Feed Gas Composition Research Articles

On the Role of Anions in Solid Catalysts with Ionic Liquid Layer (SCILL) for the Selective Hydrogenation of Highly Concentrated Acetylene Streams.

Electric plasma assisted pyrolysis of methane represents a highly promising greener alternative to produce ethylene from biogas and renewable energies compared to conventional steam cracking of naphtha. The mediocre performance of typical Pd-Ag catalysts for the downstream purification of the substantially higher concentrated acetylene impurities (≥15 vol.-%) in those ethylene streams via selective hydrogenation is yet limiting economic interest. Following the concept of solid catalysts with ionic liquid layer (SCILL), we have modified an intrinsically non-selective palladium catalyst with imidazolium based ionic liquids varying among 10 different anions and investigated them in this reaction. The best performing [C4C1IM][MeSO4]-SCILL reaches an outstanding average ethylene selectivity over 20 h on-stream of 82 % at full acetylene conversion without any sign of deactivation, clearly outperforming conventional Pd-Ag catalysts. By varying parameters like ionic liquid (IL) loading, temperature, feed gas composition, cations, and by using XPS for surface analysis we could gain a very comprehensive understanding of the underlying mechanisms that reduce the competing over-hydrogenation and oligomerisation side-reactions.

Clostridium autoethanogenum alters cofactor synthesis, redox metabolism, and lysine-acetylation in response to elevated H2:CO feedstock ratios for enhancing carbon capture efficiency

BackgroundClostridium autoethanogenum is an acetogenic bacterium that autotrophically converts carbon monoxide (CO) and carbon dioxide (CO2) gases into bioproducts and fuels via the Wood–Ljungdahl pathway (WLP). To facilitate overall carbon capture efficiency, the reaction stoichiometry requires supplementation of hydrogen at an increased ratio of H2:CO to maximize CO2 utilization; however, the molecular details and thus the ability to understand the mechanism of this supplementation are largely unknown.ResultsIn order to elucidate the microbial physiology and fermentation where at least 75% of the carbon in ethanol comes from CO2, we established controlled chemostats that facilitated a novel and high (11:1) H2:CO uptake ratio. We compared and contrasted proteomic and metabolomics profiles to replicate continuous stirred tank reactors (CSTRs) at the same growth rate from a lower (5:1) H2:CO condition where ~ 50% of the carbon in ethanol is derived from CO2. Our hypothesis was that major changes would be observed in the hydrogenases and/or redox-related proteins and the WLP to compensate for the elevated hydrogen feed gas. Our analyses did reveal protein abundance differences between the two conditions largely related to reduction–oxidation (redox) pathways and cofactor biosynthesis, but the changes were more minor than we would have expected. While the Wood–Ljungdahl pathway proteins remained consistent across the conditions, other post-translational regulatory processes, such as lysine-acetylation, were observed and appeared to be more important for fine-tuning this carbon metabolism pathway. Metabolomic analyses showed that the increase in H2:CO ratio drives the organism to higher carbon dioxide utilization resulting in lower carbon storages and accumulated fatty acid metabolite levels.ConclusionsThis research delves into the intricate dynamics of carbon fixation in C. autoethanogenum, examining the influence of highly elevated H2:CO ratios on metabolic processes and product outcomes. The study underscores the significance of optimizing gas feed composition for enhanced industrial efficiency, shedding light on potential mechanisms, such as post-translational modifications (PTMs), to fine-tune enzymatic activities and improve desired product yields.

