Mechanism Of Hydrogen Interaction Research Articles

Explore the molecular mechanism of hydrogen bond regulation in deep eutectic solvents and co-amorphous phase transitions

Hydrogen bonding is an important intermolecular force that plays a crucial regulatory role in the phase transition of substances. Although it has been thermodynamically demonstrated that the solid-state form at room temperature is determined by the change in Tg depending on the mixing ratio. However, the molecular mechanisms of hydrogen bonding influencing the deep eutectic solvents (DES) and co-amorphous phase transition processes are still unclear. Therefore, in this study, miconazole nitrate (MN)-oxymatrine (OMT) DES (1:3) was prepared, along with the co-amorphous MN-OMT (2:1), to reveal the interaction mechanism of hydrogen bonding in the “liquid-solid” phase transition process. Firstly, the MN-OMT DES (1:3) and co-amorphous MN-OMT (2:1) were prepared by the solvent method. Secondly, FT-IR and NMR were used to study the interaction between MN-OMT DES (1:3), as well as the interaction between co-amorphous MN-OMT (2:1). The molecular mechanisms of DES and co-amorphous phase transition were explored through MD simulation and DFT computation. In addition, the essence of co-amorphous and DES formation was revealed through derivations based on the Henderson-Hasselbalch and Van’t Hoff equations, and the results of quantum calculations were verified. In summary, this study successfully prepared MN-OMT DES (1:3), as well as co-amorphous MN-OMT (2:1), and evaluated the molecular mechanisms of their phase transitions, which are of great significance for understanding the principles and regularities of DES and co-amorphous phase transition. This provides theoretical guidance for the development and application of novel DES and co-amorphous drug delivery systems.

First-Principles Study on the Adsorption and Dissociation Behavior of H2 on the Surface of a Plutonium–Gallium System

In order to understand the mechanism of hydrogen interaction on the surface of a plutonium–gallium system, the adsorption and dissociation behaviors of hydrogen molecules on the surface of a plutonium–gallium system were studied using the first-principles approach. The results show that the physical adsorption of hydrogen molecules occurs on the surface with a small degree of interaction; the most stable adsorption configuration is hollow-site parallel adsorption (H-b-hor1). During adsorption, charge transfer occurs mainly in the first atomic layer, and the density of states and surface function does not change significantly before and after adsorption. When the hydrogen molecule overcomes the energy barrier of 4.96 eV, it dissociates into two hydrogen atoms chemisorbed on the surface, which reduces the energy of the whole system by 1.95 eV. The essence of the hydrogen atom–surface interaction is that the 1s orbital of the hydrogen atom hybridizes with the 4s and 4p orbitals of the gallium atom and the 6s, 7s, and 6d orbitals of the plutonium atom to form a chemical bond.

Hydrogen Adsorption on Ir(111), Ir(100) and Ir(110)—Surface and Coverage Dependence

Hydrogen adsorption on the perfect Ir(111) as well as the metastable and unreconstructed Ir(100) and Ir(110) surfaces up to saturation coverage has been systematically computed using periodic density functional theory and ab initio atomistic thermodynamics for understanding the interaction mechanism of hydrogen on iridium surfaces. On the Ir(111) surface including van der Waals dispersion, hydrogen adsorption prefers the threefold hollow sites at low coverage and the top sites at high coverage; in agreement with the experiments (Phys. Rev. B 60 (1999) 14016). The computed adsorption energy and desorption temperature of hydrogen agree with the experiments [−0.57 (fcc-3H) and −0.53 (hcp-3H) vs. −0.55 eV; 180 and 325 K vs. 190 and 310 K, respectively]. On the Ir (100) surface, the bridge adsorption sites are preferred in the whole coverage range, in agreement with the LEED pattern (Phys. Rev. B 73 (2006) 75430), however, adsorption energy and desorption temperature are slightly overestimated by including van der Waals dispersion (−1.50 vs. −1.02 ± 0.15 eV; 470 vs. 425 – 389 K). On the Ir(110) surface, short-bridge sites are preferred at low coverage and the top sites become dominant at high coverage, and the calculated desorption temperatures are close to experiments by including van der Waals dispersion (210 and 365 K vs. 220 and 375 K). At low coverage, the different configurations of hydrogen adsorption on the Ir(111) have the similar energies, indicating their negligible repulsive interaction, while the Ir(100) and Ir(110) surfaces prefer regular line-shape adsorption configurations due to attractive interaction, and such adsorption configurations have not been observed experimentally. Our results show that differences in adsorption configurations and energies are associated with their differences in surface structures, and in turn explain the need of different methods in computing the adsorption properties on different surfaces. Such surface-dependent properties should also be possible on other metal surfaces.

