Hydrogen storage of melt-spun amorphous Mg65Ni20Cu5Y10 alloy deformed by high-pressure torsion

Rapidly quenched amorphous Mg₆₅Ni₂₀Cu₅Y₁₀ metallic glass compacts were subjected to heavy shear deformation by high-pressure torsion until different amounts of ultimate strain. High-resolution X-ray diffraction analysis and scanning electron microscopy revealed that high-pressure torsion resulted in a deformation dependent microstructure. High-pressure calorimetry measurements revealed that hydrogen uptake in the fully amorphous alloy occurs at a significantly lower temperature compared to the fully crystallized state, while the amount of absorbed hydrogen increased considerably after heavy shear deformation due to the formation of Mg₂Ni crystals.     

Hydrogen absorption and its influence on the thermal stability of Zr65Al10Ni10Cu15 amorphous alloy

The hydrogen absorption properties of Zr₆₅Al₁₀Ni₁₀Cu₁₅ amorphous alloy with a wide supercooled liquid region were evaluated using a Sieverts-type apparatus. The amorphous alloy absorbs 0.34, 0.80 and 0.85 wt.% hydrogen within 10, 6 and 5 min at 373, 473 and 523 K, respectively. According to Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, the hydrogen absorption activation energy of the amorphous alloy was 1.27 kJ mol⁻¹. The pressure–composition (P–C) isotherms of the amorphous Zr₆₅Al₁₀Ni₁₀Cu₁₅ alloy at 573, 623 and 673 K did not show a plateau, and the hydrogen absorption capacities were 0.8, 1.3 and 1.7 wt.%, respectively. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analysis demonstrated that the thermal stability of the amorphous alloy was improved with an enlarged supercooled liquid region after the hydrogen uptake below 473 K, but was decreased after the hydrogenation above 523 K. The alloy still kept the amorphous structure after hydrogenation at 573 K, and transformed into the crystalline phases of ZrH₂, ZrNi and AlCu after the hydrogenation at 673 K.     

Finite element analysis of hydrogen diffusion/plasticity coupled behaviors of low-alloy ferritic steel at large strain

Hydrogen embrittlement is commonly considered as a typical failure mechanism for low-alloy ferritic steel under high pressure hydrogen environment. Currently, the hydrogen enhanced localized plasticity theory has been largely recognized for studying the hydrogen embrittlement mechanism by introducing the localized plastic flow and the hydrogen induced strain concept. However, the hydrogen induced strain and the plastic strain are often solved respectively in this theory, which may weaken the effect of hydrogen on the plastic deformation. The purpose of this paper is to propose a modified theoretical model from the microstructural level by emphasizing the coupling mechanism between the hydrogen diffusion and the plastic deformation at large strain, where the hydrogen induced strain is superimposed on the equivalent plastic strain instead of on the strain components. Fully implicit backward Euler algorithm by finite element analysis (FEA) under the corotational configuration is used to implement the proposed model, where the hydrogen induced strain is involved in the stress return process within each iteration, indicating a more direct interaction between them than existing works. FEA by using finite element software ABAQUS-UMAT subroutine is performed for the smooth tensile specimen and the notch specimen respectively under slow tensile strain rate loading and different hydrogen pressure. Developed direct coupling model is expected to further gain insight into the hydrogen embrittlement effect on the plastic deformation, especially at the trapping sites.     

Hydrogen embrittlement behavior in interstitial Mn–N austenitic stainless steel

The susceptibility to hydrogen embrittlement behavior was investigated in an interstitial Mn–N austenitic steel HR183 and stainless steel 316L. Hydrogen was introduced by cathodic hydrogen charging at 363 K. HR183 has stronger austenite stability than 316L despite its lower nickel content, the addition of manganese and nitrogen inhibited martensitic transformation during the slow strain rate tensile deformation. Due to the diffusion of hydrogen being delayed by the interstitial solution of nitrogen atoms and the uniform dislocation slips, hydrogen permeates more slowly in HR183 than 316L, contributing to an 84.79 μm thinner brittle fracture layer in HR183 steel. Hydrogen charging caused elongation losses in both 316L and HR183 steels associated with the hydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE) mechanism. However, the hydrogen embrittlement susceptibility of HR183 is 3.4 times lower than that of 316L according to the difference in elongation loss between the two steel after hydrogen charging. Deformation twins trapped a lot amount of hydrogen leading to brittle intergranular fracture in 316L. The multiple directions of slip in HR183 steel suppressed the strain localization inside grains and delayed the adverse effects conducted by HELP and HEDE mechanism, eventually inhibiting server hydrogen embrittlement in the HR183 steel. This study is assisting in the development of low-cost stainless steel with excellent hydrogen embrittlement resistance that can be used in harsh hydrogen-containing environments.     

