Doped Graphene Research Articles

The effect of non-metals (O, F) dopant on the electronic structure, Dirac cone, and optical characteristics of graphene sheets applicable for gas sensing

In order to gain a systematic comprehension of the impacts of low-level defects in graphene, ab-initio calculations were performed on monolayer graphene sheets to examine how oxygen and fluorine substitutional impurities affect their energetic stability, electronic and optical characteristics. The optimal configurations, structural stability, electronic band structures, spatial charge density, and optical spectra of graphene single-layer materials doped with oxygen and fluorine atoms are investigated. The fluorine-doped graphene, therefore, showed a lower formation energy than its oxygen-doped counterpart. Additionally, F-doped graphene shows a higher charge density around the fluorine atom than O-doped graphene. Based on band structure analysis, the lower conduction bands of graphene sheets shift below the Fermi state (EF) when two O or F impurities are substituted into it. With two O/F impurity atoms doped into graphene, the conduction states are farther displaced below the EF, resulting in n-type behavior. Consequently, altering graphene structure via an O/F-substituting scheme results from the disruption of the Dirac cone near EF, which has become flat along the high symmetry point (K-point) in the Brillouin zone. Furthermore, the substitution of graphene sheets via O or F impurities exhibit markedly modified optical spectra and refractive indices at low photon energies. As a result, with one or two O/F impurity elements inserted into graphene sheets, the reflectivity and optical conductivity spectra differ at the lowest electromagnetic radiation ranges. Additionally, the electron energy loss functions as well as X-ray absorption spectra of clean and doped graphene monolayers revealed spectral variations at a moderate energy span. These investigations surmise that novel chemical modifications to graphene sheets doped with light non-metallic elements (O/F) may offer the opportunity to tailor their optical characteristics in the infrared spectrum, which may be beneficial in sensor and electrocatalyst uses.

Performance metrics of doped graphene nanoribbons based nanoscale interconnects: DFT and NEGF analysis

Due to the scaling of devices, the interconnects delay is the most important concern of the current technology, becomes more significant than the IC delay, and leads to overall impact on the performance of the chip. In the present work, doped Zigzag Graphene Nano ribbons (GNR) have been analyzed for the possible nanoscale interconnect applications. The investigation has been performed using the density-functional theory-based ab-initio approach, discussed in terms of structural stability of ribbons, their electronic and transport properties, and the dynamical parameters. Zigzag GNR has been decorated with itssix possible sites along the width, through P and N type impurities, to select the most favorable site for the further analysis. The stability of the systems has been analyzed in terms of formation energy, the electronic properties in terms of band structure and density of states profiles, whereas, the transport properties in terms of transmission spectrum and I–V characteristics. The magnetic inductance, kinetic inductance, electrostatic capacitance, and quantum capacitance have also been calculated as interconnect parameters. The formation energy calculations suggest that the doping at the edge sites of NRs are more favorable. Further, it has been observed that the metallicity of the doped ZGNR enhances with doping, whereas, the I–V characteristics confirms that the N doped ZGNRs have linear current with constant slope. The performance metrics of ZGNRs have also been analyzed using HSPICE, discussed in terms of delay and power delay product, shows that the N doped ZGNRs have lower delay than the other considered counterparts, defends its application as interconnects in the electronic industry.

Activating doped graphene surface by cobalt-rich sulfide encapsulation toward oxygen reduction electrocatalysis

Similar to proton exchange membrane fuel cell, anion-exchange membrane fuel cell is also a significant energy conversion device for achieving the utilization of clean hydrogen energy. However, the cathodic alkaline oxygen reduction reaction (ORR) is kinetically not favored and usually requires platinum-group metal (PGM) catalysts such as Pt/C to reduce the overpotential. The major challenge in using PGM-free catalysts for ORR is their low efficiency and poor stability, which urgently demands new concepts and strategies to address this issue. Herein, we controllably manufactured a N, S-co doped graphene encapsulating uniform cobalt-rich sulfides (Co8FeS8@NSG) by a universal synthesis strategy. After encapsulation, electron transfer from the encapsulated cobalt-rich sulfides to the doped graphene was greatly promoted, which effectively optimizes the electronic structure of the doped graphene, thereby enhancing the ORR activity of the doped graphene surface. Consequently, the Co8FeS8@NSG exhibits enhanced ORR activity with a higher half-wave potential of 0.868 V (versus reversible hydrogen electrode, vs. RHE) when compared with pure NSG (0.765 V vs. RHE). Density functional theory calculations further confirm that the construction of interface for NSG encapsulating cobalt-rich sulfides could conspicuously elevate the ORR activity through slightly positively-charged C active site and thus simultaneously enhancing electronic conductivity.

