Local Hydrogen Research Articles

Chemical heterogeneity enhances hydrogen resistance in high-strength steels

The antagonism between strength and resistance to hydrogen embrittlement in metallic materials is an intrinsic obstacle to the design of lightweight yet reliable structural components operated in hydrogen-containing environments. Economical and scalable microstructural solutions to this challenge must be found. Here, we introduce a counterintuitive strategy to exploit the typically undesired chemical heterogeneity within the material’s microstructure that enables local enhancement of crack resistance and local hydrogen trapping. We use this approach in a manganese-containing high-strength steel and produce a high dispersion of manganese-rich zones within the microstructure. These solute-rich buffer regions allow for local micro-tuning of the phase stability, arresting hydrogen-induced microcracks and thus interrupting the percolation of hydrogen-assisted damage. This results in a superior hydrogen embrittlement resistance (better by a factor of two) without sacrificing the material’s strength and ductility. The strategy of exploiting chemical heterogeneities, rather than avoiding them, broadens the horizon for microstructure engineering via advanced thermomechanical processing.

The significance of inclusion morphology and composition in governing hydrogen transportation and trapping in steels

In this paper, two steels with different morphology of inclusions are studied. Scanning electron microscopy, finite element calculations, and electrochemical hydrogen permeation tests were conducted. Furthermore, in-situ observations of hydrogen de-trapping from the surface of steels were achieved using a hydrogen charging device and optical microscope. Results show that stripe-shaped complex inclusions exhibit a higher level of residual stress, especially at the boundary of oxide components. The hydrogen molecule is also prone to emerge at the oxide composition and intensifies the risks of cracking. In contrast, the residual stress levels around spherical inclusions are comparatively lower due to discrete sites of stress concentration. Thus, the effect of dispersed tiny dioxide sphere inclusions can help relieve the local hydrogen pressure and promote the resistance against hydrogen-induced cracking.

Local durability optimization of a large-scale direct methanol fuel cell: catalyst layer tuning for homogeneous operation and in-operando detection of localized hydrogen evolution

Lifetime limitations are still penalizing direct methanol fuel cell technology, otherwise outstandingly promising for sustainable portable power generation. Strong heterogeneous performance fading, related to uneven operating conditions, is known to be exacerbated in the upscaling process towards commercial applications, especially at local level. This work applies a localized optimization strategy, previously developed on lab-scale samples, on a commercial 180 cm2 membrane electrode assembly, analysing both current and potential distribution by means of a custom macro-segmented fuel cell provided with array of reference electrodes. Analysis based on local polarization curves and impedance spectroscopy demonstrates that water distribution, leading to local dehydration as well flooded areas, drives uneven operation and fading. Consequently, platinum loading at cathode electrode has been redistributed, sensibly improving current density heterogeneity and stability (voltage decay rate decreased from 148 to 53.8 μV h−1) over a 600 h degradation tests. Then, residual fading identified at outlet regions has been investigated by means of local electrodes potential analysis, demonstrating a highly uneven operation of both electrodes. This phenomenon is discussed as the evidence of localized hydrogen evolution, which is identified for the first time during nominal galvanostatic operation and suspected to contribute to uneven fading of components.

Simulative Investigation on Local Hydrogen Starvation in PEMFCs: Influence of Water Transport and Humidity Conditions

Durability targets of automotive polymer electrolyte membrane fuel cells (PEMFCs) could be crucially threatened by local hydrogen starvation, typically induced by local blockage of gas channels. To gain a deep insight on the evolving of such starvation events and related carbon corrosion losses, we have developed a numerical model with transient nature that includes detailed transport phenomena and electrochemistry. Special focus is on water transport and sensitivity of relative humidity (RH) on both anode and cathode sides, whose influences were commonly neglected in starvation-related modeling studies. Utilizing the model, we show the dominating effect of in-plane hydrogen convection within the anode gas diffusion layer, which is again determined by the accumulation of other gas species including water vapor. We demonstrate how this is again linked with the water management throughout the fuel cell. Furthermore, water transport is shown to affect local current density and membrane oxygen permeability, both being critical influential factors regarding the severity of a local starvation event. The developed model is validated by conducting transient current density distribution measurements. As RH levels are crucial operational conditions within automotive PEMFCs, this work serves as useful input towards development of future operation strategies for better PEMFC durability.

