Activation Energy For Hydrogen Diffusion Research Articles

Strain engineering for optimized hydrogen storage: Enhancing ionic conductivity and achieving near-room-temperature desorption in Mg₂NiH₄

This study investigates strain engineering to optimize hydrogen storage in Mg₂NiH₄, with a focus on enhancing ionic conductivity and approaching room-temperature desorption. Using density functional theory (DFT), we analysed the effects of uniaxial and biaxial tensile and compressive strains on the structural, mechanical, diffusion kinetics, and electronic properties of Mg₂NiH₄. The activation energy for hydrogen diffusion was found to range from 0.38 to 0.45 eV under different strain conditions. The application of strain significantly influences ionic conductivity, with uniaxial strain resulting in values between 1.18 and 25.5 S/m, and biaxial strain yielding values from 12.3 to 18.3 S/m. Mechanical analysis shows that Mg₂NiH₄ exhibits brittle behaviour across all strain conditions. Additionally, electronic structure analysis indicates that the material maintains its metallic properties under both uniaxial and biaxial strain. Although the study did not achieve room-temperature desorption, it demonstrated significant progress, with desorption occurring at approximately 500 K. These results demonstrate that strain engineering can significantly improve ionic conductivity and facilitate hydrogen desorption closer to practical room temperature, providing valuable insights for optimizing Mg₂NiH₄ for practical hydrogen storage applications.

Enhanced hydrogenation properties of two-dimensional MgH2 by doping, vacancy-like defects and strain engineering: A theoretical study

Hydrogen storage materials are crucial for the development of clean energy technologies, as they offer a sustainable solution for energy storage. Among various materials, magnesium hydride (MgH2) offers excellent storage capacity and cost performance. However, its practical application is limited by slow dehydrogenation kinetics and high operating temperatures. To overcome these challenges, novel methods with improved properties are needed. This study aims to explore a two-dimensional (2D) MgH2 structure and its modifications using density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations. We investigate the thermodynamic stability and dehydrogenation properties of pure 2D MgH2, as well as 2D MgH2 doped with transition metals (Al, Cr, and Nb) and Mg-defects. Additionally, the effects of biaxial strain on pure 2D MgH2 are explored. The results indicate that the decomposition temperature and stability can be reduced by introducing transition metals, applying biaxial strain, and creating defects. Furthermore, the Cr-doped 2D MgH2 system exhibits excellent hydrogen storage performance and dehydrogenation kinetics under ambient conditions. It has a formation enthalpy of −39.68 kJ/mol.H2, a desorption temperature of 292.53 K, and an hydrogen storage capacity of 7.368 wt%. We also calculated the activation energy for hydrogen diffusion, showing that the lowest value, 0.089 eV, is observed in the Al-doped structure, indicating the fastest hydrogen diffusion among the modifications. These results are helpful for the understanding of absorption/desorption of the 2D MgH2 system and could ultimately improve the design of Mg-based H2-storage materials.

Hydrogen diffusion and hydrogen embrittlement in iron (steel)

This article examines the diffusion of hydrogen (H-diffusion) and the temperature dependences of the diffusion coefficient of hydrogen (DH) in the metal (M)-hydrogen system. The metal used was iron and low-alloy steel. Taking into account experimental data on hydrogen diffusion in the Fe-H and steel-H systems, the main diffusion parameters were calculated and compared. It is shown that the temperature dependences of the hydrogen diffusion coefficient in metal samples in a one-stage reaction under isothermal conditions are described by the Arrhenius equation. For some M-H systems, experimental data show a deviation of the diffusion coefficient from the ideal one calculated using the Arrhenius equation. This discrepancy can be eliminated using the statistical theory of absolute reaction rates. For the temperature range 25–1250 oС, the pre-exponential coefficient and activation energy of hydrogen diffusion in a body-centered cubic (bcc) lattice of iron (α–Fe) were calculated using the Arrhenius equation. These parameters make it possible to describe the dependence of the rate of hydrogen diffusion in a metal on temperature and to predict the behavior of hydrogen diffusion when changing the conditions of the kinetic process (concentration of substances, pressure, structure, composition, etc.). Tabular values of the calculated pre-exponential factor and activation energy of hydrogen diffusion in previously studied iron-based samples are presented. The temperature dependences of the hydrogen diffusion coefficient in a lattice of iron α–Fe can be divided into low-temperature and high-temperature regions. The calculated diffusion parameters of hydrogen in the metal lattice for the low-temperature 25– 800 oC and high-temperature 800–1250 oC regions differ markedly from each other. In addition, these calculated values are significantly influenced by the structure and composition of the metal. We also studied the diffusion of hydrogen in α-iron using ab initio density functional calculations. Molecular dynamics calculations using transition state theory were used. The calculated diffusion coefficient of hydrogen in α-Fe is consistent with previously obtained experimental data. Hydrogen embrittlement (HE) is considered using internal pressure, hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion embrittlement (HEDE) theories.