Fabrication and characterization of Pd/Nb40Ti30Ni30/Pd/porous nickel support composite membrane for hydrogen separation and purification

A porous nickel support was successfully prepared by uniaxial compression of nickel powders. Microstructures and mechanical properties of Nb₄₀Ti₃₀Ni₃₀ membranes fabricated by magnetron sputtering were investigated. Deposited and annealed Nb₄₀Ti₃₀Ni₃₀ membranes consisted of amorphous and crystalline phases, respectively. Higher base temperature was shown to increase the hardness and elastic modulus of the Nb₄₀Ti₃₀Ni₃₀ membrane. Pd/Nb₄₀Ti₃₀Ni₃₀/Pd/porous nickel support composite membranes were then fabricated using a multilayer magnetron sputtering method. The hydrogen permeability of the composite membranes with amorphous and crystallized Nb₄₀Ti₃₀Ni₃₀ metal layer was measured and compared with that of self-supported Nb₄₀Ti₃₀Ni₃₀ and Pd alloys. Solid-state diffusion was shown to be the rate-controlling factor when the thickness of the Nb₄₀Ti₃₀Ni₃₀ layer was about 12 μm or greater, while other factors were in effect for thinner layers (such as 6 μm). The Pd/Nb₄₀Ti₃₀Ni₃₀/Pd/porous nickel support composite membrane exhibited excellent permeation capability and satisfactory mechanical properties. It is a promising new permeation membrane that could replace Pd and PdAg alloys for hydrogen separation and purification.     

Hydrogen embrittlement of super duplex stainless steel in acid solution

Super duplex stainless steel (SDSS) is a good choice of material when resistance to harsh environments is needed. Despite the material’s excellent corrosion resistance and high strength, a number of in-service failures have been recorded. The root cause of these failures was environmentally induced cracking initiated at manufacturing and in-service metallurgical defects. In this study the hydrogen embrittlement of pre-strained super duplex stainless steel specimens was investigated after 48 h cathodic charging in 0.1 M H₂SO₄. The metallurgical changes that resulted from four levels of cold work (4, 8, 12, and 16% plastic strain) were considered and their effect on the embrittlement of the SDSS alloy was investigated. After hydrogen charging, the specimens were pulled immediately to failure and the mechanical properties evaluated. The obtaining fracture morphology was investigated using low and high magnification microscopy. Experimental results indicated that charging the super duplex stainless steel alloy with hydrogen caused varying degrees of embrittlement depending on cold work level. Increasing cold work resulted in a reduction of the elongation to failure. Microscopic investigation confirmed the significant effect of cold work on the hydrogen embrittlement susceptibility of the super duplex stainless steel alloy investigated.     

Damage associated with interactions between microstructural characteristics and hydrogen/methane gas mixtures of pipeline steels

There is no common standard for blended hydrogen use in the natural gas grid; hydrogen content is generally based on delivery systems and end-use applications. The need for a quantitative evaluation of hydrogen-natural gas mixtures related to the mechanical performance of materials is becoming increasingly evident to obtain long lifetime, safe, and reliable pipeline structures. This study attempts to provide experimental data on the effect of H₂ concentration in a methane/hydrogen (CH₄/H₂) gas mixture used in hydrogen transportation. The mechanical performance under various blended hydrogen concentrations was compared for three pipeline steels, API X42, X65, and X70. X65 exhibited the highest risk of hydrogen-assisted crack initiation in the CH₄/H₂ gas mixture in which brittle fractures were observed even at 1% H₂. The X42 and X70 samples exhibited a significant change in their fracture mechanism in a 30% H₂ gas mixture condition; however, their ductility remained unchanged. There was an insignificant difference in the hydrogen embrittlement indices of the three steels under 10 MPa of hydrogen gas. The coexistence of delamination along with the ferrite/pearlite interface, heterogeneous deformation in the radial direction, and abundance of nonmetallic MnS inclusions in the X65 sample may induce a high stress triaxiality at the gauge length at the beginning of the slow strain rate tensile process, thereby facilitating efficient hydrogen diffusion.     

