Hydrogen Uptake Research Articles

Machine learning insights into prediction of H2 gravimetric capacity in Mg-based pure metal alloys

Hydrogen is emerging as a crucial clean energy carrier, but storage challenges remain. Magnesium has the highest hydrogen storage capacity among metals, yet its high thermodynamic stability, desorption temperature, and slow reaction rates hinder practical use. Identifying suitable metal alloys for magnesium remains challenging. This study employs ML-framework with 13 inputs to predict H2 storage and release capacity (2 outputs) in Mg-based alloys, with database comprises 792 storage and 279 release observations. Linear-models initially performed poorly, leading to the development of nonlinear models such as tree ensembles, kernel based methods, and neural networks. After hyperparameter tuning with 5-fold cross-validation, an ANN with Bayesian regularization achieved higher accuracy in predicting hydrogen gravimetric capacity (R2 = 0.86 for storage, R2 = 0.93 for release for test data). With this model, post-analysis revels key-factors influencing hydrogen uptake are particle size, Mg composition, and pressure, while temperature and time significantly affect hydrogen release. Finally, this study identifies operating ranges for these factors, providing insights for improving/accelerating Mg based hydrogen storage materials development.

Hydrogen diffusivity, uptake and embrittlement of solution annealed and cold deformed austenitic stainless steel 1.4435 at hydrogen pressures up to 1000 bar and 200 °C

Austenitic stainless steel 1.4435, a candidate material for high-pressure tubing for hydrogen applications, was investigated in two different stages of cold deformation (0 and 27 %) regarding its hydrogen embrittlement tendency. The determination of effective diffusion coefficients revealed slightly increased diffusion kinetics at 60°C for the cold-reduced material (8.0 · 10−15 m²/s) compared to the solution annealed one (5.0 · 10−15 m²/s). High-pressure gaseous hydrogen charging shows no differences regarding the degree of cold deformation with a maximum hydrogen concentration of 112 wt.-ppm. Furthermore, a significant ductility loss expressed by the ratio of the reduction of area was observed.

A new approach for in situ electrochemical nanoindentation: Side charging as a promising alternative

Understanding hydrogen embrittlement in metals is an essential task for the energy transition, where hydrogen plays a key role. Besides the economic consequences of embrittlement, safety aspects are a very important factor to consider. Therefore, materials need to be screened in order to evaluate their mechanical response under hydrogen influence. Besides macroscopic mechanical testing, in situ electrochemical nanoindentation and micromechanical testing —in general— represent promising methods as they allow to characterize individual microstructural features. In the established “front-side” charging approach, hydrogen enters the sample at the same surface on which indentation tests are performed. An alternative is “back-side” charging, where hydrogen is introduced at the opposite side of the indentation location. In the present study, a novel “side” charging cell was designed and the results were compared to those obtained by “front-side” charging. For this purpose, a ferritic steel with high chromium content (X6Cr17) underwent a grain coarsening heat treatment to ensure that multiple nanoindentation experiments can be performed within a single grain. A similar grain orientation was tested with both charging approaches. The novel “side” charging cell design outperforms the stiffness of the reference front-side charging cell by 60 %. Both cell designs yielded constant Young's moduli before, during and several hours after charging. The hardness increased during charging due to hydrogen uptake, whereas the hardness settled several hours after charging to the values before charging started. The presence of hydrogen at the indentation side was confirmed by in situ X-ray diffraction using a self-reporting titanium film.

New-Generation Materials for Hydrogen Storage in Medium-Entropy Alloys.

This study presents the design, preparation, and characterization of thirty new medium-entropy alloys (MEAs) in three systems: Al-Ti-Nb-Zr, Al-Ti-Nb-V, and Al-Ti-Nb-Hf. The hardness of the alloys ranged from 320 to 800 HV0.3. Among the alloys studied, Al15Ti40Nb30Zr15 exhibited the highest-reversible hydrogen storage capacity (1.03 wt.%), with an H/M value of 0.68, comparable to LaNi5, but with a reduced density (5.11 g·cm-3) and without rare earth elements. This study further reveals a strong correlation between hardness and hydrogen absorption/desorption; higher hardness is responsible for reduced hydrogen uptake. This finding highlights the interplay between a material's properties and hydrogen storage behavior in MEAs, and has implications for the development of efficient hydrogen storage materials.

