H2 Adsorption Energy 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.

Unraveling Lewis acid-base sites in defected MOFs for catalyzing dicyclopentadiene hydrogenation via a DFT study and descriptor exploration

The 12-connected UiO-66 MOFs with great defect regulation ability have attracted significant attention due to the easily tunable electronic structure and surface electrostatic potential distribution of metal nodes. In this density functional theory (DFT) study, we systematically explored the effect of bi-active site types as the frustrated Lewis pair (FLP) and classical Lewis pair (LP) as well as metal elements of secondary building units (SBUs) on the catalytic hydrogenation of dicyclopentadiene (DCPD) to tetrahydrodicyclopentadiene (THDCPD). These design strategies effectively modulate the frontier molecular orbital energy level that determines the binding strength between MOFs and adsorbed species *Hδ+-Hδ- and charges transfer before and after H2 chemisorption. We also found that the heterolytic H2 adsorption energy and charges transfer linearly correlate with the energy barrier. In order to unravel the clear-cut designing strategies and further simplify computational complexity, we firstly proposed the ADCH charges difference between the Lewis acid and the Lewis base centers (ΔQM-O) as an intrinsic descriptor for catalytic activity of DCPD into THDCPD, which can effectively describe the reactivity and electrostatic effects of oppositely charged bi-active sites in the system. Furthermore, the defective UiO-66(Ce) MOF with moderate ΔQM-O effectively balance the contradiction between the barriers of two primitive reaction: the heterolytically H2 dissociation to *Hδ+-*Hδ- and the desorption of the active hydrogen species to hydrogenate 8,9-dihydrodicyclopentadiene (8,9-DHDCPD), resulting in the optimal catalytic performance. This work provides a deep understanding of the catalytic mechanism of MOFs with multiple active sites and might open up avenues for the rational design of novel hydrogenation catalysts.

Theoretical investigation of cobalt cluster size on adsorption kinetics in Fischer-Tropsch synthesis

In this study, the particles of cobalt with different sizes were simulated by Materials Studio software then the adsorption of H2, CO, and CH4 and its components (CH, CH2, CH3) as Fischer-Tropsch synthesis monomers were investigated using Density-functional theory. The results showed that the suitable sites for the adsorption of CO, H2 and monomers in Fischer-Tropsch synthesis are affected by the size of cobalt clusters. Increasing in the size of the cobalt cluster, the number of suitable sites for adsorption of the species decreases. In general, H2 adsorption energy decreases with increasing cobalt cluster size because larger clusters tend to have a less reactive surface due to increased coordination number and reduced surface charge density. On the other hand, CO adsorption energy tends to increase with cluster size because the larger clusters can accommodate the linear CO molecule more effectively due to their extended surface area. With considering the deformation of adsorbed species, Mulliken charge result, density of states and partial density of states, it could be stated that all species were chemically adsorbed on the surface of clusters, except CH4 that was adsorbed on Co-10 and Co-18 clusters is physically. Kinetic parameters for H2 and CO adsorption were calculated considering the change in cobalt cluster size.

Metal-decorated M-graphene for high hydrogen storage capability and reversible hydrogen release

With the increasing demand for green energy, the design of effective hydrogen storage materials is becoming particularly important. In this work, the hydrogen storage performances of the metal atoms (Li, Ca, and Sc) decorated two–dimensional (2D) M-graphenes were investigated with density functional theory (DFT) calculations. The metal atoms can be substantially anchored on the M-graphene surface in single–atom formation revealed by the high binding energy, which is ascribed to the remarkable charge transfers between metal atom and M-graphene. Each metal atom can capture six H2 molecules at most in single–atom decorated M-graphene. The H2 adsorption energies are in the range from −0.139 to −0.375 eV, following an order of Sc@M-graphene > Ca@M-graphene > Li@M-graphene. The affinity ability of metal–decorated M-graphene for hydrogen can be enhanced by adding an external electric field. The multi–metal atoms decorated M-graphenes, Li4C16(H2)8, Ca4C16(H2)12, and Sc4C16(H2)12 complexes show high gravimetric densities (6.06 ∼ 6.78 wt%) and a favorable binding energy window (−0.167 to −0.418 eV), meeting the department of energy (DOE)’s criteria. The thermodynamic properties were in detail studied by considering temperature and pressure effects. AIMD simulations at different temperatures indicate that the efficient release of hydrogen can occur at room temperature. Our results show that the M-graphenes with Li, Ca, and Sc decorated have high hydrogen storage capacity and reversible hydrogen release performance. This work may be useful for designing novel 2D carbon–based materials for hydrogen storage.