Color change of V2O5 thin films upon exposure to organic vapors

The reaction of amorphous V₂O₅ thin films with various organic vapors is investigated using in-situ optical transmission and in-situ Raman spectroscopic measurements. When V₂O₅ thin films are exposed to vapors of methanol, ethanol, acetone, and isopropanol, changes in the Raman spectrum are observed. These changes are similar to those due to alkali ion intercalation and most pronounced for methanol and ethanol. The optical transmission also increases when the thin films are exposed to methanol and ethanol vapors. Depositing a thin catalyst layer of palladium does not promote the reaction. This result has implications for using this material in hydrogen sensor applications, as extended exposure to organic vapors may not be differentiated from the presence of hydrogen.     

Investigation of the thermochemical transformations in the LiAlH4-LiNH2 system

The thermal transformations in the lithium alanate-amide system consisting of lithium aluminum hydride (LiAlH₄) and lithium amide (LiNH₂), mixed in a 1:1 M ratio, were investigated using the pressure-composition-temperature analysis, solid-state nuclear magnetic resonance, X-ray powder diffraction, and residual gas analysis. Below 250 °C, the alanate decomposes into Al, LiH and H₂, through the formation of Li₃AlH₆, whereas the amide remains largely intact. The release of gaseous hydrogen corresponds to approximately 5 wt%. Above 250 °C, additional ∼4 wt% of hydrogen is produced through solid-state reactions among LiNH₂, LiH and metallic Al, through the formation of intermetallic Li-Al binary alloy and an unidentified intermediate. The overall reaction of the thermochemical transformation of the LiAlH₄-LiNH₂ mixture results in the production of Li₃AlN₂, metallic Al, LiH and the release of 9 wt% of gaseous hydrogen. The reaction mechanism of the thermal decomposition is different from one identified earlier during mechanical treatment of the same system. Rehydrogenation of the thermally-decomposed products of LiAlH₄-LiNH₂ mixture using high hydrogen pressure (180 bar) and heating (275 °C) yields LiNH₂ and amorphous aluminum nitride (AlN).     

Structural and electrochemical studies of WO3 films deposited by pulsed spray pyrolysis

Transparent conductive and WO₃ electrochromic thin films were deposited by spray pyrolysis technique. The films were deposited using solutions of WCl₆ in dimethylformamide on SnO₂:F (FTO) substrates with different sheet resistances. Noticeable effects of substrate on structural, morphological and optical properties of the WO₃ films and on its electrochromic behavior are presented and discussed. Hexagonal and monoclinic WO₃ structures were obtained on amorphous glass substrates; also the monoclinic structure on polycrystalline FTO substrates was obtained. Cyclic structural changes during the colored and blanched states were found from XRD and electron diffraction result analysis: The hydrogen tungsten bronze in the tetragonal phase after the hydrogen extraction change to the original WO₃ monoclinic phase.     

Strain effect on structural and dehydrogenation properties of MgH2 hydride from first-principles calculations

The structure, stability, dehydrogenation thermodynamic and kinetic properties of MgH₂ hydride under different biaxial strain conditions were investigated by using first-principles calculations based on the density functional theory (DFT). The results show that either biaxial tensile or compressive strain is likely to cause the structural deformation of MgH₂ crystal, and its lattice distortion becomes severe with increasing magnitude of strain. Due to the contribution of strain energy, the biaxial strain not only weakens the structural stability of MgH₂, but also lowers its hydrogen desorption enthalpy and dehydrogenation temperature. Furthermore, the diffusion activation energy of hydrogen atom in MgH₂ host is also decreased, which results in a remarkable improvement of dehydrogenation properties. Noticeably, the effect of tensile strain in improving dehydrogenation thermodynamics is relatively superior to that of compressive one, while the role of the latter in enhancing dehydrogenation kinetics is relatively stronger than that of the former. Further analysis of electronic structures suggests the strain-induced changes in structural and dehydrogenation properties of MgH₂ are closely associated with the value of total densities of states at the Fermi level as well as the bonding electrons number below Fermi level. These results provide an insight for developing better MgH₂-based nanocomposite hydrogen storage materials by introducing suitable interface misfit strain.     

