Low H2 Partial Pressures Research Articles

Preparation of nano Cu-Mo2C interface supported on ordered mesoporous biochar of ultrahigh surface area for reverse water gas shift reaction

High conversion rate and selectivity are challenges for CO2 utilization through catalytic reverse water gas shift (RWGS) reaction. Herein, a novel mesoporous biochar (MB) supported Cu-Mo2C nano-interface was prepared by consecutive physical activation of coconut shells followed by carbothermal hydrogen reduction of bimetal. As compared with traditional carbon materials, this MB exhibited ultra-high specific surface area (2693 m2 g–1) and mesopore volume of mesopore (0.81 cm3 g–1) with a narrow distribution (2–5 nm), responsible for the high dispersion of binary Cu-Mo2C sites, CO2 adsorption and mass transfer in the reaction system. Moderate carbothermal reduction led to the sufficient reduction of Mo ion with carbon matrix of MB and dispersive growth of nano Cu-Mo2C binary sites (~ 6.1 nm) on the surface of MB. Cu+ species were formed from Cu0 via electron transfer and showed high dispersion with simultaneous boosted bimetal loading due to the strong interaction between nano Mo2C and Cu. These were advantageous to the intrinsic activity and stability of the Cu-Mo2C binary sites and their accessibility to the reactant molecules. Under the RWGS reaction conditions of 500 °C, atmospheric pressure, and 300,000 ml/g/h gas hour space velocity, the CO2 conversion rate over Cu-Mo2C/MB reached 27.74 × 10–5 molCO2/gcat/s at very low H2 partial pressure, which was more than twice that over traditional carbon supported Cu-Mo2C catalysts. In addition, this catalyst exhibited 99.08% CO selectivity and high stability for more than 50 h without a decrease in activity and selectivity. This study offers a new development strategy and a promising candidate for industrial RWGS.Graphical

Pt3Mn/SiO2 + ZSM-5 Bifunctional Catalyst for Ethane Dehydroaromatization

Ethane dehydroaromatization (EDA) is a potentially attractive process for converting ethane to valuable aromatics such as benzene, toluene, and xylene (BTX). In this study, a Pt3Mn/SiO2 + ZSM-5 bifunctional catalyst was used to investigate the effect of dehydrogenation and the Brønsted acid catalyst ratio, hydrogen partial pressure, and reaction temperature on the product distributions for EDA. Pt3Mn/SiO2 + ZSM-5 with a 1/1 weight ratio showed the highest ethane conversion rate and BTX formation rate. Ethylene is initially formed by dehydrogenation by the Pt3Mn catalyst, which undergoes secondary reactions on ZSM-5, forming C3+ reaction intermediates. The latter form final products of CH4 and BTX. At conversions from 15 to 30%, the BTX selectivities are 82–90%. For all bifunctional catalysts, the ethane conversion significantly exceeds the ethane–ethylene equilibrium conversion due to reaction to secondary products. Low H2 partial pressures did not significantly alter the product selectivity or conversion. However, higher H2 partial pressures resulted in increased methane and decreased BTX selectivity. The excess hydrogen saturated the olefin intermediates to form alkanes, which produced methane by monomolecular cracking on ZSM-5. With an increasing reaction temperature from 550 °C to 650 °C, the benzene selectivity increased, while the highest BTX selectivity was obtained at 600 to 650 °C.

Ionic conductivity and hydrogen crossover for IT-PEMFCs: Influence of pressure, temperature, relative humidity and reinforcement

Improved knowledge on Proton Exchange Membrane Fuel Cell (PEMFC) behaviour in the Intermediate Temperature (IT: 80–120 °C) is needed. Here, ionic conductivity and H2 permeability are analysed under H2/N2 using electrochemical impedance spectroscopy, linear sweep voltammetry for three catalyst-coated membranes (CCMs): Nafion HP (reinforced), Nafion 211 (non-reinforced) and a reinforced commercial membrane (RCM, membrane thickness 13 μm). Multiple relative humidity (RH) levels and pressure configurations are analysed at IT. Results show that ionic conductivity and H2 permeability increase with temperature and RH. However, lower crossover is measured above 100 °C and wet conditions due to low H2 partial pressure. The highest crossover is measured with an overpressure on the H2 side which, especially for RCM, suggests possible convection. The membrane reinforcement might reduce the permeability and it decreases the conductivity. Mass spectrometry confirmed that sprayed CCMs suffer from higher crossover than pristine membranes, although the membrane thickness is unchanged.

