A study of the radiation-chemical transformation of n-hexane on the surface of aluminum

The radiation-chemical decomposition of n-hexane in the Al-n-hexane system under the action of gamma radiation was studied by reflectance-absorption IR spectroscopy. The radiolysis of n-hexane on the surface of aluminum at absorbed doses of 5 kGy ≤ D _γ ≤ 40 kGy was accompanied by the formation of aluminum alkyls, π-complexes of olefins, and aluminum hydrides. The kinetics of the accumulation of molecular hydrogen was analyzed to determine its radiation-chemical yield, G _ads (H₂) = 29.6 molecules/100 eV. A possible mechanism of this process is discussed.     

Efficient electrochemical reduction of CO to C2 products on the transition metal and boron co-doped black phosphorene

The synthesis of high-value multi-carbon products through the electrochemical reduction of carbon monoxide（COER） is one of the promising avenues for carbon utilization and energy storage,in which searching for efficient electrocatalysts that exhibit moderate CO intermediate binding strength and low kinetic barrier for C-C coupling is a key issue.Herein,by means of comprehensive density functional theory（DFT） computations,we theoretically designed three synergistic coupling catalysts by co-doping...     

Recent research progress of bimetallic phosphides-based nanomaterials as cocatalyst for photocatalytic hydrogen evolution

Hydrogen energy（H2） has been considered as the most possible consummate candidates for replacing the traditional fossil fuels because of its higher combustion heat value and lower environmental pollution.Photocatalytic hydrogen evolution（PHE） from water splitting based on semiconductors is a promising technology towards converting solar energy into sustainable H2fuel evolution. Developing high-activity and abundant source semiconductor materials is particularly important to realize highly effici...     

Ni2P Interlayer and Mn Doping Synergistically Expedite the Hydrogen Evolution Reaction Kinetics of Co2P

Transition metal phosphide is regarded as one of the most promising candidates to replace noble-metal hydrogen evolution reaction (HER) electrocatalysts. Nevertheless, the controllable design and synthesis of transition metal phosphide electrocatalysts with efficient and stable electrochemical performance are still very challenging. Herein, a novel hierarchical HER electrocatalyst consisting of three-dimensional (3D) coral-like Mn-doped Co₂P@an intermediate layer of Ni₂P generated in situ by phosphorization on Ni foam (MnCoP/NiP/NF) is reported. Notably, both the incorporation of Mn and introduction of the Ni₂P interlayer promote Co atoms to carry more electrons, which is beneficial to reduce the force of the Co−H bond and optimize the adsorption energy of hydrogen intermediate (|ΔG_H*|), thereby making MnCoP/NiP/NF exhibit outstanding HER performance with onset overpotential and Tafel slope as low as 31.2 mV and 61 mV dec⁻¹, respectively, in 1 m KOH electrolyte.     

Enhancing hydrogen evolution reaction performance of transition metal doped two-dimensional electride Ca2N

Two-dimensional electride Ca₂N has strong electron transfer ability and low work function, which is a potential candidate for hydrogen evolution reaction (HER) catalyst. In this work, based on density functional theory calculations, we adopt two strategies to improve the HER catalytic activity of Ca₂N monolayer: introducing Ca or N vacancy and doping transition metal atoms (TM, refers to Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ru, Hf, Ta and W). Interestingly, the Gibbs free energy ΔG_H1 of Ca₂N monolayer after introducing N vacancy is reduced to -0.146 eV, showing good HER catalytic activity. It is highlighted that, the HER catalytic activity of Ca₂N monolayer can be further enhanced with TM doping, the Gibbs free energy ΔG_H1 of single Mo and double Mn doped Ca₂N are predicted to be 0.119 and 0.139 eV, respectively. The present results will provide good theoretical guidance for the HER catalysis applications of two-dimensional electride Ca₂N monolayer.     

Transition metal decorated bismuthene for ammonia synthesis: A density functional theory study

The electrochemical nitrogen reduction reaction (NRR) for the ammonia production under ambient conditions is regarded as a sustainable alternative to the industrial Haber–Bosch process. However, the electrocatalytic systems that efficiently catalyze nitrogen reduction remain elusive. In the work, the nitrogen reduction activity of the transition metal decorated bismuthene TM@Bis is fully investigated by means of density functional theory calculations. Our results demonstrate that W@Bis delivers the best efficiency, wherein the potential-determining step is located at the last protonation step of *NH₂ + H⁺ + e^– → *NH₃ via the distal mechanism with the limiting potential U_L of 0.26 V. Furthermore, the dopants of Re and Os are also promising candidates for experimental synthesis due to its good selectivity, in despite of the slightly higher U_L of NRR with the value of 0.55 V. However, the candidates of Ti, V, Nb and Mo delivered the relative lower U_L of 0.35, 0.37, 0.41 and 0.43 V might be suffered from the side hydrogen evolution reaction. More interestingly, a volcano curve is established between U_L and valence electrons of metal elements wherein W with 4 electrons in d band located at the summit. Such phenomenon originates from the underlying acceptance-back donation mechanism. Therefore, our work provides a fundament understanding for the material design for nitrogen reduction electrocatalysis.     

