Hydrogen Diffusion Process Research Articles

Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH2 by the MnOx-Coated Ti2CTx Catalyst with Optimized Ti-H Bond Stability.

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH2, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose Tx density control of MXene-based catalysts and MnOx coating as a promising solution. The MnOx@Ti2CTx-catalyzed Mg/MgH2 can release 5.97 wt % H2 at 300 °C in 3 min and 5.60 wt % H2 at 240 °C in 15 min with an activation energy of 75.57 kJ·mol-1. In addition, the samples showed excellent de/hydrogenation-cycle stability, and the degradation of hydrogen storage capacity is negligible even after 100 cycles. DFT calculations combined with XPS analysis showed that the Tx defect on the surface of the MnOx@Ti2CTx catalyst could optimize the strength of the Ti-H bond, accelerating both hydrogen dissociation and diffusion processes. The catalyst's surface properties were protected by the MnOx coating, achieving high chemical and catalytic stability. These findings offer a strategy for surface structure optimization and protection of MXene-based catalysts, realizing controllable catalyst-hydrogen bond strength.

Molecular Dynamics Simulation of Hydrogen Barrier Performance of Modified Polyamide 6 Lining of IV Hydrogen Storage Tank with Graphene.

The polymer liner of the hydrogen storage cylinder was studied to investigate better hydrogen storage capacity in Type-IV cylinders. Molecular dynamics methods were used to simulate the adsorption and diffusion processes of hydrogen in a graphene-filled polyamide 6 (PA6) system. The solubility and diffusion characteristics of hydrogen in PA6 systems filled with different filler ratios (3 wt%, 4 wt%, 5 wt%, 6 wt%, and 7 wt%) were studied under working pressures (0.1 MPa, 35 MPa, 52 MPa, and 70 MPa). The effects of filler ratio, temperature, and pressure on hydrogen diffusion were analyzed. The results show that at atmospheric pressure when the graphene content reaches 5 wt%, its permeability coefficient is as low as 2.44 × 10-13 cm3·cm/(cm2·s·Pa), which is a 54.6% reduction compared to PA6. At 358 K and 70 MPa, the diffusion coefficient of the 5 wt% graphene/PA6 composite system is 138% higher than that at 298 K and 70 MPa. With increasing pressure, the diffusion coefficients of all materials generally decrease linearly. Among them, pure PA6 has the largest diffusion coefficient, while the 4 wt% graphene/PA6 composite system has the smallest diffusion coefficient. Additionally, the impact of FFV (free volume fraction) on the barrier properties of the material was studied, and the movement trajectory of H2 in the composite system was analyzed.

A novel method for analyzing the leakage and diffusion of hydrogen: First arrival time distribution

Hydrogen energy plays an important role in achieving the carbon peak and carbon neutrality goals. However, owing to its flammability and explosiveness, hydrogen leakage during transportation and use can easily cause severe consequences. Therefore, research on the safety of hydrogen leakage is particularly important. This study proposes a novel method for analyzing the diffusion behavior of hydrogen leakage called first arrival time distribution (FATD). The spatial distribution of the first arrival times of specific concentration values (such as explosion limit and alarm concentration) at each coordinate point in the calculation domain was obtained by processing the concentration field of hydrogen leakage and diffusion via computational fluid dynamics simulations. The hydrogen leakage and diffusion processes were simulated for multiple scenarios using Fluent software, and the method of obtaining the FATD based on the simulations was detailed. The study also analyzed the hydrogen leakage and diffusion processes as well as the effects of mesh quantity and sampling time interval on the FATD; the FATD was additionally applied in actual scenarios to obtain an alarm time distribution for guiding sensor deployment. The results show that the FATD intuitively displays the hydrogen diffusion and evolution processes via specific concentration values in the calculation domain while describing the detailed influences of obstacles on the hydrogen diffusion process. Moreover, the FATD can serve as an indicator of grid independence analysis. This provides a new method for understanding diffusion behavior, reference for accident risk and consequence assessments, and safety guidance for the utilization of hydrogen energy.

