Adsorption Of H2 Molecules Research Articles

Screening of Subnanoscale Metal Hydride Formation for Late Transition Metals Using Dimer Cations─Group IX Element.

The energetically stable structures of M2Hm+ (M = Co, Rh, Ir; m = 2, 4, 6, ...) were investigated using density functional theory calculations, and possible reaction pathways for the sequential adsorption of H2 molecules on M2+ were proposed. Based on the most stable structures, adsorption energies of H2 were calculated for each adsorption step, and the maximum numbers of adsorbed H atoms on Co2+, Rh2+, and Ir2+ were estimated to be 14, 16, and 16, respectively. Compared to group XI elements (M = Cu, Ag, and Au), which are conceivably inert to H2, more H atoms were bound to Co2+, Rh2+, and Ir2+. The adsorption of H2 on M2+ (M = Co, Rh, Ir, or Cu) in the gas phase was investigated experimentally at 300 K using mass spectrometry. Although Rh2+ and Ir2+ stored numerous H2 molecules as predicted by calculations, Co2+ was found to adsorb no H atoms. It was probably due to the insufficient adsorption energy of Co2+ and the kinetic effect in the H2 adsorption process. Thus, computational calculations can overestimate the number of adsorbed H atoms.

Investigation of the H2 dissociation and strengthening mechanism in vacancy-induced graphene

Atomic vacancies play a crucial role in hydrogen storage and local strengthening of a substance with a mechanism that is elusive. First-principles examinations of monolayer graphene unveiled the following: (i) the neighboring carbon atoms move radially away from the vacancy center with a 3–10% C–C bond contraction, generating a circumferential density ribbon of energy and electrons; (ii) the dense electrons within the ribbon polarize the edge atoms into dipoles pointing to the center; (iii) the polarized electrons coupled together to for the vacancy dipole, resulting in the Dirac-Fermion resonant peak at Fermi energy and the energy density gai raise the local strength; and (iv) the vacancy dipole induces the adsorbed H2 molecule into H+-H- dipole to stabilize H2 adsorption. The findings of vacancy reinforcement, dipole formation, and stable H2 adsorption should provide a promising mechanism contributing to the advancement of hydrogen storage theory.

Superlight Ambient Temperature Reversible Hydrogen Storage Media Based on Alkali and Alkali Earth Metal-Functionalized 2D Square-Octagon BCN Monolayer.

Energy has always been the engine of human beings; however, because of the environmental pollution caused by traditional fossil fuels, the development of more sustainable energy resources is urgently needed. The hydrogen storage medium is essential for its realization. Here, we introduce a hydrogen storage material, a two-dimensional (2D) square-octagon BCN (SO-BCN) monolayer, composed of lightweight elements (B, C, and N) and strategically functionalized with alkali and alkali earth metal atoms (Li, Na, Mg, and K). Notably, Li@SO-BCN and Mg@SO-BCN exhibit exceptional reversible hydrogen storage capabilities, surpassing the DOE standard of 5.5 wt %, with gravimetric capacities of 7.129 wt % and an impressive value of 11.656 wt %, alongside low adsorption energies of -0.21 eV/H2 and -0.268 eV/H2 at room temperature, respectively. Our investigation, which combines analysis of the atomic structure, electronic structure, and hydrogen process, reveals distinct mechanisms at play: Li activates the substrate, creating additional adsorption sites on the SO-BCN monolayer. Compared with Li, the functionalization of Mg atoms not only activates SO-BCN via charge transfer but also allows Mg2+ to act as a potent attractor for H2 molecule adsorption. This work provides both promising candidates for future hydrogen storage media based on 2D monolayers and a design paradigm for next-generation hydrogen storage materials, emphasizing the synergy of electron-donating species, substrate activation, and hierarchical porous structures.