Photocurrent kinetics at electron emission from metal to electrolyte solution: Part V. Ionization rate constants of hydrogen and deuterium atoms adsorbed on mercury

Absolute ionization rate constant values of hydrogen and deuterium atoms adsorbed on mercury were measured using the method of pulse photoelectronic emission from metal into solution. In accordance with the Tafel law, these constants decrease from 2.5×10⁷s^?1 to 9×10⁵s^?1 (Table 1) in a 1 M solution of KCl in the range ?0.25 to ?0.5 V SCE. The transfer coefficient is 0.33±0.03 and the isotope ratio about 2.5. Owing to specific anion adsorption, rate constants increase as their concentration increases and KBr is added to the solution. In 0.05 M solutions of HCl and H₂SO₄, transfer coefficients are 0.30±0.05. From a comparison of measured values, with the hydrogen ion discharge rate constants found by extrapolation of experimental values into the potential range mentioned (taking into account the transfer coefficient change), the change of the Gibbs free energy in the reaction H₃O⁺+e_Me^?→H_ads+H₂O was calculated and found to be 0.87–0.99 eV at the potential of the normal hydrogen electrode. Adsorption energy of the hydrogen atom from the gas phase on a mercury electrode is 1.55±0.10 eV.The volt-ampere dependence of the hydrogen ion discharge current in the range ?0.25 to ?2.25 V corresponding to the current change by 18 orders of magnitude, agrees with the theoretically determined values (maximum deviation in the current is less than a factor of 3) for the medium reorganization energy E_r=1.75 eV. Despite constancy of the transfer coefficients of the elementary stages, in the range ?0.5 V (SCE), the effective transfer coefficient of the total hydrogen evolution processes increases from 0.5 to 1.0, as the ionization rate of the adsorbed hydrogen atoms becomes greater than their electrochemical desorption rate.     

Selenium‐Enriched Nickel Selenide Nanosheets as a Robust Electrocatalyst for Hydrogen Generation

To address the urgent need for clean and sustainable energy, the rapid development of hydrogen‐based technologies has started to revolutionize the use of earth‐abundant noble‐metal‐free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite‐type transition‐metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se‐enriched NiSe₂ nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm^?2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H⁺ into H₂ is due to the presence of an excess of selenium in the NiSe₂ nanosheet surface.     

Cyclic and stripping voltammetry of Se(+4) and Se(−2) at the HMDE in acidic media

Electroreduction of Se(+4) and electrooxidation of Se(?2) were studied at mercury electrodes in acidic media and an improved mechanism of the reduction process was proposed. This mechanism takes into account the fact that the reduction path is concentration-dependent. At lower concentrations of Se(+4), mercury selenide and hydrogen selenide are formed at various potentials. At higher Se(+4) concentrations the electrode quickly becomes covered by a rigid deposit of mercury selenide and then the reduction starts to proceed to elemental selenium. Another form of selenium was formed in the vicinity of the mercury surface due to a chemical reaction between H₂SeO₃ and H₂Se. Oxidation of hydrogen selenide proceeds similarly, in the sense that after coverage of the electrode surface by a deposit of mercury selenide the oxidation starts to proceed to elemental selenium. The cathodic stripping peak of mercury selenide can be obtained down to 2 × 10^?8M of Se(+4), but this peak is often split and therefore the determination of traces of Se(+4) by the cathodic stripping technique is cumbersome.     

Na-coated hexagonal B36 as superior hydrogen storage materials

Based on van der Waals corrected density functional theory, we show that Na atoms acting as decoration metals are not inclined to form clusters due to a large binding energy of 3.31 eV, indicating a promising good reversible hydrogen storage. Both the polarization mechanism and the orbital hybridizations contribute to the adsorption of hydrogen molecules (storage capacity of 4.4 wt%) with optimal adsorption energy of 0.25 eV/H₂. Additionally, the dimerization of these isolated B₃₆ does not remarkably affect the number of adsorbed H₂ per Na atom. Our results may serve as a guide in the design of new hydrogen storage materials based on low-dimension boron clusters.     

