Adsorbed Hydrogen Atoms Research Articles

Adsorption of Atomic Hydrogen on Hydrogen Boride Sheets Studied by Photoelectron Spectroscopy.

Hydrogen boride (HB) sheets are emerging as a promising two-dimensional (2D) boron material, with potential applications as unique electrodes, substrates, and hydrogen storage materials. The 2D layered structure of HB was successfully synthesized using an ion-exchange method. The chemical bonding and structure of the HB sheets were investigated using Fourier Transform Infrared (FT-IR) spectroscopy and Transmission Electron Microscopy (TEM), respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the chemical states and transformation of the components before and after atomic hydrogen adsorption, thereby elucidating the atomic hydrogen adsorption process on HB sheets. Our results indicate that, upon atomic hydrogen adsorption onto the HB sheets, the B-H-B bonds were broken and converted into B-H bonds. This research highlights and demonstrates the changes in chemical states and component transformations of the boron element on the HB sheets' surface before and after atomic hydrogen adsorption, thus providing a clearer understanding of the unique bonding and structural characteristics of the HB sheets.

Molecular Dynamics Insights into Mechanical Stability, Elastic Properties, and Fracture Behavior of PHOTH-Graphene.

PHOTH-graphene is a newly predicted 2D carbon material with a low-energy structure. However, its mechanical stability and fracture properties are still elusive. The mechanical stability, elastic, and fracture properties of PHOTH-graphene were investigated using classical molecular dynamics (MD) simulations equipped with REBO potential in this study. The influence of orientation and temperature on mechanical properties was evaluated. Specifically, the Young's modulus, toughness, and ultimate stress and strain varied by -26.14%, 36.46%, 29.04%, and 25.12%, respectively, when comparing the armchair direction to the zigzag direction. The percentage reduction in ultimate stress, ultimate strain, and toughness of the material in both directions after a temperature increase of 1000 K (from 200 K to 1200 K) ranged from 56.69% to 91.80%, and the Young's modulus was reduced by 13.63% and 7.25% in both directions, respectively, with Young's modulus showing lower sensitivity. Defects usually weaken the material's strength, but adding random point defects in the range of 3% to 5% significantly increases the ultimate strain of the material. Furthermore, hydrogen atom adsorption induces crack expansion to occur earlier, and the crack tip without hydrogen atom adsorption just began to expand when the strain was 0.135, while the crack tip with hydrogen atom adsorption had already undergone significant expansion. This study provides a reference for the possible future practical application of PHOTH-graphene in terms of mechanical properties and fracture failure.

Theoretical Prediction of Enhanced Hydrogen Evolution Reaction Electrocatalysts Based on Tantalum Phosphide.

Ta-based transition metal catalysts have shown significant catalytic activity for the hydrogen evolution reaction (HER) in recent studies. However, the application of tantalum phosphide (TaP) in the HER has not been documented. Herein, a systematic study of TaP catalysts was performed through density functional theory (DFT). The performance of TaP (004) for the HER was predicted. Thermodynamic analyses of Ta-terminated and P-terminated surfaces with adsorbed hydrogen atoms were conducted, and the HER mechanism on TaP (004) surfaces was carefully investigated. Theoretical results revealed that TaP (004) exhibits excellent HER activity (ΔGH* = 0.0456 eV), and both the Ta-terminated and P-terminated surfaces follow the Volmer-Heyrovsky mechanism under acidic conditions, with the Volmer step being the rate-determining step. A mixed surface strategy was also applied to explore the synergistic effects of Ta-terminated and P-terminated surfaces, which enhanced the HER activity. Additionally, the study screened dopants to assess their impact on the HER activity, revealing that doping with S, Ni, Co, Fe, and Cr could improve the HER performance.

Neighboring Catalytic Sites Are Essential for Electrochemical Dechlorination of 2-Chlorophenol.

