Desorption Of Hydrogen Atoms Research Articles

Desorption of atomic hydrogen from graphene on hexagonal boron nitride

Desorption of atomic hydrogen from graphene on hexagonal boron nitride

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.

Reconstructing brittle hydrides using pulsed electric current to restore the degraded performance of zirconium alloys

When zirconium alloy undergoes water corrosion reaction during the service process, it absorbs hydrogen to form brittle hydrides, which is one of the main reasons for the deterioration of the mechanical properties of zirconium alloy. There is an urgent need to find an effective method to regulate brittle hydrides to restore the properties of hydrogen-containing zirconium alloys. This study conducted electropulsing treatment on the hydrogen-charged nuclear grade Zr-4 alloy, and the results showed that the electropulsing process caused the hydrides to transform from large-sized brittle stripe-shaped δ-phase to the small-sized ζ-phase. The hydrogen content in the alloy is significantly reduced, which basically restores the mechanical properties of the alloy. However, in the comparative experiment of isothermal heat treatment at 400 °C, brittle hydrides did not dissolve and their mechanical properties did not recover. A mathematical model was established for the characteristics and morphological changes of strip hydrides, and the current density distribution and introduced free energy during the microstructure evolution process were calculated and analyzed. The calculation results indicate that the pulsed current promotes the decomposition of hydrides through the introduction of free energy, reduces the activation energy of hydrogen atom diffusion, accelerates the diffusion and desorption of hydrogen atoms, and realizes the repair of mechanical properties of hydrogen-charged zirconium alloy.

Hydrogen-Stabilized ScYNdGd Medium-Entropy Alloy for Hydrogen Storage.

The research on the functional properties of medium- and high-entropy alloys (MEAs and HEAs) has been in the spotlight recently. Many significant discoveries have been made lately in hydrogen-based economy-related research where these alloys may be utilized in all of its key sectors: water electrolysis, hydrogen storage, and fuel cell applications. Despite the rapid development of MEAs and HEAs with the ability to reversibly absorb hydrogen, the research is limited to transition-metal-based alloys that crystallize in body-centered cubic solid solution or Laves phase structures. To date, no study has been devoted to the hydrogenation of rare-earth-element (REE)-based MEAs or HEAs, as well as to the alloys crystallizing in face-centered-cubic (FCC) or hexagonal-close-packed structures. Here, we elucidate the formation and hydrogen storage properties of REE-based ScYNdGd MEA. More specifically, we present the astounding stabilization of the single-phase FCC structure induced by the hydrogen absorption process. Moreover, the measured unprecedented high storage capacity of 2.5 H/M has been observed after hydrogenation conducted under mild conditions that proceeded without any phase transformation in the material. The studied MEA can be facilely activated, even after a long passivation time. The results of complementary measurements showed that the hydrogen desorption process proceeds in two steps. In the first, hydrogen is released from octahedral interstitial sites at relatively low temperatures. In the second, high-temperature process, it is associated with the desorption of hydrogen atoms stored in tetrahedral sites. The presented results may impact future research of a novel group of REE-based MEAs and HEAs with adaptable hydrogen storage properties and a broad scope of possible applications.

Crystallization features of casting alloys

It has been shown that elementary crystal lattices of basic phases and oxides of casting alloys do not satisfy the principle of structural and dimensional correspondence. Formation of crystallization centers during solidification of casting alloys is a nanostructured process. The main demodifying element in melt crystallization is adsorbed hydrogen. It prevents the integration of nanocrystals into the nucleus of crystallization of the main phases of casting alloys. When the melt overheats, adsorption and desorption of hydrogen atoms occur. The predominance of one of these processes explains the features of crystallization of cast‑ ingalloys. Prior to critical superheating of the melt, the adsorption of hydrogen atoms prevails. As a result, molds with an unmodified structure are formed. When the melt overheats above the critical one, the process of desorption of hydrogen atoms prevails. As a result, molds with a modified structure are formed.

