Candidate For Hydrogen Storage Research Articles

Ti doped [1,1,1,1] paracyclophane and its derivatives for hydrogen storage: A Computational Insight

Ti-doped [1,1,1,1] paracyclophane(PCP) and its derivatives have been designed by substituting heteroatoms boron and nitrogen and studied their hydrogen storage properties using density functional theory. Heteroatom substitution is important for stronger Ti-binding whereas Ti-doping for light weight, almost empty d-orbital and its stronger interaction with H2 molecules. Six configurations are obtained: PB1,PB2(boron substitution), PN1,PN2 (nitrogen substitution) and PBN1,PBN2(boron and nitrogen co-substitution). Stability of all Ti-doped structures has been confirmed using cohesive and formation energy. PCP, PB1, PB2, PN1, PN2, PNB1 and PNB2 show gravimetric hydrogen uptake capacity(adsorption energy) as 5.52(0.67),6.90(0.5),6.90(0.53),5.37(0.6),5.37(0.61), 5.48(0.7) and 5.48(0.74 eV) wt% respectively. Ti-doped boron substituted structures show required H2 uptake capacity, suitable adsorption energy, thermodynamically favorable H2 adsorption at ambient conditions, moderate desorption temperature, structural and thermodynamic stability, thus more suitable for hydrogen storage than nitrogen substituted and boron and nitrogen co-substituted structures. Ti-doped boron substituted PCP is a promising reversible hydrogen storage candidate.

Prediction of comprehensive properties and their hydrogen performance of Mg2XH6(X=Mn, Fe, Co, Ni) perovskite hydrides based on first principles

Hydrogen storage materials are very critical for hydrogen energy utilization. Cubic Mg2XH6(X = Mn, Fe, Co, Ni) hydrogen storage materials are investigated by first principles calculation. The structural stability are confirmed by complex consideration of phonon spectrum, formation energies and elastic constants. They are brittle and hard materials with high temperature applicable potential. Mg2MnH6 and Mg2CoH6 are magnetic compounds while Mg2FeH6 and Mg2NiH6 are non-magnetic materials. Mg2MnH6 and Mg2FeH6 are semiconductors with bandgap of 1.867 eV and 3.318 eV, respectively, indicating they are applicable in optoelectronic field, while Mg2CoH6 and Mg2NiH6 are metallic in energy band structure. They are all ionic compounds which are confirmed by Cauchy pressure, electronic density difference and electronic localization function. Their hydrogen storage capacity are all over 5.2 wt%, which are favorable in practical use. And the moderate desorption temperature of 328.9 K of Mg2MnH6 suggests it is a promising candidate for hydrogen storage.

In-situ formation of V and Mg2Co/Mg2CoH5 for boosting the hydrogen storage properties of MgH2

Among the potential candidates for solid-state hydrogen storage, magnesium hydride (MgH2) exhibits high storage capacity of 7.6 wt%. However, its commercial application is hindered by the unsatisfactory kinetics properties and stable thermodynamics. In this study, we synthesized porous spherical CoV₂O₆ and incorporated it into MgH2, reducing the initial dehydrogenation temperature of MgH2 to 190 °C. Additionally, rapid hydrogen uptake was also observed, approaching 6.5 wt% H2 within 1000 s at 190 °C. A notable decrease of 45.78 kJ/mol in the apparent activation energy (Ea) for dehydrogenation signifies an improved dehydrogenation kinetic. The formation of Mg2Co/Mg2CoH5, along with the presence of single-valence and multi-valence vanadium, facilitated multiple electron transfer pathways. In particular, vanadium elongated the Mg–H bond is responsible for the high catalytic activity in boosting the hydrogen storage performance of MgH2. These findings provide new intuitions for further research to enhance the kinetic properties of hydrogen adsorption and desorption in magnesium hydride.

The design of Mg–Ti–V–Nb–Cr lightweight high entropy alloys for hydrogen storage

In this study, body-centered-cubic Ti24V18Nb6Cr12 high entropy alloy (HEA) is selected as the matrix to design Mg–Ti–V–Nb–Cr lightweight HEAs. Based on first-principles calculations, the hydrogen storage properties of a series of Mg–Ti–V–Nb–Cr HEAs are systematically investigated. The designed Mg-based HEAs are found to be stable after hydrogenation and exhibit high gravimetric hydrogen storage capacities (HSCs). Particularly, the gravimetric HSC of Mg6Ti24V18Cr12 HEA is as high as 4.091 wt%. Besides, the dehydrogenation temperature of the Mg–Ti–V–Nb–Cr HEAs decreases obviously with increasing Mg content, which results from the weakened bonding strength of <M-H> pairs. This study demonstrates that the Mg6Ti24V18Cr12 HEA is a potential candidate for hydrogen storage.

