were prepared at lower temperature. Thus, the boron-doping method provides a new way to prepare high performance CPs at lower costs.

Graceful choreography for CO 2 and H 2 O One challenge for efficient electrochemical reduction of carbon dioxide (CO 2 ) is that the gas is hydrophobic, but many of its desirable reactions require water (H 2 O). García de Arquer et al. addressed this problem by combining a copper electrocatalyst with an ionomer assembly that intersperses sulfonate-lined paths for the H 2 O with fluorocarbon channels for the CO 2 . The electrode architecture enables production of two-carbon products such as ethylene and ethanol at current densities just over an ampere per square centimeter. Science , this issue p. 661

In this paper, we propose a mathematical model to describe the dynamics of a mixture of gases, including helium and water vapor, in a layer of a resting composite sorbent based on microspheres and a porous matrix of an aluminum oxide moisture absorber using the multiphase media mechanics approach. We show how to match the flow in a porous adsorber medium and the diffusion of gases in a cylindrical adsorbent granule, taking into account the adsorption of helium by microspheres and water vapor by the porous surface of the adsorbent.

Two-step electrochemical reduction of CO2 is investigated as an alternative to increase selectivity towards C2 and C3 products. In this type of proposed cascade electrocatalytic operation, CO is produced in a first step and subsequently reduced to multi-carbon products in a second step with significantly higher Faradaic efficiencies compared to a one-step process. Research efforts have been focused on the feasibility of the isolated second step with pure CO as reactant, however the interdependencies of both steps need to be considered. Accordingly, two-step electrochemical reduction of CO2 is studied in this work as an integrated system. Taking into account that the study of this technology at high current densities is crucial for industrial applicability, gas diffusion electrodes and flow-cells were used for operation at current densities above −200 mA cm−2 . Firstly, each step was characterized separately, the first using a silver gas diffusion electrode to generate a mixture of humidified CO, H2, and unreacted CO2; the second step using copper nanoparticles on a carbon-based gas diffusion structure to obtain C2 and C3 products. This step was studied using synthetic mixtures of CO2 and CO with different ratios. Furthermore, experiments with isotope labeled 13CO2 and 13CO were performed in order to obtain some insights on the (electrochemical) reaction path of gas mixtures containing CO2 and CO. Subsequently, the two units were integrated into a system, where the full gas output of the first unit was directly fed to the second unit. The total Faradaic efficiency towards multi-carbon products of this initial system was limited to 20% at total current density of −470 mA cm−2. These initial results together with the isotopic labeling studies indicate that the presence of significant amounts of unreacted CO2 from the first step is detrimental for the second step. A significant improvement was achieved by introducing a CO2 absorption column between the two units and after splitting the overall charge flow applied in each cell in accordance with the main reaction at each step. With this set-up a total Faradaic efficiency towards C2 and C3 products of 62% at a total current density of −300 mA cm−2 was achieved. The results confirm the need for a gas separation technique between the two steps for a feasible two-step electrochemical reduction of CO2.

Lately, only few successful gas sensors, especially those based on the sensing material of zinc oxide (ZnO), have been specifically designed for the detection of acetic acid. Herein, a new gas sensor aimed at acetic acid was designed employing a novel ZnO foam as the sensing material, which was prepared by a simple sol-gel autocombustion method. The foam presents a novel architecture decorated with numerous holes, and the designed gas sensor exhibits superior sensing performances toward acetic acid, i.e., a high response, sub-ppm detection, excellent selectivity, fine repeatability. These superior sensing performances could be attributed to the massive decorated holes, which significantly facilitates the gas diffusion and transportation.

Cell voltage reversal resulting from hydrogen starvation at anode is one of the factors that exacerbate the overall degradation of polymer electrolyte fuel cells (PEFCs). An effective material-based mitigation strategy against cell reversal is to add oxygen evolution reaction (OER) catalysts into the anode to make reversal-tolerant-anodes (RTAs). However, RTAs still suffer from an eventual sudden death, and the failure mechanisms of this sudden death have not been well studied thus far. Here we show a novel in-situ measurement technique with a distinctive partition membrane electrode assembly (MEA) to research the failure mechanism of RTAs. It is observed for the first time that the failure of RTAs is mainly attributed to the destruction of electron conducting paths caused by carbon corrosion from catalyst layers (CLs), gas diffusion layers (GDLs) and bipolar plates (BPs), rather than deactivation of the OER catalyst. As a verification, the application of additional OER catalysts on the GDL is found to effectively prolong the reversal tolerant time. These results add significant new insights into the failure mechanism of the RTA MEA and will be of practical importance in directing to design advanced MEAs and BPs that can withstand cell voltage reversal.