Repair of embrittlement induced by different hydride configurations by dissolving partial hydrides using pulsed electric current

The sudden brittle fracture of Ti, Zr and other metals caused by brittle hydride phase usually depends on the hydride network that provides the crack initiation and propagation path. Common hydride networks include continuous hydride configuration and grain boundary hydride configuration. In this study, pulsed electric current is used to effectively repair the embrittlement caused by continuous hydride configuration and grain boundary hydride configuration in pure titanium. The elongation of pure titanium with hydride configuration increased from 10% to about 20% after pulsed electric current treatment, with a certain degree of recovery of ultimate tensile strength. This is due to the dissolution of partial hydride after pulsed electric current treatment, and the hydride configuration is destroyed. Considering the introduction of pulsed electric current, hydride configuration in pure titanium is thermodynamically unstable, and the electromigration effect in kinetics also accelerates desorption of hydrogen atoms. The evolution of hydride configuration and desorption of hydrogen atoms are beneficial to the recovery of mechanical properties of hydrogenated pure titanium. In this study, the problem of hydride embrittlement caused by different hydride configurations in pure titanium was effectively repaired by pulsed electric current, which provided a new pathway and solution for dealing with the hydride induced embrittlement.

Re-Dispersion of Platinum From CNTs Substrate to α-MoC1-x to Boost the Hydrogen Evolution Reaction.

Developing high-performance electrocatalysts toward hydrogen evolution reaction (HER) is important for clean and sustainable hydrogen energy, yet still challenging. Herein, an α-MoC1-x induced redispersing strategy to construct a superior HER electrocatalyst (Pt/CNTs-N+α-MoC1-x ) by mechanical mixing of α-MoC1-x with Pt/CNTs-N followed by thermal reduction is reported. It is found that thermo-activation treatment enables partial Pt atoms to redisperse on α-MoC1-x substrate from carbon nanotubes, which creates dual active interfaces of Pt species dispersed over carbon nanotubes and α-MoC1-x . Benefiting from the strong electronic interaction between the Pt atom and α-MoC1-x , the utilization efficiency of the Pt atom and the zero-valence state of Pt is evidently enhanced. Consequently, Pt/CNTs-N+α-MoC1-x catalyst exhibits excellent HER activity with low overpotentials of 17 and 34 mV to achieve a current density of 10 mA cm-2 in acidic and alkaline electrolytes, respectively. Density functional theory calculations further reveal that the synergistic effect between Pt and α-MoC1-x makes it accessible for the dissociation of water molecules and subsequent desorption of hydrogen atoms. This work reveals the crucial roles of α-MoC1-x additives, providing practical solutions to enhance platinum dispersion, and thereby enhance the catalytic activity in HER.

Modulating Electronic Structure to Improve the Solar to Hydrogen Efficiency of Cobalt Nitride with Lattice Doping

Development of state-of-the-art catalytic systems for highly efficient solar to hydrogen energy conversion is desirable but remains a challenge. In this work, transition metal (M = V, Mo, and W) doped cobalt nitride has been synthesized for solar to hydrogen energy conversion. Neutron diffraction results suggest that the composition of our as-prepared cobalt nitride is Co3.75N0.14, which contains many lattice defects. Neutron pair distribution function (PDF) analysis confirms the structural defects and lattice distortion in M-Co3.75N0.14. The M-doping is demonstrated to tune the electronic structure and properties of Co3.75N0.14 due to the formation of M–N bonds, which significantly improves charge carrier separation efficiency and the reaction kinetics. Density functional theory (DFT) calculations suggest that the d-band center of the doped cobalt nitrides exhibit downshifts compared to pure cobalt nitride. This is beneficial for the desorption of hydrogen atoms, promoting hydrogen evolution activity. The hydrogen evolution rate of the optimal V–Co3.75N0.14-Eosin-Y system reaches 21.21 μmol·mg–1·h–1, with quantum efficiency around 38% at 405 nm excitation wavelength. This remarkable value surpasses those reported for other hybrid photocatalysts.