A new methodology for extra enhancement of hydrogen storage capacity of Mg–Ni based alloys: The role of gaseous O2/H2 mixture

In the present study, Mg–5Ni and Mg–15Ni alloys are prepared, and their (de)hydrogenation properties are investigated by thermal desorption spectroscopy (TDS). A new hydrogenation condition is developed to improve the hydrogen uptake properties of the Mg–Ni alloy. It is found that the hydrogen absorption and thermal desorption properties of both alloys are extremely sensitive to the presence of 3% O2 in the hydrogenation environment. Although O₂ accelerates hydrogen absorption, it lowers the desorption temperature and reduces the hydrogen storage capacity of the Mg–Ni alloy by consuming Mg₂Ni if it is added in every cycle. The hydrogen storage capacity of Mg–Ni alloys can be significantly increased by adding oxygen only in the second cycle instead of in all cycles. In the early stages of hydrogenation, only two TDS peaks are observed, while in later cycles a new peak appears at higher temperatures. These peaks correspond to the decomposition of Mg₂NiH₄ (peak 1), MgH₂ (peak 2), and the release of hydrogen from the bulk material (peak 3). It is also evident that the Mg–15Ni sample has a better hydrogen storage capacity than the Mg–5Ni sample.

A Review on hydrogen embrittlement behavior of steel structures and measurement methods

Hydrogen can be found within metals under a variety of industrial and environmental conditions. Hydrogen-metal interactions can take place through hydrogen embrittlement, hydrogen sulfide corrosion, or hydrogen absorption. Steel and other metals that are exposed to hydrogen may experience a difficulty known as hydrogen embrittlement that affects their mechanical properties. The material's ductility and toughness may be reduced as a result of this phenomena, it also increasing the risk of brittle fracture. In steel, atomic hydrogen mainly diffuses into the microstructure of the steel, causing hydrogen embrittlement. Localized weakening of the bonds between the metal atoms might result from hydrogen atoms occupying interstitial positions in the metal lattice. Especially when under stress, this may lead to a more susceptible to fracture and cracking. Concerns with hydrogen embrittlement arise in sectors like aerospace and oil and gas that use high-strength steels. If not appropriately handled, it may result in catastrophic failures. Use of hydrogen-resistant alloys, appropriate heat treatments, and protection from conditions that promote hydrogen uptake are examples of preventive measures. This literature review paper covers the definition of hydrogen embrittlement (HE), mechanisms causing HE, measurement of hydrogen concentration and preventive measures that restrict hydrogen diffusion to the steel.

Effectively enhanced catalytic effect of sulfur doped Ti3C2 on the kinetics and cyclic stability of hydrogen storage in MgH2

Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH2. Herein, the sulfur doped Ti3C2 (S-Ti3C2) was successfully prepared by heat treatment of Ti3C2 MXene under Ar/H2S atmosphere to facilitate the hydrogen release and uptake from MgH2. The S-Ti3C2 exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH2. The addition of 5 wt% S-Ti3C2 into MgH2 resulted in a reduction of 114 °C in the starting dehydriding temperature compared to pure MgH2. MgH2 + 5 wt% S-Ti3C2 sample could quickly release 6.6 wt% hydrogen in 17 min at 220 °C, and 6.8 wt% H2 was absorbed in 25 min at 200 °C. Cyclic testing revealed that MgH2 + 5 wt% S-Ti3C2 system achieved a reversible hydrogen capacity of 6.5 wt%. Characterization analysis demonstrated that Ti-species (Ti0, Ti2+, Ti–S, and Ti3+) as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH2, and sulfur doping can effectively improve the stability of Ti0 and Ti3+, contributing to the improvement of cyclic stability of MgH2. This study provides strategy for the construction of catalysts for hydrogen storage materials.