First-principles investigation of Irida-graphene decorated with alkali metal for reversible hydrogen storage

Irida-graphene (IG) is a novel stable graphene allotrope, which exhibits metallic property. Based on first principles calculations, the potential of IG decorated with alkali metal atoms in reversible hydrogen storage has been investigated. Compared with graphene, IG has stronger binding on alkali metal atoms. For Li, Na, and K decorated IG, the polarization mechanism plays a crucial role in the adsorption of H2, the adsorption energies of H2 are −0.286, −0.209 and −0.183 eV/H2, and the hydrogen gravimetric densities can reach 7.1, 7.8 and 5.2 wt%, respectively, indicating that K decorated IG is not suitable as a hydrogen storage medium. The desorption temperatures calculated are 365 K and 267 K for stored H2 on Li/IG and Na/IG, respectively, and ab inito MD simulation suggest that Li/IG and Na/IG are stable at high temperature, thus Li and Na decorated IG have the potential application for reversible hydrogen storage.

Highly efficient and selective hydrogenation of furfural to furfuryl alcohol and cyclopentanone over Cu-Ni bimetallic Catalysts: The crucial role of CuNi alloys and Cu+ species

The selective hydrogenation of furfural derived from biomass is of significant importance in the synthesis of valuable chemical compounds. In this work, Cu-Ni bimetallic catalysts with varying metal ratios were effectively synthesized using the urea deposition method and employed in catalytic hydrogenation of furfural (FA) to furfuryl alcohol (FOL) and cyclopentanone (CPO) in different solvents. The study revealed that the synergistic interaction between Cu and Ni favors the formation of CuNi alloys, thereby facilitating the reduction of CuO and NiO and resulting in larger amount of metallic species (Cu0/+ and Ni0), and promoting the formation of highly dispersed nanoparticles. Moreover, the formed Cu+ species can serve as Lewis acid sites and improve the adsorption of polarized C = O, thus significantly enhancing the selectivity to FOL. More importantly, the cooperation between Cu+ species and water can promote the aqueous-phase hydrogenation-rearrangement (AP-HR) of FA to CPO. Also, in-situ/on-line DRIFTS shows that Cu3Ni1/SiO2 preferentially adsorbs and activates C = O and prefers to form 4-hydroxy-2-cyclopentenone (HCP), which is the key intermediate to form CPO. DFT calculations agree with the in-situ/on-line DRIFTS, showing that Cu3Ni1 (111) crystal surface with the lowest d-band center and the strongest electronic effects presents the highest adsorption energies of H2, H2O, and FA, the lowest adsorption energies of H*, FOL, and CPO, and the lowest energy barriers of Piancatelli rearrangement of FOL to HCP. Under the optimum conditions, Cu3Ni1/SiO2 gives 99.9 % yield to FOL at 333 K in isopropanol and 96.7 % yield to CPO at 413 K in water. The low cost and high activity of Cu3Ni1/SiO2 make it a potential catalyst for the green production of FOL and CPO in industry.

Improving the hydrogen storage performance of metal-decorated tetragonal boron carbide monolayer: First-principles investigations

Recently, two-dimensional systems have attracted considerable interest from scientists, due to their high H2 storage capacity and excellent reversibility. In this context, by means of DFT computations, we predict a novel system known as boron carbide, which can be formed by replacing 50% carbon atoms with boron atoms in tetragonal-graphene. We investigate the hydrogen adsorption performance of pristine and functionalized t-B4C4 sheets with the metals Li/Sc/Ti. Results indicate that metal-decorated t-B4C4 exhibits significantly lower H2 adsorption energies compared to pristine t-B4C4. Moreover, the hydrogen storage capacities for Li/Sc/Ti@t-B4C4 are 13.32%, 10.03% and 9.74% respectively. Furthermore, the desorption temperature exceeds the critical temperature of H2. Based on activation energy, H2 can migrate quickly on the t-B4C4 sheet during the adsorption/desorption cycles. Our results indicate that t-B4C4 functionalized with Li/Sc/Ti-metals can be an efficient material for hydrogen storage.

