Hydrogen Environment Research Articles

Work-Function-Dependent Reduction of Transition Metal Nitrides in Hydrogen Environments.

Amidst the growing importance of hydrogen in a sustainable future, it is crucial to develop coatings that can protect hydrogen-sensitive system components in reactive hydrogen environments. However, the prediction of the chemical stability of materials in hydrogen is not fully understood. In this study, we show that the work function is a key parameter determining the reducibility (i.e., denitridation) of transition metal nitrides (TMNs) in hydrogen radicals (H*) at elevated temperatures. We demonstrate that, when the work function of a TMN system drops below a threshold limit (ϕTH), its reduction effectively stops. We propose that this is due to the preferential binding of H* to transition metal (TM) atoms rather than N atoms, which makes the formation of volatile species (NHx) unfavorable. This finding provides a novel perspective for comprehending the interaction of hydrogen with TM compounds and allows prediction of the chemical stability of hydrogen-protective coatings.

Research Trends and Challenges in the Strength Properties of Materials Used in Hydrogen Environments

Research Trends and Challenges in the Strength Properties of Materials Used in Hydrogen Environments

Hydrogen resistance of reduced graphene oxide coatings prepared by electrophoretic deposition on duplex stainless steel

In this study, reduced graphene oxide (rGO) coatings were fabricated on duplex stainless steel (DSS) substrates using the electrophoretic deposition (EPD) method to evaluate their hydrogen resistance performance. The successful fabrication of rGO coatings was confirmed using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The structural characteristics were characterized using Raman spectroscopy and X-ray Diffraction (XRD). The results indicate that the EPD voltage is a crucial factor affecting the surface quality of and hydrogen resistance performance of rGO. Lower voltages resulted in lower degrees of rGO reduction and higher surface wrinkle density, while higher voltages caused bubble formation, significantly degrading the coating quality and hydrogen resistance performance. The optimal hydrogen resistance was achieved at an EPD voltage of 7.5V and a deposition time of 6 minutes. Electrochemical hydrogen charging tests and thermal desorption analysis (TDA) demonstrated that rGO coatings prepared under optimal conditions exhibited excellent hydrogen resistance efficiency, significantly reducing hydrogen atom penetration in hydrogen environments. The study further revealed that bubble formation significantly reduces the hydrogen resistance of rGO, which is attributed to increased interlayer spacing and the loss of the “labyrinth effect”.

Size and shape dependence of hydrogen-induced phase transformation and sorption hysteresis in palladium nanoparticles

Abstract Phase transitions of metals in hydrogen environments are critically important for applications in energy storage, catalysis, and sensing. Nanostructured metallic particles can lead to faster charging and discharging kinetics, increased lifespan, and enhanced catalytic activities. However, establishing a direct causal link between nanoparticle structure and function remains challenging. In this work, we establish a computational framework to explore the atomic configuration of a metal-hydrogen (M-H) system when in equilibrium with a H environment. This approach combines Diffusive Molecular Dynamics with an iteration strategy, aiming to minimize the system's free energy and ensure uniform chemical potential across the system that matches that of the H environment. Applying this framework, we investigate H chemical potential-composition isotherms during the hydrogenation and dehydrogenation of palladium nanoparticles, ranging in size from $3.9$ nm to $15.6$ nm and featuring various shapes including cube, rhombic dodecahedron, octahedron, and sphere. Our findings reveal an abrupt phase transformation in all examined particles during both H loading and unloading processes, accompanied by a distinct hysteresis gap between absorption and desorption chemical potentials. Notably, as particle size increases, absorption chemical potential rises while desorption chemical potential declines, consequently widening the hysteresis gap across all shapes. Regarding shape effects, we observe that, at a given size, cubic particles exhibit the lowest absorption chemical potentials during H loading, whereas octahedral particles demonstrate the highest. Moreover, octahedral particles also exhibit the highest desorption chemical potentials during H unloading. These size and shape effects are elucidated by statistics of atomic volumetric strains resulting from specific facet orientations and inhomogeneous H distributions. Prior to phase transformation in absorption, a H-rich surface shell induces lattice expansion in the H-poor core, while before phase transformation in desorption, surface stress promotes lattice compression in the H-rich core. The magnitude of the volumetric strains correlates well with the size and shape dependence, underlining their pivotal role in the observed phenomena.

