Potential Hydrogen Storage Medium Research Articles

Reversible hydrogen storage with Na-modified Irida-Graphene: A density functional theory study

Two-Dimensional carbon-based materials as a potential hydrogen storage medium have attracted great attention. In this study, various key aspects such as structure, electronic properties, stability, and hydrogen storage performance of Na-modified Irida-Graphene (IG) were thoroughly investigated using density functional theory (DFT) calculation methods. The calculation results show that the binding energy of Na atoms with the substrate is 1.51 eV, far exceeding the cohesive energy. The AIMD results reflect the good thermal stability of the model. One Na atom can adsorb up to 5H2 molecules. The IG loaded with eight Na atoms on both sides can adsorb 32H2 molecules, achieving a hydrogen storage capacity of 7.82 wt%, far exceeding the US DOE target of 5.5 wt%. The calculated Van ’t Hoff equation indicates a desorption temperature of 248 K for the model. Moreover, reversible hydrogen storage can be achieved at medium to low pressures, with desorption temperatures ranging from 285 K to 417 K. These results suggest that Na-Modified IG models are candidate materials for reversible hydrogen storage under near-ambient conditions.

First-principles calculations of Li-decorated Dirac semimetal NP monolayer as a potential reversible hydrogen storage medium

To explore the potential applications of the recently proposed two-dimensional (2D) Dirac material, the NP monolayer, the hydrogen storage properties of a Li-decorated NP monolayer were calculated using first-principles methods. DFT calculation results revealed that a Li atom can stably bind to the surface of the NP monolayer and, in turn, is able adsorb two H2 molecules that exhibit a suitable adsorption energy (-0.20 eV/H2). As such, a hydrogen storage gravimetric density of 5.5 wt% may be achieved in the fully Li-decorated NP system (18H2-Li12N12P12). Further, MD simulations demonstrated that the H2 adsorbed on the Li12N12P12 surface were released at 300 K, and the reusability of this material was promoted by its excellent structural stability. These findings give a theoretical basis for the potential hydrogen storage application of the Li-decorated NP monolayer.

Hydrogen Storage in a Ti-Functionalized Metal Carbyne Framework: Insights from a First-Principles Study

Hydrogen (H2) has the ability to be a future green-energy source for the automotive industry due to its versatility, clean nature, and efficiency as an energy carrier. The biggest obstacle to achieving hydrogen as a potential energy source is the nonavailability of effective hydrogen storage materials. In this proposed work, the hydrogen storage capacity and reversibility of a Ti-functionalized metal carbyne framework (MCF) having carbyne as an organic linker and Mg4O as an inorganic moiety are explored. All structural relaxation and simulation calculations are performed by employing the dispersion-corrected density functional theory computation. In this Ti-functionalized MCF, each Ti can adsorb up to five H2 molecules via the Kubas mechanism, with adsorption energy lying between 0.33 and 0.44 eV, which falls within the range outlined by the U.S. Department of Energy (DOE). For a detailed study of the thermal stability of framework, hydrogen reversibility, and mechanism of hydrogen sorption, Born–Oppenheimer molecular dynamics (BOMD) simulations are carried out at various temperatures. From the findings of BOMD simulations, the Ti-functionalized MCF can reversibly adsorb the H2 molecules with a high gravimetric density of about 9.4 wt %. This proposed Ti-functionalized MCF stands out as a potential hydrogen storage medium meeting the standards established by the DOE.

Highly symmetrical B12@Mg20C12 with icosahedral B12 motif: A potential hydrogen storage medium

A highly symmetrical core–shell Ih B12@Mg20C12 structure containing icosahedral B12 motif has been proposed in the framework of density functional theory. The core–shell B12@Mg20C12 structure has good kinetic and thermodynamic stability, which is verified by vibrational frequency analysis and molecular dynamics simulations, respectively. The analysis of the electronic structure shows that multiple atoms are connected into a whole by multi-center two-electron σ bonds, which is also the fundamental reason for the structure stability. Raman and photoelectron spectroscopy are simulated theoretically to provide characterizations for future experiments. The core–shell B12@Mg20C12 structure is a potential hydrogen storage material, which can absorb about 72 H2 molecules with a hydrogen capacity as high as 16.0 wt%.

