Doped Graphene Surface Research Articles

Theoretical calculation study on enhancing the sensitivity and optical properties of graphene adsorption of nitrogen dioxide via doping

In order to study the adsorption of NO<sub>2</sub> on pristine graphene and doped graphene (N-doped, Zn-doped, and N-Zn co-doped), we simulate the adsorption process by applying the first-principles plane-wave ultrasoft pseudopotentials of the density-functional theory in this work. The adsorption energy, Mulliken distribution, differential charge density, density of states, and optical properties of NO<sub>2</sub> molecules adsorbed on the graphene surface are calculated. The results show that the doped graphene surface exhibits higher sensitivity to the adsorption of NO<sub>2</sub> compared with the pristine graphene surface, and the order of adsorption energy is as follows: N-Zn co-doped surface > Zn-doped surface > N-doped surface > pristine surface. Pristine graphene surface and N-doped graphene surface have weak interactions with and physical adsorption of NO<sub>2</sub>. Zn-doped graphene surfac and N-Zn co-doped graphene surface form chemical bonds with NO<sub>2</sub> and are chemisorbed. In the visible range, among the three doping modes, the N-Zn co-doped surface is the most effective for improving the optical properties of graphene, with the peak absorption and reflection coefficients improved by about 1.12 and 3.42 times, respectively, compared with pristine graphene. The N-Zn co-doped graphene not only enhances the interaction between the surface and NO<sub>2</sub>, but also improves the optical properties of the material, which provides theoretical support and experimental guidance for NO<sub>2</sub> gas detection and sensing based on graphene substrate.

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.

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.

Investigation of glucose electrooxidation mechanism over N-modified metal-doped graphene electrode by density functional theory approach.

In this work, various precious and non‐precious metals reported in the literature as the most effective catalysts for glucose electrooxidation reaction were investigated by the density functional theory (DFT) approach in order to reveal the mechanisms taking place over the catalysts in the fuel cell. The use of a single‐atom catalyst model was adopted by insertion of one Au, Cu, Ni, Pd, Pt, and Zn metal atom on the pyridinic N atoms doped graphene surface (NG). β form of d‐glucose in alkaline solution was used to determine the reaction mechanism and intermediates that formed during the reaction. DFT results showed that the desired glucono‐lactone was formed on the Cu‐3NG electrode in a single‐step reaction pathway whereas it was produced via different two‐step pathways on the Au and Pt‐3NG electrodes. Although the interaction of glucose with Ni, Pd, and Zn‐doped surfaces resulted in the deprotonation of the molecule, lactone product formation did not occur on these electrode surfaces. When the calculation results are evaluated in terms of energy content and product formation, it can be concluded that Cu, Pt, and especially Au doped graphene catalysts are effective for direct glucose oxidation in fuel cells reactor.

Boron doped graphene as anode material for Mg ion battery: A DFT study

The bivalent nature of Mg offers the possibility of storing more charge per ion that could allow the building of batteries with higher energy density. Currently, the promised potential of Mg ion battery (MIB) is far to achieve owing to the lack of an appropriate electrolyte, since Mg metal used as anode in MIB is not compatible with common battery electrolytes. Carbon-based electrodes function well with conventional battery electrolytes, therefore, it’s proposed that B and N-doped graphene intercalated with Mg could be an efficient anode material for MIB. Density functional calculations have been carried out to study interaction of Mg with the doped graphene surface. Adsorption energy (Ead), magnesiation potential (VMg) and specific capacity (CC) of surface doped with varying dopant percentages were investigated. The calculations predicted B-doped surface as an efficient anode material for MIB. Moreover, it shows good electrical and ionic conductivity and high cycling stability.

Atomically dispersed transition metal-N4 doped graphene as a LixOy nucleation site in nonaqueous lithium-oxygen batteries

Focusing on the catalytic mechanism of graphene with the atomically dispersed transition metal-N4 dispersed in nonaqueous lithium-oxygen battery, the adsorption models of key intermediates LixOy on the TM-N4 doped graphene surface are established by density functional theory (DFT) calculations. The nucleation and decomposition processes of Li2O2 are elucidated. Both of the charge transfer and electronic hybridization between TM-3d and O-2p orbitals influence the adsorption energies of key intermediates LixOy on the TM-N4 doped graphene surface. A greater adsorption energy usually corresponds to a greater TM atomic number. The adsorption energies of LiO2, Li3O4 and Li4O4 are the linear functions of the adsorption energy of Li2O2. The initial ORR processes on the Mn-N4, Fe-N4, Co-N4 doped graphene surfaces follow the two-electron reaction pathway, while the initial ORR processes on the Ni-N4 and Cu-N4 doped graphene surfaces might follow both of the two-electron and four-electron reaction pathways. The Co-N4 doped graphene possesses the overpotentials of 0.69 V for ORR and 0.92 V for OER, showing the optimal catalytic activity.