Efficient separation of SO2/NO2 on in-situ synthesized NaA zeolite membrane

SO2 and NO2 mixture widely exists in the desorbed gas from industrial flue gas adsorption purification process, separating the mixture into pure gas provides the key step for success in recycling them into profitable chemicals. However, effective SO2/NO2 separation is challenged due to the similar properties of both gases. In this work, we report the synthesis of an industrially-favored NaA zeolite membrane and the utilization of this membrane for SO2/NO2 separation in order to address the above-mentioned challenge. Various characterizations illustrate that the in-situ synthesis endows the NaA zeolite membrane with well-intergrown crystals, high continuity, and crystal-comparable thickness. The separation measurements at different feed pressure, temperature, and gas composition demonstrate that the NaA zeolite membrane shows superior separation performance (SO2/NO2 separation factor of 40.0, SO2 permeance of 2.93 × 10−7 mol m−2 Pa−1 s−1 at 293 K and 0.2 MPa) with strong stability (more than 7 d) compared to the previous best-performing zeolite membrane. The strong competitiveness of SO2 over NO2 on the low-silica membrane is revealed through molecular simulation, showing that the great affinity of SO2 with highly-polar zeolite structure benefits the SO2 gas preferential adsorption and energetically barrier-free permeation through the eight-membered ring of NaA zeolite. This work not only showcases an efficient strategy for the SO2/NO2 separation, but also expands the gas separation application of zeolite membranes.

Reactive Species Risk Assessment Using Optimized HET-CAM Safety Evaluation of Feed Gas-Modified Gas Plasma Technology and Anticancer Drugs.

Clinical therapies, including dermatology and oncology, require safe application. In vitro experiments allow only limited conclusions about in vivo effects, while animal studies in, e.g., rodents have ethical constraints at a large scale. Chicken embryos lack pain reception until day 15 postfertilization, making the in ovo model a suitable alternative to in vivo safety assessment. In addition, the hen's egg test on chorioallantoic membrane assay allows irritation potential analysis for topical treatments, but standardized analysis has been limited so far. Medical gas plasma is a topical, routine, approved dermatology treatment. Recent work suggests the potential of this technology in oncology. Its main mode of action is the release of various reactive species simultaneously. Intriguingly, varying plasma feed gas compositions generates customized reactive species profiles previously shown to be optimized for specific applications, such as skin cancer treatment. To support clinical implications, we developed a novel chicken embryo CAM scoring and study scheme and employed the model to analyze 16 different plasma feed gas settings generated by the atmospheric pressure plasmajet kINPen, along with common anticancer drugs (e.g., cisplatin) and physiological mediators (e.g., VEGF). Extensive gas- and liquid-phase plasma reactive species profiling was done and was found to have a surprisingly low correlation with irritation potential parameters. Despite markedly different reactive species patterns, feed gas-modulated kINPen plasma was equally tolerated compared to standard argon plasma. CAM irritation with gas plasmas but not anticancer agents was reversed 48 h after treatment, underlining the only temporary tissue effects of medical gas plasma. Our results indicate a safe therapeutic application of reactive species.

High performance Ce0.8Nd0.2O2-δ-carbonate hollow fiber membrane for high-temperature CO2 separation

Ceramic-carbonate dual phase (CCDP) membrane consisting of oxygen ionic conductor and molten carbonate has potential applications in clean energy delivery as it enabling the direct CO2 separation or capture at the elevated temperatures. The performance of previous CCDP membranes is not ideal either with a low CO2 flux or with a poor operational stability. In the present work, we looked at the CeO2-based oxygen ionic conductor (neodymium doped cerium (NDC)) as the porous ceramic hollow fiber support to form NDC-carbonate hollow fiber membranes. The NDC hollow fiber was fabricated by the combined phase inversion and sintering techniques and the preparation conditions were optimized to better accommodate the carbonate phase and maintain the mechanical stability. The NDC hollow fibers possessed good bending strength, reaching 91.5 MPa upon sintering at 1500 °C. The effects of feed gas composition and sweep flow rates on the CO2 separation performance were carefully investigated. The resultant dual phase hollow fiber membranes exhibited appreciably high CO2 permeation fluxes at temperatures exceeding 800 °C, which was required to activate both conductions of oxygen and carbonate ions. The achieved maximum CO2 flux of the optimized NDC-carbonate hollow fiber membranes was up to 5.08 mL min−1 cm−2 with 50%CO2–50%N2 as the feed gas at 900 °C. At 700 °C, the membrane exhibited a relatively stable CO2 permeation behavior over 120 h and the spent membrane maintained a stable structure. The high flux and good operational stability of the developed membrane make a huge step towards practical applications.

Long-Chain Hydrocarbons from Nonthermal Plasma-Driven Biogas Upcycling.