The electrocatalytic reduction process is a promising technology for decomposing chlorinated organic pollutants in water but is limited by the lack of low-cost catalysts that can achieve high activity and selectivity. In studying electrochemical dechlorination of 2-chlorophenol (2-CP) in aqueous media, we find that cobalt phthalocyanine molecules supported on carbon nanotubes (CoPc/CNT), which is a highly effective electrocatalyst for breaking the aliphatic C-Cl bonds in 1,2-dichloroethane (DCA) and trichloroethylene (TCE), are completely inactive for reducing the aromatic C-Cl bond in 2-CP. Detailed mechanistic investigation, including volcano plot correlation between dechlorination rate and atomic hydrogen adsorption energy on various transition metal surfaces, kinetic measurements, in situ Raman spectroscopy, and density functional theory calculations, reveals that the reduction of the aromatic C-Cl bond in 2-CP goes through a hydrodechlorination mechanism featuring a bimolecular reaction between adsorbed atomic hydrogen and 2-CP on the catalyst surface, which requires neighboring catalytic sites, whereas the aliphatic C-Cl bonds in DCA and TCE are cleaved by direct electron transfer from the catalyst, which can occur on isolated single sites. This investigation leads to the discovery of metallic Co as a highly selective and active electrocatalyst for 2-CP dechlorination. This work provides new insights into the fundamental chemistry and catalyst design of electrochemical dechlorination reactions for wastewater treatment.

Universal and large-scale transform engineering from commercial metals to micron/nanoporous metals via an induced oxidation-reduction reaction

Three-dimensional (3D) nanoporous metals are being increasingly utilized in various fields such as catalysis, energy storage, and sensing. However, the conventional fabrication approaches for 3D nanoporous metals, such as dealloying and template methods, require additional sacrificial materials and multiple fabrication steps and generate chemical waste. Herein, we propose a novel gaseous (O2 and H2) oxidation-reduction (GOR) method to directly transform various transition metals/alloys into 3D micron/nanoporous materials by utilizing the spontaneous reconstruction of metallic atoms. This method eliminates the need for sacrificial materials and acidic/alkaline solutions, making it facile, cost-effective, and environmentally friendly. The resulting micron/nanoporous Ni/Ni alloy exhibits excellent mechanical properties, atomic hydrogen adsorption capability, and hydrophilicity, leading to outstanding electrocatalytic activity and durability for hydrogen evolution reaction.

Cooperative coupling of microscopic enhanced electric field and macroscopic efficient bubble traffic for industrial hydrogen evolution

The alkaline hydrogen evolution reaction (HER) for industrial hydrogen generation is a promising way to achieve intermittent energy storage. However, challenges, such as the insufficient supply of adsorbed hydrogen atoms (*H) and slow bubble dynamics, hinder the development of industrial HER. Here, we report a cooperative strategy by leveraging both microscopic enhanced electric field and macroscopic efficient bubble traffic for industrial hydrogen evolution, demonstrated through the NiCoP nanotips on NiP nanorods (NiCoP-tip@NiP). Specifically, during the HER process, the nanotips can accumulate a large number of electrons, enhancing the electric field of the Stern layer. This enhanced electric field accelerates the dissociation of water, resulting in favorable *H for HER. Simultaneously, the confined space between the nanotips hinders the growth of bubbles generated at the tips. Newly formed bubbles will push out the existing bubbles, thus accelerating gas release. As a result, NiCoP-tip@NiP exhibits a low overpotential of 300 mV at 1000 mA cm−2 and maintains stable operation over 90 h at approximately 300 mA cm−2 during HER processes. This cooperative strategy provides profound insights for industrial hydrogen generation.

Research on Residual Gas Adsorption on Surface of Hexagonal Boron Nitride-Based Memristor.