Real-time and highly responsive hydrogen mapping in pure Fe using TiO2 thin films

A hydrogen visualization method with high responsivity and chemical stability under atmospheric corrosion is necessary to inhibit hydrogen embrittlement, which can occur with hydrogen uptake of structural materials. In this study, a highly responsive hydrogen mapping technique for steels was successfully established using a TiO2 thin film and Pd intermediate layer. The color of the TiO2 film on the hydrogen-detection side changes during hydrogen charging on the hydrogen-entry side of the Fe specimen, indicating that the color changes were attributed to the hydrogen uptake of the Fe surface and subsequent introduction of hydrogen atoms to the TiO2 film. Considering the responsivity and visibility, the optimal thickness of the TiO2 film was determined to be 20 nm. As TiO2 is a chemically stable material, the proposed mapping technique can be used to monitor the hydrogen absorbed into metallic materials under outdoor conditions.

Suppression of Enhanced Magnesium Diffusion During High‐Pressure Annealing of Implanted GaN

Activation of ion‐implanted p‐type dopants in gallium nitride has demonstrated great progress utilizing high pressures to enable novel and traditional device architectures; however, such conditions consistently exhibit anomalously enhanced diffusion up to several microns in very short periods of time for device relevant concentrations. Here, this diffusion is shown to be modulated by unintentional hydrogen content within the anneal ambient and thus controllable by inclusion of a high‐temperature hydrogen getter. Furthermore, diffusion is also shown to be greatly suppressed using co‐implanted oxygen at low concentrations while simultaneously maintaining characteristics of p‐type material in photoluminescence. Subsequently, after annealing at 1300 °C for 30 min in 3.8 kbar of nitrogen pressure, the magnesium concentration in the diffusion tail is suppressed by 28% at 1–1.5 μm in depth using a hydrogen getter alone, which reduces hydrogen uptake by 45% and fully suppressed at >1 μm in depth using co‐implantation alone and further reduced with concurrent use of a hydrogen getter. Co‐implantation alone reduces the in‐diffused magnesium dose by 60% compared to reference samples.

Exceptional Hydrogen Uptake in Crystalline InxGa1-xN Semiconductors.

The irradiation of InN and InxGa1-xN samples with low-energy H ions results in exceptionally high hydrogen uptake in a crystalline semiconductor. This phenomenon is attributed to specific In-H complex formation. By exploiting spectral fingerprints of the In-H complexes observable in In L3-edge X-ray absorption spectroscopy, we provide direct evidence of complex formation. Density functional theory calculations assist in interpreting the X-ray absorption spectra and offer insights into the energetics of complex formation. We quantify the total amount of reversibly incorporated hydrogen in these semiconductors and discuss their strengths and weaknesses as innovative materials for hydrogen storage.

Unstable Metal Hydrides for Possible On-Board Hydrogen Storage

Hydrogen storage in general is an indispensable prerequisite for the introduction of a hydrogen energy-based infrastructure. In this respect, high-pressure metal hydride (MH) tank systems appear to be one of the most promising hydrogen storage techniques for automotive applications using proton exchange membrane (PEM) fuel cells. These systems bear the potential of achieving a beneficial compromise concerning the comparably large volumetric storage density, wide working temperature range, comparably low liberation of heat, and increased safety. The debatable term “unstable metal hydride” is used in the literature in reference to metal hydrides with high dissociation pressure at a comparably low temperature. Such compounds may help to improve the merits of high-pressure MH tank systems. Consequently, in the last few years, some materials for possible on-board applications in such tank systems have been developed. This review summarizes the state-of-the-art developments of these metal hydrides, mainly including intermetallic compounds and complex hydrides, and offers some guidelines for future developments. Since typical laboratory hydrogen uptake measurements are limited to 200 bar, a possible threshold for defining unstable hydrides could be a value of their equilibrium pressure of peq > 200 bar for T < 100 °C. However, these values would mark a technological future target and most current materials, and those reported in this review, do not fulfill these requirements and need to be seen as current stages of development toward the intended target. For each of the aforementioned categories in this review, special care is taken to not only cover the pioneering and classic research but also to portray the current status and latest advances. For intermetallic compounds, key aspects focus on the influence of partial substitution on the absorption/desorption plateau pressure, hydrogen storage capacity and hysteresis properties. For complex hydrides, the preparation procedures, thermodynamics and theoretical calculation are presented. In addition, challenges, perspectives, and development tendencies in this field are also discussed.