The burgeoning necessity to discover new methodologies for the synthesis of long-chain hydrocarbons and oxygenates, independent of traditional reliance on high-temperature, high-pressure, and fossil fuel-based carbon, is increasingly urgent. In this context, we introduce a nonthermal plasma-based strategy for the initiation and propagation of long-chain carbon growth from biogas constituents (CO2 and CH4). Utilizing a plasma reactor operating at atmospheric room temperature, our approach facilitates hydrocarbon chain growth up to C40 in the solid state (including oxygenated products), predominantly when CH4 exceeds CO2 in the feedstock. This synthesis is driven by the hydrogenation of CO2 and/or amalgamation of CHx radicals. Global plasma chemistry modeling underscores the pivotal role of electron temperature and CHx radical genesis, contingent upon varying CO2/CH4 ratios in the plasma system. Concomitant with long-chain hydrocarbon production, the system also yields gaseous products, primarily syngas (H2 and CO), as well as liquid-phase alcohols and acids. Our finding demonstrates the feasibility of atmospheric room-temperature synthesis of long-chain hydrocarbons, with the potential for tuning the chain length based on the feed gas composition.

Internal dry reforming of methane in solid oxide fuel cells

In the context of global efforts to reduce greenhouse gas emissions and combat extreme global warming, the direct dry reforming of methane reaction in solid oxide fuel cells presents a promising avenue for clean energy production. This study delves into the influence of temperature, gas composition, and current density on the kinetics of dry methane reforming in solid oxide fuel cells. Power Law and Langmuir-Hinshelwood kinetic models were proposed to highlight the impact of operating conditions on dry methane reforming reactions. Results revealed that the feed gas composition strongly affects methane conversion, with higher methane contents resulting in lower conversions. Increasing the CH4/CO2 ratio increases reaction rates, and the effect decreases at a ratio of 1.25. The changes in methane concentration on dry methane reforming reaction rate are more significant than those for carbon dioxide. However, increasing carbon dioxide concentration enhances methane conversion. The exothermic nature of CO2 adsorption suggests that the adsorption process is thermodynamically favourable in dry reforming, and the elevated temperatures generally improve reaction rates and methane conversion by removing carbon deposits and providing the energy needed to break down the chemical bonds in methane which facilitating its transformation. A higher current density significantly enhances the CO2 adsorption equilibrium constant and further increases methane conversion, highlighting the positive role of electrochemical reactions on dry methane reforming. This study aims to fill the knowledge gap regarding the influence of electrochemical reactions on dry methane reforming behaviours in solid oxide fuel cells, offering critical insights for advancing anode design, thus contributing to the development of solid oxide fuel cell technologies to address global warming and reduce greenhouse gas emissions.

Effect of operating conditions on the performance of riser reactor for oxidative coupling of methane

Oxidative coupling of methane (OCM) is characterized by high temperature and strong heat released. A riser reactor is designed for the OCM process to improve gas-solid contacting and heat transfer. This work illustrates the effect of hydrodynamic conditions and feed gas composition on the performance of an OCM riser reactor. The findings suggest that oxidative reactions predominantly occur within the acceleration zone and developed flow zone. Furthermore, at the low superficial gas velocity accompanied by a high solid circulating rate, the C2 yield initially increases in the acceleration zone, followed by a decrease in the developed flow zone and deceleration zone. The optimal operating conditions are a specific region corresponding to the solids holdup ranges from 0.015 to 0.02. Moreover, the C2 yield can be elevated using an appropriate feed mixture.

Modeling analysis of water-gas-shift reaction on catalyst-packed ceramic-carbonate dual-phase membrane reactor for hydrogen production

Water-gas shift (WGS) reaction for hydrogen production and CO2 removal/capture in a catalyst-packed CO2-permselective membrane reactor is studied experimentally and simulated with a computational model. The reactor utilizes a tubular dense ceramic-carbonate dual-phase membrane with a commercial high-temperature WGS catalyst. Equations governing CO2 permeation through the membrane and WGS reaction kinetics on the catalyst were obtained through independent CO2 permeation experiments and a fixed-bed reaction kinetic study. The simulation results using the validated model are presented to examine the effects of feed gas composition, steam/CO ratio, gas hourly space velocity, temperature, reactor pressure, sweep to feed molar flow rate ratio, and the membrane area to catalyst volume ratio on the performance of the membrane reactor for WGS with CO2 removal. Under optimized conditions, the catalyst-packed membrane reactor for WGS demonstrates significantly enhanced CO conversion and product H2 purity by effectively removing/capturing CO2 from the WGS reaction side.