MOTOR INFLUENCE RESEARCH OF HYDROGEN MICRODOSES ON THE DIESEL MIDGET OF TOXICITY INDICATORS

In this article, an analysis of paths to improve the environmental performance of internal combustion engines through the use of alternative motor fuels or by modifying regular petroleum fuels with microdoses has been presented. The experience of various researchers of the hydrogen interaction mechanism with hydrocarbon fuel and its influence on the characteristics of the air-fuel mixture combustion and the performance of the operating cycle of a piston internal combustion engine has been considered. The method of improvement characteristics of toxicity diesel midget by addition in nominal diesel fuel (DF) microdoses of the atomic and molecular Hydrogen and at the expense of it decrease in level emission of harmful substances with the exhaust gases (EG) has been offered. Receiving mix of atomic and molecular Hydrogen by its generation provides a path in the compact economic electrolyzer which is powered from a DC power source with tension of 12 V. Integration of this electrolyzer type in the fuel system of the vehicle will rid from creation of an additional hydrogen power supply system of the engine with use of the bulky and fire-hazardous equipment for storage of an onboard reserve of Hydrogen. The research of toxicity indexes of the fulfilled for diesel gases with use of regular diesel fuel was conducted at the motor stand for three modes of its loading – 0.8; 1.0; 1.2 kW. At the following stage researches for the same load conditions with addition to fuel of the Hydrogen microdoses in a fraction – 0.49 ; 1.15; 1.83% (on mass) have been executed. Motor influence research results of hydrogen microdoses on diesel midget of toxicity indicators 1Ч8,5/11 have been brought to diesel fuel. The effect consists in the composition exception of the exhaust gases of the unburnt hydrocarbons and weakening of white damp in EG practically up to 0 and concentration of nitrogen oxide for 14–26%.

Interaction of hydrogen with Pd- and co-decorated C24 fullerenes: Density functional theory study

In this work, we have investigated the adsorption of a hydrogen atom and molecules on the Pd and Co-decorated C24 fullerenes by means of density functional theory. The hydrogen interaction mechanism with host cages by regarding the adsorption energy and charge density variations was studied. It is found that both Pd and Co atoms have a significant role to increase the adsorption energy as an exothermal process. This energy change is strongly dependent on the electrostatic potential variations around the Pd and Co atoms doped on the C24 fullerene. Also, the HOMO-LUMO gap (Eg) for C24 fullerene varies from 1.20 to 0.76 and 0.86eV, after decorations of Co and Pd atoms, respectively. More consideration such as thermodynamics parameter, electronic density of states, and charge density analysis are discussed in the context.

Hydrogen Chemical Configuration and Thermal Stability in Tungsten Disulfide Nanoparticles Exposed to Hydrogen Plasma.

The chemical configuration and interaction mechanism of hydrogen adsorbed in inorganic nanoparticles of WS2 are investigated. Our recent approaches of using hydrogen activated by either microwave or radiofrequency plasma dramatically increased the efficiency of its adsorption on the nanoparticles surface. In the current work we make an emphasis on elucidation of the chemical configuration of the adsorbed hydrogen. This configuration is of primary importance as it affects its adsorption stability and possibility of release. To get insight on the chemical configuration, we combined the experimental analysis methods with theoretical modeling based on the density functional theory (DFT). Micro-Raman spectroscopy was used as a primary tool to elucidate chemical bonding of hydrogen and to distinguish between chemi- and physisorption. Hydrogen adsorbed in molecular form (H2) was clearly identified in all the plasma-hydrogenated WS2 nanoparticles samples. It was shown that the adsorbed hydrogen is generally stable under high vacuum conditions at room temperature, which implies its stability at the ambient atmosphere. A DFT model was developed to simulate the adsorption of hydrogen in the WS2 nanoparticles. This model considers various adsorption sites and identifies the preferential locations of the adsorbed hydrogen in several WS2 structures, demonstrating good concordance between theory and experiment and providing tools for optimizing of hydrogen exposure conditions and the type of substrate materials.