Promoting Effect of Pd Nanoparticles on SrTi0.8Mn0.2O3 in the Reverse Water‐Gas Shift Reaction via the Mars–van Krevelen Mechanism

The reverse water‐gas shift (RWGS) reaction serves as a critical pathway for converting CO2 into diverse chemicals. The Mars–van Krevelen (MvK) mechanism, which leverages lattice oxygen as the oxidant and oxygen vacancies as reductants, offers an alternative catalytic strategy for the selective RWGS reaction. While Mn‐substituted SrTiO3 (i.e., SrTi0.8Mn0.2O3) has been shown to promote the RWGS reaction selectively via the MvK mechanism, achieving a sufficient conversion of CO2 necessitates elevated temperatures. This study investigated the effect of Pd‐loaded SrTi0.8Mn0.2O3 on the activation of adsorbed H2 molecules, which generated oxygen vacancies and enhanced CO2 conversion. Notably, 1.0 wt% Pd‐loaded SrTi0.8Mn0.2O3 yielded 13.4% of CO at 673 K, whereas pristine SrTi0.8Mn0.2O3 and Pd‐loaded SrTiO3 yielded negligible or minimal amount of CO. Hydrogen temperature‐programmed reduction and X‐ray absorption spectroscopy measurements revealed that Pd promoted the formation of oxygen vacancies via both thermodynamic and kinetic mechanisms. Fourier transform infrared spectroscopy and kinetic studies revealed that the RWGS reaction over Pd‐loaded SrTi0.8Mn0.2O3 proceeded primarily via the MvK mechanism with a partial contribution from the Langmuir–Hinshelwood mechanism. This study underscores the effectiveness of combining metal and MvK‐type catalysts to enhance the efficiency of the RWGS reaction.

Modulated bandgap and gas adsorption behavior on two-dimensional SrAl2S4 monolayer: Potential applications for photovoltaic and energy storage

The structure of a novel two-dimensional layered material SrAl2S4 monolayer has been proposed, and its kinetic and thermodynamic stability has been confirmed. Researches have shown that SrAl2S4 monolayer is a semiconductor material with a bandgap of 1.630 eV for PBE and 2.798 eV for HSE06 at the ground state. Under biaxial strain, SrAl2S4 monolayer can complete the transition from a direct bandgap semiconductor to an indirect bandgap semiconductor, and its bandgap can vary between 0.187 eV and 1.712 eV. In addition, We have considered the adsorption behavior of SrAl2S4 monolayer for hydrogen and oxygen molecules, and the results show that SrAl2S4 monolayer adsorbed H2 molecules remains a direct bandgap semiconductor, whereas SrAl2S4 monolayer adsorbed O2 molecules show indirect bandgap semiconductor properties. At the same time, the adsorption of O2 molecules causes a flat band near the Fermi level, which increases the electrical conductivity. The few charges transfer observed between the SrAl2S4 monolayer and gas molecules confirms that the adsorption process of gas molecules on SrAl2S4 monolayer is physical adsorption. The tunable bandgap characteristics and good adsorption behavior of hydrogen and oxygen exhibited by SrAl2S4 monolayer make it a promising candidate material in the fields of photovoltaics and energy storage.

Role of carbon substitutional and vacancy in tailoring the H2 adsorption energy over a hexagonal boron nitride monolayer: an ab initio study

The effect of the substitutional and vacancy type defects on the H2 adsorption energy over a monolayer hexagonal boron nitride (h-BN) substrate has been studied by using the van der Waals density functional theory calculations. Carbon doping at the boron site or formation of boron vacancy can be an effective way to increase the adsorption energy value of a pristine h-BN substrate. The repulsive lateral interaction present in between the two H2 molecules plays a vital role in case of multiple H2 molecule adsorption over the substrate. Also, the carbon cluster formation during doping can have a favorable effect in the overall storage capacity of the h-BN substrate.

Computational Investigation of a Reversible Energy Storage Medium in g-B5N3 Decorated by Lithium.