Condition‐dependent NOx adsorption/desorption over Pd/BEA: A combined microreactor and in situ DRIFTS study

AbstractPd/BEA is chosen as a model passive NOx adsorber (PNA) to elucidate the effect of the feed gas composition on the NOx adsorption/desorption behavior. The Brønsted acid and the partially hydrolyzed framework Al (P‐HAl(OH)) sites in HBEA adsorb NO and NO2 under dry conditions. Moreover, the performance of HBEA is not affected by CO, while CO inhibits nitrate formation and promotes NO adsorption via the Pd(NO)(CO) complexes formation over Pd/BEA. H2O inhibits NO adsorption over the Brønsted acid and P‐HAl(OH) sites, and ionic Pd is the only active site for NOx adsorption under wet conditions. Furthermore, NO adsorption over hydrated Pd (Pd2+(OH)(NO)(H2O)3) is weaker than NO adsorption over bare ionic Pd (Z2[Pd2+(NO)], Z[Pd2+(OH)(NO)]). Dehydration of Pd2+(OH)(NO)(H2O)3 forms more stable Z[Pd2+(OH)(NO)] during desorption. The NO adsorption capacity of Pd/BEA improves in the presence of CO under both dry and wet conditions by forming a stable carbonyl–nitrosyl complex.

On the formation of ammonia from the thermal decomposition of hydroxylammonium nitrate vapor

The ionic liquid hydroxylammonium nitrate (HAN) is a promising propellant for various types of spacecraft propulsion systems. With respect to combustion and plasma-based electric propulsion, the thermal decomposition of HAN into gas phase species provides a convenient feed gas supply. While the decomposition of HAN in the liquid phase has been extensively studied, little is known about the decomposition chemistry of HAN vapor interacting with heated surfaces. The ability to decompose HAN vapor on a reactive surface could provide a means to control the feed gas composition and enhance the performance of spacecraft propulsion systems.In this initial qualitative study, HAN was vaporized and thermally decomposed using porous 316-stainless-steel and quartz disks under vacuum conditions. Decomposition products with low vapor pressures would condense on an in-line quartz tube which was subsequently collected and analyzed with Raman spectroscopy, NMR spectroscopy, and FT-IR spectroscopy. At temperatures above 440 K the 316-stainless-steel system produced significant quantities of ammonia which reacted with vaporized nitric acid to form ammonium nitrate. Temperatures below 440 K yielded partial HAN decomposition which resulted in a binary mixture of HAN and ammonium nitrate. The degree to which HAN was consumed was determined by analysis of the 1008 cm−1N-OH asymmetric Raman band of HAN and the 1049 cm−1 symmetric stretching Raman band of the nitrate ion, NO3−. The quartz system yielded significantly different results with no ammonium nitrate detected at temperatures above 440 K. Reformed HAN was the primary product detected at lower temperatures. The difference in reported measurements and visual observations highlights the distinct differences in HAN vapor decomposition chemistry from the two materials examined.

High-efficiency recovery of methane from coal bed gas via hydrate formation in emulsions

Although the hydrate-based coal bed gas (CBG) separations have been investigated, the obtained CH4 recovery ratios were not quite satisfactory. To further improve CH4 extraction, this study developed a high-efficiency CBG recovery method via hydrate formation in emulsions facilitated by an excellent anti-agglomerant. Thermodynamic promoters were introduced to lower operating pressure and the hydrate equilibrium conditions were determined. Then the effect of water-cut (40–100 vol%), initial pressure, experimental temperature, stirring rate and feed gas composition was investigated. The CH4 concentration in equilibrium gas first decreased then increased as the water-cut increased. Specifically, it decreased from 30.16 mol% to 8.23 mol% in the 60 vol% water-cut emulsions and CH4 recovery reached 88.02 % at 274.15 K and an initial pressure of 3.0 MPa, marking the highest CH4 recovery achieved in CBG separation thus far. The CH4 recovery was increased at low temperature while decreased at high pressure conditions. After a second-stage separation, the CH4 concentration in equilibrium gas decreased to 1.64 mol% from 30.16 mol%, signifying a remarkable 94.56 % recovery of CH4 from feed gas. The CH4 contents after a three-stage enrichment exceeded 87 mol%. This study furnishes valuable insights for CH4 recovery from CBG utilizing hydrate-based separation technology.