Electric field and rotational temperature measurements based on electric field-induced coherent anti-Stokes Raman scattering in visible region (E-CARSv) in hydrogen discharge plasmas

Electric field measurements with a time resolution of a few nanoseconds using an electric field-induced coherent anti-Stokes Raman scattering in the visible region (E-CARSv) scheme were performed in a repetitively pulsed nanosecond discharge plasma in a 0.3-atm hydrogen environment. The rotational temperature was estimated using the E-CARSv scheme, which enables us to extract electric fields even at elevated gas temperatures. The estimated rotational temperature was 390 K, which reduced the E-CARSv signal intensity by approximately 50% when the rotational temperature was equal to the gas temperature. Considering the reduction, the peak electric field was estimated to be −1.4 kV/mm, which is 40% higher than −1.0 kV/mm, assuming no elevated temperatures.

Comparison of hydrogen effects on additively manufactured and conventional austenitic steels

Hydrogen and its derivatives are promising energy carriers for future renewable energy supplies. Austenitic stainless steels, such as AISI 316L, are commonly used in hydrogen transportation systems. While often thought to be resistant to hydrogen embrittlement, studies have shown that 316L is susceptible under certain conditions. As demand for hydrogen applications grows, additive manufacturing (AM) technologies offer design flexibility and customisation benefits. However, data on AM parts behaviour in hydrogen environments is lacking. This study investigates the influence of hydrogen on mechanical properties using slow strain rate testing (SSRT) on conventional AISI 304L, 316L and AM 316L specimens. The results indicate a greater effect of hydrogen on 304L compared to 316L, with AM 316L showing increased susceptibility. However, the ductility of AM 316L remains comparable to conventional 316L due to its initial ductility. The study provides insights into the performance of conventional and AM austenitic stainless steels in gaseous hydrogen environments.

Enhancing CO tolerance in hydrogen oxidation reaction through synergy of surface-modified MoOx with PtRu alloy

Even trace amounts of CO impurities present in low-cost crude hydrogen can severely poison Pt-based catalysts. For proton exchange membrane fuel cells (PEMFCs), the development of hydrogen oxidation reaction (HOR) catalysts capable of enduring CO contamination is of significant economic importance. In this study, we propose a new strategy to synergistically enhance the CO tolerance of PtRu alloys by incorporating MoOx. The MoOx modified on PtRu/C catalysts can initiate the oxidation of CO adsorbed on its surface at potentials as low as 0.125 V. The synergy effect of MoOx and bifunctional PtRu ensures sufficient HOR stability even under hydrogen containing high CO concentrations. The resulting PtRu-MoOx/C catalyst exhibits a 4.6-fold increase in remained HOR current compared to commercial PtRu/C, after two hours in a hydrogen environment containing 10,000 ppm CO. Under typical testing condition of H2/1,000 ppm CO, PtRu-MoOx/C maintains over 80 % of the initial current density even after ten hours, significantly outperforming PtRu/C (30 %) and most previously reported catalysts.

Synthesis and structure of compounds of the homological series TinO2n–1 obtained by reduction in a hydrogen environment

The paper considers one of the insufficiently explored methods for the synthesis of compounds of the homologous series TinO2n–1, in particular the method of hydrogen reduction. A series of samples (n = 2–8) were obtained from initial TiO2 powders of various chemical purities (99.0–99.99%) with modification with rutile in a wide range of temperatures and reduction times in a hydrogen environment. The influence of the purity of the initial samples, temperature and recovery time on the structure of the resulting compounds was established. Differences in the crystal structure of compounds of the homologous series TinO2n–1, as well as β- and λ-polymorphic modifications of Ti3O5, are shown. An approach to selecting the temperature and time of reduction of TiO2 powders to obtain a specific phase in compounds of the homologous series TinO2n–1 is substantiated.