Nitrogen-doped or boron-doped twin T-graphene as advanced and reversible hydrogen storage media

Two-dimensional (2D) carbon-based (C-based) materials can be regarded as potential hydrogen storage media because of their splendid chemical stability and high specific surface area. Recently, a new 2D carbon allotrope twin T-graphene (TTG) with three-atomic layers thick is reported. Motivated by the above exploration, we employed Density Functional Theory (DFT) computational studies to systematically solve twin T-graphene, nitrogen-doped (N-doped) TTG and boron-doped (B-doped) TTG, and evaluate their performance in hydrogen storage at operable thermodynamic conditions. Six hydrogen molecules were adsorbed on the pristine twin T-graphene, and the hydrogen storage capacity was 7.69 wt%. After N doping and B doping, the twin T-graphene both can adsorb eight hydrogen molecules, and the hydrogen storage capacity was increased to 9.88 wt% and 10.06 wt%, respectively. In addition, we found that the hydrogenation/dehydrogenation (desorption) temperature is predicted to be 241 K. The desorption temperature and desorption capacity of H2 under practical conditions further indicate that it can be used as a reversible hydrogen storage media. This study reveals that twin T-graphene, N-doped and B-doped twin T-graphene are promising hydrogen storage materials with splendid desorption temperature, ideal adsorption energy and high hydrogen storage capacity. Meanwhile, this research will expand the application of heteroatom-doped carbon-based materials.

(Digital Presentation) Electrocatalytic CO2 Reduction to Formic Acid: Kinetics and Equilibrium Modeling for the Downstream Separation of Formic Acid with Anion Exchange Resins

Electrocatalytic carbon dioxide reduction reaction (CO2RR) technology can simultaneously minimize the CO2 concentration in the atmosphere and generate useful chemicals and fuels. Liquid formic acid (FA) produced from CO2RR is a chemical feedstock for industrial purposes as well as a potential hydrogen storage medium. The downstream separation of liquid FA from the CO2RR effluent increases the total costs in addition to the electrolysis and can also affect the environment adversely. Therefore, efficient, low-cost, and environmentally benign technologies for FA separation from the CO2RR are important for life cycle analysis and techno-economic analysis for this technology. Ion exchange has been proven as an advanced process for FA separation from aqueous solution. This method has attractive due to its high selectivity, low cost, ease of operation and recovery, availability to integrate with other systems, and environmentally benign nature.In this work, three anion exchange resins: Ambersep 900 hydroxide, Amberlite IRA-96 free base, and Amberlite IRA-910 chloride forms have been tested to separate FA from the aqueous solution under varying resin loading (10-60 mg/mL) and initial FA concentration (0.05-0.50 M). The effect of potassium bicarbonate, a commonly used catholyte in electrochemical CO2RR on equilibrium FA adsorption capacity has been investigated with resin loading of 10 and 60 mg/mL under similar initial FA concentrations.Kinetics and equilibrium studies data for the FA adsorption on three resins are interpreted using several kinetics and isotherm models. The kinetics data fits better with pseudo first order at high initial FA concentration and pseudo second order at low initial FA concentration. The results show that the Ambersep 900 hydroxide form with adsorption capacity of 430.8 mg of FA per g of resin is more efficient than the Amberlite IRA-96 free base form (369.9 mg/g) and Amberlite IRA-910 chloride form (291.2 mg/g) in the absence of potassium bicarbonate in the range of parameters studied. However, Amberlite IRA-96 (153.4 mg/g) and Amberlite IRA-910 (143.4 mg/g) can separate FA more efficiently from the potassium bicarbonate aqueous solution than the Ambersep 900 (94.1 mg/g). The experimental data for all resins can be well explained with the Freundlich isotherm model. In the presence of potassium bicarbonate, competitive adsorption of bicarbonate and formic acid reduces the FA adsorption capacity of resins. Experimental and modeling results will be discussed.