Graphene-like materials in two dimensions hold great promise for energy storage and transformation applications owing to their distinctive features, such as lightweight composition, porous geometry, etc. Among these materials, a recently discovered unit known as g-B5N3 has demonstrated high performance in energy storage and transformation. In our efforts to enhance its applicability in adsorbing energy gases, we propose a novel composite structure by decorating Li atoms on the surface of pristine g-B5N3. The electronic properties of this composite have been comprehensively investigated using a first-principles method. Our findings reveal that the added Li atoms can be securely anchored on the g-B5N3 with an adsorption energy of -3.01 eV. Furthermore, the Li atom transfers its partial 2s electrons to the g-B5N3, exhibiting considerable electropositivity. These metallic sites effectively polarize the adsorbed H2 molecules, enhancing the mutual electrostatic interactions. Each primitive cell of Li-doped g-B5N3 can adsorb up to 13 H2 molecules, resulting in a storage capacity up to 6.3 wt %. This capacity significantly surpasses the goal of 4.5 wt % set by the U.S. Department of Energy. Furthermore, the typical adsorption energy of -0.209 eV per molecule of H2 aligns with the energy range suitable for reversible hydrogen storage. This study underscores the potential of Li-doped g-B5N3 for energy gas adsorption, shedding light on further advancements in this field.

First-principles study of adsorption, dissociation, and diffusion of hydrogen on α-U (110) surface

According to the equilibrium crystal shape of α-U, the surface of α-U (110) is more stable and has a larger area fraction than α-U (001). Therefore, the adsorption, dissociation, and diffusion behaviors of H atoms and H2 molecules on the α-U (110) surface were systematically studied by first-principles calculations. The results show that there are only two stable adsorption sites for the H atom: the surface short-bridge site (SB1) and the subsurface short-bridge site (SB2). The adsorption of H2 molecules is divided into chemical adsorption of dissociated H2 molecules and physical adsorption of undissociated H2 molecules, and the LB2-ParL adsorption configuration is the most stable adsorption configuration for H2 molecule adsorption, with an adsorption energy of −0.250 eV. The work function and charge transfer show that adsorption of the H atom or H2 molecule leads to an increase in the work function value of the α-U (110) surface, which enhances the electronic stability of the α-U (110) surface. The projected density of states shows that when the H atom or H2 molecule is close to the α-U (110) surface, the 1s orbital electrons of the H atom will hybridize with the 5f/6d orbital electrons of the nearby surface and subsurface U atoms, and new hybridized orbital peaks appear near the −4.5 eV or −7.3 eV energy level. The climbing image nudged elastic band study shows that the surface free H atoms are very easy to diffuse between the surface short-bridge sites and the subsurface short-bridge sites but the diffusion between the short-bridge site and the triangular center site is extremely difficult.

Theoretical study of hydrogen storage in Li-decorated Al12N12 clusters

The hydrogen storage capacity of Li-decorated Al12N12 clusters is investigated using density functional theory computations. The present results indicate that Li atoms are strongly attached on tops of N atoms of the Al12N12 nanocage, forming Al12N12Lim (m = 1, 2, 4, 8, 12) complexes. The binding energies of the Li atoms on the Al12N12 are in the range of 1.60–1.95 eV, which are larger than that among Li atoms. The clustering of Li atoms can be effectively prevented on the surface of the host. The charge transfer from Li atoms to the Al12N12 makes Li atoms positively charged. Each Li atom in the Li-decorated Al12N12 complexes can adsorb a maximum of 3 H2 molecules with the average adsorption energy of 0.09–0.12 eV/H2. The polarization interaction is responsible for the adsorption of H2 molecules to Li-decorated Al12N12 complexes. The fully coated Al12N12Li12 complex can hold up to 36 H2 molecules, and the corresponding gravimetric density of hydrogen is 11.2 wt%, far exceeding the ultimate target of 6.5 wt% of U. S. DOE.