Extensive screening of novel BaXH3 (X = V, Cr, Co, Ni, Cu, and Zn) perovskites for physical properties and hydrogen storage application: A DFT study

A successful transition to a sustainable economy depends on effective hydrogen storage. To achieve this, we investigate novel inorganic transition metal-based BaXH3 (X = V, Cr, Co, Ni, Cu, Zn) perovskites using Density Functional Theory (DFT). We compute key properties such as structural, electrical, magnetic, optical, mechanical, and hydrogen storage using the GGA-PBE functional. We calculate lattice constants and unit cell volume, indicate thermochemical stability with the negative formation energy of all compounds, and confirm thermodynamic stability with phonon calculations. Investigations into the band structure and density of states (DOS) show that all compounds are metallic, with BaVH3 and BaCrH3 exhibiting magnetic characteristics. We calculate the optical properties, including refractive index, dielectric function, reflectivity, loss function, conductivity, and absorption. We verified mechanical stability using the Born stability criteria. We calculated the hydrogen storage capacities and desorption temperatures. These results indicate that the studied compounds are potential candidates for hydrogen storage in a green economy.

Balancing volumetric and gravimetric capacity for hydrogen in supramolecular crystals.

The storage of hydrogen is key to its applications. Developing adsorbent materials with high volumetric and gravimetric storage capacities, both of which are essential for the efficient use of hydrogen as a fuel, is challenging. Here we report a controlled catenation strategy in hydrogen-bonded organic frameworks (RP-H100 and RP-H101) that depends on multiple hydrogen bonds to guide catenation in a point-contact manner, resulting in high volumetric and gravimetric surface areas, robustness and ideal pore diameters (~1.2-1.9 nm) for hydrogen storage. This approach involves assembling nine imidazole-annulated triptycene hexaacids into a secondary hexagonal superstructure containing three open channels through which seven of the hexagons interpenetrate to form a seven-fold catenated superstructure. RP-H101 exhibits high deliverable volumetric (53.7 g l-1) and gravimetric (9.3 wt%) capacities for hydrogen under a combined temperature and pressure swing (77 K/100 bar → 160 K/5 bar). This work illustrates the virtues of supramolecular crystals as promising candidates for hydrogen storage.

Synthesis of biochar-doped MgO catalyst for highly efficient conversion of glucose into formic acid at low temperatures

Formic acid (FA) is not only a significant platform chemical but also a promising candidate for hydrogen storage. Although homogeneous catalysts are commonly employed for the conversion of carbohydrate biomass into FA, which often come with substantial costs and inadequate reusability. It is noteworthy that there has been an increasing focus on the development of heterogeneous catalysts in this area, which aim to address these limitations and offer advantages such as easier separation and better reusability. Herein, an eco-friendly and efficient method for the catalytic conversion of glucose to FA by utilizing a biochar-MgO (BC-MgO) catalyst, which is prepared through pyrolysis of coconut husk biochar impregnated with magnesium chloride (MgCl2), is proposed. The FA yield at 74.6% is attained from glucose at 60 °C within only 3 h, utilizing a mere 0.1 g of catalyst and hydrogen peroxide (H2O2) amount of 100%. In conjunction with random forest (RF) algorithms and box-behnken experimental designs, further optimization resulted in an increased yield of 79.1%, with a selectivity of 82.7%, in only 3.8 h at 67 °C, employing 0.1 g of catalyst amount and 125% H2O2 amounts. Notably, the BC-MgO catalyst retains its catalytic efficiency over multiple cycles, only requiring a simple straightforward regeneration procedure. The mechanism underlying the glucose conversion to FA reaction system is demystified via kinetic modeling, time-gradient studies, and model compounds experiments. Life cycle assessment (LCA) indicates that when used for glucose conversion to FA, BC-MgO catalysts generate lower CO2 emissions than traditional homogeneous catalysts such as LiOH. Concurrently, an operation cost analysis indicates that operation cost of FA production from glucose is 4.1 $/kg with the BC-MgO catalyst, which is lower than LiOH catalyst (7.5 $/kg), evidencing the dual advantage of economic viability and an improved environmental impact inherent to this novel process.

