Development of sample holder for in situ neutron measurement of hydrogen absorbing alloy

We developed a sample holder for in situ measurement of hydrogen absorbing alloy. In order to prevent the hydrogen absorption by vanadium, copper is coated with 2 μm thickness on inner surface of the vanadium holder. The effect of copper coating and the performance of the holder were evaluated by neutron diffraction and PDF profiles. The lattice parameters a and c of La₂Ni₇ with Ce₂Ni₇-type structure were refined as 0.505921(4) and 2.468608(4) nm by Rietveld analysis. The Cu-Cu correlation peak around r = 0.255 nm was not observed in the PDF profile. Thus the holder is useful for in situ measurement of hydrogen absorbing alloy. The diffraction and PDF profiles of La₂Ni₇D_x (0 < x < 10.5) were collected using a deuterium pressure of 3.7 MPa, and the changes of crystal and local structures were clearly observed.     

In situ produced hydrogen (hydrogen on demand)

Pollution created by the increased number of people and by industrial and domestic activities put pressure in the planet's climate that can result in a catastrophe which may end the humans' life on the planet 6 and 7. Hydrogen is an endless source of energy, clean and efficient, which exist in the Universe in a high proportion, over 88% 1, 2, 3, 4 and 5.     

Thermal desorption of hydrogen from magnesium hydride (MgH2): An in situ microscopy study by environmental SEM and TEM

As-received magnesium hydride (MgH₂), and MgH₂ doped with lithium borohydride (LiBH₄) and titanium (III) chloride (TiCl₃) catalyst were heated - in situ - in an environmental scanning electron microscope (ESEM) and a transmission electron microscope (TEM). Morphological and structural changes during heating and hydrogen desorption were recorded in real time. The studies show that native MgH₂ undergoes dramatic and destructive structural changes upon heating, whereas the doped/catalyzed MgH₂ mixture showed a benign outgassing with little structural change. Videos of the morphological changes during heating can be viewed online at the McGrady group website: http://www.unb.ca/fredericton/science/chem/smcgrady/group/shanebeattie/InsituESEMandTEM-MgH2.html.     

Kinetics measurements and in situ Raman spectroscopy of formation of hydrogen–tetrabutylammonium bromide semi-hydrates

The kinetics of formation of H₂–TBAB semi-clathrate hydrates was studied in this work in order to elucidate their potential for H₂ storage. The influence of pressure (5–16 MPa), TBAB concentration (2.6 mol% and 3.7 mol%) and formation method (T-cycle method and T-constant method) on the hydrate nucleation, hydrate growth and H₂ storage capacity was determined. The results showed that kinetics is favored at higher pressures and solute concentrations. Additionally, the hydrate phase formation and dissociation was study for a solution of 2.6 mol% of TBAB in situ by using the Raman spectroscopy technique. The inclusion of H₂ in the semi-hydrate phase was confirmed. The results showed the importance of H₂ mass transfer on the storage capacity of the H₂–TBAB semi-hydrates.     

Synthesis and characterization of platinum nanoparticles on in situ grown carbon nanotubes based carbon paper for proton exchange membrane fuel cell cathode

Multi-walled carbon nanotubes (MWCNTs) based micro-porous layer on the carbon paper substrates was prepared by in situ growth in a chemical vapor deposition setup. Platinum nanoparticles were deposited on in situ grown MWCNTs/carbon paper by a wet chemistry route at <100 °C. The in situ MWCNTs/carbon paper was initially surface modified by silane derivative to incorporate sulfonic acid–silicate intermediate groups which act as anchors for metal ions. Platinum nanoparticles deposition on the in situ MWCNTs/carbon paper was carried out by reducing platinum (II) acetylacetonate precursor using glacial acetic acid. High resolution TEM images showed that the platinum particles are homogeneously distributed on the outer surface of MWCNTs with a size range of 1–2 nm. The Pt/MWCNTs/carbon paper electrode with a loading of 0.3 and 0.5 mg Pt cm⁻² was evaluated in proton exchange membrane single cell fuel cell using H₂/O₂. The single cells exhibited a peak power density of 600 and 800 mW cm⁻² with catalyst loadings of 0.3 and 0.5 mg Pt cm⁻², respectively with H₂/O₂ at 80 °C, using Nafion-212 electrolyte. In order to understand the intrinsically higher fuel cell performance, the electrochemically active surface area was estimated by the cyclic voltammetry of the Pt/MWCNTs/carbon paper.     