Hydrogen diffusion in BCC-Fe: DFT study of tensorial stress effects and interactions with point defects

Hydrogen embrittlement is a multifaceted phenomenon that can significantly compromise the toughness of susceptible metals. We study the critical process of hydrogen diffusion within the body-centered cubic lattice of iron (BCC-Fe or α−Fe) using ab-initio density functional theory (DFT). Beyond standard investigations on the effect of hydrostatic stress, we extend our study to incorporate the influence of uniaxial and pure shear stress states. We find substantial alterations in diffusion barriers. Moreover, we study scenarios involving paired point (zero-dimensional) defects, including one vacancy and an additional interstitial hydrogen atom. Calculations comprehend various configurations and transitions between them, providing insight into the interplay between the chemical environment and mechanical fields. The barrier values here determined offer essential data for complementary techniques, including Monte-Carlo models, to accurately describe hydrogen diffusion. This research contributes to a deeper understanding of hydrogen embrittlement, offering insight that can inform the design of safer materials used in structural engineering.

The feasibility of hydrogen storage in aquifers: A molecular dynamics simulation

Geological hydrogen storage could be an effective method for solving energy demand and climate change challenges. We focus on hydrogen diffusion in carbonate slits via molecular dynamics under subsurface conditions. We investigate the influence of pore size, moisture content, and salinity on hydrogen diffusion process. The results demonstrate that high moisture content reduces the diffusion coefficient of hydrogen due to the form of water bridge and hydrogen cluster. The impact of salinity is observed only under high moisture content conditions. Specially, CaCl2 and MgCl2 are more suitable than NaCl for hydrogen storage. Hydrogen storage is more suitable in lower NaCl concentration while it is more suitable in a higher Na2SO4 concentration. Because interfacial tension of hydrogen-salt solution could be affected by ion concentration. These results demonstrate that hydrogen diffusion could be regulated by changing salinity for high water cut reservoir. This job could provide valuable guidance for underground hydrogen storage.

Hydrogen diffusion simulation of the X80 pipeline steel girth weld zone considering the synergistic effect of the structure–stress–concentration field

Hydrogen embrittlement failure, caused by hydrogen permeation and diffusion in the girth weld zone of pipelines, is the main obstacle to large-scale hydrogen blending transportation. Accordingly, a three-dimensional model of the girth weld zone of X80 pipeline steel was established. Considering the influence of structural inhomogeneity in the weld zone, multi-field sequential coupling simulation technology was used to analyze the diffusion process of hydrogen under the combined action of the residual stress and hydrogen concentration fields. A synergistic mechanism between hydrogen enrichment, structural characteristics, and residual stress in the weld zone was revealed. The results indicated that the structural inhomogeneity in the girth weld zone and residual stress field significantly influenced the hydrogen concentration distribution. Moreover, for the hydrogen diffusion process at the grain boundaries, the impact of the residual stress was greater than that of the structural inhomogeneity. This study further clarifies the spatial distribution of hydrogen atoms induced by multi-field coupling in the weld zone and provides a reference for the safety assessment of girth weld layers from an engineering perspective.

Effects of leakage location and ventilation condition on hydrogen leakage during shipping of fuel cell vehicles

In the process of shipping hydrogen fuel cell vehicles, due to the special characteristics of the design and construction of the pure car truck carrier (PCTC) and its working environment, once hydrogen leakage occurs, it is easy to cause safety accidents, resulting in economic losses and human casualties. The current ventilation regulations are only for the shipping of vehicles with internal combustion engines and there are no clear regulations on the ventilation requirements for PCTCs during the shipping of hydrogen fuel cell vehicles. First, a PCTC and a hydrogen fuel cell vehicle were selected for the study and the corresponding geometries were modeled. For the scenario of hydrogen leakage in the cabin of the ship, the amount of hydrogen leakage is calculated according to the leakage model. Then, using Fluent software, the diffusion process of hydrogen between the two vehicles is simulated and the variation pattern of hydrogen concentration is concluded. Finally, simulations are carried out under different leakage locations and ventilation conditions to analyze the influencing factors of hydrogen diffusion distribution in the cabin of the ship. The simulation results identify the optimum location for the hydrogen sensors and provide a reference for the setting of safety measures and development of regulations on ventilation requirements when shipping hydrogen fuel cell vehicles.