Platinum nanoparticles have been synthesized on gas diffusion layers (GDLs) by means of electrochemical synthesis. Two types of GDLs were used (hydrophobic and hydrophilic) to study the effect of surface properties on the electrodeposition of Pt nanoparticles. Better coverage of Pt nanoparticles has been observed in the case of using a hydrophilic carbon GDL; nanoparticles with lower size were synthesized as well. Characterization of hydrogen evolution reaction by cyclic voltammetry showed a better performance of the electrodes synthesized by electrochemical methods when compared with commercial ones with an equal Pt loading (2 mg·cm-2)

Oxygen reduction electrodes for zinc–air batteries (ZAB) have been prepared by depositing conformal films of MnOx directly onto high surface area gas diffusion layers (GDL) via atomic layer deposit...

This article presents development of magnetron sputtering technology for catalytic Pt coating production. Low Pt-loaded gas diffusion electrodes were prepared by a single-step magnetron sputtering in different regimes. Pt and Pt-carbon films (95–97 wt% Pt) were deposited directly onto the gas diffusion layers (GDLs): carbon paper (Sigracet® 39 BC) and carbon cloths (GDL-CT, ELAT® LT 1400 W). A bipolar pulsed direct current (DC) magnetron sputtering with pulsed frequency 100 kHz was used as the method for catalysts deposition. Total Pt loading in the thin films varied in the range 0.04–0.13 mg*cm−2. Obtained catalysts onto GDLs were investigated by scanning/transmission electron microscope (S/TEM), X-ray Absorption Near Edge Structure (XANES) and potentiodynamic methods. The deposited catalysts had a high electrochemical surface area (ECSA) and stability determined by the durability stress test (DST) method. The highest ECSA was obtained with Pt target in the pulsed (100 kHz) sputtering mode. This ECSA values were rather stable during 3000 cycles of stress-tests versus 500 cycles for Pt deposited by polyol method on the same gas diffusion layers.

Kinetics of iron production via hydrogen-reduction of FeS-CaO mixture during both microwave heating and conventional heating was investigated at 750, 570, and 460 °C to clarify the effect of heating method on dominant rate-controlling mechanism. Results of conventional heating revealed that the rate controlling step during treatment in the first 500 s at 750 °C, 800 s at 570 °C, and 1000 s at 460 °C is interfacial chemical reaction; then it is changed to gas diffusion in micro pores of reduced Fe owing to the formation of Fe shell on the surface of FeS particles. In microwave treatment, the interfacial chemical reaction is rapidly progressed and gas diffusion is the dominant rate-controlling mechanism with an activation energy of 22.3 kJ.mol−1. This study demonstrated that the microwave irradiation enhances the rate of chemical reaction during iron production from FeS-CaO mixture.

Beryllium is a rare metal with many excellent properties, which make it increasingly meaningful for manufacturing precise instruments especially in the aerospace industry. Most of the small size beryllium parts consist of microgrooves that play an important role during use. In this paper, we adopted electrochemical machining (ECM) technology to process sub-millimeter microgrooves successfully on beryllium. The influences of both the electrolyte and feed rate were analyzed in detail. As a result, sodium chloride (NaCl) electrolyte always causes strong pitting corrosion, while the ECMed surface is smoother with a low concentration of sodium nitrate (NaNO3). The cross-section of the microgroove is semi-elliptical. The depth decreases, and the width remains unchanged as the feed rate increases. Flow marks appear at the bottom as a result of the gas diffusion and cathode chattering. Electrolyte of 10% (mass fraction) NaNO3 and a feed rate of 10 mm/min were considered as the proper configuration to achieve a 350 μm × 56 μm microgroove on beryllium with a Ф320 μm stainless steel cathode. Finally, a structure with uniform microgroove width has been fabricated.

A series of nanosized CeO2–Fe2O3 mixed-oxide nanocomposites with different Ce4+/Fe3+ molar ratios were successfully prepared by a co-precipitation technique. The surface area increased with Fe2O3 content increasing up to 60 wt% in the composite. However, with further increase in Fe2O3 content, the surface area began to decrease. The reduction processes of the CeO2–Fe2O3 nanocomposites were studied in a hydrogen atmosphere at 300–600 °C. The reduction rates increased by increasing both the temperature and Fe2O3 content in the nanocomposites. The microstructure of the reduced composites at 500 °C illustrated the presence of a considerable number of macro- and micro-pores. The activation energy values were calculated which were in the range of 3.56–5.37 kJ·mol−1 at the initial stages (up to 35% reduction) and 5.21–10.2 kJ·mol−1 at the final stages (up to 80% reduction) of reduction. The rate-controlling mechanisms in both the initial and final reduction stages were determined, and the initial reaction stage was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms for all the composites except for pure CeO2, which was controlled by a chemical reaction mechanism. The final reaction stage was controlled by a gaseous diffusion mechanism for some composites, while for the others it was controlled by combined gaseous diffusion and interfacial chemical reaction mechanisms. The hydrogen sorption properties of the nanocomposites were studied by pressure composition isotherms using a volumetric method. Hydrogen storage in the nanocomposites increased by increasing the temperature because of the formation of oxygen vacancies which enhance atomic H adsorption and function as strong adsorption sites forming more metal hydride covalent bonds.