Optical monitoring of adsorption of chromium (VI) molecular anions, molecules and clusters on carbon nanomaterials

Search for efficient adsorbent materials for removal of hexavalent chromium compounds from environment is a topical technological problem. In this paper, the possibility of optical monitoring of the adsorption of chromium (VI) molecular compounds on the surface of carbon nanomaterials (CNM) is examined. Theoretical calculations of optical absorption spectra of CrO42- anions and molecular clusters of such anions with metals, n*K2CrO4 (n = 1, 2, 4) and MIICrO4 (MII = Zn, Cd, Pb) adsorbed on the surfaces of bare and doped carbon nanotubes and graphene are carried out by TD-DFT method. Results of calculations are compared with experimental data on optical transmission, diffuse reflection and photoluminescence of specially prepared samples containing chromate molecular compounds and particles adsorbed on CNM.It is shown that adsorption of CrO42- anions by CNM can be detected by the appearance of characteristic bands in diffuse reflectance spectra in 310–380 nm region. Nanoparticles of K2CrO4 crystal adsorbed on CNM reveal an additional luminescence band in 600–700 nm region, and it can be utilized in the monitoring of such adsorption. The effect of CNM surface on optical spectra of chromium (VI) molecular compounds is analyzed in terms of splitting of excited electronic states of quasi-tetrahedral CrO42- anions.

Boosting of polyurethane elastomer nanocomposites by low doped graphene

Graphene reinforced polyurethane elastomer (PUE) nanocomposites have been developed for decades, and much work has focused on grafting functional groups and eliminating agglomeration to reduce the number of layers for achieving enhanced performance can meet in various requires. Generally, graphene with low oxygen functional groups is considered to be unable to compatible with polymers due to their mismatched polarity and low interfacial interaction. However, our study reported a new strategy by endowing graphene a low oxygen content, via solvent-free casting synthesis method, the small size graphene (SG) with slight polarity could be well soaked in the polyether polyols and then be uniform dispersed in PUE nanocomposites at low loading level and exhibit a multi-enhanced performance. Our research indicating that no more effort needs to be devoted to the grafting or exfoliating of graphene, this low-cost green synthesis is of great significance for the industrial application.

Effects of Heteroatom Doping and Physicochemical Character on the Electrochemical Properties of Graphene Sheets

AbstractGraphene attracted great interest in the electrochemical applications due to its stability and extremely high surface area‐to‐mass ratio. Wet chemical and electrochemical synthesis allow affordable and single to multilayer graphenes with functional groups that contribute to surface accessibility, and electrolyte diffusion. These materials also have faradaic and pseudocapacitive reaction sites which enhance the electrochemical performance while altering their capacitive nature based on reaction type and density of these sites. Therefore, heteroatom doping of graphene has been studied widely, and various outcomes, some of which have been controversial, were reported. In this study, we investigated the doping modification with multiple samples and also conduct a detailed physicochemical characterization. Oxidation‐reduction and electrochemical exfoliation methods were utilized to synthesize pristine, nitrogen‐doped, and phosphorus‐doped reduced graphene oxide as well as the phosphorus‐doped and pristine electrochemically exfoliated graphene materials. Samples have been characterized in terms of doping level, particle size, number of layers, defect density, and exfoliation homogeneity. Electrochemical measurements showed that surface wrinkling property among similarly large rGO particles (~9x) and small lateral particle size (~2x) of graphenes are effective in determination of specific capacitance (Cspecific) and capacitive characteristic of samples while heteroatom doping doesn't produce any significant change on these properties.

In Situ Synthesis of Doped Bio-Graphenes as Effective Metal-Free Catalysts in Removal of Antibiotics: Effect of Natural Precursor on Doping, Morphology, and Catalytic Activity.