H2SO4 stability of PBI-blend membranes for SO2 electrolysis

For hydrogen to become a serious contender for replacing fossil fuels, the manufacturing thereof has to be further investigated. One such process, the membrane based Hybrid Sulfur (HyS) process, where hydrogen is produced from the electrolysis of SO₂, has received considerable interest recently. Since H₂SO₄ is formed during SO₂ electrolysis, H₂SO₄ stability is a prerequisite for any membrane to be used in this process. In this study, pure as well as blended polybenzimidazole (PBI), partially fluorinated poly(arylene ether) (sFS) and nonfluorinated poly(arylene ethersulfone) (sPSU) membranes were investigated in terms of their acid stability as a function of acid concentration. Membranes were characterized using weight change, TGA, GPC, SEM/EDX and IEC. While a general stability was observed at 30 and 60 wt% H₂SO₄, the blended sFS-PBI and sPSU-PBI showed the highest stability throughout. According to the VI curve obtained for the SO₂ electrolysis, the sPSU-PBI blend membrane performed slightly better than Nafion^®117.     

Hydrogen permeation properties of Pd-coated V89.8Cr10Y0.2 alloy membrane using WGS reaction gases

The influence of co-existing gases on the hydrogen permeation was studied through a Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane. Preliminary hydrogen permeation experiments have been confirmed that hydrogen flux was 6.26 ml/min/cm² for a Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane (thick: 0.5 mm) using pure hydrogen as feed gas. Also, the hydrogen permeation flux decreased with decrease of hydrogen partial pressure at constant pressure when H₂/CO₂ and H₂/CO₂/H₂S mixture applied as feed gas respectively and permeation fluxes were satisfied with Sievert's law in different feed conditions. It was found from XRD and SEM results after permeation test that the Pd-coated V_89.8Cr₁₀Y_0.2 alloy membrane had good stability and durability for various mixture feeding conditions.     

Effect of hydrogen absorption/desorption cycling on hydrogen storage properties of a LaNi3.8Al1.0Mn0.2 alloy

The effect of long-term hydrogen absorption/desorption cycling up to 3500 cycles on the hydrogen storage properties of LaNi_3.8Al_1.0Mn_0.2 alloy was investigated. The pressure-composition (PC) isotherms for absorption/desorption and the absorption kinetics were measured at 433 K, 453 K and 473 K. X-ray diffraction analysis revealed that the alloy had a homogeneous hexagonal CaCu₅ type structure and kept this structure even after 3500 cycles, but the diffraction peaks were broadened. The degree of peak broadening was increased with increase of the cycle number, but exhibiting a maximum after initial activation. The shapes of PCT curves after 300, 2000 and 3500 cycles were similar to that after initial activation. It was found that the alloy subjected to 300 cycles did not exhibit significant changes in hydrogen storage capacity, but the long-term cycling up to 2000 and 3500 cycles resulted in obvious decrease in hydrogen storage capacity. The degradation of the hydrogen capacity might be resulted from the formation of the irreversible sites and more stable hydride phase, though no new phase was found after absorption/desorption cycling from XRD pattern as shown in Fig. 6 because of the limitation of XRD analysis sensibility. The hydrogen absorption kinetics after 300 cycles was deteriorated but improved again after 2000 and 3500 cycles compared with that of after initial activation. The changes in hydrogenation properties of the alloy induced by cycling were discussed by considering the crystal structure, lattice strain and pulverization of the sample.     

Mg2NiH4 synthesis and decomposition reactions

A ternary Mg₂NiH₄ hydride was synthesized using method that relies on a relatively short mechanical milling time (one hour) of a 2:1 MgH₂–Ni powder mixture followed by sintering at a sufficiently high hydrogen pressure (>85 bar) and temperature (>400 °C). The ternary hydride forms in less than 2.5 h (including the milling time) with a yield of ∼90% as a mixture of two polymorphic forms. The mechanisms of formation and decomposition of ternary Mg₂NiH₄ under different hydrogen pressures were studied in detail using an in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and high pressure DSC. The obtained experimental results are supported by morphological and microstructural investigations performed using SEM and high resolution STEM. Additionally, effects occurring during the desorption reaction were studied using DSC coupled with mass spectrometry.     