Hydrogen interaction with vacancy defects in tungsten: Unraveling the influence on diffusion mechanisms and mechanical properties

This study investigates hydrogen diffusion in tungsten at high temperatures using molecular dynamics simulations. It explores the effect of different hydrogen concentrations on diffusion mechanisms, the interaction of hydrogen atoms with vacancy defects, and their impact on the mechanical properties of tungsten. The activation energy for hydrogen diffusion in perfect bulk tungsten with 0.1 % hydrogen concentration is calculated as 0.235 eV, with a diffusion pre-exponential factor of 5.336 × 10-8 m2/s at temperatures ranging from 1000 to 3000 K. The investigation reveals two factors contributing to the increase in activation energy with temperature: migration paths involving TIS-TIS and TIS-OIS-TIS pathways, and an increase in migration energy. Three diffusion regimes are identified, with trapping effects dominating at temperatures below 1500 K, TIS-TIS pathway dominating at intermediate temperatures, and TIS-OIS-TIS pathway becoming more prominent at higher temperatures. Increasing hydrogen concentration up to 2 % (H/W concentrations in fusion environments) has minimal effect on diffusion in perfect tungsten. However, in a W-H-V system with a 1 % vacancy defect, increasing hydrogen concentration increases the effective diffusion coefficient and activation energy. The presence of hydrogen atoms and vacancy defects reduces the tensile strength and elastic modulus of tungsten, with hydrogen atoms having a greater impact on mechanical properties compared to vacancies. The degree of reduction in mechanical properties is proportional to the concentration of hydrogen atoms and vacancy defects.

Impurity influence on the hydrogen diffusivity in B2–TiFe

The projector augmented-wave method within the electron density functional theory is used for calculations of the hydrogen absorption energy and its migration barriers in the doped B2–TiFe. An analytical expression for the temperature-dependent diffusion coefficients of the hydrogen in the doped alloy is derived using Landman's method. An approach for estimation of the average jump rates of hydrogen that are necessary for calculations of the diffusion coefficient in the doped alloys is developed. The activation energy of hydrogen diffusion and the pre-exponential factor are estimated. The effect of impurities on the hydrogen diffusion in the alloy is discussed.

A limiting current hydrogen sensor based on BaHf0.8Fe0.2O3-δ dense diffusion barrier and BaHf0.7Sn0.1In0.2O3-δ protonic conductor

A limiting current hydrogen sensor was successfully prepared by the co-pressing and co-sintering method using proton-electron mixed conductor BaHf0.8Fe0.2O3-δ as the dense diffusion barrier instead for small hole and BaHf0.7Sn0.1In0.2O3-δ as proton conducting electrolyte. The BaHf0.8Fe0.2O3-δ and BaHf0.7Sn0.1In0.2O3-δ powders were synthesized by high temperature solid state method. The phase composition, microstructure, chemical stability and conductivity of materials were characterized. Sensing performance of the hydrogen sensor was tested. The results show that dense BaHf0.8Fe0.2O3-δ and BaHf0.7Sn0.1In0.2O3-δ layer are closely combined together by the co-pressing and co-sintering technique at 1600 °C for 8 h and clear boundaries are observed between two pure perovskite phases. BaHf0.8Fe0.2O3-δ shows excellent chemical stability for pure H2 and CO2, water steam and 200 ppm H2S/Ar. Meanwhile, as the dense diffusion barrier, BaHf0.8Fe0.2O3-δ possesses considerable proton and electron conductivity compared with small hole. The sensor shows a stable limiting current platform in 0–600 ppm H2 at 400–600 °C at a certain voltage range due to dense BaHf0.8Fe0.2O3-δ layer forming diffusion control. The limiting current (ΔIL) has a good linear dependence on the hydrogen concentration. In addition, there is a good linear relationship between log(ILT) and 1000/T, and the Arrhenius model of limiting current is log(ILT) = 6.21-4.96 × 1000/T, and the hydrogen diffusion activation energy is 0.98 eV. The sensor has good long-term stability and high anti-interference capability to O2, CO2 or H2S, but water vapor has a certain effect on sensing performance.

