Recombination Of Hydrogen Atoms Research Articles

Accelerated stress corrosion cracking of X80 pipeline steel under the combined effects of sulfate-reducing bacteria and hydrostatic pressure

The microbially mediated metal stress corrosion cracking (SCC) mechanisms in deep-sea environments remain unclear, hindering the safe use of deep-sea equipment materials. Hydrostatic pressure facilitated microbiologically influenced corrosion resulting in the pitting depth increase. The stress concentration at the pit bottom induced anodic dissolution (AD), leading to ductile fracture. Hydrostatic pressure and iron sulfides both enhanced the hydrogen evolution reaction (HER). The sulfides produced by SRB metabolism inhibit hydrogen atom recombination, leading to a higher hydrogen permeation current and inducing hydrogen embrittlement (HE) fracture. The combined effect of AD and HE increases the SCC susceptibility of deep-sea pipeline steel.

Toward Exoplanet Transit Spectroscopy Using JWST/MIRI’s Medium Resolution Spectrometer

The Mid-Infrared Instrument Medium Resolution Spectrometer (the MRS) on JWST has potentially important advantages for transit and eclipse spectroscopy of exoplanets, including lack of saturation for bright host stars, wavelength span to longward of 20 µm, and JWST’s highest spectral resolving power. We here test the performance of the MRS for time series spectroscopy by observing the secondary eclipse of the bright stellar eclipsing binary R Canis Majoris. Our observations push the MRS into saturation at the shortest wavelength, more than for any currently known exoplanet system. We find strong charge migration between pixels that we mitigate using a custom data analysis pipeline. Our data analysis recovers much of the spatial charge migration by combining detector pixels at the group level, via weighting by the point-spread function. We achieve nearly photon-limited performance in time series data at wavelengths longward of 5.2 µm. In 2017, Snellen et al. suggested that the MRS could be used to detect carbon dioxide absorption from the atmosphere of the temperate planet orbiting Proxima Centauri. We infer that the relative spectral response of the MRS versus wavelength is sufficiently stable to make that detection feasible. As regards the secondary eclipse of this Algol-type binary, we measure the eclipse depth by summing our spectra over the wavelengths in four channels, and also measuring the eclipse depth as observed by TESS. Those eclipse depths require a temperature for the secondary star that is significantly hotter than previous observations in the optical to near-IR, probably due to irradiation by the primary star. At full spectral resolution of the MRS, we find atomic hydrogen recombination emission lines in the secondary star, from principal quantum levels n = 7, 8, 10, and 14.

Ultrahigh Pt-mass-activity catalyst for alkaline hydrogen evolution synthesized by microwave method in air

Platinum (Pt) metal is widely acknowledged as a highly efficient electrocatalyst for hydrogen evolution reaction (HER) in acidic electrolyte. However, its performance in alkaline environments is significantly lower owing to the sluggish water dissociation step. Herein, we synthesized an ultrahigh Pt-mass-activity alkaline HER catalyst using microwave reduction method in air. Our catalyst, PtRu@CNT, comprises PtRu alloy nanoparticles uniformly loaded on carbon nanotubes, with Pt and Ru contents of 12.3 wt% and 4.5 wt%, respectively. The PtRu alloy nanoparticles have an average diameter of about 3 nm and a face-centered cubic structure, and the introduction of Ru has led to a modified electronic structure in Pt. As a result, an impressively low HER overpotential of 13 mV was achieved, significantly lower than commercial 20 wt% Pt/C (61 mV). PtRu@CNT exhibited a high turnover frequency based on metal mass of 3.06 s−1 at 100 mV, about 6 times higher than commercial Pt/C (0.46 s−1 at 100 mV), highlighting its excellent intrinsic activity. The HER mechanism of PtRu@CNT is a Volmer-Tafel mechanism, where the rate-limiting step changed to the recombination of hydrogen atoms from initial water dissociation, attributed to the presence of Ru. The alkaline HER activity of PtRu@CNT ranks among the best of currently reported Pt-based catalysts.