An in situ Fourier transform infrared spectroelectrochemical study on ethanol electrooxidation on Pd in alkaline solution

The mechanism of ethanol electrooxidation on a palladium electrode in alkaline solution (from 0.01 to 5 M NaOH) has been investigated by cyclic voltammetry and in situ Fourier transform infrared spectroelectrochemistry. The electrode performance has been found to depend on the pH of the fuel solution. The best performance was observed in 1 M NaOH solution (pH = 14), while the electrochemical activity decreased by either increasing or decreasing the NaOH concentration. In situ FTIR spectroscopic measurements showed the main oxidation product to be sodium acetate at NaOH concentrations higher than 0.5 M. The C-C bond cleavage of ethanol, put in evidence by the formation of CO₂, occurred at pH values ≤13. In these conditions, however, the catalytic activity for ethanol oxidation was quite low. No CO formation was detected along the oxidation of ethanol by FTIR spectroscopy.     

Synthesis and decomposition mechanisms of ternary Mg2CoH5 studied using in situ synchrotron X-ray diffraction

A ternary Mg₂CoH₅ hydride was synthesized using a novel method that relies on a relatively short mechanical milling time (1 h) of a 2:1 MgH₂-Co powder mixture followed by sintering at a sufficiently high hydrogen pressure (>85 bar) and heating from RT to 500 °C. The ternary hydride forms in less than 2.5 h (including the milling time) with a yield of ∼90% at ∼300 °C. The mechanisms of formation and decomposition of ternary Mg₂CoH₅ were studied in detail using an in situ synchrotron radiation powder X-ray diffraction (SR-PXD). The obtained experimental results are supported by morphological and microstructural investigations performed using SEM and high-resolution STEM. Additionally, thermal effects occurring during the desorption reaction were studied using DSC. The morphology of as-prepared ternary Mg₂CoH₅ is characterized by the presence of porous particles with various shapes and sizes, which, in fact, are a type of nanocomposite consisting mainly of nanocrystallites with a size of ∼5 nm. Mg₂CoH₅ decomposes at approximately 300 °C to elemental Mg and Co. Additionally, at approximately 400 °C, MgCo is formed as precipitates inserted into the Mg-Co matrix. During the rehydrogenation of the decomposed residues, prior to the formation of Mg₂CoH₅, MgH₂ appears, which confirms its key role in the synthesis of the ternary Mg₂CoH₅.     

In situ scanning electron microscopy on lithium-ion battery electrodes using an ionic liquid

We present an experimental platform that can be used for investigating lithium-ion batteries with very high spatial resolution. This in situ experiment runs inside a scanning electron microscope (SEM) and is able to track the morphology of an electrode including active and passive materials in real time. In this work it has been used to observe SnO₂ during lithium uptake and release inside a working battery electrode. The experiment strongly relies on an ionic liquid which has very low vapor pressure and can therefore be used as an electrolyte inside the vacuum chamber of the SEM. In contrast to common electrochemical characterization tools, this method allows for the observation of microscopic mechanisms in electrodes. Depending on the SEM, resolutions down to 1 nm can be achieved. As a result, the experimental platform can be used to investigate chemical reaction pathways, to monitor phase changes in electrodes or to investigate degradation effects in batteries. SnO₂ is a potential anode material for future high capacity lithium-ion batteries. Our observations reveal the formation of interface layers, large volume expansions, growth of extrusions, as well as mechanically induced cracks in the electrode particles during cycling.     

Dye-sensitized solar cells with a micro-porous TiO2 electrode and gel polymer electrolytes prepared by in situ cross-link reaction