Ultrathin NiV Layered Double Hydroxide for Methanol Electrooxidation: Understanding the Proton Detachment Kinetics and Methanol Dehydrogenation Oxidation.

Electrochemical methanol oxidation reaction (MOR) is regarded as a promising pathway to obtain value-added chemicals and drive cathodic H2 production, while the rational design of catalyst and in-depth understanding of the structure-activity relationship remains challenging. Herein, the ultrathin NiV-LDH (u-NiV-LDH) with abundant defects is successfully synthesized, and the defect-enriched structure is finely determined by X-ray adsorption fine structure etc. When applied for MOR, the as-prepared u-NiV-LDH presents a low potential of 1.41V versus RHE at 100mA cm-2, which is much lower than that of bulk NiV-LDH (1.75V vs RHE) at the same current density. The yield of H2 and formate is 98.2% and 88.1% as its initial over five cycles and the ultrathin structure of u-NiV-LDH can be well maintained. Various operando experiments and theoretical calculations prove that the few-layer stacking structure makes u-NiV-LDH free from the interlayer hydrogen diffusion process and the hydrogen can be directly detached from LDH laminate. Moreover, the abundant surface defects upshift the d-band center of u-NiV-LDH and endow a higher local methanol concentration, resulting in an accelerated dehydrogenation kinetics on u-NiV-LDH. The synergy of the proton detachment from the laminate and the methanol dehydrogenation oxidation contributes to the excellent MOR performance of u-NiV-LDH.

The anionic Tx defects of Nb2CTx MXene as the effective catalytically active center for the Mg-based hydrogen storage materials

While early transition metal-based materials, such as MXene, has emerged as an efficient catalyst for the Mg-based hydrogen storage materials, their strong interaction with hydrogen resulted in the high hydrogen diffusion barrier, hindering further improvement of catalytic activity. A MXene is characterized by rich anionic groups on its surface, significantly affecting electronic and catalytic functionalities. Using Nb2CTx as an example, we herein illustrate the critical role of anionic Tx defects on controlling hydrogen dissociation and diffusion processes in Mg-based hydrogen storage materials. The hydrogen desorption properties of MgH2 can be significantly enhanced by utilizing Tx controllable Nb2CTx, and it can release 3.57 wt.% hydrogen within 10 min under 240 °C with the reduced dehydrogenation activation barrier. It also realized stable de/hydrogenation reactions for at least 50 cycles. DFT studies combined with kinetic analysis revealed that the catalyst‒hydrogen interaction could be systematically controlled by optimizing surface Tx defect density, accelerating the hydrogen dissociation and diffusion processes at the same time. These results demonstrate that the Tx defects serve as the effective catalytically active centers of Nb2CTx, offering a flexible catalyst design guideline.

Enhanced hydrogen sorption properties of uniformly dispersed Pd-decorated three-dimensional (3D) Mg@Pd architecture

This study demonstrates the hydrogen sorption improvement of Mg through the three-dimensional decoration of a noble catalyst. An Mg@Pd composite was synthesized by decorating Pd nanoparticles onto the Mg matrix via a facile solid-gas reduction method. Electron tomography analysis confirms the formation of a three-dimensional (3D) architecture of the Mg@Pd particulate composite. The Mg@Pd composite shows excellent hydrogenation/dehydrogenation kinetics even at low temperatures as compared to a catalyst-free Mg sample. Moreover, the hydrogenated Mg@Pd composite can desorb hydrogen at as low as 246 °C that is 87 °C lower than that of the pure MgH2. Hydrogenation of the Mg@Pd composite leads to the development of a multiphase system consisted of PdH0.706, MgPd and MgH2 whereas dehydrogenation occurred via two simultaneous desorption reactions results in Mg6Pd and Mg phases. The uniform dispersion of Pd nanoparticles on the surface of the 3D Mg matrix has provided with fast catalytic interfaces via the hydrogen “spillover” mechanism while the concomitant hydrogen diffusion processes are enhanced by the “hydrogen pump” effect of PdH0.706/MgPd interfaces. Furthermore, the low temperature hydrogen sorption performances of the Mg@Pd composite can be attributed to the interphase reversibility between MgPd and Mg6Pd leading to the thermodynamic destabilization of MgH2. This study suggests that strategically new approaches can govern significant improvements in hydrogen storage properties of Mg-based systems.