Light-driven ammonia synthesis under mild conditions using lithium hydride.

Photon-driven chemical processes are usually mediated by oxides, nitrides and sulfides whose photo-conversion efficiency is limited by charge carrier recombination. Here we show that lithium hydride undergoes photolysis upon ultraviolet illumination to yield long-lived photon-generated electrons residing in hydrogen vacancies, known as F centres. We demonstrate that photon-driven dehydrogenation and dark rehydrogenation over lithium hydride can be fulfilled reversibly at room temperature, which is about 600 K lower than the corresponding thermal process. As light-driven F centre generation could provide an alternative approach to charge carrier separation to favour chemical transformations that are kinetically or thermodynamically challenging, we show that light-activated lithium hydride cleaves the N≡N triple bond to form a N-H bond under mild conditions. Co-feeding a N2/H2 mixture with low H2 partial pressure leads to photocatalytic ammonia formation at near ambient conditions. This work provides insights into the development of advanced materials and processes for light harvesting and conversion.

Catalytic Metal‐Gated Nano‐Sheet Field Effect Transistor and Nano‐Sheet Tunnel Field Effect Transistor Based Hydrogen Gas Sensor‐ A Design Perspective

AbstractIn this work, for the first time, the catalytic metal gate (CMG) based nanosheet Field Effect Transistor (NSFET) and nanosheet Tunnel Field Effect Transistor (NSTFET) are proposed for nano‐scale device dimensions, and the different design aspects of catalytic metal gate (CMG)‐based transduction for Hydrogen (H2) sensing are extensively investigated using numerical device simulation. The influence of applied biasing conditions and structural parameter specifications on the sensing performance of CMG‐NSFET and CMG‐NSTFET are methodically analyzed from device electrostatics and carrier transport mechanisms. Furthermore, the relative maximum sensitivity variations with H2‐partial pressure, ambient temperature, and the presence of ambient Oxygen are comprehensively studied. The study reveals that compared to CMG‐NSFET, the CMG‐NSTFET demonstrates a high immunity against bias and doping variations, with a notably higher (> 50%) sensitivity within low H2 partial pressures (10−15 – 10−10 Torr). Next, the sensing performance of CMG‐NSTFET is systematically optimized through a band‐gap and gate‐stack engineering approach, leading to a 180% to 650% sensitivity improvement from lower (10−15 Torr) to higher (10−5 Torr) range of H2 partial pressure. Finally, the performance of optimized CMG‐NSFET and CMG‐NSTFET are extensively benchmarked against other reported nanostructured CMG‐FET and TFET‐based H2 gas sensors, exhibiting a notably higher sensitivity in the proposed sensors.

The influence of H2 partial pressure on biogenic palladium nanoparticle production assessed by single-cell ICP-mass spectrometry.

The production of biogenic palladium nanoparticles (bio-Pd NPs) is widely studied due to their high catalytic activity, which depends on the size of nanoparticles (NPs). Smaller NPs (here defined as <100 nm) are more efficient due to their higher surface/volume ratio. In this work, inductively coupled plasma-mass spectrometry (ICP-MS), flow cytometry (FCM) and transmission electron microscopy (TEM) were combined to obtain insight into the formation of these bio-Pd NPs. The precipitation of bio-Pd NPs was evaluated on a cell-per-cell basis using single-cell ICP-MS (SC-ICP-MS) combined with TEM images to assess how homogenously the particles were distributed over the cells. The results provided by SC-ICP-MS were consistent with those provided by "bulk" ICP-MS analysis and FCM. It was observed that heterogeneity in the distribution of palladium over an entire cell population is strongly dependent on the Pd2+ concentration, biomass and partial H2 pressure. The latter three parameters affected the particle size, ranging from 15.6 to 560 nm, and exerted a significant impact on the production of the bio-Pd NPs. The TEM combined with SC-ICP-MS revealed that the mass distribution for bacteria with high Pd content (144 fg Pd cell-1 ) indicated the presence of a large number of very small NPs (D50=15.6nm). These results were obtained at high cell density (1 × 105 ± 3 × 104 cells μl-1 ) and H2 partial pressure (180 ml H2 ). In contrast, very large particles (D50=560 nm) were observed at low cell density (3 × 104 ± 10 × 102 cells μl-1 ) and H2 partial pressure (10-100 ml H2 ). The influence of the H2 partial pressure on the nanoparticle size and the possibility of size-tuned nanoparticles are presented.