The ionic conductivities and performances of dye-sensitized solar cells (DSSCs) of gel polymer electrolytes (GPEs) prepared by in situ cross-link reaction with different cross-linkers were investigated. The poly(imidazole-co-butylmethacrylate)-based GPE containing the 1,2,4,5-tetrakis(bromomethyl)benzene (B4Br) cross-linker showed a higher ionic conductivity than that containing cross-linkers with a linear structure, due to the formation of micro-phase separation that resulted in an increase in ion transport paths in the GPE. Moreover, the co-adsorbent ((4-pyridylthio) acetic acid, PAA) co-adsorbed with N3 dye on the TiO₂ electrode not only reduced dye aggregation, but also reacted with the cross-linkers in the GPE at the TiO₂/GPE interface. A decrease in the charge transport resistance at the TiO₂/GPE interface was noted after forming the gel; thus the value of J_SC significantly increased from 7.72 to 10.00 mA cm⁻². In addition, in order to reduce the ionic diffusion resistance within the TiO₂ electrode, incorporation of monodispersed PMMA in the TiO₂ paste was considered. With the optimal weight ratio of PMMA/TiO₂ (w/w=3.75), the TiO₂ electrode exhibited larger pores (ca. 350 nm) uniformly distributed after sintering at 500 °C, and the ionic diffusion resistance within the TiO₂ film could significantly be reduced. The cell conversion efficiency increased from 3.61% to 5.81% under illumination of 100 mW cm⁻², an improvement of ca. 55%.     

Development and characterization of tubular direct methanol fuel cells for use in in situ NMR analysis

The present study developed a tubular direct methanol fuel cell (tubular DMFC) for use in in situ Nuclear Magnetic Resonance (NMR) that could monitor various electrochemical reactions in real time. The tubular DMFC was fabricated in such a way as to prevent corrosion of cell components and to facilitate a supply of the reactants and removal of the products. The cell showed improved performance and durability sufficient for its use in an in situ NMR test, but problems with rapid performance decay persisted. Detailed reasons for the performance degradation were investigated through rigorous analytical work using various techniques. The tubular DMFC was also installed in an NMR probe to test signal sensitivity and resolution of ²D NMR spectra for deuterated methanol (CD₃OH) and deuterated water (D₂O). The spectral resolutions of both species were high, and their signal intensities were strong enough to realize an acceptable spectra.     

In situ measurements of stress evolution in silicon thin films during electrochemical lithiation and delithiation

We report in situ measurements of stress evolution in a silicon thin-film electrode during electrochemical lithiation and delithiation by using the multi-beam optical sensor (MOS) technique. Upon lithiation, due to substrate constraint, the silicon electrode initially undergoes elastic deformation, resulting in rapid rise of compressive stress. The electrode begins to deform plastically at a compressive stress of ca. −1.75 GPa; subsequent lithiation results in continued plastic strain, dissipating mechanical energy. Upon delithiation, the electrode first undergoes elastic straining in the opposite direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms plastically during the rest of delithiation. The plastic flow stress evolves continuously with lithium concentration. Thus, mechanical energy is dissipated in plastic deformation during both lithiation and delithiation, and it can be calculated from the stress measurements; we show that it is comparable to the polarization loss. Upon current interruption, both the film stress and the electrode potential relax with similar time constants, suggesting that stress contributes significantly to the chemical potential of lithiated silicon.     

In operando study of TiVCr additive in MgH2 composites

We report an in operando study of the hydrogenation and dehydrogenation of MgH₂–TiVCr composites. The experiment was performed by means of in situ synchrotron XRD in order to get insights on the influence of the TiVCr additive on the sorption properties of the MgH₂ based composite. Sequential Rietveld refinement analysis was performed to investigate the structural changes of MgH₂ and of the additive during hydrogenation and dehydrogenation processes. Significant non-monotonic changes in the lattice volume of the TiVCrH_x solid solution were observed concomitantly to the MgH₂ formation or decomposition. These volume changes are assigned to the variation of the hydrogen content in TiVCrH_x. These results provide evidence of cooperative effects between the H₂ storage material and the additive.     

Biological hydrogen production of the genus Clostridium: Metabolic study and mathematical model simulation

The biochemical hydrogen potential (BHP) tests were conducted to investigate the metabolism of glucose fermentation and hydrogen production performance of four Clostridial species, including C. acetobutylicum M121, C. butyricum ATCC19398, C. tyrobutyricum FYa102, and C. beijerinckii L9. Batch experiments showed that all the tested strains fermented glucose, reduced medium pH from 7.2 to a value between 4.6 and 5.0, and produced butyrate (0.37–0.67 mmol/mmol-glucose) and acetate (0.34–0.42 mmol/mmol-glucose) as primary soluble metabolites. Meanwhile, a significant amount of hydrogen gas was produced accompanied with glucose degradation and acid production. Among the strains examined, C. beijerinckii L9 had the highest hydrogen production yield of 2.81 mmol/mmol-glucose. A kinetic model was developed to evaluate the metabolism of glucose fermentation of those Clostridium species in the batch cultures. The model, in general, was able to accurately describe the profile of glucose degradation as well as production of biomass, butyrate, acetate, ethanol, and hydrogen observed in the batch tests. In the glucose re-feeding experiments, the C. tyrobutyricum FYa102 and C. beijerinckii L9 isolates fermented additional glucose during re-feeding tests, producing a substantial amount of hydrogen. In contrast, C. butyricum ATCC19398 was unable to produce more hydrogen despite additional supply of glucose, presumably due to the metabolic shift from acetate/butyrate to lactate/ethanol production.     