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.

The dependence of hydrogen embrittlement on hydrogen transport in selective laser melted 304L stainless steel

The mechanical property and hydrogen transport characteristics of selective laser melting (SLM) 304L stainless steel were investigated by tensile tests and thermal desorption spectroscopy (TDS). The heat treatment affected the hydrogen embrittlement (HE) susceptibility and the treatment at 950 °C showed the larger HE effects. Cellular structures and melt-pool boundaries were dissolved at 850 and 950 °C, respectively. TDS results indicate that the hydrogen diffusivity of the as-received SLM 304L was lower than that of wrought 304L and the hydrogen diffusion activation energy increased with the recrystallisation degree, which was related to the dislocation density. Dislocations, rather than strain-induced martensite, were the main cause of HE owing to the high austenite stability of the samples. The pre-existing dislocations in the SLM 304L sample heat-treated at 950 °C for 4 h affected the hydrogen transport behaviour during sample stretching and led to severe HE.

Influence of oxygen on trap-limited diffusion of hydrogen in proton-irradiated n-type silicon for power devices

The growing demand for power devices has led to the use of magnetic field-applied Czochralski (m:Cz) wafers owing to the limited production capacity and available diameters of the traditionally used floating zone (FZ) wafers. Consequently, the influence of oxygen impurities in the wafers on the electrical properties of devices, regardless of the growth method, needs to be investigated to achieve a stable fabrication process for power devices. Using the proton irradiation doping process and spreading resistance profiling technique, we evaluated the effective diffusion coefficient (Deff) related to trap-limited diffusion of hydrogen and the effects of impurities on diffusivity. We irradiated n-type silicon wafers, which have different carbon, oxygen, and phosphorus concentrations, with 2 MeV protons and annealed them at 300–400 °C. By analyzing the width of the n-type region, where hydrogen-related shallow donors (HDs) are induced, we estimated Deff to be five to six orders of magnitude lower than the intrinsic diffusion coefficient, indicating that hydrogen motion is highly trap-limited. Deff was significantly dependent on the oxygen concentration, and the activation energy of hydrogen diffusion varied from 0.57 ± 0.15 eV (pure epitaxial wafer) to 2.19 ± 0.15 eV (m:Cz wafer). This trend suggests that oxygen-related defects preferentially trap the mobile hydrogen released from thermally dissociated HDs. This study also reveals that the diffusion coefficients of different materials when annealed at 400 °C are comparable. This information is essential to realize the cost-effective production of power devices because we can treat m:Cz and FZ wafers equivalently during the doping process.

A new perspective on hydrogen diffusion and hydrogen embrittlement in low-alloy high strength steel

Hydrogen diffusion and hydrogen induced embrittlement have been studied in low-alloyhigh strength steel tempered at three different temperature using electrochemical permeation and mechanical tensile tests, respectively. After multiple hydrogen trap sites around dislocation core was first proposed, the quantitative relations between hydrogen diffusivity, hydrogen concentration, as well as activation energy for hydrogen diffusion and hydrogen trap sites density were developed. In addition, the hydrogen-induced embrittlement would result from higher trap density and higher hydrogen concentration. Hence the connection among hydrogen diffusion, microstructure and hydrogen induced embrittlement were established where the hydrogen trap sites density served as a bridge.

Hydrogen diffusion through Ru thin films

In this paper, an experimental measurement of the diffusion constant of hydrogen in ruthenium is presented. By using a hydrogen indicative Y layer, placed under the Ru layer, the hydrogen flux through Ru was obtained by measuring the optical changes in the Y layer. We use optical transmission measurements to obtain the hydrogenation rate of Y in a temperature range from room temperature to 100 °C. We show that the measured hydrogenation rate is limited mainly by the hydrogen diffusion in Ru. These measurements were used to estimate the diffusion coefficient, D, and activation energy of hydrogen diffusion in Ru thin films to be D = 5.9 × 10−14 m2/s ∙ exp (-0.33 eV/kBτ), with kB the Boltzmann constant and τ the temperature.