Machine learning accelerates design of bilayer-modified graphene hydrogen storage materials

To accelerate the exploration of modified graphene hydrogen storage materials, this paper proposes a Data-Driven Exploration Framework (DDEF) based on the best-fitting machine learning (ML) algorithms (Random Forest: Recall = 0.83, Accuracy = 0.83, Gradient boosted regression: R2 = 0.90, RMSE = 0.06) and density functional theory (DFT). The hydrogen storage capacity of bilayer double-deficient graphene (BDG[Li]) doped with B atoms and modified with Li and Ti atoms was predicted using ML, which shortens the design cycle of hydrogen storage materials. The interlayer composite hydrogen storage mechanism of the BDG[Li] structure is revealed by electronic property analysis. For the first time, the calculation method of the interlayer electrostatic force energy (Ej) is proposed, and the equation for calculating the interlayer H2 adsorption energy is optimized. The hydrogen storage data of BDG[Li] and the construction of Ej provide new feature data for subsequent ML calculations. Both DDEF and Ej are computationally verified to have high accuracy and generalizability, which is of research significance for accelerating the design of hydrogen storage materials.

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.

Borophene/graphene heterostructure for effective hydrogen storage with facile dehydrogenation

A theoretical investigation of the hydrogen adsorption on a β12-borophene monolayer and a β12-borophene/graphene bilayer heterostructure is performed to tailor the substrate properties via functionalization to increase its hydrogen (H2) physisorption strength and enhance its gravimetric capacity. The results using the density-functional theory show that the H2 adsorption energy significantly increases as the substrate changes from monolayer to bilayer heterostructure. This enhancement in H2 adsorption energy is attributed to the synergetic effects of the interlayer interaction in the heterostructure via analysis of the chemical bonding. The lithium decoration of the bilayer heterostructure has indeed increased both the H2 adsorption energy and gravimetric capacity. Further enhancement of these latter attributes is shown to be plausible to achieve through the application of an electric field normal to the surface and directed upward toward the molecules. The thermodynamic analysis based on the Langmuir adsorption model finds that the high storage capacity should be maintained high with an effective gravimetric capacity of 13.64 wt% at ambient conditions. Our findings demonstrated that the Li-decorated β12-borophene/graphene bilayer heterostructure should be a promising candidate for efficient hydrogen storage applications.

WOx boosted hollow Ni nanoreactors for the hydrodeoxygenation of lignin derivatives

Reasonable design of non-noble metal catalysts with hollow open structure for hydrodeoxygenation (HDO) of lignin derivatives to value-added chemicals is of great significance but challenging. Herein, a novel MOF-derived multilayer hollow sphere coated nickel‑tungsten bimetallic catalyst (Ni2-WOx@CN-700) was fabricated via by confined pyrolysis strategy using bimetallic MOFs as a self-sacrificial template, which exhibits robust activity for the typical model HDO of vanillin to 2-methoxy-4-methylphenol (Yield of 100 % at 140 °C for no less than 10 cycles). The characterizations revealed that WOx facilitated the dispersion of Ni nanoparticles and adjusted the acidic capacity of the catalyst through the formed Ni-WOx heterojunction. Density functional theory (DFT) calculations confirms that WOx species enhanced the electron-rich nature of the active sites, while the adsorption energies of H2 and vanillin on Ni-WOx decreased from −0.572 eV and − 0.622 eV on Ni to −3.969 eV and − 4.922 eV, respectively. These results further indicated that the high activity of Ni2-WOx@CN-700 was attributed to the Ni-WOx heterojunction. Based on the characterizations and the thermodynamic calculations, the reaction mechanism was proposed. In addition, the catalyst shows good substrate universality, which enables its good commercial application prospect.