Revealing grain refinement and hydrogen trapping mechanism for anti-hydrogen susceptibility of Nb-alloyed 34MnB5 press hardened steel

Hydrogen embrittlement (HE) extant a substantial concern to press-hardened steel (PHS) owing to superior strength. The high strength to light-weight automobile structures necessitates the advancement of superior HE resistance PHS. This study investigated the HE susceptibility of Nb-microalloyed PHS by slow strain rate tensile testing, u-shaped constant bending load test, and thermal desorption spectroscopy. Nb enhances microstructure and HE resistance by introducing retained austenite, refining prior austenite grains (21.14–13.73 μm), forming low-angle grain boundaries, and nano-scale precipitates. Nb-alloyed steel exhibits no-cracking over 300 h under high pre-bending stress and decreases elongation loss up to 48% in hydrogen environment as compared to Nb-free steel. Diffusible H-content in 0.12 wt% Nb-steel reduces to 14.9% of that in Nb-free steel owing to enhanced hydrogen traps, the Fcc/Bcc matrix, and carbide precipitation. The multi-phase microstructure with nano-scale NbC precipitation impeded the localized H-dispersion, enhancing the HE resistance in PHS despite its high strength.

Chemically Stable Group IV-V Transition Metal Carbide Thin Films in Hydrogen Radical Environments.

Hydrogen is a crucial element in the green energy transition. However, its tendency to react with and diffuse into surrounding materials poses a significant challenge. Therefore, developing coatings to protect system components in hydrogen environments (molecular, radicals (H*), and plasma) is essential. In this work, we report group IV-V transition metal carbide (TMC) thin films as potential candidates for protective coatings in H* environments at elevated temperatures. We expose TiC, ZrC, HfC, VC, NbC, TaC, and Co2C thin films, with native surface oxycarbides/oxides (TMO x C y /TMO x ), to H* at elevated temperatures. Based on X-ray photoelectron spectroscopy performed on the samples before and after H*-exposure, we identify three classes of TMCs. HfC, ZrC, TiC, TaC, NbC, and VC (class A) are found to have a stable carbidic-C (TM-C) content, with a further subdivision into partial (class A1: HfC, ZrC, and TiC) and strong (class A2: TaC, NbC, and VC) surface deoxidation. In contrast to class A, a strong carbide reduction is observed in Co2C (class B), along with a strong surface deoxidation. The H* interaction with TMC/TMO x C y /TMO x is hypothesized to entail three processes: (i) hydrogenation of surface C/O atoms, (ii) formation of CH x /OH x species, and (iii) subsurface C/O atom diffusion to the surface vacancies. The number of adsorbed H atoms required to form CH x /OH x species (i) and the corresponding thermodynamic energy barriers (ii) are estimated based on the change in the Gibbs free energy (ΔG) for the reduction reactions of TMCs and TMO x . Hydrogenation of surface carbidic-C atoms is proposed to limit the reduction of TMCs, whereas the deoxidation of TMC surfaces is governed by the thermodynamic energy barrier for forming H2O.

Research progress of hydrogen blocking coatings

In the context of carbon peak and carbon neutrality, the use of clean energy has become the focus of attention. Hydrogen energy as the most potential secondary energy has a very important position in various fields, so the storage and transport of hydrogen energy is one of our most important concerns. Long distance pipeline is regarded as an effective means to transport hydrogen, but the high pressure hydrogen environment is easy to cause hydrogen embrittleness and other problems in the pipeline, which seriously threatens the safety of pipeline transportation. Hydrogen blocking coatings are one of the most effective ways to solve such problems. In this paper, the research results in recent years are reviewed and summarized. The article points out the hydrogen barrier mechanism, advantages and disadvantages of various types of hydrogen barrier coatings, the current status of research, as well as future research focus and development trend.