A First-Principles Study on Titanium-Decorated Adsorbent for Hydrogen Storage

Based on density functional theory calculation, we screened suitable Ti-decorated carbon-based hydrogen adsorbent structures. The adsorption characteristics and adsorption mechanism of hydrogen molecules on the adsorbent were also discussed. The results indicated that Ti-decorated double vacancy (2 × 2) graphene cells seem to be an efficient material for hydrogen storage. Ti atoms are stably embedded on the double vacancy sites above and below the graphene plane, with binding energy higher than the cohesive energy of Ti. For both sides of Ti-decorated double vacancy graphene, up to six H2 molecules can be adsorbed around each Ti atom when the adsorption energy per molecule is −0.25 eV/H2, and the gravimetric hydrogen storage capacity is 6.67 wt.%. Partial density of states (PDOS) analysis showed that orbital hybridization occurs between the d orbital of the adsorbed Ti atom and p orbital of C atom in the graphene layer, while the bonding process is not obvious during hydrogen adsorption. We expect that Ti-decorated double vacancy graphene can be considered as a potential hydrogen storage medium under ambient conditions.

Enhanced hydrogen-storage properties of MgH2 by Fe–Ni catalyst modified three-dimensional graphene

High dehydrogenation temperature and slow dehydrogenation kinetics impede the practical application of magnesium hydride (MgH2) serving as a potential hydrogen storage medium. In this paper, Fe–Ni catalyst modified three-dimensional graphene was added to MgH2 by ball milling to optimize the hydrogen storage performance, the impacts and mechanisms of which are systematically investigated based on the thermodynamic and kinetic analysis. The MgH2+10 wt%Fe–Ni@3DG composite system can absorb 6.35 wt% within 100 s (300 °C, 50 atm H2 pressure) and release 5.13 wt% within 500 s (300 °C, 0.5 atm H2 pressure). In addition, it can absorb 6.5 wt% and release 5.7 wt% within 10 min during 7 cycles, exhibiting excellent cycle stability without degradation. The absorption-desorption mechanism of MgH2 can be changed by the synergistic effects of the two catalyst materials, which significantly promotes the improvement of kinetic performance of dehydrogenation process and reduces the hydrogen desorption temperature.

DFT study of hydrogen sorption on light metal (Li, Be, and Na) decorated novel fullerene-CNTs networks

Novel carbon-based periodic networks of crossed nanotubes with fullerene junctions (FNT-nets) has been designed as a potential solid hydrogen storage medium. Density functional theory calculations and molecular dynamics simulations have been performed to explore the structural stability and the hydrogen-storage potential of FNT-nets. Via the B-doping strategy, the binding energies of the alkali metal (Li, Na) and alkaline-earth metal (Be) were effectively improved to 2.47, 2.10, and 1.98 eV, respectively. The Li, Na, and Be atoms could be firmly dispersed atomically on the surface of B-FNT-nets, donating 0.732, 0.711, and 1.455 e to the substrate. The positive charge on the metal proved to be proportional to the strength of H2 polarization. Overall, up to four hydrogen molecules could be stored around one lithium with an average adsorption energy of 0.20 eV. Five hydrogen molecules were found to be around sodium and beryllium atoms with 0.17 and 0.27 eV in the range of reversible physical adsorption. The corresponding theoretical uptakes for Li@C158B22, Na@C132B24, and Be@C132B24 systems (13.95, 10.09, and 10.85 wt%, respectively) exceed the ultimate goal (6.5 wt%) as laid out by US Department of Energy. Our results reveal that the FNT-nets are good candidates for hydrogen storage.

Vacancy-Mediated Hydrogen Spillover Improving Hydrogen Storage Properties and Air Stability of Metal Hydrides.

Hydrogen storage in metal hydrides is a promising solution for sustainable and clean energy carriers. Although Mg-based metal hydrides are considered as potential hydrogen storage media, severe surface passivation has limited their industrial application. In this study, a simple, cheap, and efficient method is proposed to produce highly reactive and air-stable bulk Mg-Ni-based hydrides by rapid treatment with water for 3 min. The nickel-decorated Mg(OH)2 nanosheets formed in situ during hydrolysis can provide a pathway for hydrogen desorption via vacancy-mediated hydrogen spillover, as revealed by density functional theory calculations, thereby significantly decreasing the peak dehydrogenation temperature by 108.2 °C. Moreover, water-activated hydrides can be stored under ambient conditions without surface decay and activity loss, exhibiting excellent air stability, which can be attributed to the chemical stability of the surface layer. The results provide alternative insights into the design of highly active, air-stable metal hydrides with low cost and promote the industrial application of hydrogenenergy.