Enhanced hydrogen storage of single-layer blue phosphorus by synergistic effect between doped lightweight elements and grafted lithium atoms

Single-layer blue phosphorus (SLBP) has displayed charming photoelectric performances, but its property in hydrogen storage is not outstanding due to the weak interactions. To expand the application of SLBP in hydrogen storage, we attempt to screen SLBP-based materials with stable structures and strong polarity using density functional theory by doping lightweight elements and grafting alkali metal atoms. The simulation results indicate that the lightweight elements (B, C, N, O and F) doped SLBP systems have more stable structures due to the strong orbital interaction than pure SLBP, and exhibit electron deficient characteristics. Compared to the pure SLBP, the H2 adsorption energies of the doped systems improve and range from 0.05 to 0.09 eV, but it still cannot meet the requirements of ideal hydrogen storage. Therefore, the lightweight element doped SLBP systems are further grafted by Li atom. Under the synergistic effect of doping lightweight elements and grafting Li atoms, H2 molecules are strongly polarized, and the corresponding adsorption energies of H2 reach to 0.16, 0.26, 0.28, 0.30, and 0.10 eV, respectively. It is worth emphasizing in the C-doped SLBP system that the hydrogen storage capacity of reaches 5.53 wt% for each Li atom adsorbs one hydrogen molecule and the corresponding adsorption energy is 0.23 eV/H2 when the ratio of C to P atoms increases to 6:26. For each Li atom adsorbs two hydrogen molecules in the same hydrogen storage system, the hydrogen storage capacity reaches 10.48 wt% with 0.18 eV/H2 adsorption energy. We hope these results can provide theoretical basis and scientific guidance for searching for SLBP-based materials with excellent hydrogen storage performances at ambient temperature.

Hydrogen Storage Capacity of Cobalt Cluster Ions.

The adsorption of H2 on gas-phase Con± (n = 5-12) clusters at 300 K and the desorption of H2 from ConHm± upon heating were studied experimentally by combining thermal desorption spectrometry and mass spectrometry to elucidate the hydrogen storage property of the Co clusters. Hydrogen atoms adsorbed well on Con+ (n = 5, 10-12) and Con- (n = 5-12) at 300 K to form ConHm±. The atomic ratios, m/n, for ConHm- (0.9-1.4) were higher than those for ConHm+ (0.2-1.1). According to density functional theory (DFT) calculations, the first few H2 molecules had a tendency to dissociatively adsorb onto the Co clusters. Further, the bonding nature of the H atoms was ionic, similar to the H atoms in the metallic hydrides. In contrast, H2, adsorbed molecularly, was explained in terms of σ complex formation. H2 molecules were desorbed from the clusters upon heating. The temperature dependences showed that ConHm- released H2 at a higher temperature (700-800 K) than ConHm+ (600-700 K), suggesting that Con- should have a higher affinity to hydrogen than Con+. The desorption temperatures were lower than those of VnHm+, which was consistent with the fact that the adsorption energies of H2 were lower for the Co clusters than those for the V clusters. The low adsorption energies were ascribed to their large highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps in the Co clusters.

Hydrogen storage properties of Ti-doped C20 nanocage and its derivatives: A comprehensive density functional theory investigation

We have innovatively designed and assessed the hydrogen storage properties of a single Ti-doped C20 nanocage and its B, N or B and N heteroatom substituted derivatives with the help of the density functional theory approach for the first time to the best of our knowledge. Out of fifteen designed structures by substituting heteroatoms, only 8 structures are found to be suitable for Ti doping and H2 adsorption viz. C20, C12N8, C12B8, C12B4N4, C10B5N5, C10B10, B10C10 and B10N10. Their formation energy and cohesive energy values confirm the stability of all the structures. Ti atom binds more strongly with B, N or B and N heteroatom substituted C20 nanocage than unsubstituted C20 nanocage which is necessary to avoid clustering for multiple Ti doped nanocages. Among the eight Ti doped nanocages considered, H2 molecules strongly interact with Ti-doped C12B4N4 nanocage. The binding strength of Ti atom with nanocages decreases during the hydrogen adsorption process. The obtained H2 adsorption energy values for all the structures are within the range of 0.2–0.7 eV, which is conducive to reversible hydrogen storage. Calculated Gibbs free energy-corrected H2 adsorption energy values at different temperature and pressure indicate favorable H2 adsorption over the entire pressure range at room temperature. For Ti doped C20, C12N8, C12B8, C10B5N5, C10B10, B10N10, and B10C10 nanocages, H2 adsorption is thermodynamically favorable below 360, 350, 300, 285, 235, 277, and 251 K, respectively at 1 atm pressure. From PDOS analysis, it is observed that the 1s orbital of H overlaps with 3d orbital of Ti atom. The highest H2 desorption temperature is observed for the C12B4N4Ti nanocage, and the lowest for C10B10Ti, aligning well with the calculated adsorption energy values. As H2 desorption temperature is high, the stability of Ti-doped nanocages at high temperature (634 K) is confirmed using ab initio molecular dynamics simulations. Bader's quantum theory in atoms in molecules is used to prove the weak non-covalent interaction between all the atoms.