Efficient hydrolytic dehydrogenation of ammonia borane catalyzed by ultrafine Pt clusters confined in Ni–Ti layered double hydroxides with closo-dodecaborate

Ammonia borane (NH3BH3, AB) is a highly promising candidate for hydrogen storage. Nevertheless, there is an urgent need to develop an efficient and stable catalyst that can control hydrogen generation under mild conditions. The use of catalysts with numerous surface atoms anchored to a carrier to achieve a synergistic effect is an appealing approach in catalysis. In this work, a series of highly dispersed metal clusters NiTi-LDH@B12H12@M (M = Au, Pd, Pt, Ag) catalysts were successfully synthesized at room temperature by leveraging the reductivity of [closo-B12H12]2- immobilized in the layered double hydroxide (LDH) laminate, along with the spatial confinement and anion exchange capabilities of LDH. Specifically, utilizing the optimal catalyst NiTi-LDH@B12H12@Pt 2.4% (wt. Pt), the AB hydrolysis reaction exhibited extraordinary catalytic activity. It exhibited a first-order reaction rate with respect to Pt and a near zero-order reaction rate with respect to AB concentration. The AB hydrolysis can be achieved in a mere 29 s at 25 °C with a conversion rate of 100%. The corresponding turnover frequency (TOF) attains a value of 454.06 molH2molPtmin−1, and the apparent activation energy (Ea) is 41.8 kJ mol−1, surpassing numerous previously reported Pt-based catalysts. The outstanding catalytic performance can be ascribed to the uniform distribution of ultrafine Pt clusters, along with the synergistic effect conferred by NiTi-LDH and intercalated anions ([closo-B12H12]2-).

Subnanometer palladium-manganese clusters in hydrophilic amino-functionalized zeolites for efficient formic acid dehydrogenation

Formic acid (FA) has emerged as a promising candidate for hydrogen storage, due to its excellent stability, low cost, and renewability. The rational design of catalysts for FA dehydrogenation is crucial for integrating FA into the hydrogen economy system. Herein, subnanometric bimetallic Pd-Mn clusters were encapsulated within hydrophilic amino-functionalized silicalite-1 (S-1) zeolite via an in-situ ligand-protection direct H2 reduction method. The graft of amino groups within zeolites not only endowed the zeolites with alkaline sites, but also significantly improved the hydrophilicity of zeolites, and enhanced the interaction between zeolite supports and encapsulated metal species, forming highly active electron-enriched Pd species. Thanks to the high dispersion of metal species and synergy between Pd and Mn species as well as the additive alkaline sites and hydrophilicity of zeolites, the optimized PdMn0.25@S-1-NH2 catalyst exhibited a superhigh H2 evolution rate from FA decomposition, with a turnover frequency value of 11,401 molH2·molPd−1·h−1 at 333 K without any additives, overcoming almost all of the state-of-the-art heterogeneous catalysts under the similar catalytic condition. This study highlights the effective synergistic effect between metal species and supports for improving catalytic efficiency in FA dehydrogenation reactions, and also opens a new paradigm for the design of functionalized zeolite-encapsulated metal catalysts for other important catalytic reactions.

NH4+][BxH3x+1-] (x = 1-5): Role of Polynuclear Superhalogens in High-Capacity Hydrogen Storage.

Superhalogen anions are characterized by a higher vertical detachment energy (VDE) than those of halides. Ammonium borohydride, [NH4+][BH4-], is a potential candidate for high-capacity hydrogen storage but is not practically used due to its instability against dissociation to ammonia borane. Interestingly, BH4- is a superhalogen anion, and therefore, we use polynuclear BxH3x+1- superhalogen anions and study [NH4+][BxH3x+1-] complexes for x = 2-5 using density functional theory. The gravimetric hydrogen density of these complexes is smaller than that of [NH4+][BH4-] only slightly. We calculate the dehydrogenation energy and the Gibbs free energy of [NH4+][BxH3x+1-] complexes through ammonia borane. We notice that these complexes are more stable than [NH4+][BH4-], whose stability increases with an increase in x. The enhanced stability of [NH4+][BxH3x+1-] complexes appears as a consequence of the increase in the VDE of polynuclear BxH3x+1- superhalogen anions. We believe that these findings might attract experimentalists to synthesize these complexes.