Determination of Critical Hydrogen Concentration and Its Effect on Mechanical Performance of 2200 MPa and 600 HBW Martensitic Ultra-High-Strength Steel

The influence of hydrogen on the mechanical performance of a hot-rolled martensitic steel was studied by means of constant extension rate test (CERT) and constant load test (CLT) followed with thermal desorption spectroscopy measurements. The steel shows a reduction in tensile strength up to 25% of ultimate tensile strength (UTS) at critical hydrogen concentrations determined to be about 1.1 wt.ppm and 50% of UTS at hydrogen concentrations of 2 wt.ppm. No further strength degradation was observed up to hydrogen concentrations of 4.8 wt.ppm. It was observed that the interplay between local hydrogen concentrations and local stress states, accompanied with the presence of total average hydrogen reducing the general plasticity of the specimen are responsible for the observed strength degradation of the steel at the critical concentrations of hydrogen. Under CLT, the steel does not show sensitivity to hydrogen at applied loads below 50% of UTS under continuous electrochemical hydrogen charging up to 85 h. Hydrogen enhanced creep rates during constant load increased linearly with increasing hydrogen concentration in the steel.

Implications for the Nb aggregation inherited from melt to γ phase of U-Nb alloy

By means of ab initio molecular dynamics (AIMD) simulations, Nudged Elastic Band (NEB) method and cluster expansion (CE) combined with the Monte Carlo (MC) techniques, we have investigated that the elemental interactions and local structural dynamics in the melt and γ phase of U-Nb alloy and hydrogen diffusion behavior in γ-U-Nb alloy. It has been found that the aggregation of Nb atoms inherited from melt to γ phase plays a significant role in improving mechanical property and protecting γ-U-Nb alloy from hydrogen damage. The analyses of chemical short-range order parameters attest that there exists the similarity of element interactions between the melt and γ phase of U-Nb alloy. The U-Nb pairs in both melt and γ phase exhibit the repulsive interactions, whereas the attractive U-U and Nb-Nb interactions exits. These results demonstrate that the U and Nb atoms prefer to stay in their own shells to form the localized clusters in both melt and γ phase of U-Nb alloy. Furthermore, the analyses of hydrogen diffusion behavior in γ-U-Nb alloy, our NEB calculations have further proved that the hydrogen atoms prefer to be trapped by Nb atoms and, this trend is further reinforced by the aggregation of Nb atoms. It implies that, once Nb is added into U alloys, the Nb addition plays an important role in slowing down the diffusion of hydrogen atoms in γ-U-Nb alloy. The uniform distribution of Nb clusters helps to avoid the occurrence of excessive local hydrogen concentration.

Hydrogen Bonds between Ions of Opposite and Like Charge in Hydroxyl-Functionalized Ionic Liquids: an Exhaustive Examination of the Interplay between Global and Local Motions and Intermolecular Hydrogen Bond Lifetimes and Kinetics.

Hydroxyl-functionalized ionic liquids (ILs) represent a new interesting class of ILs where hydrogen bonds (HBs) play an important role: here, "typical" HBs between cations and anions (ca) are competing with "atypical" HBs connecting pairs of cations (cc). We study the equilibrium and kinetics of (cc) and (ca) HBs in 1-(n-hydroxyalkyl)-pyridinium bis(trifluoromethlysulfonyl)imide [HOCnPy][NTf2] ILs by means of molecular dynamics simulations. (cc) HBs are found to be between 0.96 and 3.76 kJ mol-1 stronger than their (ca) counterparts, depending on the alkyl chain length. HB lifetimes and kinetics are analyzed by means of HB population and reactive flux correlation functions. Essentially, four different HB lifetimes have to be considered, spanning about 3 orders of magnitude, each valid in its own right and each associated with different aspects of HB breaking and HB reformation. The long-time limiting behavior of the HB population correlation function is controlled by diffusion of the ions and can be quantitatively described by analytical expressions. The short-time HB behavior is tied to the localized dynamics of the hydroxyl group exploring its local solvation environment. A minimalist kinetic two-domain model is introduced to realistically describe the time evolution of the HB population correlation function for both (ca) and (cc) HBs over 5 orders of magnitude. By employing the reactive flux method, we determine the kinetics of HB breaking, unaffected by diffusion processes. We determine both, the ultrafast upper boundary and the average rate of HB breaking, allowing recrossing-events during the transient relaxation time period. For sufficiently long alkyl chains, all those computed HB lifetimes indicate a higher kinetic stability of (cc) HBs over (ca) HBs; for short chains, it is vice-versa.