Lithium and calcium decorated triphenylene-graphdiyne as potential high-capacity hydrogen storage medium: A first-principles prediction

Recently, a novel layered two-dimensional carbon nanomaterial was synthesized named triphenylene-graphdiyne (TpG). The acetylenic ring and triphenylene are included in primitive cell of this structure. In this work, many different strategies have been adopted to investigate hydrogen storage capacity of Li- and Ca-decorated pristine and B-doped TpG by first-principles calculations. The maximum three H2 molecules are captured around every one Li atom by Li-decorated on the acetylenic ring only for TpG. The hydrogen storage gravimetric capacity of 8.17 wt% with an approximate ideal average H2 adsorption energy of 0.18 eV/H2. Moreover, both acetylenic ring and triphenylene are decorated by Li and two H2 molecules are adsorbed for each Li atom. The hydrogen storage capacity reaches to 9.70 wt% with an ideal average hydrogen adsorption energy of 0.27 eV/H2. After two C atoms are doped by B atoms, two more Li atoms are introduced to the triphenylene. Here, maximum 20 H2 molecules are adsorbed on Li-decorated B-doped TpG. The hydrogen storage capacity reaches to 8.77 wt%, with ideal average hydrogen adsorption energy of 0.24 eV/H2. Four H2 molecules can be adsorbed effectively by Ca-decorated pristine TpG with the average hydrogen adsorption energy of 0.19 eV/H2. We also calculated the H2 storage of Ca-decorated B-doped TpG and 5.51 wt% of gravimetric with ideal average hydrogen adsorption energy of 0.25 eV/H2 can be obtained. Our calculation indicates that the Li- and Ca-decorated B-doped TpG and Li-decorated pristine TpG can be a very promising material for reversible hydrogen storage.

Synthesis and characterization of microporous hybrid nanocomposite membrane as potential hydrogen storage medium towards fuel cell applications

Hydrogen is believed to be the clean energy source for the future, since water is the only by-product of hydrogen fuel cell. However, the great obstacle for the blooming of hydrogen economy is the development of safe, efficient, and economical onboard hydrogen storage medium. This paper describes the hydrogen storage performance of microporous polyetherimide/acid-treated halloysite nanotube/activated hexagonal boron nitride (PEI/A-HNT/Ah-BN) hybrid nanocomposite membranes. The microporous PEI/A-HNT/Ah-BN hybrid nanocomposite membranes were synthesized by a facile phase inversion technique. The synthesized hybrid nanocomposite membranes were characterized extensively by techniques like X-ray diffraction (XRD), micro-Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and CHNS elemental analysis. The microporous throughout the membrane matrix and the superior dispersion of A-HNT, Ah-BN nanomaterials on the surface of PEI were confirmed by SEM. The hydrogen storage properties were investigated by Sieverts-like hydrogenation setup. The outcomes indicated that the PEI/A-HNT/Ah-BN hybrid nanocomposite membrane exhibits best hydrogen storage capacity as 4.2 wt% compared with PEI/A-HNT (3.6 wt%), PEI/Ah-BN (2.4 wt%), and pristine PEI (0.8 wt%) membranes. Furthermore, the binding energy of stored hydrogen for PEI/A-HNT/Ah-BN hybrid nanocomposite is found to be 0.32 eV. In addition, the reusability of PEI/A-HNT/Ah-BN hybrid nanocomposite was studied and also exhibited good long-term stability (91.43%) even after 5th cycles. These results indicate that the proposed microporous PEI/A-HNT/Ah-BN hybrid nanocomposite membrane strategy provides a direction for new materials that meet the U.S. Department of Energy (DOE) hydrogen storage targets 2020 for fuel call applications.