Advancing hydrogen storage predictions in metal-organic frameworks: A comparative study of LightGBM and random forest models with data enhancement

The escalating consumption of fossil fuels has given rise to a substantial upsurge in greenhouse gas concentrations and global temperatures, which, in turn, has triggered severe climate-related consequences. The critical imperative to reduce CO2 emissions and combat global warming has spurred extensive investigations into clean energy alternatives, with hydrogen emerging as a compelling zero-emission energy source. As a pivotal component of clean energy strategies, hydrogen requires designing compact, lightweight, and efficient storage systems. This study focuses on the development and evaluation of machine learning models for predicting the efficiency of Metal-Organic Frameworks (MOFs) in hydrogen storage, a key aspect of advancing clean energy technologies. MOFs, a class of nanoporous materials, show remarkable potential for hydrogen storage due to their high surface area and porosity. However, selecting the most suitable MOF for this application from a vast array of possible structures is a daunting task. In this context, machine learning algorithms offer an efficient alternative for predicting MOF suitability by considering their structural and chemical properties. We used ensemble learning methods, specifically Light Gradient Boosting Machine (LightGBM) and Random Forest (RF), to predict hydrogen uptake of MOFs based on a dataset of 219 experimentally tested samples. Two modeling scenarios were considered: one using the entire dataset, and the other involving strategic data pre-processing, including outlier removal and feature engineering. The results demonstrate that the measures taken to refine the dataset significantly enhance the predictive performance of the developed models, reducing prediction errors and improving overall goodness of fit. Specifically, the Mean Absolute Error (MAE) values for both the LightGBM and random forest models were reduced from 0.48 and 0.94, respectively, to 0.16 for both models, and the coefficients of determination (R2) increased substantially from 0.84 and 0.72 to 0.95, in both cases. Moreover, feature importance analysis unveiled that pressure-related features make the most significant contributions to the formation of tree ensembles during the model training process. A parametric sensitivity analysis was conducted revealing that H2 uptake in MOFs is most sensitive to changes in adsorption enthalpy, followed by surface area and temperature, while showing lower sensitivity to variations in pressure, consistent with established literature. These results underscore the pivotal role of data enhancement methods in refining machine learning models and can be instrumental in accelerating the development and optimization of MOF materials for clean energy applications.

Hydrogen trapping and embrittlement of titanium- and vanadium carbide-containing steels after high-temperature hydrogen charging

This work studies the effect of TiC and VC precipitate sizes on hydrogen trapping and embrittlement. Two experimental ferritic HSLA steels containing either TiC or VC carbides for precipitation strengthening are annealed in nitrogen and hydrogen gas. This results in a hydrogen uptake of up to 0.91 and 0.44 wppm in the TiC and VC steels, respectively. TEM and TDS analysis indicate that semi-coherent TiC particles trap hydrogen in misfit dislocations with an activation energy of 43 kJ/mol. Coherent VC particles are suggested to trap hydrogen in interface carbon vacancies, with an energy between 53 and 72 kJ/mol. Carbon vacancies are the likely trapping site in incoherent precipitates, where SIMS imaging confirms that incoherent TiC precipitates trap preferentially near the interface, whereas incoherent VC precipitates trap throughout their bulk. Neither alloy is embrittled in SSRT tests after hydrogen absorption, which shows that these precipitates can be used as both a hydrogen sink and a strengthening mechanism in steels.Graphical abstract

The Synergistic Effect of Carbon Black/Carbon Nanotube Hybrid Fillers on the Physical and Mechanical Properties of EPDM Composites after Exposure to High-Pressure Hydrogen Gas.