Composition and size dependence of hydrogen interaction with carbon supported bulk-immiscible Pd–Rh nanoalloys

In-depth clarification of hydrogen interaction with noble metal nanoparticles and nanoalloys is essential for further development and design of efficient catalysts and hydrogen storage nanomaterials. This issue becomes even more challenging for nanoalloys of bulk-immiscible metals. The hydrogen interaction with bulk-immiscible Pd–Rh nanoalloys (3–6 nm) supported on mesoporous carbon is studied by both laboratory and large scale facility techniques. X-ray diffraction (XRD) reveals a single phase fcc structure for all nanoparticles confirming the formation of nanoalloys in the whole composition range. In situ extended x-ray absorption fine structure (EXAFS) experiments suggest segregated local structures into Pd-rich surface and Rh-rich core coexisting within the nanoparticles. Hydrogen sorption can be tuned by chemical composition: Pd-rich nanoparticles form a hydride phase, whereas Rh-rich phases do not absorb hydrogen under ambient temperature and pressure conditions. The thermodynamics of hydride formation can be tailored by the composition without affecting hydrogen capacity at full hydrogenation. Furthermore, for hydrogen absorbing nanoalloys, in situ EXAFS reveals a preferential occupation of hydrogen for the interstitial sites around Pd atoms. To our knowledge, this is the first study providing insights into the hydrogen interaction mechanism with Pd–Rh nanoalloys that can guide the design of catalysts for hydrogenation reactions and the development of nanomaterials for hydrogen storage.

Experimental Challenges in Studying Hydrogen Absorption in Ultrasmall Metal Nanoparticles

Recent advances on synthesis, characterisation and hydrogen absorption properties of ultra-small metal nanoparticles (defined here as objects with average size ≤ 3 nm) are briefly reviewed in the first part of this work. The experimental challenges encountered in performing accurate measurements of hydrogen absorption in Mg- and noble metal-based ultra-small nanoparticles are addressed. The second part of this work reports original results obtained for ultra-small bulk immiscible Pd-Rh nanoparticles. Carbon supported Pd-Rh nanoalloys in the whole binary chemical composition range have been successfully prepared by liquid impregnation method followed by reduction at 300 °C. EXAFS investigations suggested that the local structure of these nanoalloys is partially segregated into Rh-rich core and Pd-rich surface coexisting within the same nanoparticles. Downsizing to ultra-small dimensions completely suppresses the hydride formation in Pd-rich nanoalloys at ambient conditions, contrary to bulk and larger nanosized (5-6 nm) counterparts. The ultra-small Pd90Rh10 nanoalloy can absorb hydrogen forming solid solutions under these conditions, as suggested by in situ XRD. Apart from this composition, common laboratory techniques such as, in situ XRD, DSC and PCI failed to clarify the hydrogen interaction mechanism : either adsorption on developed surfaces or both adsorption and absorption with formation of solid solutions. Concluding insights were brought by in situ EXAFS experiments at synchrotron: ultra-small Pd75Rh25 and Pd50Rh50 nanoalloys absorb hydrogen forming solid solutions at ambient conditions. Moreover, the hydrogen solubility in these solid solutions is higher with increasing Pd content and this trend can be understood in terms of hydrogen preferential occupation in the Pd-rich regions, as suggested by in situ EXAFS. The Rh-rich nanoalloys (Pd25Rh75 and Pd10Rh90) only adsorb hydrogen on the developed surface of ultra-small nanoparticles. In summary, in situ characterization techniques carried out at large scale facilities are unique and powerful tools for in-depth investigation of hydrogen interaction with ultra-small nanoparticles at local level.

Characterization of the Metal-Semiconductor Interface of Pt-GaN Diode Hydrogen Sensors

In this paper, interaction mechanism of hydrogen with GaN metal-insulator-semiconductor (MIS) diodes has been investigated, focusing on the metal/semiconductor interfaces. As a result, the following three points are revealed: First, MIS Pt-SiO2-GaN diodes show a marked improvement in detection sensitivity, suggesting that the device interface plays a critical role in sensing. Second, exposure of the diodes to hydrogen is found to change the conduction mechanisms from Fowler-Nordheim tunneling to Pool-Frenkel emission. Third, interface trap level density of the diodes is found to be reduced by hydrogen exposure even at room temperature. These results support the validity of the hydrogen-induced dipole layer model.