Effects of hydrogen on the fretting wear behavior of laser cladded FeCoCrNiMo0.2 high entropy alloy coating

This study investigates laser-cladded high entropy alloy (HEA) coatings on high-speed train axles to enhance wear resistance under specific fretting conditions. Axles in humid and acidic environments absorb hydrogen, leading to accumulation in grain boundaries, which weakens their structure and causes damage under alternating stress. Despite this, the impact of hydrogen damage on the fretting wear behavior of HEA coatings has not been explored. To address this, we performed fretting wear tests on a laser-cladded FeCoCrNiMo0.2 coating and a GCr15 steel ball friction system, evaluating their performance before and after hydrogen exposure. The results of the study indicate that under a constant load of Fn = 10N and a displacement amplitude of D = 50 μm, the friction coefficient, maximum wear depth, wear volume, and wear rate increased when the system was in the hydrogen charging state compared to the non-hydrogen charging state. Specifically, the friction coefficient increased from 0.60 to 0.93, the maximum wear depth increased from 2.82 μm to 3.63 μm, the wear volume increased from 14.106 × 104μm3 to 22.098 × 104μm3, and the wear rate increased from 28.213 × 10−6 mm/Nm to 36.600 × 10−6 mm/Nm. Under the hydrogen charging state, the friction coefficient, maximum wear depth, wear volume, and wear rate all increased. This is due to hydrogen damage, including the formation of pitting pits and cracks on the surface of the coating, stress concentration, and brittle failure caused by hydrogen infiltration into the material. The presence of hydrogen makes the surface of the coating more prone to detachment, resulting in finer wear debris, deeper grooves, and increased oxidation. These factors accelerate the wear of the coating. This finding will contribute to the development and improvement of advanced surface modification techniques for materials in the hydrogen environment.

The regulation of dislocation and precipitated phase improving hydrogen embrittlement resistance of pipeline steel in high pressure hydrogen environment

In this study, the hydrogen embrittlement behavior of quenched pipeline steel tempered at 550 °C to 650 °C in a high-pressure hydrogen environment was analyzed. Hydrogen permeation tests and microstructural analyses indicated that the dislocation density of the steel decreases with increasing tempering temperature, while precipitates gradually nucleate and grow. These hydrogen traps interact with hydrogen atoms, resulting in significantly higher diffusible hydrogen content in steel tempered at 550 °C compared to that tempered at 600 °C and 650 °C. Fatigue crack growth (FCG) test results show that steel tempered at 600 °C and 650 °C exhibits significantly better hydrogen embrittlement resistance than steel tempered at 550 °C. This is primarily due to the combined effect of the high hydrogen concentration, high dislocation density and low nano carbide content in the steel tempered at 550 °C, which inhibits dislocation slip and emission, leading to high crack tip stress and rapid crack propagation. In contrast, the low dislocation density and and dispersed nano carbides in steel tempered at 600 °C and 650 °C facilitate some dislocation slip and emission, result in crack tip stress relaxation and reduced crack propagation rate. Properly controlling the initial dislocation density and increasing the density of irreversible hydrogen traps can enhance the strength of materials while improving their resistance to hydrogen embrittlement.

Trapping and diffusion in high-pressure hydrogen charged CoCrFeMnNi high entropy alloy compared to austenitic steel 316L

High entropy alloys (HEAs) have attracted considerable research attention as potential substitute materials for austenitic steels in high-pressure hydrogen environments. The corresponding hydrogen absorption, diffusion and trapping has received less scientific attention. Therefore, the CoCrFeMnNi-HEA was investigated and compared to an austenitic steel AISI 316L. Both were subjected to high-pressure hydrogen charging at 200 bar and 1000 bar. Thermal Desorption Analysis (TDA) was used to clarify the specific desorption behavior and hydrogen trapping. For this purpose, the underlying TDA spectra were analyzed in terms of a reasonable peak deconvolution into a defined number of peaks and the activation energies for the respective and predominant hydrogen trapping sites were then calculated. Both materials show comparable hydrogen diffusivity. However, there were significant differences in the absorbed hydrogen concentrations at both charging pressures. The calculated activation energies suggest strong hydrogen trapping in the CoCrFeMnNi-HEA.