Measurements of atomic hydrogen recombination coefficients and the reduction of Al2O3 using a heat flux sensor

The knowledge of atomic hydrogen recombination coefficient (γ) is essential for plasma simulations to calculate accurate atomic hydrogen fluxes. However, γ is a complex material property, and it is affected by the experimental conditions under which it is measured. Therefore, values of γ can differ even by a few orders of magnitude for the same material. In this paper, we demonstrate measurements of hydrogen recombination coefficients at room temperature using an in-house-built catalytic sensor for two selected materials: aluminum Al-5083 (alimex) and stainless steel 316 l, under the load of low-temperature H2 plasma with an admixture of H2O or N2 gases. The plasma settings were carefully chosen to mimic properties of the so-called extreme ultraviolet-generated plasma.1 The measured γ values agree well with literature data obtained for similar plasma conditions and show a correlation with ion energy. Additionally, we show a novel application of the sensor for indirect measurements of the reduction of oxidized surfaces as a function of ion dose. In these experiments, a correlation between reduction time and background water pressure is observed.

MINDS: Mid-infrared atomic and molecular hydrogen lines in the inner disk around a low-mass star

Context. Understanding the physical conditions of circumstellar material around young stars is crucial to star and planet formation studies. In particular, very low-mass stars (M★ < 0.2 M⊙) are interesting sources to characterize as they are known to host a diverse population of rocky planets. Molecular and atomic hydrogen lines can probe the properties of the circumstellar gas. Aims. This work aims to measure the mass accretion rate, the accretion luminosity, and more generally the physical conditions of the warm emitting gas in the inner disk of the very low-mass star 2MASS-J16053215-1933159. We investigate the source mid-infrared spectrum for atomic and molecular hydrogen line emission. Methods. We present the full James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) spectrum of the protoplanetary disk around the very low-mass star 2MASS-J16053215-1933159 from the MINDS GTO program, previously shown to be abundant in hydrocarbon molecules. We analyzed the atomic and molecular hydrogen lines in this source by fitting one or multiple Gaussian profiles. We then built a rotational diagram for the H2 lines to constrain the rotational temperature and column density of the gas. Finally, we compared the observed atomic line fluxes to predictions from two standard emission models. Results. We identify five molecular hydrogen pure rotational lines and 16 atomic hydrogen recombination lines in the 5–20 µm spectral range. The spectrum indicates optically thin emission for both species. We use the molecular hydrogen lines to constrain the mass and temperature of the warm emitting gas. We derive a total gas mass of only 2.3 × 10−5 MJup and a temperature of 635 K for the warm H2 gas component located in the very inner disk (r < 0.033 au), which only accounts for a small fraction of the upper limit for the disk mass from continuum observations (0.2 MJup). The HI (7−6) recombination line is used to measure the mass accretion rate (4.0 × 10−10 M⊙ yr−1) and luminosity (3.1 × 10−3 L⊙) onto the central source. This line falls close to the HI (11−8) line, however at the spectral resolution of JWST MIRI we managed to measure both separately. Previous studies based on Spitzer have measured the combined flux of both lines to measure accretion rates. HI recombination lines can also be used to derive the physical properties of the gas using atomic recombination models. The model predictions of the atomic line relative intensities constrain the atomic hydrogen density to about 109−1010 cm−3 and temperatures up to 5000 K. Conclusions. The JWST-MIRI MRS observations for the very low-mass star 2MASS-J16053215-1933159 reveal a large number of emission lines, many originating from atomic and molecular hydrogen because we are able to look into the disk warm molecular layer. Their analysis constrains the physical properties of the emitting gas and showcases the potential of JWST to deepen our understanding of the physical and chemical structure of protoplanetary disks.

NiMo₂S₄-VS₂ heterostructure on nickel Foam: A promising electrocatalyst for alkaline oxygen evolution reaction