Single‐Atom Molybdenum‐N3 Sites for Selective Hydrogenation of CO2 to CO

AbstractThe design of efficient non‐noble metal catalysts for CO2 hydrogenation to fuels and chemicals is desired yet remains a challenge. Herein, we report that single Mo atoms with a MoN3 (pyrrolic) moiety enable remarkable CO2 adsorption and hydrogenation to CO, as predicted by density functional theory studies and evidenced by a high and stable conversion of CO2 reaching about 30.4 % with a CO selectivity of almost 100 % at 500 °C and very low H2 partial pressure. Atomically dispersed MoN3 is calculated to facilitate CO2 activation and reduces CO2 to CO* via the direct dissociation path. Furthermore, the highest transition state energy in CO formation is 0.82 eV, which is substantially lower than that of CH4 formation (2.16 eV) and accounts for the dominant yield of CO. The enhanced catalytic performances of Mo/NC originate from facile CO desorption with the help of dispersed Mo on nitrogen‐doped carbon (Mo/NC), and in the absence of Mo nanoparticles. The resulting catalyst preserves good stability without degradation of CO2 conversion rate even after 68 hours of continuous reaction. This finding provides a promising route for the construction of highly active, selective, and robust single‐atom non‐precious metal catalysts for reverse water–gas shift reaction.

Single-Atom Molybdenum-N3 Sites for Selective Hydrogenation of CO2 to CO.

The design of efficient non-noble metal catalysts for CO2 hydrogenation to fuels and chemicals is desired yet remains a challenge. Herein, we report that single Mo atoms with a MoN3 (pyrrolic) moiety enable remarkable CO2 adsorption and hydrogenation to CO, as predicted by density functional theory studies and evidenced by a high and stable conversion of CO2 reaching about 30.4 % with a CO selectivity of almost 100 % at 500 °C and very low H2 partial pressure. Atomically dispersed MoN3 is calculated to facilitate CO2 activation and reduces CO2 to CO* via the direct dissociation path. Furthermore, the highest transition state energy in CO formation is 0.82 eV, which is substantially lower than that of CH4 formation (2.16 eV) and accounts for the dominant yield of CO. The enhanced catalytic performances of Mo/NC originate from facile CO desorption with the help of dispersed Mo on nitrogen-doped carbon (Mo/NC), and in the absence of Mo nanoparticles. The resulting catalyst preserves good stability without degradation of CO2 conversion rate even after 68 hours of continuous reaction. This finding provides a promising route for the construction of highly active, selective, and robust single-atom non-precious metal catalysts for reverse water-gas shift reaction.

Hydride vapor phase epitaxial growth of AlGaN

The growth of AlGaN layers on GaN and AlN templates by hydride vapor phase epitaxy (HVPE) was experimentally investigated in detail. Linear control of the Al solid fraction with respect to that of the gas phase was established under conditions with a relatively low H2 partial pressure. Severe surface deterioration caused by microcrystal inclusion and hillock formation were effectively removed through the use of HVPE conditions that enhanced an etching effect and suppressed parasitic reactions. As a result, AlGaN layers with good surface and crystal qualities were successfully prepared within almost the entire Al-fraction range by the HVPE method.