Preliminary Data Monitoring In Vivo Sources of Reactive Oxygen Species Production in Human Obesity

Introduction Excessive reactive oxygen species (ROS) production is a prominent feature of obesity-related conditions including impairments in endothelial function. NADPH oxidases (Nox) and mitochondria are major sources of ROS production within the vasculature. However, studies involving direct measurement of in vivo ROS production are limited in humans. Thus, the relative contributions of Nox- and mitochondrial-derived ROS in human obesity remain to be fully characterized. The objective of this study was to determine the predominant sources of in vivo ROS production in the skeletal muscle microvasculature of individuals with obesity. We hypothesize that both Nox- and mitochondria-dependent ROS production are upregulated in human obesity. Methods Two sedentary men with Class II and above obesity (body mass index ≥ 35 kg/m2) and the Metabolic Syndrome were studied. Microdialysis was used for measurements of in vivo skeletal muscle ROS production. Microdialysis probes were perfused with saline containing Amplex Ultrared, horseradish peroxidase and superoxide dismutase to measure local hydrogen peroxide and superoxide concentrations. To assess ROS production from distinct sources, microdialysis probes were perfused with the following: apocynin (non-specific Nox inhibitor), MitoTEMPO (mitochondrial-ROS inhibitor), and GKT 137831 (specific Nox 4 inhibitor). Results The concentrations of hydrogen peroxide and superoxide decreased upon addition of apocynin to microdialysis probes (mean ± SEM; hydrogen peroxide: 1.18 ± 0.58 to 0.76 ± 0.01 μM; superoxide: 1.47 ± 0.46 to 1.10 ± 0.62 μM). MitoTEMPO perfusion elicited an increase in hydrogen peroxide (1.12 ± 0.76 to 1.51 ± 1.08 μM) and decrease in superoxide (1.47 ± 0.46 to 0.78 ± 0.10 μM). The combination of apocynin plus MitoTEMPO resulted in concentrations of hydrogen peroxide (0.22 ± 0.10 μM) and superoxide (0.23 ± 0.06 μM) that were 69.7% and 79.1% lower than apocynin alone. In addition, the hydrogen peroxide (0.56 ± 0.25 μM) and superoxide (0.43 ± 0.18 μM) concentrations with co-perfusion of apocynin and GKT were 26.3% and 60.9% lower than with apocynin alone. Conclusions Our preliminary data suggest that mitochondria and Nox together are significant sources of ROS production within the skeletal muscle microvasculature of obese individuals. The local inhibition of Nox- and mitochondrial-derived ROS resulted in marked decreases in extracellular ROS levels within the skeletal muscle microvasculature. Although the small sample size currently limits our interpretation of the results, this study is anticipated to become the first to report on distinct sources of in vivo ROS production in human obesity.

2D-layered Mg(OH)2 material adsorbing cellobiose via interfacial chemical coupling and its applications in handling toxic Cd2+ and UO22+ ions

The interfacial chemistry of nanocomposite materials is of overarching importance in the separation and purification science; moreover, its understanding helps to guide synthesis, clarify structure-property relationship and unearth novel applications. However, the composites feature rather complicated local structures and hydrogen bonds are often involved in the interface and the vicinity of active sites. In this regard, density functional theory first-principle calculations associated with experimental study have synergistically examined two-dimensional (2D) magnesium hydroxide material with different layers and their adsorption toward cellobiose. Hydrogen bonds are found responsible for the interfacial coupling, which make it vital to cover the dispersion correction in the calculation. The average adsorption energy ranges from −0.29 to −0.35 eV, falling well within the range of reported hydrogen-bonding strength. On the basis of calculated structural/interfacial properties and experimental findings, the 2D Mg(OH)2 in terms of three-layer model was unraveled to substitute toxic Cd2+ ion and sorb radioactive UO22+ that is coordinated by water and hydroxyl groups. These reactions are thermodynamically feasible. The ion-exchanging mechanism was proposed for cadmium removal and the outer-sphere adsorption one for uranium extraction.