Oxygen Evolution Reaction (OER) is a slow process; therefore, improved kinetics require catalytic active centers and higher charge transfer capacities. In the present study, a novel heterostructure made of nickel molybdenum sulfide and vanadium disulfide supported on nickel foam (NiMo2S4-VS2/NF) substrate is fabricated using a single-step hydrothermal process. The structural, morphological, elemental, and textural properties of the fabricated materials are confirmed via various analytical techniques. Furthermore, at the current density of 10 mA cm−2, the observed overpotentials was approximately 318 mV corresponding to an OER in 1 M potassium hydroxide electrolyte. It also shows a lower Tafel slope of 78 mV/dec with large turnover frequency of 2.56 s−1. The resulting NiMo2S4-VS2/NF showed enhanced charge transfer properties and frequent integrated active sites. Hence the remarkable activity of this catalyst is significantly influenced by the synergistic effect of these combined features and resulted in an efficient overall water splitting. This was ascribed to NiMo2S4 which increases OER at the anode by providing active sites for oxidizing water molecules. In NiMo2S4, Mo and S elements aid to maintain active sites and accelerate reaction kinetics, while Ni sites operate as electrocatalytic efforts for water oxidation. In general, VS2 promotes hydrogen atom recombination into molecular hydrogen while also encouraging HER at the cathode via hydrogen atom adsorption. In general, NiMo2S4-VS2/NF is a suitable option for water splitting applications due to the close proximity of these two components within the structure of the catalyst, which enables charge transfer and surface reactions and also allow for effective OER. This unique approach for designing the catalyst and engineering the heterointerface is a promising strategy to develop novel and efficient OER catalysts.

Unraveling Enyne Bonding via Dehydrogenation–Hydrogenation Processes in On‐Surface Synthesis with Terminal Alkynes

AbstractOn‐surface reactions of terminal alkynes in ultrahigh vacuum have attracted widespread attention due to their high technological promise. However, employing different precursors and substrate materials often intricate reaction schemes appear far from being well‐understood. Thus, recent investigations of alkyne coupling on noble metal surfaces suggest non‐dehydrogenative scenarios, contradicting earlier reports. Herein, the study employs noncontact atomic force microscopy (nc‐AFM) with high spatial resolution to conclusively characterize exemplary alkyne coupling products. Contrary to initial interpretations proposing dehydrogenative homocoupling on Ag(111), bond‐resolved AFM imaging reveals the expression of enyne motifs. Based on complementary, extensive density functional theory calculations, the pertaining reaction mechanisms are explored. It is proposed that enyne formation initiates with a direct carbon–carbon coupling between two alkyne groups, followed by surface‐assisted dehydrogenation‐hydrogenation processes. Thereby consecutive steps of atomic hydrogen cleavage, surface migration and recombination to a different carbon atom enable bridging via carbon–carbon double bonding. The new results shed light on subtle, but crucial surface‐mediated hydrogen transfer processes involved in the chemical bond formation, which are suggested to be of general relevance in on‐surface synthesis.

Influence of the phase evolution and hydrogen storage behaviors of Mg-based alloy catalyzed by Gd-Fe compound

In order to further optimize the kinetic and thermal properties of Mg-based hydrogen storage alloy, the Mg + 10 wt% GdFe alloy is prepared by using vacuum induction melting. The XRD, SEM, EDS, TEM, PCT and TG-DTA are used to characterize the microstructure of the alloy and phase transition in the reaction process. The results show that the sample is composed of the main phase Mg and the remaining Mg5Gd. In addition, Fe elements are evenly distributed in dissolved in the Mg matrix. After hydrogen absorption, all these phases disappear and are transformed into MgH2 and GdH2. After hydrogen desorption, MgH2 transforms to Mg phase, but the GdH2 phase remains unchanged. During the reaction, Fe always exists in the Mg/MgH2 lattice in the form of simple substance, which is beneficial to the recombination and dissociation of hydrogen atoms. Meanwhile, the GdH2 phase also provides abundant the active sites and diffusion admittance. The alloy has a reversible hydrogen content of 5.8 wt% H2 and an activation energy of 144.1 kJ/mol. It also shows excellent kinetic properties, which can absorb 4.3 wt% H2 at 360 °C in 10 min, and complete hydrogen desorption at the same temperature requires only 18 min. The thermodynamics energy increases only slightly, but the initial hydrogen release temperature and peak temperature are much lower than those of Mg.