In situ confocal-Raman measurement of water and methanol concentration profiles in Nafion membrane under cross-transport conditions

The local concentration gradients of water and methanol within a Nafion^® membrane are measured with a new microfluidic cell specially designed for depth measurement by confocal micro-Raman spectroscopy. The experimental concentration profiles of solvents, obtained in situ under cross-transport conditions, are fitted taking into account the contribution of the experimental set-up to the Raman response. This method allows to measure the concentration ratios of methanol and water at the solution–membrane interface as well as the real concentration gradients of these solvents within the membrane medium. These parameters are critical for a better understanding of membrane transport properties and cannot be directly measured by other techniques. Indeed, results here reported show that internal gradients differ from those that can be estimated from methods measuring external concentrations.     

Kinetic analysis of photosynthetic growth,hydrogen production and dual substrate utilization by Rhodobacter capsulatus

Rhodobacter capsulatus is purple non-sulfur (PNS) bacterium which can produce hydrogen and CO₂ by utilizing volatile organic acids in presence of light under anaerobic conditions. Photofermentation by PNS bacteria is strongly affected by temperature and light intensity. In the present study we present the kinetic analysis of growth, hydrogen production, and dual consumption of acetic acid and lactic acid at different temperatures (20, 30 and 38 °C) and light intensities (1500, 2000, 3000, 4000 and 5000 lux). The cell growth data fitted well to the logistic model and the cumulative hydrogen production data fitted well to the Modified Gompertz Model. The model parameters were affected by temperature and light intensity. Lactic acid was found to be consumed by first order kinetics. Rate of consumption of acetic acid was zero order until most of the lactic acid was consumed, and then it shifted to first order. The results revealed that the optimum light intensities for maximum hydrogen production were 5000 lux for 20 °C and 3000 lux for 30 °C and 38 °C.     

Improvement of the hydrogen storage kinetics of NaAlH4 with nanocrystalline titanium dioxide loaded carbon spheres (Ti-CSs) by melt infiltration

Nanocrystalline titanium dioxide loaded carbon spheres (Ti-CSs) with 10wt% TiO₂ were synthesized through an easy one-step method using phenolic resols, titania nanoparticles and Pluronic F127 as organic carbon sources, inorganic precursors and surfactant, respectively. The results show that the as-prepared Ti-CSs composite is spherical shape with a diameter ranging from 0.3 to 2 μm, and rutile TiO₂ nanoparticles are distributed on the surface of the carbon spheres. Then the kinetics of NaAlH₄ was improved through depositing it on the surface of as-prepared Ti-CSs by melt infiltration. The results show that NaAlH₄ with Ti-CSs exhibits better hydrogen desorption kinetics than TiF₃ or nanocrystalline TiO₂ catalysted-NaAlH₄, and it starts to release hydrogen at about 40 °C and releases about 25% of the hydrogen content during heating to 60 °C. The results from SEM and XPS show that hydrogen storage properties of NaAlH₄ were considerably improved due to the formation of special structure during melt infiltration and the nanocrystalline TiO₂ and/or amorphous phase Ti–Al clusters near the subsurface sites, which succeed in combining catalyst addition (TiO₂ nanoparticles) and nanoconfinement to improve the kinetics of NaAlH₄.     