Hydrogen storage in Ti doped 4-6-8 biphenylene (Ti.C468): Insights from density functional theory

Hydrogen storage exploration in carbon-based materials is pivotal for advancing energy technologies. This study employs first-principles Density Functional Theory (DFT) calculations, utilizing the PBE functional with the VASP code, to investigate the 4-6-8 biphenylene (C468) and its derivatives, a distinctive 2D carbon structure. Both pristine C468 and its titanium-decorated variants (1TiC468 and 2TiC468) are analyzed. 1TiC468 and 2TiC468 exhibit maximum hydrogen molecule accommodation of up to 12 and 24, achieving gravimetric densities of 6.713 wt% and 11.188 wt%, respectively, with adsorption energies ranging from −0.132 eV/H2 to −0.399 eV/H2. These gravimetric values align with or surpass DOE guidelines. Additionally, comparative analysis indicates enhanced hydrogen adsorption due to Ti presence in C468. Molecular dynamics (MD) and phonon dispersion studies confirm the stability of mTiC468 (m = 1 and 2) systems at 300K. These findings underscore the potential of Ti-decorated C468 as hydrogen storage candidates, expanding the applications of carbon-based materials in energy storage.

Hydrogen storage ability of hexagonal boron nitride

The development of hydrogen energy is capable of solving a number of important issues that modern society is facing, including global warming and various environmental impacts. Currently, there is an intensive search for natural sources of hydrogen as well as low-carbon techniques for mass production of hydrogen from natural gas, associated petroleum gas, and water. In parallel, efforts to develop technologies for the subsequent management of hydrogen are underway, and the creation of its safe and efficient storage is one of the highest priority goals. For the transportation and storage of hydrogen today, a number of solutions are offered, each of which has both positive and negative aspects. The boron nitride family of materials with high thermal and chemical stability, variability of morphologies, and flexibility of structure has been considered as a candidate for efficient hydrogen storage. This review offers to familiarize readers with the progress in the research and application of hexagonal boron nitride (h-BN), as well as BN-based materials in comparison with other materials, as promising hydrogen storage. Experimental and theoretical data obtained for different morphologies and internal structures were reviewed in relevance to the material`s sorption capacity with respect to hydrogen. Various approaches to improve the efficiency of hydrogen storage were analyzed, and the highest storage capabilities published were mentioned. Thus, BN-based materials are very promising as hydrogen storage, even for an automotive application, but the development of new mass production technologies should be carried out.

Strategies for hydrogen storage in a depleted sandstone reservoir from the San Joaquin Basin, California (USA) based on high-fidelity numerical simulations

Depleted hydrocarbon reservoirs are promising candidates for underground hydrogen (H2) storage (UHS) due to their known (and often high) storage capacity, well-identified geological conditions, reduced cushion gas requirements, and adaptable existing infrastructure. While these reservoirs have shown success in natural gas storage, their performance for pure H2 storage remains untested, necessitating further research. To address this knowledge gap, we conduct high-fidelity multiphase compositional reservoir simulations to evaluate the technical feasibility of UHS in a depleted hydrocarbon reservoir within the Temblor Formation at the North Belridge Field from the San Joaquin Basin, California, USA. This reservoir zone comprises five distinct sand layers separated by four shale intervals and is bounded above and below by thick shales (overburden and underburden, respectively). This research has two primary objectives: (a) to assess the feasibility of two distinct UHS strategies—one that involves storing H2 across all sand layers and another that stores an equal amount of H2 in the single thickest sand layer, and (b) to evaluate the effect of interbedded shale permeability on UHS performance. Our findings indicate that UHS in the Temblor Formation is technically viable, showing enhanced H2 withdrawal efficiency and produced H2 purity over successive cycles with minimal leakage risk. The two storage strategies significantly impact UHS performance in the interbedded sandstone sequence. Storing H2 across all sand layers results in higher H2 withdrawal efficiency, but lower produced H2 purity. In contrast, storing H2 in a single sand layer leads to lower withdrawal efficiency but consistently high H2 purity. In addition, H2 storage in a single sand layer results in higher reservoir pressure buildup, implying greater geomechanical risks. The impact of interbedded shale permeability on UHS performance is negligible across the range of uncertainty for shale permeability. This research not only lays the groundwork for potential UHS implementation in the abundant sandstones of the San Joaquin Basin of California, but also offers valuable insights for other depleted hydrocarbon reservoirs under consideration for UHS that share similar properties.