Effects of La3+ on the hydrogen permeation and evolution kinetics in X70 pipeline steel

The inhibitory effect of La3+ on the hydrogen permeation of X70 pipeline steel was investigated via steady-state hydrogen permeation current (i∞) through electrochemical hydrogen permeation tests. The experimental permeation data were fitted with a constant concentration model and Electrochemical Impedance Spectroscopy (EIS) tests were conducted to characterize the activity of Hydrogen Evolution Reaction (HER) after the optimization of electrochemically active surface area. Additionally, the kinetics of HER and the adsorption/desorption process is calculated by Iyer-Pickering-Zamanzadeh (IPZ) and surface effect models, of which the results demonstrate that the La3+ in the corrosion products could effectively reduce the rate of Volmer reaction and hydrogen adsorption process, and accelerate the process of hydrogen atom desorption, thus leading to the remarkable decrease in C0.

Existing States of Co-Deposited Hydrogen in Electrolessly Deposited Copper Films from EDTA Complex Bath

The existing states of co-deposited hydrogen in copper films electrolessly deposited from an ethylenediaminetetraacetatic acid complex bath were investigated using thermal desorption spectroscopy. Small desorption peaks at 500–700 K and large desorption peaks at 900–1300 K were observed in the as-deposited copper film, and these were attributed to the break-up of vacancy-hydrogen clusters and the desorption of molecular hydrogen from nanovoids, respectively. Moreover, an unknown desorption peak appeared at around 390 K. The total amount of desorbed hydrogen from the copper film in atomic ratio was 1.2 × 10−2, most of which was non-diffusible hydrogen desorbed above 800 K. A large number of nanovoids distributed in the grains were observed in the copper film. After 7 days, no significant change in hydrogen desorption above 500 K was observed, while the unknown desorption peak around 390 K disappeared. The as-deposited copper film showed lattice expansion and compressive residual stress, which were reduced after 7 days. Therefore, we attributed the unknown desorption peak appearing at around 390 K to the desorption of hydrogen atoms trapped by regular interstitial sites in the copper lattice.

Dissolution of hydrogen in metals and casting alloys

Thermodynamic calculations have shown that hydrogen from atmospheric water vapors can penetrate aluminum, iron and copper, especially into their melts. Hydrogen atoms in these metals are in free and adsorbed states. Strong and dense oxide films on the surfaces of aluminum, iron and copper significantly reduce the solubility of hydrogen in these metals. Copper and iron nanocrystals more actively adsorb atomic hydrogen than aluminum nanocrystals. This is one of the main reasons for the weak solubility of hydrogen in aluminum and the large desorption of hydrogen atoms in the crystallization of aluminum compared to iron and copper.

Constructing porous boron doped nickel phosphide (Ni2P) rod arrays with optimized electron coordination for alkaline hydrogen evolution

Transition metal-based phosphides (TMPs) show great potential for hydrogen evolution reaction (HER). The fine regulation of the electronic structure of metal-rich phosphides is an effective and challenging strategy for better activity. Herein, a simple and effective molten salt treatment is designed to synthesize porous boron doped Ni2P rod nanoarrays (M-B-Ni2P) for alkaline HER. The molten salt treatment facilitates the formation of unique porous Ni2P rod nanoarrays with homogeneous boron doping. The synthesized porous M-B-Ni2P exhibit excellent catalytic performance in alkaline media, requiring only an overpotential of 217 mV to drive 100 mA cm−2, which is 79 mV lower than binary nickel phosphide (M-Ni2P). The boron doping not only optimizes the porous geometry to increase the number of active sites, but also regulates the electronic coordination to promote the dissociation of water and the adsorption and desorption of hydrogen atoms. In addition, the self-supported monolithic M-B-Ni2P electrode can operate at a larger current density of 100 mA cm−2 for at least 100 h. This study on realizing boron doping based on molten salt treatment provides a new strategy for constructing transition metal-based phosphides as electrocatalysts.