Molecular and Atomic Hydrogen Diffusion Behavior by Reaction Kinetic Analysis in Projection Range of Hydrocarbon Molecular Ion for CMOS Image Sensors

In this study, two types of hydrogen diffusion behavior in the projection range of a hydrocarbon molecular ion after high‐temperature heat treatment for the passivation of interface state defects at SiO2/Si interface of the CMOS image sensor is presented. The hydrogen peak concentration in the hydrocarbon ion projection range is observed by secondary ion mass spectrometry analysis after silicon epitaxial growth and the subsequent high‐temperature heat treatment. Moreover, the hydrogen peak concentration strongly depends on heat treatment time after epitaxial growth and the subsequent heat treatment. Two dissociation activation energies by reaction kinetic analysis using the results of the time dependence of hydrogen diffusion behavior are also determined. Assuming two dissociation reactions, the activation energy from the projection range of a hydrocarbon molecular ion is derived. The results of reaction kinetic analysis show that the dissociation activation energies are 0.79 eV for molecular hydrogen and 0.42 eV for atomic hydrogen. The dissociation activation energy of 0.79 eV indicates molecular hydrogen diffusion activation energy, whereas that of 0.42 eV indicates atomic hydrogen diffusion from the projection range of a hydrocarbon molecular ion. Therefore, it is believed that the molecular and atomic hydrogen diffusion behavior of the hydrocarbon molecular ion implanted silicon epitaxial wafers can contribute to the effective reduction in the density of interface state defects at the SiO2/Si interface.

The effect of graphene oxide reduction temperature on the kinetics of low-temperature sorption of hydrogen

The effect of thermal reduction of graphene oxide on the hydrogen sorption and desorption kinetics was studied by temperature-programmed desorption in the 7–120 K temperature range. The heat treatment of graphene oxide samples resulted in a decrease in the activation energy for hydrogen diffusion by more than an order of magnitude (by a factor of 12–13) compared with the initial graphite oxide. This change in the activation energy is, most likely, caused by exfoliation (loosening) of the graphite oxide carbon sheets upon the thermal removal of intercalated water, which changes the sorption character by decreasing the influence of the opposite walls in the interlayer spaces.

Effect of Microstructure on Hydrogen Permeation in EA4T and 30CrNiMoV12 Railway Axle Steels

A comparative study was conducted to reveal the effect of microstructure on hydrogen permeation in the EA4T and 30CrNiMoV12 railway axle steels. Unlike the EA4T with its sorbite structure, 30CrNiMoV12 steel shows a typical tempered martensitic structure, in which a large number of fine, short, rod-like, and spherical carbides are uniformly dispersed at boundaries and inside laths. More importantly, this structure possesses plentifully strong hydrogen traps, such as nanosized Cr7C3, Mo2C, VC, and V4C3, thus resulting in a high density of trapping sites (N = 1.17 × 1022 cm−3). The hydrogen permeation experiments further demonstrated that, compared to EA4T, the 30CrNiMoV12 steel not only delivered minimally effective hydrogen diffusivity but also had a high hydrogen concentration. The activation energy for hydrogen diffusion of the 30CrNiMoV12 steel was greatly increased from 23.27 ± 1.94 of EA4T to 47.82 ± 2.14 kJ mol−1.

Effects of alloying elements and heat treatment on hydrogen diffusion in SCRAM steels

In this paper, the effects of alloying elements Ti and N, different heat treatments and permeation temperature on hydrogen diffusion in SCRAM steels were investigated. Devanathan-Stachurshi electrochemical hydrogen permeation technique was used to determine the hydrogen diffusivity. The results show that increasing the content of Ti and N can decrease the hydrogen diffusion coefficient of SCRAM steels. Compared with the traditional quenching and tempering heat treatment process, the process including an intermediate hold can refine the M23C6 phase, increase the volume fraction of MX phase but coarsen the martensitic lath. The twice quenching and tempering heat treatment process can not only refine the martensitic lath and M23C6 phase, but also increase the volume fraction of MX phase, resulting in a decrease of hydrogen diffusivity. The hydrogen permeation steady-state current density and the hydrogen diffusivity increase with the rise of permeation temperature. The temperature dependence of hydrogen diffusion coefficient conforms with the Arrhenius relationship. And the activation energy for hydrogen diffusion of two SCRAM steels with different heat treatments was determined.