Theoretical model and simulations to extract chemical reaction parameters ruling resistive switching in sputter-deposited silicon oxide film on Si substrate

This paper proposes a physics-based model based on possible chemical processes responsible for the resistive switching of sputter-deposited silicon oxide films. Diffusion–reaction differential equations are utilized to pursue physical and chemical origins of the switching phenomenon. Based on the theoretical model, the chemical reaction process is analytically and numerically solved, and an analytical model is proposed to elucidate the phenomenon. Theoretical simulation results are examined from the point of view of suitability of parameter values, and the analytical model is used to interpret the simulation results. Simulation results greatly assist in understanding the switching processes of silicon oxide films; that is, the diffusion processes of hydrogen and water molecules primarily rule the switching processes, and the displacement of oxygen atoms is assisted by those processes. The analytical model predicts that high-speed switching requires a large number of traps in the oxide, a relatively large binding energy, and a low leakage current; all of them can easily be satisfied for sputter-deposited oxide films. A combination of the theoretical simulation model and the analytical model gives a guideline of how the sputter-deposited silicon oxide films can be made suitable for high-speed resistive switching applications.

Hydrogen Diffusion in Organic-Rich Porous Media: Implications for Hydrogen Geo-storage

Subsurface hydrogen storage for large-scale energy supply to decarbonize a variety of greenhouse gas-emitting activities is gaining momentum worldwide to combat climate change. Hydrogen’s extensive range of flammable concentrations and low minimum ignition energy in air combined with its highly diffusive nature mandate implementation of comprehensive risk management protocols to maintain storage safety. In particular, the role of hydrogen diffusion process (self-diffusion) needs further investigation to understand H2 transport behavior and elude the associated risk of leakage for the long-term safety of the underground hydrogen storage process. Recent molecular simulation studies suggest that, compared to other subsurface storage options, depleted shale reservoirs may offer preferential storage characteristics due to excellent sealing and adsorption capabilities of shale. Data on hydrogen diffusion in organic (kerogen)-rich shale is scarce. Here, we applied molecular dynamics to compute hydrogen self-diffusivity in kerogen systems with different structures at various pressures, ranging from 3 to 41 MPa, and under an isothermal condition of 360 K. Two kerogen types of varying maturity (II-A and II-C) were utilized to create slit nanopores of 0.5 and 2 nm in size. The Knudsen number was calculated based on the mean free path and determined by the density values obtained from simulation to improve diffusion coefficient estimates. Results obtained indicate the Kn data in the range from 0.64 to 9.72, demonstrating that the main transport mechanism was transitional in nature. With increasing pressure, diffusivity declined regardless of the slit pore size or kerogen type. H2 diffusion was greater for the 2 nm pore system compared to both the 0.5 nm in II-A (0.004–0.02 cm2/s) and II-C (0.0037 to 0.019 cm2/s). In addition, for a fixed nanopore size, thermal maturity does not seem to impact diffusivity. Finally, simulation results were regressed to delineate a continuous description for diffusivity as a function of pressure. For curve fitting, R2 values were found to be 98 and 92% for 2 nm pore size of II-A and II-C, respectively, while 97 and 79% for 0.5 nm pore size of II-A and II-C, respectively. The results obtained are not only of interest for storage of hydrogen in shale but also for any subsurface hydrogen storage approach where a shale layer acts as a seal to form a trap.