Tailoring hydrogen storage performance in γ-graphyne through valence band modulation of adsorbed Li via doping and strain

Hydrogen storage is indeed fundamental to utilizing H2 effectively, and porous carbon materials have emerged as highly promising supports for this purpose. γ-Graphyne (γGy) possesses abundant chemical bonds, considerable porosity, and exceptional chemical stability, positioning it as a promising candidate for hydrogen storage and transport applications. In this study, we conducted density functional theory calculations to investigate the potential of Li- and Na-loaded γGy as hydrogen storage materials. Our findings reveal that the hydrogen storage capacity (HSC) of Na-loaded γGy falls significantly short of expectations, whereas Li-loaded γGy demonstrates a notably higher HSC. Subsequently, our calculations indicate that B-doping of γGy does not promote favorable HSC, whereas N-doping exhibits a beneficial effect. Furthermore, we observed that tensile strain favors the hydrogen storage properties of 4Li@γGy and 4Li@N-γGy, while compressive strain enhances the hydrogen storage characteristics of 4Li@B-γGy. Notably, we discovered the capacity to adjust the valence band center of Li (ɛVB), consequently influencing the hydrogen storage performance of γGy. Our investigation suggests that increased overlap between ɛVB in Li-loaded graphyne and the effective alignment of H2 and the supporting structure augments the binding force between Li and H2, thereby amplifying the HSC.

Tuning clusters-metal oxide promoters electronic interaction of Ru-based catalyst for ammonia synthesis under mild conditions

Ammonia (NH3) is an excellent candidate for hydrogen storage and transport. However, producing NH3 under mild conditions is a long-term, arduous task. Atomic cluster catalysts (ACCs) have been shown to be effective for catalytic N2-to-NH3 conversion, opening the door to the development of efficient catalysts under mild conditions. Still, ACC formation with thermally stable catalytic sites remains a challenge because of their high surface free energy. Herein, we report anchoring Ba and/or Ce onto Ru ACCs (2 wt% Ru atomic clusters supported on N-doped carbon) to form so-called clusters–metal oxide promoters electronic interaction (CMEI) to stabilize the Ru atomic clusters. The resulting Ba/Ce/Ru ACCs significantly boost the NH3 synthesis rate to 56.2 mmolNH3 gcat−1 h−1 at 400 °C and 1 MPa, which is 7.5-fold higher than that of Ru ACC. The strengthened CMEI between the Ba/Ce and Ru atomic clusters across the Ba/Ce/Ru ACC enables electron transfer from Ba and/or Ce to Ru atomic clusters. As such, the electron-enriched Ru atom could facilitate electron transfer to N≡N bond π* orbitals, which would weaken the N≡N bond and drive the eventual conversion of N2 to NH3. This study offers insight into the role of CMEI in Ru ACCs and provides an effective approach for designing stable atomic cluster catalysts for NH3 synthesis.

From Back to Stage: Superior Cycling Stability of 2LiBH4−MgH2 Enabled by Anion Tuning

Abstract2LiBH4−MgH2 (Li‐RHC) is a potential hydrogen storage candidate with a capacity of 11.5 wt.%. However, its further application is severely limited by the long nucleation induction period and poor reversibility of end‐product. Unlike the traditional focus on the catalytical role of cation, herein, a new perspective of previously ignore anion tuning has been proposed, in which S2− bridges the reversible conversion between Li2S and MgS during de‐/hydrogenation cycling of Li‐RHC. Such conversion not only enhances the migration of Li+, leading to the rapid destabilization of B─H bonds without obvious nucleation period of MgB2, but also improves the cycling stability of Li‐RHC with capacity retention over 90% even after 50 cycles. The universal of this anion modulation has been verified, along with the matching criteria of the corresponding transition metal cation. The results highlight the contribution of anion, push anion modulation from back to stage and eventually broaden the selection of catalysts for Li‐RHC.

Nitrogen-Doped Graphene-Supported Nickel Nanoparticles Reveal Low Dehydrogenation Temperature and Long Cyclic Life of Magnesium Hydrides.