As a promising nonvolatile memory device with two ends, the memristor has received extensive attention for its industrial manufacture. Density functional theory was used to analyze the adsorption properties of residual gas on hexagonal boron nitride (h-BN)-based memristor model surfaces with Stone-Wales-5577 grain boundary defects [h-BN(SW)]. First, by calculating the adsorption energy, geometric parameters, and charge transfer, we identified the most stable adsorption sites for hydrogen atoms (H-TB1) and H2 molecules (H2-TN2). We observed a tendency toward chemisorption for hydrogen atoms and physical adsorption for H2 molecules at these sites. Furthermore, two coadsorption configurations were formed by introducing H2 molecules and hydrogen atoms into single adsorption configurations: namely H-TB1_H2-TN1TN2 and H2-TN2_H-TB1TN1TN3. In the case of hydrogen-based configuration, there is weak dissociation of the H2 molecule, which does not facilitate hydrogen atom adsorption. However, adjacent hydrogen atoms tend to form stable dimers, while excess hydrogen atoms have a tendency to weakly chemisorb in the case of H2-based configuration. The pristine h-BN surface is more favorable for hydrogen atom migration compared to the h-BN(SW) surface due to its higher adsorption energy. On the h-BN(SW) surface, hydrogen atoms tend to migrate inward from the center of adjacent heptagonal boron nitride rings while coadsorption has a minimal impact on their vertical migration as well as that of H2 molecules. This work provides theoretical insights into the H/H2 trace gas interaction during h-BN wafer-level fabrication for memristor devices.

Cobalt-vanadium coating deposition via programmed electrolysis mode

In the current work, the co-deposition of cobalt with vanadium from a complex citrate electrolyte via stationary and pulse electrolysis modes was investigated. The process was carried out at a current density of 1–15 Adm–2 in stationary electrolysis mode and 2–10 Adm–2 in pulse electrolysis mode, with variable ratio of pulse time to pause time at a temperature range of 35–400С and pH 3.0–3.5. According to the results of X-ray fluorescence spectrometry, the maximum content of vanadium in the coating obtained via the programmed electrolysis mode is 1.20–1.45%, which is tens of times higher than in the coating deposited by the stationary electrolysis mode (vanadium content of 0.007–0.017%) under similar conditions. The obtained results may confirm the hypothesis of additional vanadium reduction from oxo-anions by adsorbed hydrogen atoms formed on the cathode surface during the pause period. Based on the results of the analysis of 3D graphs, the optimal parameters of the process for fabricating a cobalt-vanadium coating with the maximum vanadium content in the alloy and a coating current efficiency of 80% have been established.

The kinetics of hydrogen evolution reaction accompanied by hydrogen absorption reaction with consideration of subsurface hydrogen as an adsorbed species: Faradaic impedance

An equation has been obtained for the Faradaic impedance of the hydrogen evolution reaction (HER), parallel to which the hydrogen absorption reaction (HAR) occurs, taking into account subsurface hydrogen (hydrogen atoms between the first and second layers of metal atoms) as a separate state. A new equivalent electrical circuit for the HER + HAR process has been proposed. It has been shown that the improvement in the quality of approximation of the impedance spectra of TiFe and TiFe2 cathodes in 0.5 M H2SO4 when using this equivalent circuit is statistically significant. Based on the impedance data, a HER + HAR mechanism is suggested for the TiFe electrode. The interactions in the layer of adsorbed hydrogen atoms and in the subsurface layer are discussed qualitatively.

An active learning workflow for predicting hydrogen atom adsorption energies on binary oxides based on local electronic transfer features

Machine learning combined with density functional theory (DFT) enables rapid exploration of catalyst descriptors space such as adsorption energy, facilitating rapid and effective catalyst screening. However, there is still a lack of models for predicting adsorption energies on oxides, due to the complexity of elemental species and the ambiguous coordination environment. This work proposes an active learning workflow (LeNN) founded on local electronic transfer features (e) and the principle of coordinate rotation invariance. By accurately characterizing the electron transfer to adsorption site atoms and their surrounding geometric structures, LeNN mitigates abrupt feature changes due to different element types and clarifies coordination environments. As a result, it enables the prediction of ∗H adsorption energy on binary oxide surfaces with a mean absolute error (MAE) below 0.18 eV. Moreover, we incorporate local coverage (θl) and leverage neutral network ensemble to establish an active learning workflow, attaining a prediction MAE below 0.2 eV for 5419 multi-∗H adsorption structures. These findings validate the universality and capability of the proposed features in predicting ∗H adsorption energy on binary oxide surfaces.