ON THE EFFECT OF OXYGEN ON PLASMA CHEMICAL KINETICS IN CF4 + O2 AND C4F8 + O2 GAS MIXTURES

In this work, we performed the comparative study of electro-physical plasma parameters, densities of active species and fluorine atom kinetics in CF4 + O2 and C4F8 + O2 gas mixtures with variable initial compositions at constant gas pressure and input power. The combination of plasma diagnostics by Langmuir probes and plasma modeling confirmed known features of plasma properties in individual fluorocarbon gases as well as allowed one to figure out key chemical processes determining plasma parameters in the presence of oxygen. It was shown that an increase in O2 content with a proportional decrease in the fraction of any fluorocarbon component a) causes relatively weak changes in electrons- and ions-related plasma parameters; b) results in more drastic (compared with the dilution effect) decrease in densities of fluorocarbon radicals due to their oxidation into CFxO, FO and COx compounds; and c) sufficiently influences both formation and decay kinetics of fluorine atoms. The non-monotonic (with a maximum at ~ 40-50% O2) change in the F atom density in the CF4 + O2 plasma repeats behavior of their formation rate after the contribution of processes involving CFxO и FO species. The monotonic increase (with a constancy region up to ~ 40-50% O2) in the F atom density in the C4F8 + O2 plasma contradicts with the change in their formation rate, but results from decreasing decay frequency in gas-phase atom-molecular processes. The predictive analysis of heterogeneous process kinetics was carried out using model-yielded data on fluxes of plasma active species. It was found that a) the addition of oxygen always lowers the plasma polymerizing ability; and b) the C4F8 + O2 plasma keeps the higher polymerizing ability at any feed gas composition.

Local electrochemical and thermal investigation of a segmented reversible solid oxide fuel cell and electrolyzer

A novel setup has been designed and mounted to investigate the local electrochemical and thermal behavior of a cell from a 4-cell short stack under reversible operation solid oxide fuel cell/solid oxide electrolyzer (SOFC/SOE). It consists in the partition of the cell's oxygen electrode into 20 segments, where each segment is controlled by a specific electronic load. This allows to control the segments independently in galvanostatic or potentiostatic mode. The configuration also enables local electrochemical impedance spectroscopy (EIS) measurements of each segment. 20 thermocouples were added to measure the local temperature of the segments in order to gain a deeper insight into the cell thermal distribution. This helps correlating the local thermal and electrochemical responses to the operating parameters. This specific setup allowed mapping the cell's local behavior based on a multidimensional operating conditions matrix, including current density, temperature, feed gas composition, sweep gas flow and polarization. Moreover, a durability test of more than 1,000 h helped investigating the local long-term degradation in a reversible (day SOE, night SOFC) configuration. These results are of significant importance towards optimal operation of a reversible SOC with enhanced durability.

Molecular dynamics study of carbon dioxide and nitrogen selectivity through poly[bis((methoxyethoxy)ethoxy)phosphazene] (MEEP) membrane

A molecular dynamics simulation model was developed to comprehensively understand carbon dioxide over nitrogen (CO2/N2) selectivity through polyphosphazene-based membrane comprising of poly[bis((methoxyethoxy)ethoxy)phosphazene] (MEEP) selective layer at the molecular level. The effects of temperature, pressure, and initial feed gas composition on the CO2 transport on a polymer membrane were studied. The computed free energy and density profile of the permeating gas mixture exhibited that CO2 molecules express higher interactions with the membrane than N2 molecules, resulting in higher CO2/N2 selectivity. Statistical analysis of gas molecules (CO2, water (H2O), and N2) transportation suggested that hydro- and CO2-philic functional groups in the membrane significantly impact CO2 permeability and CO2/N2 selectivity. This study suggested that Lewis acid–base and hydrogen bonding combinations contribute to CO2 permeation and CO2/N2 selectivity. An equal CO2/N2 selectivity was observed with and without water vapor in the feed gas suggesting that water does not hinder CO2 transport through the membrane.