Wastewater contaminated with antibiotics is a major environmental challenge. The oxidation process is one of the most common and effective ways to remove these pollutants. The use of metal-free, green, and inexpensive catalysts can be a good alternative to metal-containing photocatalysts in environmental applications. We developed here the green synthesis of bio-graphenes by using natural precursors (Xanthan, Chitosan, Boswellia, Tragacanth). The use of these precursors can act as templates to create 3D doped graphene structures with special morphology. Also, this method is a simple method for in situ synthesis of doped graphenes. The elements present in the natural biopolymers (N) and other elements in the natural composition (P, S) are easily placed in the graphene structure and improve the catalytic activity due to the structural defects, surface charges, increased electron transfers, and high absorption. The results have shown that the hollow cubic Chitosan-derived graphene has shown the best performance due to the doping of N, S, and P. The Boswellia-derived graphene shows the highest surface area but a lower catalytic performance, which indicates the more effective role of doping in the catalytic activity. In this mechanism, O2 dissolved in water absorbs onto the positively charged C adjacent to N dopants to create oxygenated radicals, which enables the degradation of antibiotic molecules. Light irradiation increases the amount of radicals and rate of antibiotic removal.

Enhancing persulfate activation by carbon − based Mn − Fe nanoparticles for groundwater ISCO treatment: Efficiency, stability and mechanism

Persulfate − based in situ chemical oxidation (ISCO) is a promising approach for groundwater treatment due to its potential. However, the development of catalysts with sufficient activity and stability in persulfate oxidation remains a long − term goal. In this study, we aimed to address this challenge by preparing bimetallic nanoparticles coated with porous nitrogen − doped graphene shells, known as MnFe − NC, to activate peroxydisulfate (PDS). The unique structural feature of MnFe − NC, with metallic crystal nanoparticles encapsulated in carbon shells, ensured excellent persulfate activation performance of MnFe − NC, even during repeated cycles and extended periods of storage. To evaluate the practical application of MnFe − NC, MnFe − NC/PDS was installed in sand columns for the ISCO of sulpiride (SPR), achieving removal efficiencies of approximately 100 % during a continuous 7 − day reaction process. MnFe − NC/PDS exhibited remarkable tolerance to pH changes and environmental interference commonly encountered in groundwater treatment scenarios. Combined with density functional theory calculations, Mn5C2 and Fe2N were identified as the key active site for MnFe − NC activation of PDS. The decomposition mechanism of SPR in the system was further analyzed, including the cleavage of C–N/C–C, denitration reaction, and substitution reaction. These findings provide important insights into the intricate processes involved in the degradation of refractory organic pollutants. The developed MnFe − NC catalyst for PDS − based ISCO exhibits great potential in the remediation of refractory organic pollutant − contaminated groundwater.

High-performance electrochemical detection of glucose in human blood serum using a hierarchical NiO2 nanostructure supported on phosphorus doped graphene

This report describes the development of high-performing non-enzymatic glucose sensors based on a combination of a phosphorous doped graphene (PG) layer and a composite metal oxide. Using a reflux technique and high-temperature annealing, a combined sheet-like NiO2@PG nanocomposite was created. This structure was examined using a variety of physicochemical methods, including thermogravimetric analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. The NiO2@PG nanocomposite offers a large surface area and an easily penetrable structure, allowing for greater chemical sensitivity to glucose oxidation. The dynamic range of the developed glucose sensor is relatively broad, ranging 10–170 μM. It exhibits a sensitivity of 70.28 μA μM−1 cm−2 , a small limit of detection of 7.83 μM, with a rapid response time of 1.07 s. The sensor also shows outstanding selectivity, long-term stability, reproducibility, and favorable repeatability, and can detect glucose in human serum samples. Additionally, the NiO2@PG composites sensing ability can be enhanced through ligand-to-metal charge-transfer, as validated by density functional theory. Studies on the mechanism of sensing and chemical structure of the composite after stabilization suggest it should prove useful in real-world applications.

All-Solid-State Mg-Air Battery Enhanced with Free-Standing N-Doped 3D Nanoporous Graphene.