Breakdown Voltage Instability Mechanism on the Field Limiting Rings Edge Termination of Buried Layer Rectifier

In this article, an innovated buried layer rectifier (BLR) breakdown voltage (BV) instability has been tested and analyzed. Under the reverse current stress (RCS) condition, the BV read-out profiles show walk-in and walk-out phenomena. Based on the experimental results and surface traps theory, a sort of time-dependent degraded simulation is developed by TCAD tools, which is considered with hydrogen depassivation and diffusion process. In order to explore the inner mechanism, the dynamic electric parameters are analyzed during the degraded period. Due to the hole interface traps, the termination Si-SiO2 surface leakage current is deteriorated and the depletion boundary is shrunk, which reveal the BV values instability. Thus, the proposed physical model could clearly explain the whole process of degradation, while it fits BV and junction temperature curves to the experimental results identically. Furthermore, the investigated mechanism will be helpful to future device design and failure situations analysis.

Boosting room temperature response of Pd-based hydrogen sensor by constructing in situ nanoparticles

Palladium-based H 2 sensors have attracted increased attention due to the high selectivity for H 2 , yet evident limitations like hydrogen embrittlement and slow response rates, have impeded the further development. Aiming to address these issues, adding other metals to form Pd-based alloys and optimize coincided surface structure, are widely considered as effective approaches. Here in this work, Pd/Ti alloy films with proper elemental ratios were prepared by using a magnetron co-sputtering technique, and the coincided sensing features have been further regulated by in situ nanostructuring. For the Pd/Ti film with an atomic ratio of 74.1/25.9, the H 2 response values characterizations revealed that the limit of detection (LoD) could be 50 ppm at room temperature, combined with a response time of 61.3 s at 2 vt.% H 2 concentration. Based on the first-principles calculations, the effects from hydrogen diffusion process of Pd and Pd/Ti alloys have been evaluated to be ignorable, however, the specific nanostructures constructed on the surface then become the main reason for the boosted response performance. More importantly, the approach of forming proper in situ nanoparticles has been identified as a significant guidance, for extensive and rapid response of H 2 detection of Pd-based sensors used upon low power consumption. • Pd/Ti alloy films with nanoparticles are prepared by magnetron sputtering. • Samples have response to 50 ppm - 4 vt.% H 2 concentration at room temperature. • Nanoparticles can absorb H 2 molecules and facilitate their decomposition into H atoms. • The results of the first-principles calculations confirmed the optimization effect of nanoparticles.

Hydrogen-Enriched Compressed Natural Gas Network Simulation for Consuming Green Hydrogen Considering the Hydrogen Diffusion Process

Transporting green hydrogen by existing natural gas networks has become a practical means to accommodate curtailed wind and solar power. Restricted by pipe materials and pressure levels, there is an upper limit on the hydrogen blending ratio of hydrogen-enriched compressed natural gas (HCNG) that can be transported by natural gas pipelines, which affects whether the natural gas network can supply energy safely and reliably. To this end, this paper investigates the effects of the intermittent and fluctuating green hydrogen produced by different types of renewable energy on the dynamic distribution of hydrogen concentration after it is blended into natural gas pipelines. Based on the isothermal steady-state simulation results of the natural gas network, two convection–diffusion models for the dynamic simulation of hydrogen injections are proposed. Finally, the dynamic changes of hydrogen concentration in the pipelines under scenarios of multiple green hydrogen types and multiple injection nodes are simulated on a seven-node natural gas network. The simulation results indicate that, compared with the solar-power-dominated hydrogen production-blending scenario, the hydrogen concentrations in the natural gas pipelines are more uniformly distributed in the wind-power-dominated scenario and the solar–wind power balance scenario. To be specific, in the solar-power-dominated scenario, the hydrogen concentration exceeds the limit for more time whilst the overall hydrogen production is low, and the local hydrogen concentration in the natural gas network exceeds the limit for nearly 50% of the time in a day. By comparison, in the wind-power-dominated scenario, all pipelines can work under safe conditions. The hydrogen concentration overrun time in the solar–wind power balance scenario is also improved compared with the solar-power-dominated scenario, and the limit-exceeding time of the hydrogen concentration in Pipe 5 and Pipe 6 is reduced to 91.24% and 91.99% of the solar-power-dominated scenario. This work can help verify the day-ahead scheduling strategy of the electricity-HCNG integrated energy system (IES) and provide a reference for the design of local hydrogen production-blending systems.