Hijacking the hydrogen atoms in photo-splitting of H2O2 for efficient reduction of CO2 to CH3OH

Photo-splitting of H2O2 in visible light is achieved by Cu-MOFs of Cu nodes and 1, 3, 5-benzene tricarboxylic acid (BTC) organic linkers (CuM) decorated with CdS (C) at varying concentrations of CdS in the CuMC composite. This process produces abundant nascent hydrogen atoms to promote the efficient catalytic reduction of CO2 to methanol (CH3OH) in visible light. The slow rate of recombination of the nascent hydrogen atoms produced by the H2O2 photo-splitting on the surface of the CdS quantum dots ensures a high steady-state concentration of hydrogen atoms with significantly reduced production of the less reactive hydrogen gas. With slow recombination of the photo-generated charges and the large surface areas for CO2 adsorption by the MOF, one of the CuMC composites is capable of convertingCO2 into CH3OH with a quantum efficiency approaching 80 %. A mechanism for the selective conversion of CO2 into CH3OH is proposed.

Investigating the Eley-Rideal recombination of hydrogen atoms on Cu (111) via a high-dimensional neural network potential energy surface.

As a prototypical system for studying the Eley-Rideal (ER) mechanism at the gas-surface interface, the reaction between incident H/D atoms and pre-covered D/H atoms on Cu (111) has attracted much experimental and theoretical interest. Detailed final state-resolved experimental data have been available for about thirty-years, leading to the discovery of many interesting dynamical features. However, previous theoretical models have suffered from reduced-dimensional approximations and/or omitting energy transfer to surface phonons and electrons, or the high cost of on-the-fly ab initio molecular dynamics, preventing quantitative comparisons with experimental data. Herein, we report the first high-dimensional neural network potential (NNP) for this ER reaction based on first-principles calculations including all molecular and surface degrees of freedom. Thanks to the high efficiency of this NNP, we are able to perform extensive quasi-classical molecular dynamics simulations with the inclusion of the excitation of low-lying electron-hole pairs (EHPs), which generally yield good agreement with various experimental results. More importantly, the isotopic and/or EHP effects in total reaction cross-sections and distributions of the product energy, scattering angle, and individual ro-vibrational states have been more clearly shown and discussed. This study sheds valuable light on this important ER prototype and opens a new avenue for further investigations of ER reactions using various initial conditions, surface temperatures, and coverages in the future.

Oxidation–reduction reactions and hydrogenation of steels of different structures in chloride-acetate solutions in the presence of iron sulfides

Abstract The influence of iron sulfide on the rate of cathodic and anodic processes of steels with ferrite, perlite and ferrite perlite structure was shown. It was established that the hydrogenation and corrosion rate of steels with different structures depends not only its structure, but also the nature of sulfide-containing products of corrosion. The well-known scheme of the influence of hydrogen sulfide on the processes of corrosion and hydrogenation of steel was supplemented by reactions of formation iron sulfides. They can affect the rate of recombination of hydrogen atoms and, respectively, its molation and absorption by metals.

Adsorption and Absorption Energies of Hydrogen with Palladium.

Thermal recombinative desorption rates of HD on Pd(111) and Pd(332) are reported from transient kinetic experiments performed between 523 and 1023 K. A detailed kinetic model accurately describes the competition between recombination of surface-adsorbed hydrogen and deuterium atoms and their diffusion into the bulk. By fitting the model to observed rates, we derive the dissociative adsorption energies (E0, adsH2 = 0.98 eV; E0, adsD2 = 1.00 eV; E0, adsHD = 0.99 eV) as well as the classical dissociative binding energy ϵads = 1.02 ± 0.03 eV, which provides a benchmark for electronic structure theory. In a similar way, we obtain the classical energy required to move an H or D atom from the surface to the bulk (ϵsb = 0.46 ± 0.01 eV) and the isotope specific energies, E0, sbH = 0.41 eV and E0, sbD = 0.43 eV. Detailed insights into the process of transient bulk diffusion are obtained from kinetic Monte Carlo simulations.

Quantum effects in thermal reaction rates at metal surfaces.

There is wide interest in developing accurate theories for predicting rates of chemical reactions that occur at metal surfaces, especially for applications in industrial catalysis. Conventional methods contain many approximations that lack experimental validation. In practice, there are few reactions where sufficiently accurate experimental data exist to even allow meaningful comparisons to theory. Here, we present experimentally derived thermal rate constants for hydrogen atom recombination on platinum single-crystal surfaces, which are accurate enough to test established theoretical approximations. A quantum rate model is also presented, making possible a direct evaluation of the accuracy of commonly used approximations to adsorbate entropy. We find that neglecting the wave nature of adsorbed hydrogen atoms and their electronic spin degeneracy leads to a 10× to 1000× overestimation of the rate constant for temperatures relevant to heterogeneous catalysis. These quantum effects are also found to be important for nanoparticle catalysts.