Nitrogen (N) doping of graphene with a three-dimensional (3D) porous structure, high flexibility, and low cost exhibits potential for developing metal-air batteries to power electric/electronic devices. The optimization of N-doping into graphene and the design of interconnected and monolithic graphene-based 3D porous structures are crucial for mass/ion diffusion and the final oxygen reduction reaction (ORR)/battery performance. Aqueous-type and all-solid-state primary Mg-air batteries using N-doped nanoporous graphene as air cathodes are assembled. N-doped nanoporous graphene with 50-150nm pores and ≈99% porosity is found to exhibit a Pt-comparable ORR performance, along with satisfactory durability in both neutral and alkaline media. Remarkably, the all-solid-state battery exhibits a peak power density of 72.1mW cm-2 ; this value is higher than that of a battery using Pt/carbon cathodes (54.3mW cm-2 ) owing to the enhanced catalytic activity induced by N-doping and rapid air breathing in the 3D porous structure. Additionally, the all-solid-state battery demonstrates better performances than the aqueous-type battery owing to slow corrosion of the Mg anode by solid electrolytes. This study sheds light on the design of free-standing and catalytically active 3D nanoporous graphene that enhances the performance of both Mg-air batteries and various carbon-neutral-technologies using neutral electrolytes.

Electrochemical sensor based on nitrogen-fluorine double doped graphene composite for dopamine detection

Metal-free catalysts with low cost and long - term stability are considered as the most promising electrocatalysts. Nitrogen-fluorine double doped graphene (NFG) was prepared by hydrothermal method which includes the reduction of graphene oxide by triethylamine trihydrofluorate as a novel dopamine (DA) electrochemical sensor. The morphologies and structures of GO and NFG were characterized via scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectra and BET. Cyclic voltammetry, and differential pulse voltammetry were used to investigate the electrochemical behavior of DA on the NFG/glassy carbon electrode (GCE). Impressively, all the fluorine in NFG is in the form of carbon-fluorine semi-ionic bonds. Based on these characteristics, the prepared nitrofl-doped graphene showed high performance in the electrochemical detection of DA. In the ranges of 1–50 μM, the peak current exhibited an excellent linear relationship with DA concentration and the detection limit was 0.3 μM. The proposed sensor has high sensitivity, low-detection limit, and a wide linear range. Notably, the adsorption of H+ by the carbon-fluorine semi-ionic bond accelerates the oxidation of DA. The synergistic effect between N, F and rGO affects the oxidation of DA, which is confirmed by the calculation of density functional theory (DFT).

Outstanding inhibition of H2O2 generation in doubly doped graphene: The synergy of two heteroatoms opens a new chemical path

Dual sulfur-nitrogen (SN) doped graphene surfaces have been revealed as a powerful active material in fuel cell applications. The experimental results presented in this work show a clear preference of the material doped with SN towards a 4-electron mechanism, almost completely inhibiting the formation of H2O2. However, materials doped only with nitrogen (N) or sulfur (S) favor the 2-electron mechanism, and therefore, the production of H2O2. A reasonable theoretical explanation is proposed to justify the inhibition of the H2O2 reaction with the use of SN doped graphenes in accordance with the experimental results. The interactions and charge transfer between N and S are the origin of an alternative dissociative step that inhibits the generation of H2O2, which is energetically favored, according to Density Functional Theory (DFT) calculations. These two dopant atoms generate a frustrated Lewis pair (FLP), resulting in an enhancement of the catalytic activity of the graphene. Atomic Dipole Corrected Hirshfeld charges (ADCH model) and Non-Covalent Interactions (NCI) are employed to identify the most active sites and support the explanation of the dissociative pathway which inhibits H2O2 formation.

Density Functional Theory Analysis of the Impact of Boron Concentration and Surface Oxidation in Boron-Doped Graphene for Sodium and Aluminum Storage

Graphene is thought to be a promising material for many applications. However, pristine graphene is not suitable for most electrochemical devices, where defect engineering is crucial for its performance. We demonstrate how the boron doping of graphene can alter its reactivity, electrical conductivity and potential application for sodium and aluminum storage, with an emphasis on novel metal-ion batteries. Using Density Functional Theory calculations, we investigate both the influence of boron concentration and the oxidation of the material on the mentioned properties. It is demonstrated that the presence of boron in graphene increases its reactivity towards atomic hydrogen and oxygen-containing species; in other words, it makes B-doped graphene more prone to oxidation. Additionally, the presence of these surface functional groups significantly alters the type and strength of the interaction of Na and Al with the given materials. Boron-doping and the oxidation of graphene is found to increase the Na storage capacity of graphene by a factor of up to four, and the calculated sodiation potentials indicate the possibility of using these materials as electrode materials in high-voltage Na-ion batteries.