Genome-centric metagenomics analysis revealed the metabolic function of abundant microbial communities in thermal hydrolysis-assisted thermophilic anaerobic digesters under propionate stress

The ecological roles of microbial communities and how they interact with each other in thermal hydrolysis process (THP) assisted thermophilic anaerobic digestion (THP-AD) reactors remain largely unknown, especially under propionate stress. Two thermophilic THP-AD reactors had methane yield of 240–248 mL/g VSadded, but accumulated approximately 2000 mg/L propionate. Genome-centric metagenomics analysis showed that 68 metagenome-assembled genomes (MAGs) were recovered, 32 MAGs of which were substantially enriched. Firmicutes spp. dominated the enriched microbial community, including hydrolytic/fermentative bacteria and syntrophs. Methanogenic activities were mainly mediated by Methanosarcina sp. and Methanothermobacter spp. In addition to hydrogenotrophic methanogens, Thermodesulfovibrio sp. could also be a vital H2 scavenger, contributing to maintaining low H2 partial pressure in the bioreactors. The remarkable accumulation of propionate could be likely attributed to the weak syntrophic propionate-oxidizing activity or its absence. These findings advanced our knowledge about the mutualistic symbiosis of carbon metabolism in thermophilic THP-AD reactors.

Thermodynamic approach to foresee experimental CO2 reduction to organic compounds

Anaerobic gas fermentation is a promising approach to transform carbon dioxide (CO2) into chemical building blocks. However, the main operational conditions to enhance the process and its selectivity are still unknown. The main objective of this study was to trigger chain elongation from a joint perspective of thermodynamic and experimental assessment. Thermodynamics revealed that acetic acid formation was the most spontaneous reaction, followed by n-caproic and n-butyric acids, while the doorway for alcohols production was bounded by the selected conditions. Best parameters combinations were applied in three 0.12 L fermenters. Experimentally, n-caproic acid formation was boosted at pH 7, 37 °C, Acetate:Ethanol mass ratio of 1:3 and low H2 partial pressure. Though these conditions did not match with those required to produce their main substrates, the unification of both perspectives yielded the highest n-caproic acid concentration (>11 g L−1) so far from simple substrates, accounting for 77 % of the total products.

Directional etching for high aspect ratio nano-trenches on hexagonal boron nitride by catalytic metal particles

Stimulated by the attractive performance of multi-dimensional heterostructures involving hexagonal boron nitride (hBN), intense attentions have been paid to creation of sharp boundary/interface, which could bring hBN nano-structures additional appealing physical properties. However, the lack of controllable synthesis limits further experimental investigation on hBN nano-structures. Here, the directional etching of transitional metal nano-particles (NPs) on the surface of hBN to produce nano-trenches with sharp edges was systematic investigated. It is found that, only Pt and Ir NPs can produce armchair-oriented nano-trenches at low H2 partial pressure, while other transitional metals lead to zigzag oriented nano-trenches. The density and width of the nano-trenches always increase with etching temperature and the pre-treated solution concentration while the trench orientation depends on both H2 partial pressure and etching temperature. The aspect ratio of nano-trenches may reach several thousand under optimized conditions. The method exhibited here shines a light on edge-selective patterning of 2D crystals.

Preparation and hydrogen storage properties of Pd1-x Ag x (x=0–0.29) alloy nanoparticles by a solution reduction method

This paper provides Pd-Ag solid solution nanoparticles (NPs) which were prepared by the simple solution method and their characteristic hydrogen storage properties. The solid solution between Pd and Ag was achieved on NPs with crystal sizes of 7–9 nm. The isotherms of these alloy NPs showed no typical plateau region and the PCT curve changed in increasing tendency in pressure as H/M increases even in a plateau region. More important findings included the increase of H/M at the very low H2 pressure conditions of 0.001 MPa. H/M was approximately 0.2 in the x range of 0.05–0.09 in Pd1-x Ag x NPs. Thus, the combination of the nanoparticular state and Ag doping in Pd brought better hydrogen storage and/or H2-related catalytic material which could be used at low H2 partial pressure condition.

Cobalt and Titanium substituted SrFeO3 based perovskite as efficient symmetrical electrode for solid oxide fuel cell