Hydrogen influence on material interaction with ZDDP and MoDTC lubricant additives

In this paper the interaction of lubricant additives with hydrogen at the frictional interface has been investigated. Three different states of the base AISI 52100 alloy steel have been tested: untreated, nitrided and sulphonitrided, with different combinations of PAO6 base oil and ZDDP/MoDTC (Zinc DialkylDithioPhosphate and Molybdenum Dialkyldithiocarbamate) additives. Experiments have been carried out on pin-on-plate reciprocating tester, immersed in the lubricant heated to 100°C. In the boundary lubricated regime the results showed the best friction behaviour for treated surfaces tested in presence of PAO6 with additives suggesting some interaction at the frictional interface of nitrided and sulphonitrided surfaces with lubricant additives. The minimum recorded value of coefficient of friction was as low as 0.05 for the sulphonitrided sample with PAO6+MoDTC oil. In the case of the treated surfaces a characteristic “low friction phase” has been observed when tested with PAO6 with additives. After a given time, the coefficient of friction was increasing to a higher steady-state value and the duration of this low friction phase varied from sample to sample. This can be explained by the mechanism of hydrogen interaction in the boundary lubrication regime, which was postulated for the base oil case by some of the authors in their previous papers. To validate the hypothesis, an experiment has been carried out where the test was stopped at the end of the “low friction phase” and during the hold period the sample was re-saturated with hydrogen. After resuming the experiment the low friction regime was again observed. The effect of a potential synergistic mechanism between hydrogen and ZDDP or MoDTC lubricant additives on frictional behaviour of nitrided and sulphonitrided surfaces is discussed in this paper.

Hydrogen species within the metals: Role of molecular hydrogen ion H2+

AbstractNovel mechanism of hydrogen interaction with transition metals via stepwise reversible dissociative ionization of H2 molecule is proposed instead of a commonly accepted dissociative adsorption. It involves ionization of H2 to molecular ion (H2+)ad on the outer surface of metal phase, its subsequent absorption and dissociation within the metal phase into (H+)ab ions, i.e., absorbed protons, as described by: H2⇄(H2+)ad+e− and (H2+)ad⇄(H2+)ab⇄2(H+)ab+e−. Absorption here is treated as adsorption on the inner surface of the tetrahedral and octahedral voids within metal lattice. The mechanism is based on the first principles and explains consistently the dependence of mechanical properties of metals on the amount of absorbed hydrogen as well as the mechanism of hydrogenation and hydrogen transport through the metals. The proposed dissociative ionization mechanism is well supported by thermodynamic and steric arguments. In the case of noble metals the presented mechanism carries versatile character as it is valid for both gaseous phase and aqueous solutions.

Hydrogen interaction with GaN metal–insulator–semiconductor diodes

Interaction mechanism of hydrogen with GaN metal–insulator–semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO2 dielectric, the current–voltage (I–V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler–Nordheim tunneling to Poole–Frenkel emission. In sharp contrast, Pt-SixNy-GaN diodes exhibit Poole–Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance–voltage (C–V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.

Interaction of hydrogen and water with oxygen adsorbed on silver

The identity of surface silver hydroxides produced by hydrogenation or hydration of surface silver oxide was demonstrated. A two-route mechanism of hydrogen interaction with oxygen adsorbed on silver was suggested. The first route includes two consecutive-parallel steps: formation of adsorbed hydroxyl groups and their interaction with hydrogen; the second route consists of two consecutive steps: formation of adsorbed hydroxyl groups and their disproportionation yielding water and adsorbed oxygen.

Hydrogen Sensors Using Nitride-Based Semiconductor Diodes: The Role of Metal/Semiconductor Interfaces

In this paper, I review my recent results in investigating hydrogen sensors using nitride-based semiconductor diodes, focusing on the interaction mechanism of hydrogen with the devices. Firstly, effects of interfacial modification in the devices on hydrogen detection sensitivity are discussed. Surface defects of GaN under Schottky electrodes do not play a critical role in hydrogen sensing characteristics. However, dielectric layers inserted in metal/semiconductor interfaces are found to cause dramatic changes in hydrogen sensing performance, implying that chemical selectivity to hydrogen could be realized. The capacitance-voltage (C–V) characteristics reveal that the work function change in the Schottky metal is not responsible mechanism for hydrogen sensitivity. The interface between the metal and the semiconductor plays a critical role in the interaction of hydrogen with semiconductor devises. Secondly, low-frequency C–V characterization is employed to investigate the interaction mechanism of hydrogen with diodes. As a result, it is suggested that the formation of a metal/semiconductor interfacial polarization could be attributed to hydrogen-related dipoles. In addition, using low-frequency C–V characterization leads to clear detection of 100 ppm hydrogen even at room temperature where it is hard to detect hydrogen by using conventional current-voltage (I–V) characterization, suggesting that low-frequency C–V method would be effective in detecting very low hydrogen concentrations.