A review of the effects of hydrogen,carbon dioxide,and water vapor addition on soot formation in hydrocarbon flames

Addition of reactive or inert substances is one of the most effective and practical ways to control soot formation in combustion of hydrocarbon fuels. In this paper, the research progress on the effects of hydrogen, carbon dioxide, and water vapor addition on soot formation in hydrocarbon flames in the last few decades is systematically summarized. The summary shows that the number of studies on the effects of these three common diluents has increased dramatically in the last five years. Although the overall effects of all these three common diluents suppress soot formation, there is inconsistency with regard to the role of their chemical effects. The chemical effect of hydrogen (CE-H₂) mainly acts on the soot nucleation process, followed by the soot surface growth and finally the soot oxidation process. CE-H₂ seems significantly affected by the fuel type, oxygen concentration, and the ambient pressure. The chemical effect of carbon dioxide (CE-CO₂) affects soot formation indirectly mainly through the reaction CO + OH ↔ CO₂ + H. Some studies believe that CE-CO₂ suppresses soot production by increasing the hydroxyl radical (OH) concentration, while other studies believe that it is primarily attributed to the decrease of the hydrogen radical (H) concentration. The reaction H₂O + H ↔ H₂ + OH plays a vital role in the chemical effect of water vapor (CE-H₂O) addition on inhibiting soot formation. Most studies support the view that the chemical effect of water vapor mainly increases the OH concentration and suppresses soot formation by weakening the soot nucleation process. Moreover, we believe that reaction H₂O + O ↔ OH + OH and phenylacetylene also play an essential effect on the CE-H₂O.     

Kinetic interactions between hydrogen and carbon monoxide oxidation over platinum

The heterogeneous chemistry coupling of H₂ and CO over platinum was investigated experimentally and numerically for H₂/CO/O₂/N₂ mixtures with overall lean equivalence ratios φ = 0.13–0.26, H₂:CO molar ratios 1:5–3:1, and a pressure of 5 bar. Experiments were performed in an optically accessible channel-flow reactor at surface temperatures 510–827 K and involved in situ Raman measurements of major gas-phase species concentrations and thermocouple measurements of surface temperatures. Emphasis was placed on the low temperature range 510–600 K, whereby H₂ inhibited the CO oxidation, and which was of particular relevance to gas turbine idling and part-load operation. Comparisons of measurements with 2-D simulations attested the aptness of the employed kinetic scheme, not only for H₂/CO fuel mixtures but also for pure CO. Measured and predicted transition temperatures below which H₂ inhibited CO oxidation agreed well with each other, showing a main dependence on the overall equivalence ratio (550 ± 5 K at φ = 0.13 and 600 ± 5 K at φ = 0.26) and a weaker dependence on the H₂:CO ratio. Furthermore, this inhibition was non-monotonically dependent on the H₂:CO ratio, becoming higher at a value of 1:1. The inhibiting kinetic effect of H₂ was an outcome of the competition between H₂ and CO/O₂ for surface adsorption and, most importantly, of the competition between the adsorbed H(s) and CO(s) for surface-deficient O(s). Finally, transient simulations in practical catalytic channels revealed the interplay between kinetic and thermal effects. While at φ = 0.13 the H₂/CO reactive mixture exothermicity was insufficient to overtake the kinetic inhibition, at φ = 0.26 catalytic ignition could still be achieved at temperatures well-below the transition temperature. The effect of H₂:CO molar ratio on the light-off times was quite strong, suggesting care when designing syngas catalytic rectors with varying compositions.     

In situ X-ray diffraction studies on the mechanism of capacity retention improvement by coating at the surface of LiCoO2

Synchrotron based in situ X-ray diffraction technique has been used to study the mechanism of capacity fading of LiCoO₂ cycled to a higher voltage above the normal 4.2 V limit and to investigate the mechanism of capacity retention improvement by ZrO₂ surface coating on LiCoO₂. It was found that the capacity fading of LiCoO₂ cycled at higher voltage limit is closely related to the increased polarization rather than the bulk crystal structure damage. The capacity of uncoated LiCoO₂ sample dropped to less than 70 mAh g⁻¹ when charged to 4.8 V after high voltage cycling. However, when the voltage limit was further increased to 8.35 V, the capacity was partially restored and the corresponding structural changes were recovered to the similar level as seen in fresh sample. This indicates that the integrity of the bulk crystal structure of LiCoO₂ was not seriously damaged during cycling to 4.8 V. The increased polarization seems to be responsible for the fading capacity and the uncompleted phase transformation of LiCoO₂. The polarization-induced capacity fading can be significantly improved by ZrO₂ surface coating. It was proposed that the effect of ZrO₂-coating layer on the capacity retention during high voltage cycling is through the formation of protection layer on the surface of LiCoO₂ particles, which can reduce the decomposition of the electrolyte at higher voltages.