One of the key tasks in solid oxide fuel cell research is to develop cost-competitive electrodes that work efficiently in wide range of air and fuel utilizations. Herein, we promote our study to a series of Cobalt and Titanium substituted La0.4Sr0.6Fe0.7Ti0.3-xCoxO3-δ (LSFTC, x = 0, 0.05, 0.1, 0.2) perovskite oxides. It is shown that Cobalt doping effectively improves the electrical conductivity and oxygen electrochemical reduction activity, yielding decreased cathode polarization resistance and lower dependence of pO2 change. For example, σ600°C = 81 S/cm and Rp,C750°C = 0.1 Ω cm2 for LSFTC-5 are obtained in pO2=0.21atm. In anode conditions of wet H2, the LSFTC cubic perovskites are partially reduced to hybrid structure of ABO3-A2BO4-metal with Cobalt doping amount less than 10% and are fully decomposed to A2BO4-metal with 20% doping. The higher Cobalt substitution generates more nano particles exsolution, which promotes anode processes at low temperatures. However, the generated AO-rich compositions are shown detrimental to anode performance in both conducting property and anode catalytic activity under low H2 partial pressures. In current study, the electrodes are evaluated under practical working conditions with broad pO2 and pH2, which provides guidelines for industrial-applicable SrFeO3 based symmetrical electrode development.

Extracellular Electron Uptake by Acetogenic Bacteria: Does H2 Consumption Favor the H2 Evolution Reaction on a Cathode or Metallic Iron?

Some acetogenic bacteria are capable of using solid electron donors, such as a cathode or metallic iron [Fe(0)]. Acetogens using a cathode as electron donor are of interest for novel applications such as microbial electrosynthesis, while microorganisms using Fe(0) as electron donor cause detrimental microbial induced corrosion. The capacity to use solid electron donors strongly differs between acetogenic strains, which likely relates to their extracellular electron transfer (EET) mechanism. Different EET mechanisms have been proposed for acetogenic bacteria, including a direct mechanism and a H2 dependent indirect mechanism combined with extracellular hydrogenases catalyzing the H2 evolution reaction on the cathode or Fe(0) surface. Interestingly, low H2 partial pressures often prevail during acetogenesis with solid electron donors. Hence, an additional mechanism is here proposed: the maintenance of low H2 partial pressures by microbial H2 consumption, which thermodynamically favors the H2 evolution reaction on the cathode or Fe(0) surface. This work elaborates how the H2 partial pressure affects the H2 evolution onset potential and the H2 evolution rate on a cathode, as well as the free energy change of the anoxic corrosion reaction. In addition, the H2 consumption characteristics, i.e., H2 threshold (thermodynamic limit for H2 consumption) and H2 consumption kinetic parameters, of acetogenic bacteria are reviewed and evidence is discussed for strongly different H2 consumption characteristics. Different acetogenic strains are thus expected to maintain different H2 partial pressures on a cathode or Fe(0) surface, while those that maintain lower H2 partial pressures (lower H2 threshold, higher H2 affinity) more strongly increase the H2 evolution reaction. Consequently, I hypothesize that the different capacities of acetogenic bacteria to use solid electron donors are related to differences in their H2 consumption characteristics. The focus of this work is on acetogenic bacteria, but similar considerations are likely also relevant for other hydrogenotrophic microorganisms.

Phloroglucinol Degradation in the Rumen Promotes the Capture of Excess Hydrogen Generated from Methanogenesis Inhibition.

Strategies to manage metabolic hydrogen ([H]) in the rumen should be considered when reducing ruminant methane (CH4) emissions. However, little is known about the use of dietary treatments to stimulate rumen microorganisms capable of capturing the [H] available when CH4 is inhibited in vivo. The effects of the phenolic compound phloroglucinol on CH4 production, [H] flows and subsequent responses in rumen fermentation and microbial community composition when methanogenesis is inhibited were investigated in cattle. Eight rumen fistulated Brahman steers were randomly allocated in two groups receiving chloroform as an antimethanogenic compound for 21 days. Following that period one group received chloroform + phloroglucinol for another 16 days, whilst the other group received only chloroform during the same period. The chloroform treatment resulted in a decrease in CH4 production and an increase in H2 expelled with a shift in rumen fermentation toward higher levels of propionate and formate and lower levels of acetate at day 21 of treatment. Bacterial operational taxonomic units (OTUs) assigned to Prevotella were promoted whilst Archaea and Synergistetes OTUs were decreased with the chloroform treatment as expected. The shift toward formate coincided with increases in Ruminococcus flavefaciens, Butyrivibrio fibrisolvens, and Methanobrevibacter ruminantium species. The addition of chloroform + phloroglucinol in the rumen resulted in a decrease of H2 expelled (g) per kg of DMI and moles of H2 expelled per mol of CH4 decreased compared with the chloroform only treated animals. A shift toward acetate and a decrease in formate were observed for the chloroform + phloroglucinol-treated animals at day 37. These changes in the rumen fermentation profile were accompanied by a relative increase of OTUs assigned to Coprococcus spp., which could suggest this genus is a significant contributor to the metabolism of this phenolic compound in the rumen. This study demonstrates for the first time in vivo that under methanogenesis inhibition, H2 gas accumulation can be decreased by redirecting [H] toward alternative sinks through the nutritional stimulation of specific microbial groups. This results in the generation of metabolites of value for the host while also helping to maintain a low H2 partial pressure in the methane-inhibited rumen.