How do defects affect hydrogen spillover on graphene-supported Pt? A DFT study

Hydrogen dissociation, adsorption, and spillover on Pt4 supported on defective graphene that contains vacancy defects, such as single and di-vacancy graphenes (SVG and DVG), have been studied using density functional theory (DFT) with dispersion correction (Grimme-D3). Vacancy defects lead to n-type doping of graphene from the Pt4 cluster, which is contrary to the p-type doping on pristine graphene. Also, the metal–support interactions increase with the presence of a vacancy defect as indicated by more negative Pt4 binding energies on the SVG, and 5-8-5, 5555-6-7777, and 555–777 DVGs of −8.60, −4.51, −4.15 and −3.63 eV, respectively, compared to that on pristine graphene (−2.16 eV). Atomic hydrogen adsorption is more stable on all defective graphenes with adsorption energies of −2.24, −0.16, 0.05, and −0.27 eV for SVG, 5-8-5, 5555-6-7777, and 555–777 DVGs, respectively, as compared to that on pristine graphene (+1.38 eV). Spontaneous hydrogen dissociative adsorption on the two-fold coordinated C site of bare SVG occurs with an adsorption energy per hydrogen atom of −1.77 eV, while those on the three types of DVGs are in the range of ∼0.03–0.29 eV; these are all more stable than those on pristine graphene that fall in the range of 0.89–1.53 eV. The energy barriers for hydrogen spillover from Pt4 to the defective graphene are 0.91, 1.09, 0.90, and 0.71 eV for SVG, 5-8-5, 5555-6-7777, and 555–777 DVGs, respectively. Ab initio molecular dynamics (AIMD) simulations show that the adsorption of up to six hydrogen molecules, with and without spillover, on the four Pt4/defective graphene systems, is stable at room temperature. This study demonstrates that the presence of vacancy defects on graphene could improve hydrogen adsorption and spillover. A trend is discovered—when the magnitude of binding energies of metal–support interaction is stronger than −3.5 eV and the adsorption energies of atomic hydrogen on the support are negative or close to zero, there is potential to facilitate the occurrence of hydrogen spillover, correlating with the hydrogen storage capacity of the materials. Thus, our findings could provide useful criteria for designing hydrogen storage materials and a fundamental understanding of the correlation between metal–support interactions and hydrogen spillover mechanisms.

Nitrogen and aluminum-nitrogen doped graphene for non-volatile resistive memory applications

Doping is a key strategy used to tune the electronic properties of graphene. Calculations have shown that graphene doped with Al has potential applications in the sensing of toxic gases. However, the realization of Al-doped graphene in experiments has proven to be a challenge. In this study, we successfully doped graphene with both N and a combination of Al and N using a microwave process suitable for large-scale production. Several characterization methods such as Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), and energy dispersive x-ray spectroscopy (EDX) were used to confirm the composition, and therefore the successful doping, of the graphene. Doping and co-doping are found to increase the conductivity of graphene. It is also demonstrated that the doped graphene shows well-defined resistive memory properties when included in a sandwich structure consisting of polystyrene/doped graphene/polystyrene. The on-and-off voltage is found to be 2 V, making the Al-N co-doped graphene suitable for applications in resistive memory devices.

Improving the anti-corrosive performance of epoxy/zinc composite coatings with N-doped 3D reduced graphene oxide

Three-dimensional reduced graphene oxide (3DRGO) doped with N heteroatoms was innovatively incorporated into a Zn-containing epoxy (EP/Zn) composite coating. Comprehensive investigations that introducing 3DRGO significantly improved the anti-corrosion performance of the coating, and the optimal 3DRGO content was only 0.05 wt%. The effects of both the spatial structure and chemical doping of graphene on the surface protection performance of their EP/Zn coating were revealed for the first time. Compared with the conventional 2-dimensional reduced GO (RGO) sheets and 3D graphene (3DG) with similar 3D structures, 3DRGO exhibited superior effect on promoting the corrosion resistance of its composite coating. This can be attributed to not only the unique 3D porous strut structure of 3DRGO, but also its N-doping, which plays important roles in increasing its interaction with the epoxy matrix, preventing 3DRGO agglomeration, improving the barrier property of the coating, facilitating the construction of an electrical conduction network between Zn particles, and exploiting the cathodic protection function of Zn more efficiently.