Hot hydrogen testing of Mo30W matrix surrogate cermets

High temperature hydrogen exposure is one of the most challenging material issues for nuclear thermal propulsion (NTP) fuel development. Under legacy NTP programs, ceramic-metallic (cermet) fuel forms with a refractory metal matrix and dispersed uranium dioxide (UO2) fuel particles were developed and showed promising performance following hot hydrogen testing. However, since the conclusion of those programs, established fabrication techniques, material feedstocks, and the ability to use highly enriched have been reduced or lost all together. In this study, a cermet consisting of a solid solution alloy of molybdenum with 30 wt percent tungsten (Mo30W) was fabricated using spark plasma sintering. Fabrication process parameters were selected to optimize the cermet microstructure using lessons learned from historic NTP programs. Yttria stabilized zirconia particles (50 to 70 % volumetric loading) were used as a fuel particle surrogate. To evaluate whether as-fabricated microstructures exhibited similar resilience as legacy cermet fuels to a hot hydrogen environment, samples were exposed to hot flowing hydrogen from 1920 to 2500 °C (∼2290 to 2770 K). The cermets performed well with minimal mass loss, minor to no cracking, and good retention of internal surrogate particles. Based on these findings, recommendations for future studies with Mo30W-UO2 cermets as an NTP fuel form are provided.

Catalytic hydrothermal liquefaction of Azolla filiculoides into hydrocarbon rich bio-oil over a nickel catalyst in supercritical ethanol

Hydrothermal liquefaction (HTL) is one of the most promising thermochemical techniques for converting wet biomass into crude oil-like products (bio-oil). In this study, Catalytic hydrothermal liquefaction of Azolla filiculoides (AZ) was performed over a various loading of nickel (Ni) on magnesium oxide (MgO) catalyst for the higher and quality bio-oil production. The key operating parameters such as temperature, reaction holding time, amount of Ni on MgO supports catalyst, and reaction solvents were investigated in the presence of a hydrogen environment. There was a 12.8 wt% increase in bio-oil yield and a 6.3 wt% decrease in biochar yield with addition of 15 wt% Ni catalysts compared to the non-catalytic reaction bio-oil yield (44.0 wt%). Results confirmed the highest total bio-oil yield of 56.8 wt% was attained at 280 °C with the catalyst amount of 15 wt% at a residence time of 45 min. Gas chromatography-mass spectrometry (GC-MS), FT-IR, CHNS, TGA, and NMR analyses were performed on the bio-oil, identifying 32.8 % long-chain hydrocarbons (C12-C16) along with small amounts of alcohols, alkanes, and esters. The boiling point distribution revealed that bio-oil produced using the Ni/MgO catalyst contained a significantly higher proportion of diesel-range hydrocarbons (42.4 %). Furthermore, the bio-oil yield under ethanol solvent and Ni catalysts showed higher heating value (HHV) 42.2 MJ/kg. Overall in the presence of Ni hydrogenation efficient catalysts on MgO in the liquefaction reaction promoted the deoxygenation and hydrogenation reaction.

The evolution of model Rh/Fe3O4(001) catalysts in hydrogen environments

Single metal atoms dispersed on oxides are a new emerging class of catalysts owing to their unique electronic and chemical properties. In this study, we have prepared a series of model single-atom catalysts possessing well-characterized Rh sites that include Rh adatoms (Rhad), mixed surface layers with octahedrally-coordinated Rh (Rhoct), as well as metallic Rh clusters and nanoparticles (Rhmet) on Fe3O4(001). Using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), we investigated the activity of such model systems towards H2 and their stability in reducing environments. Our results show that the atomically dispersed Rhad and Rhoct species do not activate H2, which would result in the formation of surface hydroxyls on Fe3O4(001). In contrast, the presence of Rhmet in H2 results in the formation of hydroxyls and subsequent etching of the Fe3O4(001) at higher temperatures (≥ 500 K) due to water formation via the Mars−van Krevelen mechanism. Additionally, such surface etching leads to the release of the Rhoct from the surface lattice and their sintering to Rhmet. To bridge the material gap between the surface science models and high surface area catalysts, we perform parallel studies on powder Rh/Fe3O4 catalysts. The XPS characterization shows remarkable similarities between these systems. Further, our surface science studies provide an atomistic picture of the behavior of high surface area catalysts in the H2 atmosphere.