Unravelling the synergy in platinum-nickel bimetal catalysts designed by atomic layer deposition for efficient hydrolytic dehydrogenation of ammonia borane

Bimetal catalysis has been one of the major categories in heterogeneous catalysis field, and the efficient and durable catalysts can be well achieved by the bimetal synergy. Herein we report a remarkable achievement of both dehydrogenation activity of ammonia borane and durability by controllably engineering Pt-Ni interfacial sites via the Pt and the following NiO atomic layer deposition strategy, which can also realize the controllable synthesis of other Pt-M (M=Co, Cu, Fe and Zn) bimetal catalysts. Multiple characterization techniques, kinetic-isotopic analyses and density functional theory calculations were employed to unravel the nature of the Pt-Ni synergy. Experimental and theoretical results reveal that the decoration of nickel species on the Pt nanoparticles constructing the targeted Pt-Ni interfacial sites could lower the reaction activation energy, promote the adsorption, activation and dissociation of H2O molecules, and facilitate the desorption of hydrogen atoms, resulting in the doubly enhanced activity with a turnover frequency value of 751.6 molH2 molPt-1 min-1 and the remarkably improved durability. Our work offers an alternative and general strategy for the rational design of bimetal catalysts with specific interfacial structure and provides fundamental guidance for in-depth understanding of the bimetal synergy.

Methodology and results of studying the states of hydrogen in graphene structures

In this work, an effective methodology of analysis of thermal desorption spectra (TDS) of hydrogen in carbon materials was further developed and applied. The methodology makes it possible, from TDS data of one heating rate, to determine the activation energies and pre-exponential factors of the rate constants of desorption processes. The TDS data of Rajasekaran et al. for hydrogenated epitaxial graphenes with a diamond-like structure (as in graphane) were analyzed. Some new information was obtained about the states of hydrogen in such unusual structures. It was shown that about half of the hydrogen contained in the samples is localized in the interfacial regions (between graphene and the substrate), while the desorption of such hydrogen is limited by diffusion (with three activation energies (34 kJ/mol(H2), 45 kJ/mol(H2), and 68 kJ/mol(H2)) of hydrogen molecules in these regions to the lateral surfaces of the samples. It was also shown that the rest of the hydrogen is localized on the top surface of the samples, while desorption of hydrogen atoms occurs with two activation energies and frequency factors (174 kJ/mol(H), 2 × 1013 s−1, and 256 kJ/mol(H), 3 × 1018 s−1); the obtained quantities are comparable to the related characteristics for graphane.

The Central Role of Nitrogen Atoms in a Zeolitic Imidazolate Framework-Derived Catalyst for Cathodic Hydrogen Evolution.

Platinum usually offers the most effective active center for hydrogen evolution reaction (HER), because of the optimal trade-off between the adsorption and desorption of hydrogeN atoms (H*) on Pt atoms. Herein, we report an unusual result regarding the active center of a HER catalyst, which was synthesized by electrodepositing traces of Pt nanoparticles (NPs) into a porous nitrogen-rich dodecahedron matrix derived from zeolitic imidazolate framework ZIF-8. With an ultra-low Pt loading of 2.76 μg cm-2 , the N-Pt-bonded catalyst can produce a current density of 117 mA cm-2 for the HER in 1.0 m H2 SO4 at an overpotential of 50 mV, whereas the commercial Pt/C (300 μg cm-2 Pt) can only reach 50 mA cm-2 under the same conditions. Cyclic voltammetry demonstrates that both the H* adsorption and the Pt oxidation are not allowed to occur on this catalyst, due to a full surface coverage of the trace Pt NPs by imidazole. The results from the specially designed experiments indicate that the imidazole N atoms may act as proton anchor-sites for the HER due to their electron donor nature. Density functional theory calculations also support a catalytic HER mechanism centered at the Pt-supported N active center, which needs a Gibbs free energy of H* absorption (ΔGH* ) significantly smaller than the absolute value of ΔGH* on the Pt(111) surface. We hope that the results of this study will encourage the research on novel N-centered catalysts for the HER.