Thin film encapsulation (TFE) using a multilayer film composed of SiOx and SiNxOyCz layers deposited by plasma-enhanced atomic layer deposition is demonstrated. To investigate the mechanism of suppressed moisture penetration for the multilayer film, chemical analyses were performed using Fourier transform infrared and Auger electron spectroscopy, and the encapsulation ability was evaluated using the water vapor transmission rate (WVTR). The encapsulation ability of the multilayer film is affected by the nitrogen content in the SiNxOyCz layer and the number of interfaces in the multilayer film. Consequently, TFE using a multilayer film of 20-nm-SiNxOyCz/20-nm-SiOx/20-nm-SiNxOyCz resulted in excellent encapsulation ability, with a WVTR of 7.63 × 10−4 g m−2 day−1.

Mesoporous palladium oxide (PdO)-functionalized tin dioxide (SnO2) composite nanotubes (SPCTs) were prepared via one-step synthesis by electrospinning technology using ethanol and N,N-dimethylformamide (DMF) as solvents. Compared with pure SnO2 nanotubes, there were abundant mesopores and multiheterojunctions in PdO-functionalized SnO2 nanotubes. The sample with the molar ratio of SnO2:PdO of 100:3 (3-SPCT) exhibited excellent response (∼20.30) as a sensor with fast gas response speed (∼1.33 s) to 100 ppm nitrogen dioxide (NO2) at room temperature (RT), and the detection limit reached to 10 ppb. The improved gas sensing performance of the 3-SPCT sensor was mainly attributed to the synergistic effect: the unique SnO2 tubular structure and well-dispersed mesopores provided the gas diffusion and adsorption channels, oxygen defects and chemisorbed oxygen were taken as the electron trap and charge transfer active sites, and a large number of heterojunctions acted as electron transport channels, thereby increasing the transfer rate.

Two complementary modeling approaches (1D and 2D) are developed to explain the temperature-dependent growth kinetics of PECVD graphene formation on cobalt substrate. The gas temperature and the species concentrations are predicted for different process conditions by involving gas-phase and surface reaction mechanisms which consist of 15 gas species, 43 gas reactions, 10 surface species and 34 surface reactions. The influence of the growth temperature, the microwave power and the methane flow rate, affecting the gas species mole fractions in the reactor and the surface coverage is evaluated. The numerical results clearly indicate that the hydrogen atoms play an important role in the graphene growth in microwave plasma systems. A global sensitivity analysis is then performed in order to understand the basic mechanisms that lead to the transport of reactants by gas diffusion from the main gas stream through the boundary layer providing insight regarding the growth of graphene on the cobalt substrate.

Wettability of titanium thin/tunable liquid/gas diffusion layers (TT-LGDLs) may affect the oxygen bubble dynamics and detachment process, and impact the performance (cell voltage) in proton exchange membrane electrolyzer cells (PEMECs). In this study, a silane monolayer is applied to tune the TT-LGDL wettability for the first time. The ultra-fast and micro-scale oxygen gas bubble dynamics and the two-phase flow in the channel are studied in situ for hydrophobically treated and hydrophilic titanium thin/tunable LGDLs (TT-LGDLs) with a high-speed and micro-scale visualization system (HMVS). The HMVS shows that the micro oxygen bubbles occur only along the CL/TT-LGDL interfaces at the rim of pores on TT-LGDLs. Bubbles more easily coalescence to form a large one in hydrophobic TT-LGDLs. Pore-scale analysis on the single bubble evolution process shows that the detachment diameter and frequency of oxygen bubbles in the hydrophobic TT-LGDLs are much larger than those in the hydrophilic TT-LGDLs. The PEMEC performance with the hydrophobic and hydrophilic TT-LGDLs are very close under 2.0 A/cm2, which means that the wettability has limited effect on TT-LGDLs mainly due to their thin features and unique structures with straight pores.