(Invited) Pd Monolayer Catalyst As Transformative Concept for Electrolytic Hydrogen Isotope Separation

The effect of strain in Pd monolayer catalyst is explored for electrolytic hydrogen isotope separation. Positive/negative strain increases/decreases strength of adsorbed hydrogen bond in overpotential region where recombination of hydrogen atoms is the rate determining step in hydrogen evolution reaction. As a result, the increased/decreased hydrogen isotope separation efficiency of Pd monolayers is expected as compared to bulk Pd. The positive/negative strain rises/lowers diffusion barrier for adsorbed hydrogen atoms. This effect favors/retards recombination of isotopes with smaller mass. As the surface is stretched/compressed, the neighboring adsorption sites separate/approach each other which affects heavier hydrogen isotopes more/less and result in their lower/higher probability for recombination. All these fundamental consideration indicate that Pd monolayers with different level of strain should have much different separation factors than corresponding bulk electrodes. To study described effects, Pd monolayers we synthesized electrochemically on Au(111) and Ru(0001) electrodes each yielding qualitatively different strain levels (Au-positive, Ru-negative). The adsorption strength of hydrogen isotopes is studied by infra-red spectroscopy. These results are input in classical models for isotope separation[1] T calculations. The calculated ratio between the rates of hydrogen and deuterium recombination and separation factors for Pd monolayers and corresponding bulk electrodes are compared to experimentally measured ones. The following discussion focuses on understanding and quantification of strain effects on separation efficiency of Pd monolayers. [1] B. E. Conway, Proceedings of The Royal Society of London, A. Mathematical and Physical Sciences, 247, 400 (1958).

Identification of the twopeak spectrum of hydrogen thermal desorption

The spectra of thermal desorption (TDS spectra) of hydrogen isotopes from structural materials are investigated by various mathematical models, in particular, in the form of a first-order reaction for the volume-averaged concentration (in the case of limitation by diffusion), second-order models (taking into account the recombination of hydrogen atoms on the surface into molecules), and more detailed models reflecting multistage transport (diffusion in the bulk, migration to the surface, recombination, desorption). It is interesting to analyze the structure of the spectrum in order to identify the causes and «driving forces» of a physical and chemical nature corresponding to each peak. The article provides an analysis of some of the mentioned models for two-peak spectra and the results of numerical modeling

Research of Nanomaterials as Electrodes for Electrochemical Energy Storage.

This paper has experimentally proved that hydrogen accumulates in large quantities in metal-ceramic and pocket electrodes of alkaline batteries during their operation. Hydrogen accumulates in the electrodes in an atomic form. After the release of hydrogen from the electrodes, a powerful exothermic reaction of atomic hydrogen recombination with a large energy release occurs. This exothermic reaction is the cause of thermal runaway in alkaline batteries. For the KSL-15 battery, the gravimetric capacity of sintered nickel matrix of the oxide-nickel electrode, as hydrogen storage, is 20.2 wt%, and cadmium electrode is 11.5 wt%. The stored energy density in the metal-ceramic matrix of the oxide-nickel electrode of the battery KSL-15 is 44 kJ/g, and in the cadmium electrode it is 25 kJ/g. The similar values for the KPL-14 battery are as follows. The gravimetric capacity of the active substance of the pocket oxide-nickel electrode, as a hydrogen storage, is 22 wt%, and the cadmium electrode is 16.9 wt%. The density of the stored energy in the active substance oxide-nickel electrode is 48 kJ/g, and in the active substance of the cadmium electrode it is 36.8 kJ/g. The obtained results of the accumulation of hydrogen energy in the electrodes by the electrochemical method are three times higher than any previously obtained results using the traditional thermochemical method.

Selective decomposition of hydrazine over metal free carbonaceous materials.