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.

LHHW/RSM reaction rate modeling for Co-Mn/SiO2 nanocatalyst in Fishcher-Tropsch synthesis

This study aims to assess the kinetics of Fischer–Tropsch (FT) reaction over the cobalt-manganese nanoparticles supported by silica oxide. Nanoparticles were synthesized by the thermal decomposition method using "[Co(NH3)4CO3]MnO4" complex and characterized by XRD, TEM, and BET techniques. The kinetics of the process were evaluated using a combination of Langmuir–Hinshelwood-Hougen-Watson (LHHW) and response surface methodology. Correlation factors of 0.9902 and 0.962 were obtained for the response surface method (RSM) and LHHW, respectively. The two methods were in good agreement, and the results showed that the rate-determining step was the reaction of the adsorbed methylene with the adsorbed hydrogen atom, and only carbon monoxide molecules were the most active species on the catalyst surface. A temperature of 502.53 K and a CO partial pressure of 2.76 bar are proposed as the optimal conditions by RSM analysis. The activation energy of CO consumption reaction was estimated to be 61.06 kJ/mol.

Computational exploration of two-dimensional vacancy-free boridene sheet and its derivatives: high stabilities and the promise for hydrogen evolution reaction

The recent synthesis of a two-dimensional (2D) MBene sheet, referred to as the boridene sheet (Mo4B6Tz), has ignited considerable interest in exploring 2D transition metal borides. Boridene has an ordered arrangement of metal vacancies, which are pivotal to its stability. Employing first-principles calculations, we explored the stable phases, electronic properties and catalytic abilities of boridene with different vacancy concentrations (Vm). Our results demonstrate that Vm significantly influences the cohesive energies of boridene sheets. Phonon spectrum and ab initio molecular dynamics simulations reveal the high stability of the vacancy-free boridene Mo6B6T6 (T = O, -OH), underscoring their potential for experimental realization. Substituting Mo atoms with Nb, Ta, or W enhances the structural stability of boridene sheets, leading to the identification of four stable variants: Nb6B6F6, Ta6B6F6, Ta6B6O6, and W6B6O6. These boridene sheets exhibit metallic behavior, with five structures displaying near-zero Gibbs free energy for hydrogen atom adsorption, indicating their potential as catalysts for the hydrogen evolution reaction. The uncovering of vacancy-free boridenes and their 2D derivatives greatly broadens the scope of the MBene family.

Non-Metal Doping as a First-Principles Study for Promoting the Hydrogen Evolution of Two-Dimensional Electride Y2C Electrocatalysts

The two-dimensional electrochemical Y2C’s low work function and strong charge transfer qualities limit its applicability in catalysis due to its poor catalytic activity. In this paper, based on density functional theory calculations, we use two techniques to increase the HER catalytic activity of the Y2C monolayer: substitution doping (XC) and adsorption doping (XT) of non-metal (X = N, P, O, S, and F). The results showed that the absolute values of hydrogen free energies (ΔGH*) of the substitutional dopants of PC, SC and adsorptive dopants of NT, OT, ST, and PT had increased catalytic activity compared with those of the pristine Y2C monolayer (−0.673 eV). It was highlighted that the adsorption doping of PT can further reduce the adsorption free energy of the pristine Y2C monolayer to −0.19 eV, which is close to the optimal zero value, and the binding energy of the hydrogen atoms on the Y2C surface significantly increased from −0.913 to −0.438 eV, which is more favorable for the desorption of hydrogen atoms. These results demonstrate that the doping of non-metals activates the adsorption of hydrogen atoms on monolayer Y2C and provides a feasible method for hydrogen generation.