Enhanced H2 storage in silicene through lithium decoration and single vacancy and Stone‐Wales defects: A density functional theory investigation

AbstractDefect engineering and metal decoration onto 2‐D materials have gained major attention as a means of creating viable hydrogen storage materials. This Density Functional Theory (DFT) based study presents lithium decorated single vacancy (SV) and Stone‐Wales (SW) defective silicene as a viable media for storing hydrogen via physisorption. Introducing defects increases the Li adatom's binding energy from −2.36 eV in pristine silicene to −3.44 and −2.73 eV in SV and SW silicene, respectively, preventing Li adatom clustering. The presence of defects and Li adatom further aid hydrogen adsorption onto the substrates with binding energies present between the US‐DOE set range of −0.2 to −0.7 eV/H2 with the highest binding energy measured to be −0.389 eV/H2. The enhanced H2 binding energies are a result of a combined contribution of the Li(p) and Li(s) orbitals with the H(s) orbital with an indirect electronic transfer from the silicene substrate to the Li adatom. Upon double side Li decoration, both the Li‐decorated defective systems were able to effectively store multiple H2 molecules up to 28 H2 with the highest gravimetric density being 5.97 wt%. Ab Initio molecular dynamic simulations conducted at 300 K and 310 K confirm the stability of the Li adatom as well as the adsorbed H2 molecules at room temperature and establish the viability of these systems as effective, high gravimetric density, physisorption‐based hydrogen storage media.

Heterolytic H2 Activation in Heterogeneous Hydrogenation/Hydroprocessing Catalysis

AbstractIn heterogeneous catalysis, heterolytic H2 activation for (selective) hydrogenation and hydroprocessing reactions involves the dissociation of adsorbed H2 molecules into proton (Hδ+) and hydride (Hδ−) on the catalyst surface. This approach offers several advantages, including high selectivity for polar bond (s), a low energy barrier for H2 dissociation, a high capacity for reaction‐favorable H2 adsorption, and reduced catalyst poisoning. This requires the construction of frustrated Lewis pairs on the catalyst surface, satisfying specific criteria, such as having an abundant quantity of Lewis pairs with steric hindrance and maintaining a certain distance of 3–5 Å between the pairs. This review highlights intrinsic catalyst properties for heterolytic H2 activation based on state‐of‐the‐art reports. The main components necessary for this activation include supports with strong basic sites and/or oxygen vacancies, and/or metals of single atom. For this purpose, designed catalytic materials aim to strengthen the Lewis acidity and basicity, improve the polarization of Lewis pairs, enrich oxygen vacancies, maximize the interfacial area between metal species and Lewis base, and enhance metal–support interaction. Therefore, heterogeneous catalysts retaining such heterolytic H2 activation characteristics will be significantly effective in various hydrogenation and hydroprocessing reactions.

Deformation behaviors of hydrogen filled boron nitride and boron nitride - carbon nanotubes: Molecular dynamics simulations of proposed materials for hydrogen storage, gas sensing, and radiation shielding

Boron nitride nanotubes (BNNTs) have been extensively studied for hydrogen storage, sensing, and radiation shielding applications. The deformation behaviors of pristine, defective, and H2-encapsulated closed-end armchair BNNTs and BNNT-carbon nanotube (CNT) heterostructures are investigated using molecular dynamics employing the ReaxFF interatomic potential and a combination of Tersoff, adaptive intermolecular reactive empirical bond order, and Lennard-Jones potentials. The calculated elastic properties for pristine BNNTs and CNTs are in excellent agreement with published reliable data. The nanotube length and diameter, defects, entrapped hydrogen content, and temperature all affect the mechanical properties significantly. The ReaxFF potential predicts H2 molecule adsorption on B atoms of undeformed BNNTs whilst under strain, the H2 molecules show preference for the N atoms. Hydrogen adsorption leads to lowering of the elastic and fracture strength of BNNTs. The ReaxFF potential is shown to be a reliable forcefield for investigating the interaction of H2 molecules with BNNTs and BNNT-CNT heterotubes.

Interaction of N2, O2 and H2 Molecules with Superalkalis.