Diffusion monte carlo study of the hydrogen molecules adsorbed on C4H3Li

Diffusion Monte Carlo (DMC) simulations were used to calculate the binding energies for hydrogen molecules adsorbed on the lithium metal–organic complex C₄H₃Li. The calculations use all‐electron DMC techniques where every electron is explicitly included in the simulation. Also we have systematically studied it using density functional theory (DFT) methods, revealing that each C₄H₃Li can hold up to four H₂ molecules and the adsorption distance is about 2.2 Å. The DMC binding energies are in the range of 0.055–0.143 eV and are compared with those obtained with DFT using various exchange‐correlation functionals, with values ranging from 0.029 to 0.504 eV. These results indicate that caution is required applying DFT methods to weakly bound systems such as hydrogen storage materials based on lithium‐doped metal–organic frameworks. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Hydrogen physisorption energies for bumpy,saturated, nitrogen-doped single-walled carbon nanotubes

Finite saturated regular carbon nanotubes (CNTs) are predicted to exhibit higher capacity as hydrogen storage media compared to unsaturated regular CNTs. In the present study, molecular hydrogen physisorption energies (MHPEs) for finite saturated and unsaturated bumpy defected CNTs were calculated by density functional theory (DFT-D3) methods at the B3LYP/6-31G(d) theory level, with rigorous inclusion of van der Waals interactions. The calculated MHPEs for both regular and bumpy defected armchair, chiral and zigzag CNTs with similar diameters and lengths, with and without nitrogen doping, were compared in terms of Eph/H₂, defined as the MHPE per hydrogen molecule adsorbed inside the nanotube. For all studied systems, Eph/H₂ increased with the number of physisorbed hydrogen molecules. Nitrogen doping of regular and bumpy CNTs resulted in an increase in the Eph/H₂ values, with the exception of bumpy chiral nanotubes. The results of this study demonstrate that bumpy defects are important nanotube structural features whose effects depend on nanotube chirality. For instance, bumpy defects were beneficial for undoped and doped zigzag nanotubes, resulting in a decrease in Eph/H₂ values for regular structures from 0.5 and 0.74 to 0.26 and 0.42 eV, respectively. By contrast, for doped armchair regular structures with an Eph/H₂ value of 0.38 eV, bumpy defects increased Eph/H₂ to 0.45 eV. These Eph/H₂ values for bumpy doped armchair and the zigzag nanotubes are all within the range of 0.1–0.5 eV/H₂ reported as ideal for reversible hydrogen storage under environmental conditions.     

Functionalized boranes for hydrogen storage

Using density functional theory, the generalized gradient approximation for the exchange‐correlation potential and Møller–Plesset perturbation theory we study the hydrogen uptake of Li‐ and Mg‐doped boranes. Specifically, we calculate the structures and binding energies of hydrogen molecules sequentially attached to LiB₆H₇, LiB₁₂H₁₃, Li₂B₆H₆, Li₂B₁₂H_12, MgB₆H₆, and MgB₁₂H₁₂. Up to three H₂ molecules can be bound quasi‐molecularly to each of the metal cations with binding energies per H₂ molecule ranging between 0.07 eV and 0.27 eV. The corresponding gravimetric densities lie in the range of 3.49 to 12 wt %, not counting the H atoms bound chemically to the B atoms.     

Selective synthesis of ZIFs from zinc and nickel nitrate solution for photocatalytic H2O2 production

Hydrogen peroxide (H₂O₂) is one of the most promising, green, and effective oxidants that can be used in different applications. In this study, zeolitic imidazolate frameworks (ZIFs), consisting of organic ligands and metal sites, were selectively prepared from zinc or nickel nitrate solutions for use in photocatalytic H₂O₂ production. High concentrations of zinc nitrate solution provided more metal sites to coordinate with 2-methylimidazole, producing ZIF-8 with larger particle size, whereas low zinc nitrate concentrations resulted in more interconnected N–H⋯N hydrogen bonds, forming 2D-layered ZIF-L, with smaller particle size. Various concentrations of zinc and nickel nitrate solutions produced ZIFs that exhibited ZIF-8 or ZIF-L topology, with bandgap energies of 5.45 and 4.85 eV, respectively. These samples could serve as promising photocatalyst for the successful production of H₂O₂ under Xenon lamp irradiation.     

Effects of hydroxyl group on H2 dissociation on graphene: A density functional theory study

Graphene-based materials are promising for hydrogen production and storage. In this work, using density functional theory calculations, we explored how a hydroxyl group influences H₂ dissociation on graphene. Presence of the hydroxyl group makes the binding of H atom with graphene stronger, as the binding energy of H atom with the hydroxyl-modified graphene is higher than that with the pristine graphene. The para-site is the most favorable site for H₂ dissociation on both the pristine and hydroxyl-modified graphene. The energy barrier of H₂ dissociation at para-site on the pristine graphene is 3.10 eV whereas that on the hydroxyl-modified graphene is 2.46 eV, indicating a more facile H₂ dissociation on the hydroxyl-modified graphene.     