Evaluation of hydrogen storage capacity of two-dimensional Sc2N MXene: A DFT study

In this work, the efficiency of hydrogen storage on Sc2N MXenes monolayer is systematically investigated using first-principles calculations. After determining the structural stability of designed monolayer, adsorption sites for the storage of hydrogen atoms (H) and molecules (H2) are identified. The calculated binding energies have indicated that the hydrogen atoms have favorable adsorption at the center or H site of the Sc atoms and hydrogen molecules are found to be the most stable when adsorbed on the top/T site of Sc atoms. The binding energy assessment identified the chemisorption for hydrogen atoms and Kubas-type interactions for H2. To further ascertain the suitability of the Sc2N monolayer for hydrogen storage various analyses including binding energy, partial density of states (PDOS), electron localization function (ELF), Mullikan charge analysis and Hirshfeld charge analysis are conducted. In order to determine the thermal stability of the Sc2N monolayer, desorption temperature with respect to pressure and molecular dynamics study has also been conducted and found the monolayer thermally stable. Desorption isotherms condition with increasing pressure confirms the gravimetric storage uptake. The obtained results have revealed that the hydrogen storage capacity considered monolayer has reached up to 10.8 wt%, which is reasonably high. Hence, the obtained results of hydrogen atom and molecules adsorption have clearly established that Sc2N monolayer is as an exemplary, stable, reliable and efficient medium for hydrogen storage applications.

Biologically templated formation of Cobalt-Phosphide-Graphene hybrids with charge redistribution for efficient hydrogen evolution

Developing highly efficient and sustainable hydrogen evolution reaction (HER) electrocatalysts is important for the practical application of emerging energy technologies. The spherical structure and phosphorus-rich properties of Chlorella can facilitate the construction of comparable transition metal phosphide electrocatalysts. Here, a microorganism template strategy is proposed to construct a cobalt-phosphide-graphene hybrid. Chlorella can absorb metal ions, and the generated rough spherical nanoparticles are uniformly distributed around the reduced graphene oxide nanosheets. This designed catalyst has comparable HER performance in acidic electrolytes and needs an overpotential of only 153 mV at a current density of 10 mA cm−2. The experimental and density functional theory results imply that the charge redistribution between Co2P and pyrrole-N is the key factor in enhancing the HER activity. The induced electron aggregation at the N and P sites can serve as a key active site for absorbing the adsorbed hydrogen atom intermediate to accelerate the HER process, contributing to the active sites of Co2P- and pyrrole-N-doped carbon with 0 eV hydrogen adsorption free energy. This work provides a broad idea for synthesizing advanced catalysts by a biological template approach, facilitating the innovative integration of biology and emerging electrochemical energy technologies.

Effects of Alloying Element on Hydrogen Adsorption and Diffusion on α-Fe(110) Surfaces: First Principles Study

Based on first principles density functional theory (DFT) methods, this study employed the Cambridge Serial Total Energy Package (CASTEP) module within Materials Studio (MS) software under the generalized gradient approximation to investigate the adsorption, diffusion behavior, and electronic properties of hydrogen atoms on α-Fe(110) and α-Fe(110)-Me (Mn, Cr, Ni, Mo) surfaces, including calculations of their adsorption energies and density of states (DOS). The results demonstrated that doping with alloy atoms Me increased the physical adsorption energy of H2 molecules on the surface. Specifically, Mo doping elevated the adsorption energy from −1.00825 eV to −0.70226 eV, with the largest relative change being 30.35%. After doping with Me, the chemical adsorption energy of two hydrogen atoms does not change significantly, among which doping with Cr results in a decrease in the chemical adsorption energy. Building on this, further analysis of the chemical adsorption of single atoms on the surface was conducted. By comparing the adsorption energy and the bond length between a hydrogen atom and iron/dopant metal atom, it was found that Mo doping has the greatest impact, increasing the bond length by 58.58%. Analysis of the DOS functions under different doping conditions validated the interaction between different alloy elements and H atoms. Simultaneously, simulations were carried out on the energy barrier crossed by H atoms diffusing into the metal interior. The results indicate that Ni doping facilitates the diffusion of H atoms, while Cr, Mn, and Mo hinder their diffusion, with Mo having the most significant effect, where its barrier is 21.88 times that of the undoped surface. This conclusion offers deep insights into the impact of different doping elements on hydrogen adsorption and diffusion, aiding in the design of materials resistant to hydrogen embrittlement.