Superalkalis (SAs) are exotic clusters having lower ionization energy than alkali atoms, which makes them strong reducing agents. In the quest for the reduction of diatomic molecules (X2) such as N2, O2, and H2 using Møller-Plesset perturbation theory (MP2), we have studied their interaction with typical superalkalis such as FLi2, OLi3, and NLi4 and calculated various parameters of the resulting SA-X2 complexes. We noticed that the SA-O2 complex and its isomers possess strong ionic interaction, which leads to the reduction of O2 to O2 - anion. On the contrary, there are both ionic and covalent interactions in SA-N2 complexes such that the lowest energy isomers are covalently bonded with no charge transfer from SA. Further, the interaction between SA and H2 leads to weakly bound complexes, which results in the adsorption of H2 molecules. The nature of interaction is found to be closely related to the electron affinity of diatomic molecules. These findings might be useful in the study of the activation, reduction, and adsorption of small molecules, which can be further explored for their possible applications.

Hydrogen storage capacity and reversibility of BC3N2 monolayers with and without Li decoration insights from first-principles methods

The identification and development of novel materials for effective hydrogen storage is of paramount significance in the context of hydrogen-based economies. In this investigation, the hydrogen storage capabilities of the BC3N2 monolayer both with and without lithium (Li) decoration was examined by utilizing first-principles approaches. The findings indicate that the BC3N2 monolayer possesses a notable hydrogen storage capacity of 13.8 wt%. However, it is noteworthy that the average adsorption energy of H2 molecules is approximately 0.16 eV, resulting in a relatively low desorption temperature. This characteristic poses a significant obstacle to the practical utilization of the BC3N2 monolayer. Decoration of the BC3N2 monolayer with Li atoms was shown to be thermodynamically beneficial and resulted in non-aggregation on the surface. The monolayers of BC3N2 decorated with Li exhibited a remarkably high capacity for hydrogen adsorption, reaching 9.9 wt%. The ideal adsorption energies for this system were found to be in the range of 0.32–0.47 eV/H2. These results exceed the target set by the US DOE (6.5 wt%) and demonstrate superior performance compared to the majority of CN-based monolayers. The electrostatic properties of the interaction between H2 molecules and the monolayer decorated with Li were verified through the analysis of ELF and DOS. The reversibility of H2 molecule adsorption and desorption on Li-decorated BC3N2 monolayers has been demonstrated through the analysis of occupation number and desorption temperature under practical working conditions. The results of the study indicate that the incorporation of Li into BC3N2 monolayers has great potential as a highly efficient medium for hydrogen storage.

Impact of Alloy Elements on the Adsorption and Dissociation of Gaseous Hydrogen on Surfaces of Ni–Cr–Mo Steel

In this study, the effect of alloying elements on the adsorption and dissociation behaviors of hydrogen molecules on the bcc-Fe (001) surface has been investigated using first-principles calculations. H2 molecules can easily dissociate on the hollow site, and the dissociated hydrogen atoms bond with the surrounding metal atoms. Doping Cr and Mo atoms on the surface would reduce the H2 molecule adsorption energy, which promotes the H2 molecule adsorption and dissociation. When only one or two Ni atoms doping on the surface, it improves the adsorption energies, which in turn can hinder the H2 molecule adsorption and dissociation. However, three or four Ni atoms doping on the surface is beneficial to the H2 molecule adsorption and dissociation. Thus, the nickel content in Ni–Cr–Mo steel should be reasonably controlled to improve the hydrogen embrittlement resistance of the steel.

Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction.

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H2. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt1/d-TiO2) to facilitate electron transfer from edge-share O atoms (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H2 molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.

Selective hydrogenation of levulinic acid at room temperature: Boosting ruthenium nanoparticle efficiency via coupling with in-situ pyridinic-N-doped carbon nanoflowers

Integrating unique morphology and tunable electronic state of supported metallic catalysts via one-step is an attractive pathway to boost their catalytic behaviors in selective hydrogenation reactions. Here, electronic state-tunable Ru nanoparticles (NPs) coupled with three-dimensional (3D) hierarchical carbon nanoflowers with in-situ generated pyridinic-nitrogen (Ru/PNC) are devised. Combining with systematical characterizations, kinetics investigations, and density functional theory (DFT) computations, the pyridinic-N species is proved to facilitate the formation of electron-rich Ru, which insures the weaker adsorption of levulinic acid but stronger adsorption of H2 molecules on Ru, ultimately reducing the apparent activation energy of selective hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). As a result, a high turnover frequency (TOF) of 5042.5 h−1 and a GVL selectivity of > 99% are achieved on the most electron-rich Ru/PNC catalyst. A positive linearity between the TOFs and the surface pyridinic-N/Ru0 ratios is recognized, further corroborating the electron-rich Ru-mediated intrinsic activity enhancement evoked by the surface pyridinic-N species on carbon nanoflowers.