G phonon linewidth and phonon-phonon interaction in p-type doped CVD graphene crystals

We employed conventional and time-resolved Raman spectroscopy to study the effects of electron-phonon and phonon-phonon interactions on the linewidth of the G phonon in both unintentionally and intentionally doped polycrystalline chemical vapor deposited (CVD) graphene samples. We directly measured the G phonon lifetime, observing a ≈14% decrease with doping up to EF = 270 meV. The anticipated reduction of G phonon linewidth due to a decrement in electron-phonon contribution deviates from first principles calculations. CVD samples exhibit a ≈30% decrease in the electron-phonon coupling constant, λΓ(EF = 0), compared to exfoliated graphene samples. Additionally, phonon-defect scattering makes a significant contribution to the G band linewidth in CVD graphene samples, owing to their lower crystal quality compared to exfoliated graphene.

Fine-Tuning of the Electronic and Optical Properties of Dodecabenzocoronene through Boron and Nitrogen Doping: A DFT Insight

Nanographene provides a wide range of possibilities in graphene engineering for future applications due to the higher degrees of configurational freedom with the electronic parameters that may also be continuous or discrete, depending on the intended application. Therefore, the optical and electronic properties of nanographene are of substantial technological interest. Moreover, doping of graphene with heteroatoms (B, P, N, and S, etc.) alters their chemical and electronic characteristics which are suitable for the economical construction of optoelectronic devices. Herein, geometric, electronic, and optical properties of nanographene are evaluated as a function of the nature and position of dopant. Three different nanographene including coronene, hexabenzocoronene (HBC), and dodecabenzocoronene (DBC) are considered for doping (N and B as dopants) in this study with the key focus on DBC-doped systems. For any dopant number, all possible dopant sites are studied except edge position in order to avoid the edge effect. Frontier molecular orbital (FMO) analysis is performed to evaluate the perturbations in electronic characteristics of doped nanographene. A decrease in energy gap is seen for all doped systems. Natural bond orbital (NBO) analysis indicates that doping of boron (B) and nitrogen (N) results in variation in distribution of charges over the nanographene surfaces. The density of states (DOS) analysis reveals that Fermi level ([Formula: see text] is shifted for all B- and N-doped systems. The UV-visible (UV-Vis) absorption spectra are computed to evaluate the changes in the intensity and maximum adsorption wavelength ([Formula: see text] in all doped DBC. Various chemical reactivity descriptors are also evaluated which reveal the degree of stability and chemical reactivity of doped systems. The results indicate that multiple B and N atoms doping offers a new possibility for fine-tuning of electronic and optical properties of nanographene at atomic level, thus providing guidance in development of future advanced optoelectronic devices.

Understanding adsorption of divalent metals ions (Mg, Ca) on Nitrogen-, Boron- doped, and defective graphene in nanofiltration process using van der Waals density functional method

Removal of divalent metal ions (Mg and Ca) by graphene membrane has a great implication for manufacturing chitin and chitosan in filtration process. Despite its importance, influences of the doping and vacancy in graphene on the adsorption of those metal ions remain unclear. Here, we study the adsorption of those metal ions on several graphene surfaces, namely pristine graphene (Gra), graphitic N- and B- doped graphene (N- and B-Gra), monovacancy graphene (MV-Gra), monovacancy graphene functionalized by an epoxy (O-MV-Gra), and monovacancy graphene functionalized by an hydroxyl group (OH-MV-Gra) by van der Waals density functional (vdW-DF) method. It was found all considered graphene surfaces have strong interactions with Ca, whereas Mg only chemisorbs on MV-Gra and B-Gra. Energetically, comparing with Ca adosprtion on pristine graphene, both B doping and vacancy creation strengthen the Ca adsorption, while N doping slight decreases it. The electronic structure analysis uncovers enhancement of the Cagraphene interaction by B doping and vacancy formation. Because of the results that have been observed, the removal of Ca ions from aqueous solution can be enhanced by the creation of nanopore or B doping in graphene, in which Ca atom are strongly captured by graphene.

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.