Effects of hydrogen on the tribological performance of heavily loaded lubricated contacts

The objectives of this investigation were to experimentally characterize the effect of hydrogen on the tribological performance of heavily loaded lubricated contacts. In order to achieve these objectives, a ball-on-disk film thickness and traction measurement test rig and a four-ball wear tester were modified to introduce gaseous hydrogen into the lubricated contact. Using the ball-on-disk test rig, lubricant film thickness, and traction were measured operating in air, nitrogen, and hydrogen environments. The results indicate that hydrogen environment has no effect on the lubricant film thickness and traction coefficient. The wear performance of the lubricant was evaluated in air, nitrogen, and hydrogen environments using the four-ball tester according to ASTM D4172 standard. Wear scar dimensions were determined through optical profilometry and compared for each condition. The results demonstrated that the wear scar diameter is slightly higher in a hydrogen environment. Additionally, the effects of hydrogen embrittlement on the wear performance were investigated using the four-ball tester. The balls used in the four-ball tester were precharged with hydrogen in Ammonium Thiocyanate. Wear scar profilometry results showed significantly larger wear scars and excessive pitting on the worn surface of precharged specimens. Results from this investigation shows that a gaseous hydrogen environment has a negligible effect on friction and wear as compared to diffused hydrogen in the material.

Green synthesis of ZIF-67 nanoparticles via microfluidics: Towards sustainable nanomaterial production

This study explored the synthesis of zeolitic imidazolate framework-67 (ZIF-67) nanoparticles using a microfluidic reactor, focusing on the effects of reactant concentration, temperature, and flow rate on the material’s properties. Design Expert software was utilized to optimize these variables to enhance the synthesis process while preventing reactor clogging due to precipitate formation. The experiments varied concentrations of cobalt (II) nitrate hexahydrate and 2-methylimidazole, along with temperature and flow rates. After synthesis, the samples underwent extensive characterization, including FTIR, NMR, TEM, SAED, and XRD analyses. FTIR results confirmed the successful formation of ZIF-67, with varying conditions leading to shifts in peak positions and intensities, indicating changes in bonding and molecular structure. NMR spectra provided insights into the hydrogen environments within the nanoparticles. TEM and SAED analyses revealed that the nanoparticles predominantly exhibited a uniform rhombic dodecahedral morphology with diameters ranging from 5 to 10 nm. XRD patterns were consistent with simulated data, showing variations in peak positions and crystallinity with changes in synthesis conditions. The study highlighted that increasing reactant concentrations, temperature, and flow rate generally enhanced the production rate and crystallinity of ZIF-67, with 2-methylimidazole concentration having the most significant impact. The findings contributed to optimizing ZIF-67 synthesis, demonstrating the feasibility of using microfluidic reactors and green solvents for producing high-quality nanoparticles with controlled properties.

Nuclear Magnetic Resonance (NMR) Assessment of Bio and Crude Oil-Based Rejuvenation

Asphalt binders in pavements lose their stability through aging and eventually fail in the field. Using nuclear magnetic resonance (NMR) to monitor the primary longitudinal relaxation time of asphalt samples and the ratio of material that carries this primary relaxation time has been shown to indicate the impact of ultraviolet (UV) radiation on the aging of asphalt pavements. Longitudinal NMR relaxation was used to investigate two types of proposed asphalt rejuvenators, a bio-oil-based rejuvenator and a crude-oil-based rejuvenator. Two different binders with the performance grades (PG) 64-22 and 76-22 were considered for their interactions with the rejuvenators. After 72 h of exposure to intense UV radiation, specifically designed NMR relaxometry experiments were applied to compare the rejuvenation capabilities of the two rejuvenator samples. The crude oil-based rejuvenator was found to exhibit relaxation times similar to the binder samples while the bio-based material showed relaxation times that pointed to different nuclear hydrogen environments. Both rejuvenators reduced the primary relaxation time of the PG 76-22 binder, which indicates that their stiffness was reduced. Both types of rejuvenators also seemed to prevent the effects of UV aging. Two mechanisms of rejuvenation were identified by NMR relaxometry. The primary relaxation time can be used to indicate a change in stiffness while the primary ratio of the material is tied to oxidative aging. Oxidative aging creates distinct hydrogen environments due to asphaltene aggregation. The bio-based rejuvenator only reduced the binder’s stiffness, while the crude oil-based rejuvenator also reduced the aggregation of asphaltenes. Consequently, the bio-based rejuvenator could be classified as an asphalt softener, while the oil-based material acted like a true rejuvenator.