Synergistic Effect of FeNi Bimetallic Clusters for the Catalytic of Hydrogen Dissociation and Desorption: A Density Functional Theory Study

Cognition to the metal-metal interactions is of vital importance for the catalytic process and would help exploring novel catalysts. In the present study, the model system of FexNiy (x + y = 6) bimetallic clusters was utilized to study how metal-metal interactions influence the catalytic performance. The formation energies of different FeNi clusters, the hydrogen chemisorption energies together with the maximum hydrogen capacity and the saturated hydrogen atoms desorption energies were calculated. Bimetallic clusters exhibit a superior performance than pure clusters. Especially, Fe2Ni4 cluster has the highest hydrogen loading capacity, the most facile hydrogen molecule dissociation activation energy barrier and the lowest hydrogen atom desorption energy, suggesting that it is easier to dissociate H2 and release the H atoms. As a consequence, by adjusting appropriate metal/metal ratios, it is possible to design bimetallic catalysts with excellent catalytic performance.

Exploring the nature of hydrogen of Rutile TiO2(110) at 78 K

The hydrogen on the surface or in the subsurface of rutile TiO2 play an important role in the surface chemical reactions and understanding the catalytic reactions due to its excess electrons. In this work, we have systematically explored the nature of hydrogen atom by atomic force microscopy (AFM)/scanning tunneling microscopy (STM) and investigated the behaviors and mechanism of hydrogen atom desorption and transfer between the surface and subsurface by Kelvin probe force spectroscopy (KPFS). The atomic contrast of surface hydrogen (Hsurf) and subsurface hydrogen (Hsub) are clearly identified by dynamic and static STM. The Hsub-Hsub interactions are systematically investigated, demonstrating the unusual no-repulsive effect of species with the same polarity. Importantly, the reversible hydrogen atom transfer between the sample surface and subsurface was successfully manipulated by KPFS performance, and mechanism of hydrogen transfer proceeds was proposed that force field together with electric field between the tip-sample space reduce the height and width of barrier resulting in the hydrogen atom transfer. The present study is expected to provide some new insights into the nature and manipulation of hydrogen atom and is useful to design the new catalyst of metal oxide.

Surface Sulfur Vacancy Engineering of Metal Sulfides Promoted Desorption of Hydrogen Atoms for Enhanced Electrocatalytic Hydrogen Evolution

Sulfur vacancy (SV) engineering is an evolving approach to improve the performance of metal sulfides for hydrogen evolution reactions (HER); however, a simple and universal method for creating SV i...

On the encounter desorption of hydrogen atoms on an ice mantle

At low temperatures (∼10 K), hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules, which cover a notable fraction of grain surface. The desorption energy of H atoms on H2 substrates is much less than that on water ice. The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H2 substrates. Using a small reaction network, we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method. For a full gas-grain model, H atom encounter desorption can reduce surface H abundances. Therefore, if a model adopts the encounter desorption of H atoms, it becomes more difficult for hydrogenation products such as methanol to form, but it is easier for C, O and N atoms to bond with each other on grain surfaces.

Stone—Wales Graphane: Its Structure, Properties, and Thermal Stability

A new two-dimensional hydrocarbon material formed upon complete chemical bonding of hydrogen to the both sides of Stone-Wales graphene, which is a recently predicted new allotrope of graphene, is numerically studied. The band gap Eg = 5.48 eV, the binding energy, and bond lengths, as well as the electron and phonon densities states, are determined. The anisotropy of the Young modulus is revealed. The heating-induced processes of defect formation are studied by the real-time molecular dynamics method. It is shown that the main thermal decomposition channel is the desorption of atomic hydrogen. The second most important decomposition channel is the desorption of molecular hydrogen. For the main decomposition channel, the activation energy Ea = 2.62 eV and the frequency-dependent factor A = 1.1 × 1018 s−1 in the Arrhenius law are determined.