The Electrochemical Hydrogen Evolution Reaction Based on Helical Chain Stacked 2D Tellurium Nanoflakes

AbstractA crucial factor in advancing the broad utilization of electrocatalytic hydrogen evolution reaction (HER) is the development of efficient catalysts with sufficient active sites. Herein, a hydrothermal approach is utilized to fabricate helical chain stacked two‐dimensional (2D) tellurium (Te) nanoflakes, whose HER performance hasn't been systematically studied yet. It is found that Te nanoflakes transferred on carbon fiber paper (CFP) exhibit impressive HER properties and show a load dependence. The overpotential required for HER is significantly reduced to 279 mV under a load condition of 0.86 mg cm−2 at a current density of 10 mA cm−2. Density functional theory (DFT) calculations are further systematically carried out on Te catalytic sites along the helical chain at [0001] direction with a threefold screw symmetry. It is found that the Gibbs free energy of adsorbed hydrogen atom (ΔGH*) on Te sites is significantly lower than that of molybdenum disulfide (MoS2). Besides, the active sites based on surface atom density calculation reveal that Te provides more adsorption sites than layered MoS2. The decreased adsorption energy and efficient adsorption sites in Te may highlight the promising application of elemental crystal Te in electrocatalytic hydrogen production and pave the way for developing new types of electrocatalysts.

Mechanical behaviour and micro-mechanism of atomically precise edge graphene nanoribbons mechanical cutting guided by hydrogen atom adsorption

The preparation of graphene nanoribbons with atomically precise edges is a major challenge. In this paper, we proposed a mechanical cutting method for graphene nanoribbons guided by hydrogen atom adsorption and analysed the mechanical behaviour and microscopic cutting mechanism of graphene with hydrogen atom adsorption using reactive molecular dynamics simulations. The results showed that hydrogen atom adsorption weakened the mechanical properties and improved the cutting performance of graphene. Hydrogen atom adsorption showed a substantial guiding effect on graphene cutting, increasing the regular edge ratio from 12.21 % to 91.89 %, and graphene nanoribbons with atomically precise edges were prepared using this method. We determined that the cutting mechanism of graphene without hydrogen atom adsorption was a tensile-breaking mechanism. In contrast, graphene with hydrogen atom adsorption exhibited a shear-breaking mechanism. The cutting performance of the armchair-H graphene was lower than that of the zigzag-H graphene owing to the unique hexagonal distribution of carbon atoms. This study provides new insights into the cutting mechanism of graphene guided by hydrogen atom adsorption and establishes the method for preparing atomically precise edge graphene nanoribbons by mechanical cutting.

Understanding the Reducibility of CeO2 Surfaces by Proton-Electron Transfer from CpCr(CO)3H.

CeO2 is a popular material in heterogeneous catalysis, molecular sensors, and electronics and owes many of its special properties to the redox activity of Ce, present as both Ce3+ and Ce4+. However, the reduction of CeO2 with H2 (thought to occur through proton-electron transfer (PET) giving Ce3+ and new OH bonds) is poorly understood due to the high reduction temperatures necessary and the ill-defined nature of the hydrogen atom sources typically used. We have previously shown that transition-metal hydrides with weak M-H bonds react with reducible metal oxides at room temperature by PET. Here, we show that CpCr(CO)3H (1) transfers protons and electrons to CeO2 due to its weak Cr-H bond. We can titrate CeO2 with 1 and measure not only the number of surface Ce3+ sites formed (in agreement with X-ray absorption spectroscopy) but also the lower limit of the hydrogen atom adsorption free energy (HAFE). The results match the extent of reduction achieved from H2 treatment and hydrogen spillover on CeO2 in a wide range of applications.