This study investigated the synergistic effect of carbon black/multi-wall carbon nanotube (CB/MWCNT) hybrid fillers on the physical and mechanical properties of Ethylene propylene diene rubber (EPDM) composites after exposure to high-pressure hydrogen gas. The EPDM/CB/CNT hybrid composites were prepared by using the EPDM/MWCNT master batch (MB) with 10 phr CNTs to enhance the dispersion of CNTs in hybrid composites. The investigation included a detailed analysis of cure characteristics, crosslink density, Payne effect, mechanical properties, and hydrogen permeation properties. After exposure to 96.3 MPa hydrogen gas, the hydrogen uptake and the change in volume and mechanical properties of the composites were assessed. We found that as the MWCNT volume fraction in fillers increased, the crosslink density, filler-filler interaction, and modulus of hybrid composites increased. The hydrogen uptake and the solubility of the composites decreased with an increasing MWCNT volume fraction in fillers. Moreover, after exposure to hydrogen gas, the change in volume and mechanical properties exhibited a diminishing trend with a higher MWCNT volume fraction. We conclude that the hybridization of CB and CNTs formed strong filler-filler networks in hybrid composites, consequently reinforcing the EPDM composites and enhancing the barrier properties of hydrogen gas.

The effect of low hydrogen content on hydrogen embrittlement of additively manufactured 17–4 stainless steel

This work aims to evaluate the impact of small amounts of hydrogen on the hydrogen-assisted cracking (HAC) of 17-4 martensitic stainless steel (SS) prepared by additive manufacturing (AM). To elucidate the effect of processing on the hydrogen–material interactions, the obtained results were compared with a conventionally manufactured (CM) counterpart. It was found that the hydrogen uptake of AM 17-4 SS is higher compared to CM; however, its resistance to HAC is improved. These differences are attributed to the presence of stronger hydrogen trapping sites, retained austenite and the absence of Nb-rich precipitates in the AM 17-4 SS. The effect of processing on the microstructure and the susceptibility to hydrogen-induced damage and hydrogen embrittlement is discussed in detail.

The relationship between thermal management methods and hydrogen storage performance of the metal hydride tank

Solid-state hydrogen storage tanks are key equipment for fuel cell vehicles and hydrogen storage. However, the low heat transfer properties of hydrogen storage tanks result in the inability to meet the hydrogen supply requirements of fuel cells. In this study, different thermal management approaches were explored through the design of LaNi5-based solid-state hydrogen storage tanks. We experimentally studied the effects of different internal heat transfer methods, that is, expanded natural graphite (ENG), copper foam, and copper fins on the hydrogen absorption and desorption performance. We also studied the effects of external cooling methods with natural convection, air cooling, and water cooling, respectively. Under the same external cooling method of natural convection, a solid hydrogen storage tank filled with 5 wt.% ENG has similar performance to a tank filled with copper foam. Compared to natural convection, air and water cooling can significantly improve the heating performance of metal hydride (MH) beds by increasing the external heat transfer coefficient. The effect of water cooling is better than that of air cooling, and in these two enhanced performance conditions, the tank filled with copper foam performs better than with ENG. In the case of water cooling, by adding copper fins to a hydrogen storage tank filled with 5 wt.% ENG, the tank was saturated with hydrogen absorption in only 29.4 min, which is 55.6 % shorter than the hydrogen uptake time in a hydrogen storage reactor without copper fins. And its stable hydrogen desorption (1 NL/min) has reached 98.1 % of the total hydrogen released. The results show that the effective thermal conductivity and heat transfer area of metal hydride bed play key roles in improving heat transfer and reaction rate. In addition, heat transfer is more important than mass transfer to improve the performance of the hydrogen storage tank.