Proton transfer in electrochemically active “solid hydroxide proton conductor-hydrogenated metal” heterostructures

The electrochemical activity of solid-state heterostructures containing a hydrogenated metal and a solid proton conductor is investigated in the temperature ranges of 360–458 K, 360–370 K, and 320–420 K. The eutectics KOH/NaOH or KOH/KOH · H₂O and the chemical compound KOH · H₂O were chosen as the proton conductor. The conductivity of these electrolytes is higher than 1 mS/cm and their activation energies lower than 0.4 eV. Proton conductivity of the electrolytes is established by the emf method and confirmed by the isotope effect (H?D) in the conductivities of KOH · H₂O and the high-temperature form of KOH/NaOH (the protium forms are ≈1.4 times higher). Anomalies in the temperature dependence of conductivity and heat capacity are characteristic of eutectics in the region of 360 ± 1 K, and this has an effect on the electrochemical properties of the PdH _x |KOH/NaOH|PdO _y and TiH _x |KOH · H₂O|C heterostructures. Transport of atomic particles of hydrogen—most likely protons—across (Pd/Ti)H _x |MOH heteroboundaries where MOH = KOH · H₂O, KOH/NaOH, KOH/KOH · H₂O has a reversible character, which is shown by isotope and impedance measurements. The importance of the self-organized microheterogeneous solid eutectics KOH/NaOH and KOH/KOH · H₂O for their high conductivity compared to NaOH, KOH, and KOH · H₂O taken individually is discussed.     

Defect engineering for high-selection-performance of NO reduction to NH3 over CeO2（111） surface: A DFT study

To reduce the greenhouse effect caused by the surgery of nitrogen-oxides concentration in the atmosphere and develop a future energy carrier of renewables, it is very critical to develop more efficient,controllable, and highly sensitive catalytic materials. In our work, we proposed that nitric oxide（NO）, as a supplement to N₂ for the synthesis of ammonia, which is equipped with a lower barrier. And the study highlighted the potential of CeO₂（111） nanosheets with La doping a...     

Monolayer 1T and 1T′ MoSO as Promising Electrocatalyst for Hydrogen Evolution based on First Principle Calculations

Molybdenum disulfide (MoS₂) has been regarded as one of the most promising candidates for replacing Pt group noble metals as an efficient electrocatalyst to enhance the hydrogen evolution reaction (HER) in consideration of its relatively high earth abundance. Recent studies show that the catalytic efficiency of MoS₂ for HER can be promoted by the presence of 1T-phase MoS₂. It is hard to precisely control the formation of 1T-MoS₂, however, due to its metastability relative to 2H-MoS₂. Elevating the stability of 1T phase allotrope is therefore of great importance and could be realized by replacing divalent S with monovalent elements or groups according to crystal field theory, which has been demonstrated through our first-principles density functional theory (DFT) calculation results. Differential Gibbs free energy analysis for hydrogen adsorption (ΔG_H*) suggest that 1T and 1T′ MoSO (O doped MoS₂) might be taken as potential candidate catalysts for HER process with better performance than 1T and 1T′ MoS₂. We also propose a probable approach to synthesize 1T and 1T′ MoSO under oxidation circumstance environment of graphene oxide.     

CoP‐Doped MOF‐Based Electrocatalyst for pH‐Universal Hydrogen Evolution Reaction

Although electrocatalysts based on transition metal phosphides (TMPs) with cationic/anionic doping have been widely studied for hydrogen evolution reaction (HER), the origin of performance enhancement still remains elusive mainly due to the random dispersion of dopants. Herein, we report a controllable partial phosphorization strategy to generate CoP species within the Co‐based metal‐organic framework (Co‐MOF). Density functional theory calculations and experimental results reveal that the electron transfer from CoP to Co‐MOF through N‐P/N‐Co bonds could lead to the optimized adsorption energy of H₂O (ΔG ) and hydrogen (ΔG_H*), which, together with the unique porous structure of Co‐MOF, contributes to the remarkable HER performance with an overpotential of 49 mV at a current density of 10 mA cm^?2 in 1 m phosphate buffer solution (PBS, pH 7.0). The excellent catalytic performance exceeds almost all the documented TMP‐based and non‐noble‐metal‐based electrocatalysts. In addition, the CoP/Co‐MOF hybrid also displays Pt‐like performance in 0.5 m H₂SO₄ and 1 m KOH, with the overpotentials of 27 and 34 mV, respectively, at a current density of 10 mA cm^?2.