DFT study of Hydrogen storage capacity on Hf doped graphene

We explored the molecular hydrogen storage capacity of complex system with Hafnium doped graphene (Gr-Hf) using the Density Functional Theory (DFT) method. We efficiently adsorbed molecular six hydrogens on the Hf doped graphene surface. The quantum chemically calculated adsorption energy is found negatively in the range of - 344.433 Ry to -333.836 Ry this implies as increasing the adsorbed hydrogen molecule on hafnium doped graphene (Gr-Hf) sheet the adsorption energy decreases continuously. The binding energy of after adsorbing second hydrogen molecule too much larger than the next adsorbed H2 molecules i.e., the binding energy per hydrogen molecule highly decreases when we increase adsorbed atom (2.197 Ry in 2H2 to 1.048 Ry in 3H2) then small decreases for next adsorbed H2 molecules. The extracted binding energy found in the range 2.197 Ry to 2.120 Ry, fermi energy found minimum for 1H2 shows the minimum electron occupancy at the different energy levels. The fermi energy increases accordingly, the electron occupancy also increases and evaluates higher electron occupancy with fermi energy 2.850 eV for 6H2 and density of states (DOS) confirm the weak interaction between σ bonding electrons of H2 molecule with Hf doped graphene complex system. The proposed system opens a new insight for hydrogen storage-based devices.

Activation of Molecules H<sub>2</sub> on Platinum and Platinovanadium Clusters: Quantum-Chemical DFT Modeling

The NEB DFT/PBE0/def2tzvp quantum-chemical method with the construction of minimum energy paths (MEP) was used to study the activation of H2 molecules by Pt4 and Pt3V clusters. It is shown that, in the case of Pt4 and Pt3V clusters, barrier-free dissociative adsorption of H2 molecules occurs on platinum centers, while molecular adsorption of hydrogen occurs on the vanadium atom in Pt3V with a slight weakening of the H–H bond, but without its breaking. The noted features of the coordination of H2 molecules are explained at the level of the MO method. It has been established that the migration of the H atom from one cluster metal center to another in the considered model clusters, as, possibly, in the phenomenon of hydrogen spillover, occurs at small activation barriers in the direction of the displacement vector corresponding to the normal vibration of the system in the transition state. In the process of hydrogen migration, a significant role of Pt–H–Pt and V–H–Pt bridging groups, which facilitate the transition of H atoms from one metal center of the cluster to another, has been revealed.

The Adsorption Behaviors of CO and H2 to FeO onto CaO Surfaces: A Density Functional Theory Study.

The adsorption behaviors of CO and H2 to FeO onto CaO surfaces have been studied using the density functional theory (DFT) to determine the reactions of FeO by CO and H2. The adsorption mechanisms of FeO clusters on the CaO(100) and CaO(110) surfaces were calculated first. The structure of the Ca(110) surface renders it highly chemically reactive compared with the Ca(100) surface because of low coordination. After gas adsorption, CO bonds to the O atom of FeO, forming CO2 compounds in both configurations through the C atom. H2 favors the O atom of FeO, forming H2O compounds and breaking the Fe-O bond. Comparing the adsorption behavior of two reducing gases to FeO on the Ca surface, the reaction of the CO molecule being adsorbed to generate CO2 compounds is exothermic. The reaction of H2 molecule adsorption to generate H2O compounds is endothermic. This property is essential for the inertial-collision stage of the reduction. However, the dissociation of the CO2 compound from the reaction interface will overcome a high energy barrier and slow down the reduction. The H2O compound dissociates from the surface more easily, which can accelerate the reduction.