New Insight on the Hydrogen Absorption Evolution of the Mg–Fe–H System under Equilibrium Conditions

Mg2FeH6 is regarded as potential hydrogen and thermochemical storage medium due to its high volumetric hydrogen (150 kg/m3) and energy (0.49 kWh/L) densities. In this work, the mechanism of formation of Mg2FeH6 under equilibrium conditions is thoroughly investigated applying volumetric measurements, X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and the combination of scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and high-resolution transmission electron microscopy (HR-TEM). Starting from a 2Mg:Fe stoichiometric powder ratio, thorough characterizations of samples taken at different states upon hydrogenation under equilibrium conditions confirm that the formation mechanism of Mg2FeH6 occurs from elemental Mg and Fe by columnar nucleation of the complex hydride at boundaries of the Fe seeds. The formation of MgH2 is enhanced by the presence of Fe. However, MgH2 does not take part as intermediate for the formation of Mg2FeH6 and acts as solid-solid diffusion barrier which hinders the complete formation of Mg2FeH6. This work provides novel insight about the formation mechanism of Mg2FeH6.

Li-decorated carbon ene-yne as a potential high-capacity hydrogen storage medium.

Based on comprehensive first-principles calculations, we predict that Li-decorated carbon ene-yne (CEY) can serve as a reversible and high density hydrogen storage medium. The adsorption structures, charge transfer, electronic properties and energy storage characteristics of Li-decorated CEY are investigated. It is established that Li can bind strongly to sp and sp2 hybridized CEY without the formation of Li clusters. The strong interaction between Li and CEY is attributed to the sp binding C px/py states which hybridize heavily with the Li 2s/2p states. After Li decoration, CEY undergoes a transition from a semiconductor to a metal. Each Li atom anchors seven H2 molecules with the average adsorption energy falling in a suitable range (-0.2 to -0.4 eV per H2). The adsorption mechanism of H2 molecules has also been discussed. Two Li atom decorated CEY can obtain up to a 9.96 wt% hydrogen storage capacity.

Hydrogen storage capacity on Ti-decorated porous graphene: First-principles investigation

Hydrogen storage capacity on Titanium (Ti) decorated porous graphene (PG) has been investigated using density functional theory simulations with generalized gradient approximation method. The possible adsorption sites of Ti atom on PG and electronic properties of Ti-PG system are also discussed.The results show a Ti atom prefers to strongly adsorb on the center site above the C hexagon with the binding energy of 3.65eV, and the polarization and the hybridization mechanisms both contribute to the Ti atom adsorption on PG. To avoid a tendency of clustering among Ti atoms, the single side of the PG unit cell should only contain one Ti atom. For the single side of PG, four H2 molecules can be adsorbed around Ti atom, and the adsorption mechanism of H2 molecules come from not only the polarization mechanism between Ti and H atoms but also the orbital hybridization among Ti atom, H2 molecules and C atoms. For the case of double sides of PG, eight H2 molecules can be adsorbed on Ti-decorated PG unit cell with the average adsorption energy of −0.457eV, and the gravimetric hydrogen storage capacity is 6.11wt.%. Furthermore, ab inito molecular-dynaics simulation result shows that six H2 molecules can be adsorbed on double sides of unit cell of Ti-PG system and the configuration of Ti-PG is very stable at 300K and without external pressure, which indicates Ti-decorated PG could be considered as a potential hydrogen storage medium at ambient conditions.

The high hydrogen storage capacities of Li-decorated borophene

In this work, we calculate stabilities, electronic properties and hydrogen adsorption properties of Li-decorated freestanding borophene. It was studied through three functionals (vDW, LDA and PBE) of the first principles density functional theory (DFT) methods. It was found that the adsorption energy ofH2 on the pure borophene was small. The Li atoms decoration can improve the H2adsorption capacity. By virtue of the larger binding energy than that for bulk Li, Li atoms can be adsorbed steadily and not form the clusters on the 2×2 borophene supercell surface. For single Li atom adsorbed, the maximum number ofuptake is three hydrogen molecules. But for Li adsorbed on both sides of borophene, each Li atom can absorb up to four H2 molecules. Its hydrogen storage capacity reaches up to 13.7wt% with an average adsorption energy of 0.142 and 0.176eV/H2 for vDW and LDA functional without the consideration of temperature, respectively.At the room temperature, the hydrogen capacity is up to 9.1wt%. This study suggests that Li-decorated borophene is a potential hydrogen storage medium.