Comparative analysis of hydrogen uptake and release kinetics in MgH2/C composites synthesized using varied surface areas graphite powders

Comparative analysis of hydrogen uptake and release kinetics in MgH2/C composites synthesized using varied surface areas graphite powders

Tracking investigation of archaeal composition and methanogenesis function from parental to offspring pigs

Archaea play a crucial role in microbial systems, including driving biochemical reactions and affecting host health by producing methane through hydrogen. The study of swine gut archaea has a positive significance in reducing methane emissions and improving feed utilization efficiency. However, the development and functional changes of archaea in the pig intestines have been overlooked for a long time. In this study, 54 fecal samples were collected from 36 parental pigs (18 boars and 18 pregnant/lactating sows), and 108 fecal samples from 18 offspring pigs during lactation, nursery, growing, and finishing stages were tracked and collected for metagenomic sequencing. We obtained 14 archaeal non-redundant metagenome-assembled genomes (MAGs). These archaea were classified as Methanobacteriota and Thermoplasmatota at the phylum level, and Methanobrevibacter, Methanosphaera, MX-02, and UBA71 at the genus level, involving hydrogenotrophic, methylotrophic, and acetoclastic pathways. The hydrogenotrophic pathway dominated the methanogenesis function, and the vast majority of archaea participated in it. Dietary changes profoundly affected the archaeal composition and methanogenesis function in pigs. The abundance of hydrogen-producing bacteria in parental pigs fed high-fiber diets was higher than that in offspring pigs fed low-fiber diets. The methanogenesis function was positively correlated with fiber decomposition functions and negatively correlated with the starch decomposition function. Increased abundance of sulfate reductase and fumarate reductase, as well as decreased acetate/propionate ratio, indicated that the upregulation of alternative hydrogen uptake pathways competing with methanogens may be the reason for the reduced methanogenesis function. These findings contribute to providing information and direction in the pig industry for the development of strategies to reduce methane emissions, improve feed efficiency, and maintain intestinal health.

Hydrogen trapping and embrittlement in metals – A review

Hydrogen embrittlement in metals (HE) is a serious challenge for the use of high strength materials in engineering practice and a major barrier to the use of hydrogen for global decarbonization. Here we describe the factors and variables that determine HE susceptibility and provide an overview of the latest understanding of HE mechanisms. We discuss hydrogen uptake and how it can be managed. We summarize hydrogen trapping and the techniques used for its characterization. We also review literature that argues that hydrogen trapping can be used to decrease HE susceptibility. We discuss the future research that is required to advance the understanding of HE and hydrogen trapping and to develop HE-resistant alloys.

Operational performance and metal droplet formation in pulsed-shielded metal arc underwater welding

Underwater Shielded Metal Arc Welding (SMAW) is highly affected by the welding depth. The arc and molten metal in contact with the surrounding environment cause operational and metallurgical challenges regarding arc stability, metal transfer, gas formation, high-cooling rates, and diffusible hydrogen uptake. The hydrostatic pressure causes losses in consumable fusion efficiency, constricts the arc, increases the number of short-circuit events, and consequently decreases the welded joint’s process quality. In the present study, the novel approach of pulsed welding current is applied to wet shielded metal arc welding and is operational characteristics are evaluated in detail. Automated welding using an arc-voltage control system was used to obtain reproducible results. For the pulse conditions, two values of pulse current combinations, taking 140 A as the mean value, were set (ΔI of 40 A and 80 A). The same pulse and base duration were chosen, giving pulsing frequencies of 2.5 Hz and 25 Hz. The voltage and current signals were acquired and the short-circuit numbers and melting rates were calculated by processing the data stability factors. As a result, it was possible to weld with lower average welding currents through pulsed-current technology. This new approach can improve the stability of the wet SMAW process and contribute to obtaining better-quality welds without any changes for the underwater welder.