Dependence of trapping states on the hydrogen content of high-carbon ferrite-austenite dual-phase steel

States of hydrogen present in high carbon ferrite (α)-austenite (γ) dual phase steel were analyzed under various hydrogen charging conditions using thermal desorption analysis (TDA). Specimens including 0%γ and 10%γ in α were prepared. The 10%γ specimen consisted of bainitic ferrite and thermally stable retained austenite. When the 10%γ specimen were charged with hydrogen under high fugacity condition, the amount of hydrogen rapidly increased, the end temperature of hydrogen desorption in TDA profile increased, the hydrogen degassing time at 30 ° C increased, and the trap activation energy increased from about 30 kJ/mol to 47 kJ/mol. This 47 kJ/mol value is in excellent agree with the activation energy of hydrogen diffusion in γ phase. These results probably indicated that hydrogen is not absorbed in γ phase but α phase under lower fugacity conditions, i.e., lower amount of hydrogen. In contrast, hydrogen is absorbed in not only α phase but also γ phase under higher fugacity conditions, i.e., higher amount of hydrogen.

Thermocatalytic pyrolysis of CO molecules. Structure and sorption characteristics of the carbon nanomaterial

A carbon nanocondensate containing multiwalled carbon nanotubes has been produced by dissociation of CO molecules on an iron-nickel catalyst at temperatures of 400–500 °C. X-ray diffraction is used to show that this condensate contains two phases with different densities and degrees of ordering. Elevated synthesis temperatures lead to a higher density and smaller differences in the phases, which are related to increased freedom from defects in the carbon layers and a greater number of layers in the multiwalled carbon nanotubes. Studies of the sorption and subsequent desorption kinetics of hydrogen by the synthesized samples at temperatures of 7–120 K showed that when the temperature is lowered from 120 to 65 K, an increased sorption time for H2, which is typical of thermally activated diffusion, was observed in all the samples. At temperatures below 65 K the characteristic hydrogen sorption times depended weakly on temperature; this can be explained by a predominance of tunnel diffusion over thermally activated diffusion. At temperatures of 7–20 K, the temperature dependence of the characteristic times had features that appear to be related to the formation of a monolayer of H2 molecules on the inner surface of the nanotube cavities. The dependence of the hydrogen diffusion activation energy on the temperature at which the samples were synthesized correlates well with x-ray spectroscopy data: n rise in the activation energy is observed as the relative amount of the highly ordered carbon phase increases.

Hydrogen diffusion in ultrafine-grained iron with the body-centered cubic crystal structure

The role of grain boundaries in Fe on hydrogen diffusion has been investigated by electrochemical permeation tests using ultrafine-grained Fe produced by high-pressure torsion (HPT) processing. Permeation tests were also conducted on cold-rolled and water-quenched Fe to understand the trapping effect of dislocations and vacancies. Hydrogen diffusion was delayed in all these discs. However, the delay mechanism in the HPT-processed disc was different from that in rolled and water-quenched Fe. Grain boundaries do not act as trapping sites but slow the diffusion. The diffusion coefficients of hydrogen were significantly decreased by HPT processing on account of the high activation energy for hydrogen diffusion in grain boundaries.

Kinetics of hydrogen adsorption in MIL-101 single pellets

A new type of MIL-101: aluminum composites with improved thermal conductivity is reported and their hydrogen adsorption rate investigated in a systematic study of hydrogen adsorption/desorption kinetics of MIL-101 single pellets, filling the gap of data on hydrogen sorption kinetics by compressed monoliths in the cryo-adsorption storage conditions.Kinetic curves were measured within a wide range of pressure in the temperature range 77–159 K and the hydrogen diffusivity were estimated from the rate constants obtained by fitting the fractional uptake with the kinetic equations. In order to compare MIL-101 with other metal-organic frameworks (MOFs), measurements on pellets of MIL-100(Fe) and HKUST-1 were also performed. As expected, the results, together with some data available in literature, reveal that the hydrogen diffusivity obtained from kinetic studies is strongly related to the pore diameter. The activation energy of hydrogen diffusion in MIL-101, calculated from the rate constants, is 1.6 kJ mol−1, close to the literature values reported for other MOFs. Kinetic studies on composite pellets of MIL-101 with Al tapes (8–10%) with improved thermal conductivity (∼0.5 W m−1K−1) are also reported. They show indeed higher uptake rates, consistent with the requirement of fast filling time (less than 3 min) required for applications. The adsorption/desorption rate at 77 K allows ∼90% fractional uptake in about 40 s, promising for applications of cryo-adsorption storage. The results show that the time required to reach saturation and thermal equilibrium depends on pellet geometry and hydrogen diffusivity.

Reduced hydrogen diffusion in strained amorphous SiO2: understanding ageing in MOSFET devices

Hydrogen diffusion activation energy in amorphous silicon dioxide is reduced by straining the material, which can reduce aging of MOSFETs.