Applications of Neutron Scattering in Technical Catalysis: Characterisation of Hydrogenous Species on/in Unsupported and Supported Palladium

Recent results from inelastic neutron scattering (INS) measurements are reviewed that show the synergy between research on hydrogen adsorption/absorption on/in catalysts and chemical engineering. The proton dynamics of catalysts for large scale reactor technology are compared. The focus is the identification and quantification of hydrogenous species on, and inside, fresh, hydrogenated and dehydrogenated palladium black and supported palladium catalysts of different particle size, type of support and, therefore, morphology. INS studies of in-situ hydrogenation/ dehydrogenation of catalysts of 25–60 g size per sample are carried out in stainless steel cans as a function of varying hydrogen pressures. Differences in hysteresis effects in retaining hydrogen inside the catalyst in desorption from palladium hydrides and hydrogen bonding in adsorption sites in varying particle morphologies on different supports were evaluated. This aids the understanding of hydrogen/palladium interactions in catalytic processes with varying local hydrogen partial pressure, e.g. in loop reactors. The importance of the measured on-top Pd–H site in catalytic hydrogenation reactions is discussed together with previous INS results on the degree of deactivation of a technical catalyst by molecular blocking of the on-top site.

Model of local hydrogen permeability in stainless steel with two\xa0coexisting structures

The dynamics of hydrogen in metals with mixed grain structure is not well understood at a microscopic scale. One of the biggest issues facing the hydrogen economy is “hydrogen embrittlement” of metal induced by hydrogen entering and diffusing into the material. Hydrogen diffusion in metallic materials is difficult to grasp owing to the non-uniform compositions and structures of metal. Here a time-resolved “operando hydrogen microscope” was used to interpret local diffusion behaviour of hydrogen in the microstructure of a stainless steel with austenite and martensite structures. The martensite/austenite ratios differed in each local region of the sample. The path of hydrogen permeation was inferred from the time evolution of hydrogen permeation in several regions. We proposed a model of hydrogen diffusion in a dual-structure material and verified the validity of the model by simulations that took into account the transfer of hydrogen at the interfaces.

NanoSIMS analysis of hydrogen and deuterium in metallic alloys: Artefacts and best practice

Hydrogen embrittlement can cause catastrophic failure of high strength alloys, yet determining localised hydrogen in the microstructure is analytically challenging. NanoSIMS is one of the few techniques that can map hydrogen and deuterium in metal samples at microstructurally relevant length scales. Therefore it is essential to understand the artefacts and determine the optimum methodology for its reliable detection. An experimental methodology/protocol for NanoSIMS analysis of deuterium (as a proxy for hydrogen) has been established uncovering unreported artefacts and a new approach is presented to minimise these artefacts in mapping hydrogen and deuterium in alloys. This method was used to map deuterium distributions in electrochemically charged austenitic stainless steel and precipitation hardened nickel-based alloys. Residual deuterium contamination was detected in the analysis chamber as a result of deuterium outgassing from the samples, and the impact of this deuterium contamination was assessed by a series of NanoSIMS experiments. A new analysis protocol was developed that involves mapping deuterium in the passive oxide layer thus mitigating beam damage effects that may prevent the detection of localised deuterium signals when the surface is highly deuterated.

Local initiative hydrogen production by utilization of aluminum waste materials and natural acidic hot-spring water

Hydrogen is gaining attention as an energy source, but its production through fossil-fuel use is not environmentally friendly. A more sustainable source could be the hydrothermal reaction involving aluminum and water reaction, which owns technical issues on aluminum passivation and material sources for the upscale application. This study analyzes the aluminum-water hydrothermal reaction at laboratory and field scales and includes an environmental assessment of H2 fuel production involving hot-spring water with extremely low pH (~1) and boiling temperature (~373 K). Acidic hot-spring alternates water sources, and its unique feature activates aluminum surface by attacking oxide layer, hence enables H2 generation. Aluminum waste sources include dross and cutting chips, which could replace primary aluminum metal. The highest H2 yield could be obtained of about ~55 mmol H2 gAl−1 for the chip (almost reached theoretical yield) and a smaller amount of ~20 mmol H2 gAl−1 for dross. The environmental assessment comprises carbon dioxide emissions and energy consumption from the overall H2 fuel system resulting in a reduced environmental impact. The proposed hydrogen production method encourages hydrogen energy development from the local scale. In addition, the use of aluminum waste materials is a new and useful waste management strategy than direct disposal, and hot-springs use advances its direct utilization.