Magnesium hydride (MgH2) is a promising hydrogen storage candidate due to its large capacity; however, high dehydrogenation temperature and slow kinetic rates are the main bottlenecks. Herein, we proposed a strategy for designing nitrogen-doped graphene-supported Ni nanoparticles (NPs) (Ni@NC) to tackle these problems. The results showed that the MgH2 + 15 wt % Ni@NC nanocomposite reduced the on-set dehydrogenation temperature to 195 °C, which was 175 °C lower than pristine MgH2. In addition, MgH2 + 15 wt % Ni@NC achieved 1.7 and 6.5 wt % desorption capacities at 225 and 300 °C, respectively, while absorbing 5.5 wt % hydrogen at 100 °C. The MgH2 + 15 wt % Ni@NC nanocomposite showed high cyclic stability, achieving 98.0% capacity retention after 100 cycles at 270 °C with negligible loss in capacity. This remarkable hydrogen storage performance can be attributed to the homogeneous distribution of Ni NPs on N-doped graphene layers, in situ formed Mg2NiH2 NPs, and multiphasic regions, promoting the nucleation and growth process during hydrogenation/dehydrogenation, which stabilized and improved the cyclic stability. This strategy paves the way to developing high-performance MgH2 for large-scale applications.

Mg-decorated CN monolayer with enhanced hydrogen storage

Current hydrogen storage confronts safety and high energy cost challenges. Solid-state hydrogen storage provides an efficient pathway with lower cost and pressure conditions. Here, we perform density functional theory (DFT) calculations measuring the hydrogen storage properties of Mg-decorated CN monolayer. 8Mg@CN structure is confirmed based on energetic and geometric criteria and it can absorb up to 40 H2 molecules, achieving a high gravimetric density of 8.92 wt% over the US Department of Energy (DOE) target. The polarized H2 molecules are proven to be physiosorbed on Mg atoms to guarantee desorption. The electronic properties are studied to illustrate the electrostatic attractions between the H2 molecules and the Mg-decorated CN monolayer. Moreover, the desorption temperatures and adsorption pressures are calculated to illustrate the reversibility of hydrogen storage applications on 8Mg@CN. These results indicate 8Mg@CN could be a promising candidate for hydrogen storage with potentially reversible application.

Machine learning assisted design of BCC high entropy alloys for room temperature hydrogen storage

Body-centered cubic (BCC) alloy systems can theoretically store double amounts of hydrogen compared with commercial metal hydrides at room temperature, and BCC high entropy alloys (HEAs) have shown the potential to reach this theoretic limit. However, the high thermodynamic stability of the dihydrides formed during hydrogen storage results in high operating temperatures. Here, by employing multi-objective Bayesian optimization-aided density functional theory calculations, we discovered 8 new HEA candidates for hydrogen storage, including the VNbCrMoMn HEA that can store 2.83 wt% hydrogen at room temperature and atmospheric pressure, vastly exceeding the hydrogen capacities of 1.38 wt% and 1.91 wt% for commercial LaNi5H6 and TiFeH2. Such a high performance of VNbCrMoMn is ascribed to the optimized hydrogen absorption thermodynamics, which is achieved under the guidance of interpretable machine learning which revealed that the thermodynamics of the first and second stages of absorption are largely determined by the bulk modulus and the number of states in the d-band, respectively.

Density Functional Theory-Based Approaches to Improving Hydrogen Storage in Graphene-Based Materials.

Various technologies have been developed for the safe and efficient storage of hydrogen. Hydrogen storage in its solid form is an attractive option to overcome challenges such as storage and cost. Specifically, hydrogen storage in carbon-based structures is a good solution. To date, numerous theoretical studies have explored hydrogen storage in different carbon structures. Consequently, in this review, density functional theory (DFT) studies on hydrogen storage in graphene-based structures are examined in detail. Different modifications of graphene structures to improve their hydrogen storage properties are comprehensively reviewed. To date, various modified graphene structures, such as decorated graphene, doped graphene, graphene with vacancies, graphene with vacancies-doping, as well as decorated-doped graphene, have been explored to modify the reactivity of pristine graphene. Most of these modified graphene structures are good candidates for hydrogen storage. The DFT-based theoretical studies analyzed in this review should motivate experimental groups to experimentally validate the theoretical predictions as many modified graphene systems are shown to be good candidates for hydrogen storage.