Interaction of water, hydrogen and their mixtures with SnO2 based materials: the role of surface hydroxyl groups in detection mechanisms

DRIFTS, TGA and resistance measurements have been used to study the mechanism of water and hydrogen interaction accompanied by a resistance change (sensor signal) of blank and Pd doped SnO(2). It was found that a highly hydroxylated surface of blank SnO(2) reacts with gases through bridging hydroxyl groups, whereas the Pd doped materials interact with hydrogen and water through bridging oxygen. In the case of blank SnO(2) the sensor signal maximum towards H(2) in dry air (R(0)/R(g)) is observed at approximately 345 degrees C, and towards water, at approximately 180 degrees C, which results in high selectivity to hydrogen in the presence of water vapors (minor humidity effect). In contrast, on doping with Pd the response to hydrogen in dry air and to water occurred in the same temperature region (ca. 140 degrees C) leading to low selectivity with a high effect of humidity. An increase in water concentration in the gas phase changes the hydrogen interaction mechanism of Pd doped materials, while that of blank SnO(2) is unchanged. The interaction of hydrogen with the catalyst doped SnO(2) occurs predominantly through hydroxyl groups when the volumetric concentration of water in the gas phase is higher than that of H(2) by a factor of 1000.

Core−Corona Polymer Composite Particles by Self-Assembled Heterocoagulation Based on a Hydrogen-Bonding Interaction

Poly(ethylene glycol dimethacrylate-co-acrylic acid) (poly(EGDMA-co-AA)) small microspheres were effectively self-assembled on poly(ethylene glycol dimethacrylate-co-4-vinylpyridine) (poly(EGDMA-co-VPy)) surfaces to form a core-corona structure with a raspberry-like polymer composite by a hydrogen interaction mechanism through an affinity complex between the carboxylic acid group and pyridine group. The control of coverage of the poly(EGDMA-co-AA) corona on the surface of poly(EGDMA-co-VPy) was studied in detail via adjustment of the nature of the mass ratio between the core and corona. The effects of the pH and solvent used on the morphology of the self-assembled core-corona polymer composites were investigated. The nature of the interaction between the core and corona polymer particles was identified as hydrogen bonding with FT-IR spectroscopy.

Mechanism of hydrogen interaction with the growing silicon film

The hydrogen reaction on a hydrogenated silicon film is in two phases. This is manifested in slowing down of the hydrogen loss at the growing film. The slow down occurs in phases and both the processes have exponential character. The first phase consists of hydrogen incorporation into the layer and this occurs within the first 50 s. The second phase is of etching. This is confirmed by the similarity between the rate of hydrogen loss in the second phase and the rate of production of silyl species.

Mechanism of Ni Film CVD with a Ni(ktfaa)2 Precursor on a Copper Substrate

AbstractThe mechanisms of pyrolysis in He and reduction in H2 of a Ni(ktfaa)2 chelate and nickel film deposition on copper substrates are discussed. The Ni films produced by CVD with the Ni(ktfaa)2 chelate as a precursor are continuous. Pyrolysis of the Ni(ktfaa)2 chelate takes place above 300 °C. The hydrogen atmosphere allows the reaction temperature to be decreased to 213 °C, but the film deposition rate is low. 300 °C is the optimal temperature for continuous Ni film deposition on Cu substrates. The mechanism of hydrogen interaction with the adsorbed Ni(ktfaa)2 chelate is discussed.

Low and High-Temperature In Situ X-Ray Absorption Study of the Local Order in Orthorhombic α-MoO3Upon Hydrogen Reduction

In-situ x-ray absorption spectroscopy has been applied to the study of the modifications of the short range order in orthorhombic α-MoO 3 under low and high-temperature hydrogen reduction. It was observed that at low-temperature (T 110°C) reduction, a formation of molybdenum bronzes H x MoO 3 (x ≤ 2) occurs while at high-temperature (T ≥ 400°C) reduction, α-MoO 3 transforms into MoO 2 . Both processes have great applied importance since they are related to electrochromic and catalytic properties of α-MoO 3 . The information on the local atomic and electronic structure, obtained from the Mo K-edge XAFS and XANES analyses, allowed us to follow all steps of the reduction process and to formulate a mechanism of hydrogen interaction with the layered-type structure of α-MoO 3 .

Interaction mechanism of hydrogen with the CaCu 5-type crystal structure intermetallic compounds

The methodological technique of the ‘calorimetry titration’ using differential calorimetry was applied for the first time to study the interaction mechanism of hydrogen with metallic phase in ‘IMC-H 2’ systems, where the IMC-LaNi, Cu. It is shown, that the process of formation α- and β-hydriding phases in such systems proceeds by different mechanisms. The data obtained are well correlated with the results of the isotherms for the ‘IMC-H 2’ systems.