High-performance heterometallic photocatalysts afforded by polyoxometalate synthons for efficient H2 production

MoS2-based materials have emerged as photoelectric semiconductors characterized by a narrow band gap, high capacity for absorbing visible light, and reduced H2 adsorption energy comparable to Pt. These attributes render them appealing for application in photocatalytic hydrogen production. Despite these advantages, the widespread adoption of MoS2-based materials remains hindered by challenges associated with limited exposure to active sites and suboptimal catalytic hydrogen production efficiency. To address these issues, we have designed and synthesized a new class of highly dispersed bimetallic/trimetallic sulfide materials. This was achieved by developing polyoxometalate synthons containing Ni-Mo elements, which were subsequently reacted with thiourea and CdS. The resulting Ni3S2-MoS2 and Ni3S2-MoS2-CdS materials achieve photocatalytic hydrogen production rates of 2770 and 2873 μmol g–1h−1, respectively. Notably, the rate of 2873 μmol g–1h−1 for Ni3S2-MoS2-CdS surpassed triple (3.23 times) the performance of CdS and nearly sextuple (5.77 times) that of single MoS2. These materials outperformed the majority of MoS2-based photocatalysts. Overall, this study introduces a straightforward methodology for synthesizing bimetallic/trimetallic sulfides with enhanced photocatalytic H2 evolution performance. Our findings underscore the potential of transition metal sulfide semiconductors in the realm of photocatalysis and pave the way for the development of more sustainable energy production systems.

Computational investigation of charge injection into modified graphdiyne nanosheet via Al doping and Li decoration to improve hydrogen adsorption

The utilization of hydrogen as a clean fuel has been made feasible by the expanding development of cutting-edge materials for hydrogen adsorption and storage. In this study, we thoroughly assessed hydrogen storage capability on both neutral and charge-injected graphdiyne (GDY) nanosheets modified with Al doping and Li decorating (Li.Al-GDY). According to the findings, pure GDY has an adsorption energy of −0.093 eV, while GDY modified with Al and Li atoms has an improved adsorption energy of −0.577 eV. The highest H2 adsorption energy of −0.760 eV was calculated for the applied charge of −2 e to the Li.Al-GDY nanosheet, indicating a significant enhancement in the adsorption energy with the charge injection. While the pristine GDY nanosheet serves as a very poor H2 molecule adsorber and cannot even hold one H2 molecule, the charged Li.Al-GDY nanosheet maintains 13 H2 molecules with an average adsorption energy of −0.287 eV. According to the results, injecting charge into the nanosheet along with modification techniques such as doping and decorating can significantly boost the effectiveness of weak carbon adsorbents in terms of hydrogen adsorption. Such approaches enable the realization of the goal of using carbon adsorbents as H2 green fuel storage.

Insights into Selective Mechanism of NiO-TiO2 Heterojunction to H2 and CO.

The construction of p-n heterojunctions has become a widely adopted strategy for achieving the selective detection of reducing gases, including H2 and CO. Nevertheless, the elucidation of the gas selectivity mechanism at the nanoscale remains elusive. First-principle calculations provide an attractive avenue for comprehending the influence of coordination structures on gas-sensitive selectivity, thereby unveiling the structure-activity relationship of p-n heterojunction sites. In this study, we investigate the selective adsorption behavior of H2 and CO on a NiO-TiO2 heterojunction using density functional theory. The results of d-band center analysis confirm that the NiO-TiO2 heterojunction with adsorbed oxygen significantly enhances the adsorption stability of reducing gases. Intriguingly, our calculations reveal that H2 has a higher affinity for adsorbed oxygen on the heterojunction surface compared to that of CO, corresponding to a lower H2 adsorption energy. Density of states (DOS) results indicate that the NiO-TiO2 heterojunction, with preadsorbed oxygen, exhibits ultrahigh selectivity with an n-type gas-sensitive response to H2, effectively eliminating the cross-sensitivity observed with CO, as confirmed by gas-sensitive characterization research. The sensing mechanism of the NiO-TiO2 heterojunction's selective detection of H2 without interference from CO can be visually explained by electron transfer and potential barrier changes, paving the way for future developments in novel, selective gas-sensitive materials.