Crucial Role of Self‐Exsolved Heterostructured Cermet Nanoparticles in Highly Active Spinel Electrodes for CO2/H2O Co‐Electrolysis

AbstractThe versatility of the spinel (AB2O4) oxides means they are of great interest for a variety of catalysis and energy conversion applications, involving gas reactions and reforming. CuFe2O4 spinel is identified as a highly efficient fuel electrode for CO2/H2O co‐electrolysis due to its promising electrocatalytic activity. To identify the actual active sites, the electrochemical characteristics, composition, chemical state, and microstructure are systematically investigated while optimizing the electrolysis performance by varying the feed gas composition. Markedly enhanced electrolysis current density is achieved under a CO2‐enriched composition of 50%CO2/10%H2O‐Ar. This promising performance is attributed to the in situ exsolution of heterostructural “Cu/Fe3O4” nanoparticles on the parent CuFe2O4 surface during co‐electrolysis. Interestingly, a strong correlation of the electrolysis performance with the amount of the formed heterostructural cermet is observed. The exsolved cermet heterostructure plays a crucial role in CO2/H2O electroreduction, as also confirmed by density‐functional‐theory studies. The self‐exsolved Cu/Fe3O4 nanoparticles present exceptional strength due to a strong interaction between the formed metallic Cu and Fe3O4, enabling the electrode to remain active and stable under such high electrical polarization. The excellent durability and stability of the self‐exsolved heterostructural nanoparticles are clearly confirmed by long‐term operation at high‐working voltage with an outstanding Faradaic efficiency (nearly 100%).

Adaptive Catalysts for the Selective Hydrogenation of Bicyclic Heteroaromatics using Ruthenium Nanoparticles on a CO2 -Responsive Support.

Ruthenium nanoparticles (NPs) immobilized on an amine-functionalized polymer-grafted silica support act as adaptive catalysts for the hydrogenation of bicyclic heteroaromatics. Whereas full hydrogenation of benzofuran and quinoline derivatives is achieved under pure H2 , introducing CO2 into the H2 gas phase leads to an effective shutdown of the arene hydrogenation while preserving the activity for the hydrogenation of the heteroaromatic part. The selectivity switch originates from the generation of ammonium formate species on the surface of the materials by catalytic hydrogenation of CO2 . The CO2 hydrogenation is fully reversible, resulting in a robust and rapid switch between the two states of the catalyst adapting its performance in response to the feed gas composition. A variety of benzofuran and quinoline derivatives were hydrogenated to fully or partially saturated products in high selectivity and yields simply by altering the composition of the feed gas from H2 to H2 /CO2 . The adaptive catalytic system thus provides controlled access to valuable products using a single catalyst rather than two specific and distinct catalysts with static reactivity.

Adaptive Catalysts for the Selective Hydrogenation of Bicyclic Heteroaromatics using Ruthenium Nanoparticles on a CO2‐Responsive Support

AbstractRuthenium nanoparticles (NPs) immobilized on an amine‐functionalized polymer‐grafted silica support act as adaptive catalysts for the hydrogenation of bicyclic heteroaromatics. Whereas full hydrogenation of benzofuran and quinoline derivatives is achieved under pure H2, introducing CO2 into the H2 gas phase leads to an effective shutdown of the arene hydrogenation while preserving the activity for the hydrogenation of the heteroaromatic part. The selectivity switch originates from the generation of ammonium formate species on the surface of the materials by catalytic hydrogenation of CO2. The CO2 hydrogenation is fully reversible, resulting in a robust and rapid switch between the two states of the catalyst adapting its performance in response to the feed gas composition. A variety of benzofuran and quinoline derivatives were hydrogenated to fully or partially saturated products in high selectivity and yields simply by altering the composition of the feed gas from H2 to H2/CO2. The adaptive catalytic system thus provides controlled access to valuable products using a single catalyst rather than two specific and distinct catalysts with static reactivity.