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

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

Experimental Investigation of ZrCo Getter Beds as Candidate Process for the Tritium Extraction Systems of the European Test Blanket Modules

ZrCo is a well-known tritium storage material and has been studied intensively in the literature. The most interesting properties with regards to the thermodynamics of the ZrCo-H system are the very low H2 partial pressure in equilibrium with ZrCoH3 at room temperature and the ease to reach sufficiently high temperature to completely release the stored H2. These properties motivate also to use ZrCo not as a simple storage, but rather as a concentrator of hydrogen isotopologues from inert gases like He. With such function, ZrCo getter beds are the reference solution adopted in the conceptual design of the tritium extraction system of the European Test Blanket Modules (TBM) to replace the cryogenic molecular sieve bed previously proposed. An experimental campaign was carried out on ZrCo in order to consolidate this choice. The results confirmed that ZrCo performs well as getter material but only substantially below the maximum loading capacity. They revealed that the dynamic thermo-mechanical response of the material, controlled by temperature and H2 concentration, is the main limiting factor for the component performance.

The role of hydrogen in oxygen-assisted chemical vapor deposition growth of millimeter-sized graphene single crystals.

Involving oxygen in the traditional chemical vapor deposition (CVD) process has proven a promising approach to achieve large-scale graphene single crystals (GSCs), but its many relevant fundamental aspects are still not fully understood. Here we report a systematic study on the role of hydrogen in the growth of millimeter-sized GSCs using enclosure-like Cu structures via the oxygen-assisted CVD process. Results show that GSCs have different first layer growth behaviors on the inside and outside surfaces of a Cu enclosure when the H2 environment is varied, and these behaviors will consequently and strongly influence the adlayer formation in these GSCs, leading to two entirely different growth modes. Low H2 partial pressure (PH2) tends to result in fast growth of dendritically shaped GSCs with multiple small adlayers, but high PH2 can modify the GSC shape into hexagons with single large adlayer nuclei. This difference of adlayers is attributed to the different C diffusion paths determined by the shapes of their host GSCs. On the basis of these observations, we developed an isothermal two-step method to obtain GSCs with significantly improved growth rate and sample quality, in which low PH2 is first set to accelerate the growth rate followed by high PH2 to restrict the adlayer nuclei. Our results prove that the growth of GSCs can reach a reasonable optimization between their growth rates and sample quality by simply adjusting the CVD H2 environment, which we believe will lead to more improvements in graphene synthesis and fundamental insight into the related growth mechanisms.

High organic loading treatment for industrial molasses wastewater and microbial community shifts corresponding to system development

Molasses wastewater contains high levels of organic compounds, cations, and anions, causing operational problems for anaerobic biological treatment. To establish a high organic loading treatment system for industrial molasses wastewater, this study designed a combined system comprising an acidification tank, a thermophilic multi-stage (MS)-upflow anaerobic sludge blanket (UASB) reactor, mesophilic UASB reactor, and down-flow hanging sponge reactor. The average total chemical oxygen demand (COD) and biochemical oxygen demand removal rates were 85%±3% and 95%±2%, respectively, at an organic loading rate of 42kgCODcrm−3d−1 in the MS-UASB reactor. By installation of the acidification tank, the MS-UASB reactor achieved low H2-partial pressure. The abundance of syntrophs such as fatty acid-degrading bacteria increased in the MS-UASB and 2nd-UASB reactors. Thus, the acidification tank contributed to maintaining a favorable environment for syntrophic associations. This study provides new information regarding microbial community composition in a molasses wastewater treatment system.