Hydrogen embrittlement and hydrogen diffusion behavior in interstitial nitrogen-alloyed austenitic steel

The susceptibility to hydrogen embrittlement and diffusion behavior of hydrogen were evaluated in interstitial nitrogen-alloyed austenitic steel QN1803 and 304 and 316 L stainless steels. The amount of transformed martensite and the activation energy of hydrogen diffusion were revealed via electron backscattering diffraction and thermal desorption spectroscopy. The austenite stability of QN1803 during the deformation process was higher than that of 304 and 316 L. However, the hydrogen content of QN1803 was high because of the small grain size and low activation energy of hydrogen diffusion. For the stable QN1803 and 316 L austenitic steels, martensite had no evident harmful effect because of its discrete distribution. A planar dislocation slip was observed in QN1803 during deformation. Hydrogen charging enhanced dislocation mobility, leading to severe strain localization. Thus, the severe strain in QN1803 promoted microcracking.     

Self-humidification of a PEM fuel cell using a novel Pt/SiO2/C anode catalyst

In this work, a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) operating under no external humidification has been successfully fabricated by using a composite Pt/SiO₂/C catalyst at the anode. In the composite catalyst, amorphous silica, which originated from the hydrolysis of tetraethyl orthosilicate (TEOS), was immobilized on the surface of carbon powder to enhance the stability of silica and provide a well-humidified surrounding for proton transport in the catalyst layer. The characteristics of silica in the composite catalyst were investigated by XRD, SEM and XPS analysis. The single cell tests showed that the performance of the novel MEA was comparable to MEAs prepared using a standard commercial Pt/C catalyst with 100% external humidification, when both were operated on hydrogen and air. However, in the absence of humidification, the MEA using Pt/SiO₂/C catalyst at the anode continued to show excellent performance, while the performance of the MEA containing only the Pt/C catalyst rapidly decayed. Long-term testing for 80 h further confirmed the high performance of the non-humidified MEA prepared with the composite catalyst. Based on the experimental data, a possible self-humidifying mechanism was proposed.     

Detection of voids in hydrogen embrittled iron using transmission X-ray microscopy

Hydrogen embrittlement remains a barrier to widespread adoption of hydrogen as a carbon-neutral energy source. Here, hydrogen embrittlement mechanisms are investigated across length scales in iron using transmission X-ray microscopy (TXM), digital image correlation (DIC), and notched tensile testing during in-situ electrochemical hydrogen charging. TXM reveals void size and spatial distribution ahead of a propagating crack. We find hydrogen charging leads to voids within ～10 μm of the crack tip and suppression of voids beyond this distance. Near the crack tip, voids are elongated in the direction of the crack and are smaller than voids in an uncharged sample. In the presence of hydrogen, these voids lead to quasi-cleavage fracture and a sharper crack tip. DIC shows localization and reduction of plastic strain with hydrogen charging, and tensile testing reveals a reduction in fracture energy and elongation at failure. These results are discussed in the context of hydrogen embrittlement mechanisms.     

Influence of surface martensite layer on hydrogen embrittlement of Fe-Mn-C-Mo steels in wet H2S environment

This study investigated the effect of thermally induced surface martensite layer on hydrogen embrittlement of Fe-16Mn-0.4C-2Mo (wt.%) (16Mn) and Fe-25Mn-0.4C-2Mo (wt.%) (25Mn) steels through slow strain rate stress corrosion cracking testing and proof ring testing in wet H₂S environment. The 16Mn steel had a surface layer of less than 150 μm in depth containing ε-martensite, α′-martensite and austenitic twins. The martensite layer is found to reduce the hydrogen embrittlement resistance of the steel. In comparison, the 25Mn steel developed a full α′-martensite surface layer, which exhibited practically nil effect on the hydrogen embrittlement resistance of the steel. The ε-martensite provides much larger interface areas with the mechanical twins of the austenite in the 16Mn steel than the α′-martensite/austenite interfaces in the 25Mn steel. These interfaces are hydrogen trapping sites and are prone to initiate surface cracks, as observed in the scanning electron microscope. The formation of the cracks is attributed to hydrogen concentration at the ε-martensite and austenitic twin interfaces, which accelerates material fracture.