Herein we report a combined experimental and computational investigation unravelling the hydrazine hydrate decomposition reaction on metal-free catalysts. The study focuses on commercial graphite and two different carbon nanofibers, pyrolytically stripped (CNF-PS) and high heat-treated (CNF-HHT), respectively, treated at 700 and 3000 °C to increase their intrinsic defects. Raman spectroscopy demonstrated a correlation between the initial catalytic activity and the intrinsic defectiveness of carbonaceous materials. CNF-PS with higher defectivity (ID/IG = 1.54) was found to be the best performing metal-free catalyst, showing a hydrazine conversion of 94% after 6 hours of reaction and a selectivity to H2 of 89%. In addition, to unveil the role of NaOH, CNF-PS was also tested in the absence of alkaline solution, showing a decrease in the reaction rate and selectivity to H2. Density functional theory (DFT) demonstrated that the single vacancies (SV) present on the graphitic layer are the only active sites promoting hydrazine decomposition, whereas other defects such as double vacancy (DV) and Stone-Wales (SW) defects are unable to adsorb hydrazine fragments. Two symmetrical and one asymmetrical dehydrogenation pathways were found, in addition to an incomplete decomposition pathway forming N2 and NH3. On the most stable hydrogen production pathway, the effect of the alkaline medium was elucidated through calculations concerning the diffusion and recombination of atomic hydrogen. Indeed, the presence of NaOH helps the extraction of H species without additional energetic barriers, as opposed to the calculations performed in a polarizable continuum medium. Considering the initial hydrazine dissociative adsorption, the first step of the dehydrogenation pathway is more favourable than the scission of the N-N bond, which leads to NH3 as the product. This first reaction step is crucial to define the reaction mechanisms and the computational results are in agreement with the experimental ones. Moreover, comparing two different hydrogen production pathways (with and without diffusion and recombination), we confirmed that the presence of sodium hydroxide in the experimental reaction environment can modify the energy gap between the two pathways, leading to an increased reaction rate and selectivity to H2.

Roughening improves hydrogen embrittlement resistance of Ti-6Al-4V

Polished surfaces of Ti-6Al-4V, the most commonly used titanium alloy, were observed to suffer from hydride growth and associated embrittlement during hydrogen charging, whereas rough surfaces suffered no such susceptibility. Direct microscopic analyses of recombined hydrogen bubbles and thermal desorption spectroscopy (TDS) revealed that the surface roughening promotes recombination of atomic hydrogen to molecular hydrogen, in turn, reducing the relative amount of atomic hydrogen uptake. Subsurface time-of-flight secondary-ion mass spectrometry (ToF-SIMS) further revealed that the high defect density underneath the roughened surface impedes hydrogen diffusion into the bulk. These combined effects mean that, unexpectedly, roughening significantly reduces hydrogen uptake into Ti-6Al-4V and enhances its resistance against hydrogen embrittlement – all resulting from a simple surface treatment.

Ni-N4 sites in a single-atom Ni catalyst on N-doped carbon for hydrogen production from formic acid

The purposes of this research were to synthesize single-atom 1 wt% Ni catalysts for the hydrogen production from formic acid using a simple impregnation of N-doped carbon with Ni acetate, to elucidate the nature of the Ni site using a combination of experimental methods with density functional theory calculations, to propose a reaction mechanism with this Ni site and to compare the catalytic properties of the single-atom catalysts with those of a traditional Ni catalyst with nanoparticles (3.9 nm). We found that the single Ni atom formed a Ni-N4 site in a double vacancy of curved N-doped graphene. Mass-based catalytic activities of the single-atom and traditional catalysts were close. The mechanism of the reaction involved the formation of formate through participation of the Ni and N atoms. The highest energy barrier (1.088 eV) was determined for the step of recombination of hydrogen atoms. This barrier corresponded well to the experimental apparent activation energy.

Mechanisms investigation of cathodic-anodic coupling reaction of Zr-H2O at 360 °C by long-term in-situ electrochemical polarization analyses

Long-term on-line monitoring of in-situ electrochemical polarization curves were conducted on two zirconium claddings during corrosion in 360 °C water. Results suggest that cathodic reaction is activation-controlled, while anodic reaction is diffusion-controlled. Cathodic Tafel constants match well with the value predicted by Tafel kinetics and different hydrogen evolution reaction mechanisms of alloys with corrosion time are observed. Generally, recombination of hydrogen atoms becomes harder with time and is even harder in one of the alloys, which is proposed to increase the diffusion probability of hydrogen atoms into zirconium matrix. This proposal is in good agreement with experimental data.