Blocking Hydrogen Diffusion in Palladium Cathode i—Analyzed by Electrochemistry; ii—Analyzed by Chaos

Electrochemical chaos is caused when, during diffusion, hydrogen and, at worst, tritium is trapped in palladium after the formation of adsorbates. The mechanism leads to cracking corrosion, as seen by scanning electron microscopy. The instabilities were apprehended from voltammetry and electrochemical impedance spectroscopy in the active potential where the cathodic hydrogen is charged from two models of transients. Tests performed using an electrochemical chaos analyzer simplify the expertise of the palladium cathode in focusing on the blocking diffusion of hydrogen. A complex electrical circuit of chaos is considered for adsorption and the blocking diffusion. Depending on the active potential, distinct behavior such as the transformation of transients and limited diffusion can occur. Phase-space spectra are obtained, and synchronization has been developed to clarify the chaos leading to the cracking of palladium. By applying these different analytical tests for the restricted diffusion, it is possible to interpret the processes from the power spectra, autocorrelation function, or the divergence coefficient in the region of active potentials. Analyzers can detect flaws in this hydrogen diffusion process and suggest corrective measures.

Hydrogen absorption and diffusion behaviors in cube-shaped palladium nanoparticles revealed by ambient-pressure X-ray photoelectron spectroscopy

The hydrogen absorption and diffusion processes in cube-shaped palladium (Pd) nanoparticles (NPs) were studied by the combination of ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory (DFT) calculations. A size dependence of the subsurface hydrogen absorption was observed. More hydrogen atoms were absorbed in the subsurface of the smaller-sized Pd NPs owing to the enhancement of the diffusivity of H atoms from the surface into the subsurface rather than the adsorption or absorption rates at the initial stages. This results from the weakened Pd-H bond caused by surface disordering of Pd NPs with the reduction of the size of the particles. Furthermore, we discuss the H absorption sites in the bulk by comparing the relative Pd 3d core-level binding energy shifts of the Pd atoms obtained from the AP-XPS results and the theoretical calculations. The octahedral (O) sites are shown to be more favorable than the tetrahedral (T) sites for hydrogen occupation by comparing the experimental results and theoretical calculations. Finally, we proposed an interaction model between hydrogen and the Pd NPs during H2 absorption and diffusion to provide new insights into the hydrogen absorption process.

Some Implications of Dislocation Cells and Internal Stresses on the Hydrogen Diffusion and Trapping Processes in Tensile Strengthening (100) Nickel Single Crystal

Some Implications of Dislocation Cells and Internal Stresses on the Hydrogen Diffusion and Trapping Processes in Tensile Strengthening (100) Nickel Single Crystal

Some Implications of Dislocation Cells and Internal Stresses on the Hydrogen Diffusion and Trapping Processes in Tensile Strengthening (100) Nickel Single Crystal

Some Implications of Dislocation Cells and Internal Stresses on the Hydrogen Diffusion and Trapping Processes in Tensile Strengthening (100) Nickel Single Crystal

Application of the Electrochemical Permeation Method for Hydrogen Diffusion Coefficient Determination in Pipeline Steel 10G2

In this article, we conduct research on the effect of corrosion tests on the hydrogen diffusion process in gas steel in electrochemical permeability tests. This tests show that a long corrosion test time reduces the hydrogen diffusion coefficient by an order of magnitude, indicating the formation of aging defects in the steel. During operation, the diffusion coefficient decreases by two orders of magnitude, which also indicates the formation of a large number of defects in the steel. Consequently, based on the change in the diffusion coefficient in the material, it is possible to assess the degree of material failure.