Morphological Effect on the Surface Activity and Hydrogen Evolution Catalytic Performance of Cu2O and Cu2O/rGO Composites

Different cuprous oxide (Cu2O) particle forms, including the octahedron, truncated octahedron, cube, and star-like forms, are synthesized through chemical reduction under different reaction conditions. The correlation between the morphology and the catalytic activity of hydrogen evolution reactions (HERs) is investigated. It is discovered that the Cu2O particles with a higher 111/100 facets (r) ratio have a higher oxidation resistance and higher activity in HER catalysis, as supported by the density functional theory (DFT) calculation results. This improvement is attributed to the fact that more Cu+ terminated atoms on facet 111 provide more active sites, as measured using their electroactive area, as well as the lower H2 adsorption energy on that facet. To enhance Cu2O’s HER performance, cuprous oxide particles are deposited on reduced graphene oxide (rGO) through a hydrothermal method. XPS and XRD show a CuO layer on the composite surface, which reduces the Cu2O corrosion in the reaction. Overall, Cu2O/rGO composites exhibit a better particle distribution, increased active sites, and improved charge separation. The best electrocatalyst in this study is the Cu2O/rGO with a star-shaped form, with an overpotential of −458 mV. Its improved performance is attributed to the presence of unsaturated active sites with a higher reactivity, such as the edges and corners. SEM studies of this composite after catalysis indicate that Cu2O undergoes structural reconstruction during the reaction and reaches a more stable structure.

Li-decorated 2D Irida-graphene as a potential hydrogen storage material: A dispersion-corrected density functional theory calculations

In this research, density functional theory with van der Waals (vdW) dispersion-corrected method is employed to systematically investigate H2 adsorption behaviors on Li-decorated two-dimensional (2D) Irida-graphene (IG). Our results expose that the adsorption performance between H2 and original IG is extremely weak, while Li-decorated IG can significantly promote H2 adsorption capability. Due to a large binding energy, Li atoms strongly bind on the top of octagonal carbon-ring of IG and prevent decorated Li atoms from aggregation. Moreover, single-sided Li decorated IG and double-sided Li decorated IG can adsorb up to 16H2 molecules and 24H2 molecules with the corresponding H2 adsorption energy of −0.230 eV/H2 and −0.276 eV/H2, respectively. Meanwhile, the calculated H2 adsorption energy for each H2-adsorbed Li-decorated IG configuration falls into the range of −0.1 eV/H2 and −0.4 eV/H2 for reversible hydrogen storage. In addition, the obtained hydrogen storage gravimetric density achieves 7.06 wt%, which surpasses the latest standard of 6.5 wt% established by U.S. Department of Energy (DOE). These findings reveals Li-decorated IG can be served as an outstanding hydrogen storage material for on board mobile applications.

Insights into the mechanism of electric field regulating hydrogen adsorption on Li-functionalized N-doped defective graphene: A first-principles perspective

The hydrogen storage properties of lithium functionalized graphene under external electric fields have been studied in this work employing density functional theory (DFT) calculations. Lithium modified nitrogen doped double-vacancy graphene (Li_NDVG) was constructed as hydrogen storage material. It is examined in terms of the system’s electronic properties, H2 adsorption energy, and stable configuration. The results demonstrate that Li atoms can be distributed on the substrate surface and incorporated into defect centers without producing metal clusters. In comparison to pristine graphene, the adsorption energy of H2 on Li_NDVG is four times higher. The Coulomb force between Li atom and H2 molecule grows as the positive electric field’s strength increases, and the adsorption distance shrinks. On the contrary, the H2 adsorption energy decreases as the negative electric field’s strength increases, and the adsorption distance expands. Furthermore, adsorption occurs spontaneously within the range of 0–300 K and 1–100 atm, and the promoting effect of a positive electric field on adsorption only occurs in the temperature range of 0–140 K. Hydrogen storage properties of functionalized graphene modified with lithium trimer and tetramer respond to the electric field in the same way as single atom. And the presence of clusters and positive electric field increases the bond length of the H2 molecule, causing a tendency for the H2 molecule to dissociate.