Method for Evaluating Hydrogen Embrittlement of High-Strength Steel Sheets Considering Press Formation and Hydrogen Existence State in Steel

High strength steel sheets are increasingly being used due to the growing need to improve fuel efficiency by reducing vehicle weight. Steel sheets are usually used as automotive parts formed by pressing, etc., and complicated strain is generated in the steel sheet after forming. This strain is thought to affect the occurrence of hydrogen embrittlement. In this study, a new hydrogen embrittlement evaluation method using a forming limit diagram was devised. A forming limit diagram of a steel sheet with a strength level adjusted to 1470 MPa was prepared for uniaxial, plane strain and biaxial modes, and stress and hydrogen were applied to the specimens formed with respective strain modes to evaluate the occurrence of fracture. In order to examine the relationship between the hydrogen content and the cracking, evaluation of the hydrogen content by Thermal Desorption Analysis, visualization of hydrogen by Secondary Ion Mass Spectrometry and microstructure analysis by Electron BackScatter Diffraction were carried out. It was found that cracks are generated in the strain mode in which hydrogen accumulates locally in the steel even when the apparent hydrogen content is small, and it was clarified experimentally that evaluation of local hydrogen concentration is important for the evaluation of hydrogen embrittlement.

Visualization of Hydrogen in Stress and Strain Fields Using SIMS

In order to clarify the mechanism of hydrogen embrittlement in high strength steel, it is necessary to evaluate local hydrogen concentration in stress and strain fields where hydrogen embrittlement is considered to occur. There are several ways to visualize hydrogen, but SIMS is advantageous in that it can detect hydrogen directly without reaction. In this study, visualization of hydrogen accumulated in stress and strain field was tried using SIMS. Hydrogen flux intensity in the bent portion of the U-bend specimen, where the stress gradient exists, changed according to the stress gradient, and the hydrogen flux intensity was higher on the outside of the bending than on the inside, with the center of the plate thickness at the boundary. On the shearing surface with strain field, the hydrogen flux intensity had a positive correlation with the stress. On the other hand, it remained constant with respect to the strain. From these observations, the hydrogen partitioning behavior in steel could be visualized semi-quantitatively by using the isotope labeling method with SIMS.

Photolithographic Fabrication of a Micro-electrode Surface on a Carbon Steel Sheet for Local Hydrogen Permeation Measurements

Photolithographic Fabrication of a Micro-electrode Surface on a Carbon Steel Sheet for Local Hydrogen Permeation Measurements

Effects of local stress, strain, and hydrogen content on hydrogen-related fracture behavior in low-carbon martensitic steel

The present study investigated the hydrogen-related fracture behavior of specimens with different stress concentration factors through microstructure observation, finite element (FE) simulation, and digital image correlation (DIC) analysis. The alloy studied was a simple model alloy (Fe-0.2C binary alloy) with fully martensite structure. When the hydrogen content was large (2.21 mass ppm (121 at ppm)), the crack initiation and propagation occurred along the prior austenite grain boundaries. Through the FE simulations, we found that the crack initiation sites corresponded to the region with high stress and high hydrogen content. Although the stress concentration factors were different, the stress level and the hydrogen content at the crack initiation sites were almost the same, indicating that the hydrogen-related intergranular fracture originated from stress-controlled decohesion at the prior austenite grain boundaries. For the specimen with small hydrogen content (0.41 mass ppm (22.5 at ppm)), the quasi-cleavage cracks formed at the surface of the notch root and propagated along the {011} planes. The FE simulations revealed that the plastic strains were maximum at the initiation sites of the quasi-cleavage cracks. Moreover, we confirmed that hydrogen enhanced the local plastic deformation by DIC analysis. As the local values of maximum principal stress, plastic strain, and hydrogen content at the initiation sites of the quasi-cleavage cracks were different depending on the stress concentration factor, the critical quantitative condition for the initiation of quasi-cleavage cracking was not simple compared to that of the case of intergranular cracking.