Improved hydrogen desorption properties of MgH2 by graphite and NiF2 addition: experimental and first-principles investigations

The high dehydrogenation temperature is still the impediment for the practical application of magnesium-based hydride (MgH2) as a potential hydrogen storage medium. In order to improve the hydrogen desorption properties of MgH2, the graphite and NiF2 are selected as additives, and the MgH2–graphite and MgH2–graphite–NiF2 composites are prepared by high-energy ball milling. Using experimental X-ray diffraction, scanning electron microscopy, differential scanning calorimetry characterizations and first-principle calculations, the effects and mechanisms of graphite and NiF2 addition on the hydrogen desorption properties of MgH2 are systematically investigated. Experimental results show that the single addition of graphite is beneficial to the refinement of MgH2 grains and particles. The size of MgH2 particles can be further decreased after the co-addition of graphite and NiF2. Either the single addition of graphite or the co-addition of graphite and NiF2 reduces the dehydrogenation temperature of MgH2. As compared with pure milled MgH2, the dehydrogenation peak temperatures are decreased by 31 and 63 °C for MgH2–graphite and MgH2–graphite–NiF2 composites, respectively. Apparently, the co-addition of graphite and NiF2 exhibits the synergistic catalytic effects in improving the hydrogen desorption properties of MgH2. The first-principle calculations reveal that the co-addition of graphite and NiF2 leads to the structural distortion of MgH2 and results in the charge transfer between the additives and MgH2, which induce the weakened structural stability and decreased dehydrogenation enthalpy of MgH2. These may be the underlying reasons for the reduced dehydrogenation temperature of MgH2 with graphite and NiF2 addition.

Chemical grafting of Co9S8 onto C60 for hydrogen spillover and storage.

Metal modified C60 is considered to be a potential hydrogen storage medium due to its high theoretical capacity. Research interest is growing in various hybrid inorganic compounds-C60. While the design and synthesis of a novel hybrid inorganic compound-C60 is difficult to attain, it has been theorized that the atomic hydrogen could transfer from the inorganic compound to the adjacent C60 surfaces via spillover and surface diffusion. Here, as a proof of concept experiment, we graft Co9S8 onto C60via a facile high energy ball milling process. The Raman, XPS, XRD, TEM, HTEM and EELS measurements have been conducted to evaluate the composition and structure of the pizza-like hybrid material. In addition, the electrochemical measurements and calculated results demonstrate that the chemical "bridges" (C-S bonds) between these two materials enhance the binding strength and, hence, facilitate the hydriding reaction of C60 during the hydrogen storage process. As a result, an increased hydrogen storage capacity of 4.03 wt% is achieved, along with a favorable cycling stability of ∼80% after 50 cycles. Excluding the direct hydrogen storage contribution from Co9S8 in the hybrid paper, the hydrogen storage ability of C60 was enhanced by 5.9× through the hydriding reaction caused by the Co9S8 modifier. Based on these experimental measurements and theoretical calculations, the unique chemical structure reported here could potentially inspire other C60-based advanced hybrids.

Hydrogen adsorption and storage on Palladium – functionalized graphene with NH-dopant: A first principles calculation

We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0K with an average binding energy in the range 1.315–0.567eVA gravimetric hydrogen density of 3.622wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H2 molecules, which helps also to avoid the desorption of Pd(H2)n (n=1–5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

Calcium decorated two dimensional carbon allotropes for hydrogen storage: A first-principles study

Graphene has attracted tremendous interest as a potential hydrogen storage medium due to its extraordinary properties granted by its two-dimensional nature. In this study, we investigated the hydrogen storage ability of five 2D carbon allotropes: C40, C41, C63, C64 and C65 with calcium decoration by adopting the first-principles method based on density functional theory. The probable adsorption sites for a Ca atom and different Ca coverages were examined, and the hydrogen molecules were added one by one to investigate the maximum hydrogen gravimetric density. Our results show that Ca atom prefers to stay on the hollow site above the largest polygons instead of small polygons. Up to 6 hydrogen molecules can be adsorbed on one single Ca atom with the average adsorption energy in the reasonable range. The hydrogen gravimetric density for these carbon allotropes with Ca decoration are 3.53–4.48wt.% at low Ca coverage and 7.5–8.57wt.% at high Ca coverage.