Xe Recovery from Nuclear Power Plants Off-Gas Streams: Molecular Simulations of Gas Permeation through DD3R Zeolite Membrane.

Recent experimental work has shown zeolite membrane-based separation as a promising potential technology for Kr/Xe gas mixtures due to its much lower energy requirements in comparison to cryogenic distillation, the conventional separation method for such mixtures. Such a separation is also economically rewarding because Xe is in high demand, as a valuable product for many applications/processes. In this work, we have used Molecular Dynamics (MD) simulations to study the effects of different conditions, i.e., temperature, pressure, and gas feed composition, on Kr/Xe separation performance via DD3R zeolite membranes. We provide a comprehensive study of the permeation of the different gas species, density profiles, and diffusion coefficients. Molecular simulations show that if the feed is changed from pure Kr/Xe to an equimolar mixture, the Kr/Xe separation factor increases, which agrees with experiments. In addition, when Ar is introduced as a sweep gas, the adsorption of both Kr and Xe increases, while the permeation of pure Kr increases. A similar behavior is observed with equimolar mixtures of Kr/Xe with Ar as the sweep gas. High-separation Kr/Xe selectivity is observed at 50 atm and 425 K but with low total permeation rates. Changing pressure and temperature are found to have profound effects on optimizing the separation selectivity and the permeation throughput.

Performance and Degradation of Electrolyte Supported SOECs with Advanced GDC Thin-film Layers in Long-term Stack Test

Solid oxide electrolyser (SOE) based on electrolyte-supported cell (ESC) architecture is proven to be highly efficient and reliable technology for green hydrogen production via high temperature electrolysis. Operating under industrial conditions, the performance, lifetime and robustness of the cells and stacks belong to the most important factors for an up-scaled penetration of the SOE technology into energy and chemistry sectors. A typical ESC consists of scandia- or yttria-stabilized zirconia electrolyte, Ni-cermet fuel electrode, lanthanum strontium cobalt ferrite (LSCF) oxygen electrode and either one or two Gd-doped ceria (GDC) layers with a thickness of 5-7 µm between electrolyte and electrodes. At the oxygen electrode side, the GDC layer prevents interdiffusion (mainly of Sr), whereas at the fuel electrode side, the GDC layer may improve the electrode adherence to electrolyte and reduce the interfacial resistance. State-of-the-art fabrication route of the GDC layers is screen-printing followed by partially sintering at high temperature between 1200 °C to 1300 °C. This fabrication process usually results in porous structure in the GDC layers and residual stresses which reduce the mechanical strength of the cells.Aiming to improve the mechanical strength of ESCs and the properties (e.g. porosity and electrical conductivity) of GDC layers, the conventional screen-printed GDC layers either only at the oxygen electrode or at both electrodes were replaced by 0.5 µm thick thin-film GDC layers fabricated by electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. These EB-PVD-fabricated thin-film GDC layers were electrochemically characterized in a so-called “rainbow” stack with 30 repeat units (RUs), including 4 RUs with EB-PVD GDC layers at the oxygen electrode and screen-printed GDC at fuel electrode, 3 RUs with EB-PVD GDC layers at both electrodes and 23 RUs with state-of-the-art screen-printed GDC layers at both electrodes. The stack was operated for over 5000 h in SOEC mode under a current density of -410 mA cm−2 and 75 % steam conversion, with a feed gas composition of 80 % steam + 10 % H2 + 10 % N2 on the fuel electrode and air on oxygen electrode.In this paper, the investigation focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers during the SOEC stack testing. The performance and degradation behavior of the stack and representative RUs were investigated and compared by means of current-voltage curves and electrochemical impedance spectroscopy (EIS). The initial performance and the degradation of the voltage and resistances of the stack and the RUs with EB-PVD GDC thin-film layers were determined and discussed in order to evaluate the effectiveness of the modifications in the scenario of long-term SOEC stack testing.The German Federal Ministry for Education and Research (BMBF) is acknowledged for the financial supports within the project H2GiGa-HTEL (grant no. 03HY124E).