Study on silicon removal property and surface smoothing phenomenon by moderate-pressure microwave hydrogen plasma

The Si removal property achieved by a localized microwave hydrogen plasma was investigated. The relationship between plasma generation parameters (input power, H2 gas flow rate, and initial surface roughness) and the removal property (etching rate and surface roughness) was revealed. Stress relief and removal of the affected Si layer by H2 plasma etching were also demonstrated. Moreover, this H2 plasma etching technique presents no etching-rate dependence on the crystal plane orientation. Therefore, even though a multi-crystalline Si sample was etched, a mirror surface could be revealed. In addition, a 100-μm-thick Si sample could be thinned to 5.7 μm by H2 plasma etching without breaking the sample. The surface roughness of the etched Si sample depends on the etching rate. A critical etching rate exists, which determines whether the etched Si surface becomes rough or smooth. When the etching rate is significantly lower than the critical etching rate, large surface roughness is generated owing to the formation of {111} platelet defects induced by H atoms in Si crystal. By contrast, when the etching rate is higher than the critical value, the roughness formation is suppressed, and the Si surface becomes smooth despite the high H flux supplied to the Si surface. The suppression of roughness formation is discussed by comparing the etching rate with the diffusion rate of H atoms into Si. It is important to maintain the Si etching rate higher than the H diffusion rate to obtain a smooth etched Si surface.

Numerical investigation of pH control on dark fermentation and hydrogen production in a microbioreactor

The efficiency of dark fermentation, as one of the most promising bioconversion technologies to produce biohydrogen , largely depends on some important parameters, such as pH, due to the sensitivity of anaerobic bacteria and biological metabolism to pH values. Understanding mechanisms of controlling the bacteria growth and dark fermentation is critical for effective improvements in biohydrogen production in bioreactors. In this study, a pore-scale model has been developed within a coupled lattice Boltzmann method and cellular automata (LBM-CA) platform to account for effects of spatiotemporal pH variations on dark fermentation and hydrogen production. We applied the model to simulate the dark fermentation processes and hydrogen production in a porous microbioreactor to quantify (1) the effects of local acids concentrations and pH on biofilm growth, (2) the effect of dynamic local acids concentrations on pH and overall hydrogen production and extraction, and (3) the effects of acid additives on local and average pH values and hydrogen production. The results showed the importance of acid and pH in biohydrogen production and extraction rates. The production rate reduced more than 25% when inlet pH was reduced from 5 to 6. Acid injection was able to increase up to 40% more biohydrogen extraction. It was observed that the biofilm growth can decrease (up to 63.18%) in the domain when pH changes from 4 to 6. This demonstrates that the present dark fermentation model can be applied for design of high-throughout bioreactor for effective improvement of dark fermentation and hydrogen production.

Tensile properties evolution of hydrogen-induced TA10 titanium alloy welded joints

Hydrogen embrittlement of titanium alloy weldments often occur at low hydrogen concentrations. The effect of hydrogen content on tensile properties of titanium alloy welded joints and its mechanism were studied. The results show that with the increase of hydrogen content, the room temperature strength was significantly improved, the plasticity was significantly deteriorated. At 0.05 wt.% H, solid solution hydrogen had a limited effect on tissue strengthening and a slight increase in tensile strength; solid solution hydrogen reduced the pinning effect of solute atom on dislocation movement, yield strength decreased; solid solution hydrogen only depend on the diffusion and accumulation to cause the local micro-region hydrogen concentration to increase, which had a little effect on the plasticity. After 0.12 wt.% H, the pinning effect of the hydride was strengthened, the hydrogen-induced dislocation cross-slip was more difficult, and the strength at room temperature was significantly increased; the brittle hydride itself fractured, precipitated, or accelerated separation from the matrix, resulting in significant plasticity decline. When not charged with hydrogen or 0.05 wt.% H, the ductile fracture occurred in the welded joint; After 0.12 wt.% H, the brittle fracture was the main; solid solution hydrogen and the hydride had a direct effect on fracture mode transformation.