A DFT study of the oxygen reduction reaction mechanism on be doped graphene

Graphene despite its high surface area has very limited activity towards the oxygen reduction reaction (ORR), demonstrating selectivity towards the unfavorable two-electron mechanism. We have employed the spin polarized density functional theory method to investigate the oxygen reduction reaction activity of the heteroatom p-type beryllium (Be) doped graphene in gas and aqueous media. The preferred doping sites, active sites and reaction mechanisms available on the doped graphene surfaces were investigated with increasing Be concentrations of 0.03 ML, 0.06 ML and 0.09 ML. Our results reveal that oxygen is physisorbed on bare graphene, however, Be at the lattice sites provides site for oxygen adsorption and ORR. Generally, Be concentration increase in a single honey-comb of graphene from 1 to 2, increasing oxygen activation and dissociation on graphene, compared to their isolated defective counterparts. Considering the conjugated Be defective surfaces, oxygen binds dissociatively on the doped surfaces preferentially in the order 0.06 ML > 0.09 ML > 0.03 ML. Whereby strong binding at the 0.06 ML doped surface corresponds to least charge loss to oxygen. Surfaces with the least affinity for O*, OH* and H2O*, and can transfer the most charges to O2 leading to dissociation (as seen on the 0.03 ML surface), shows the highest reaction activity towards the ORR. From these results surfaces that bind O2 weakly and dissociatively could hold promise for the ORR reaction. Single atom catalyst of Be, based on graphene is promising for the ORR. Graphical abstract

New insights in the electronic structure of doped graphene on adsorption with oxides of nitrogen

The electronic effects produced by molecular adsorption of some environmentally potent oxides of nitrogen, N2O, NO, and NO2 on chemically modified surfaces of graphene are investigated, employing spin-polarized density functional calculations. Graphene surface is modified chemically with substitutional doping through boron, nitrogen, and co-doping, with combinations of boron and nitrogen. In the case of adsorption of the paramagnetic species, NO and NO2, rather exotic effects on adsorption are observed, with unusual electronic structure leading to flat bands in the band structure. The significant alterations of the electronic structure are primarily due to the adsorbate-adsorbent orbital mixing. The adsorption-induced dispersion-less flat bands are produced, eventually turning some of the doped, semiconducting surfaces into a metallic one. These dispersion-less bands are due to stronger interactions of the gaseous molecule with the surface leading to the localization of the molecule over the surface. It is observed that with the adsorption of paramagnetic oxides of nitrogen, the flat bands are introduced between the valence and the conduction band resulting in the loss of dispersion. For some of the configurational patterns of the dopant, chemically driven adsorption of the molecules onto the doped graphene surface take place, characterized by strong adsorption energies and charge transfers.

A comparative experimental and density functional study of glucose adsorption and electrooxidation on the Au-graphene and Pt-graphene electrodes

At present, the graphene is covered on Cu foil with the 5 sccm hexane (C6H14) flow rate, 50 sccm hydrogen (H2) flow rate, and 20 min deposition time parameters by the CVD method. The graphene on the Cu foil is then covered onto few-layer ITO electrode. Furthermore, the Pt and Au metals are electrodeposited on graphene/ITO electrode with electrochemical method. These electrodes are characterized by Raman spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-Ray analysis (SEM-EDX). The graphene structure is approved via Raman analysis. Au, Pt, and graphene network are openly visible from SEM results. In addition, glucose (C6H12O6) electrooxidation is investigated with cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. As a result, Pt-graphene/ITO indicates the best C6H12O6 electrooxidation activity with 9.21 mA cm−2 specific activity (highly above the values reported in the literature). In all electrochemical measurements, Pt-graphene/ITO exhibits best electrocatalytic activity, stability, and resistance compared to the other electrodes. The adsorption of the C6H12O6 molecule is examined theoretically over metal atom (gold and platinum)-doped graphene surfaces using the density functional theory (DFT) method. The interaction between C6H12O6 molecule and OH adsorbed Pt-doped surface is stronger than that of OH adsorbed Au-doped graphene surface thermodynamically according to the reaction energy values.

Computational Approach To Understand the Adsorption Behavior of Iron(II) Phthalocyanine on the Doped Graphene Surface

We have employed dispersion-corrected density functional theory (DFT-D)-based calculations to elucidate the adsorption behavior of Iron(II) phthalocyanine on the doped graphene surface, which is also experimentally tailored recently. The experimental realization of electronic modulations through noncovalent interactions is well-appreciated from the electronic structure calculations. It is important to note that the spin-dependent electronic properties of the iron(II) phthalocyanine can be precisely tuned depending on the nature of the graphene surface beneath. Qualitative interpretations of the forces instituted from the interaction between the disintegrated magnetic moment of the components are also realized (based on some analytical expression). Further, the compelling, magnetic perturbations accounted from the long-range interaction in the overall system are addressed through a series of systematic investigations. Current findings ingrained the manipulation of electronic and magnetic properties of the ...

Nickel‐Nanoparticles on Doped Graphene: A Highly Active Electrocatalyst for Alcohol and Carbohydrate Electrooxidation for Energy Production

AbstractNickel nanoparticles supported on nitrogen doped graphene (Ni−NGr) as highly efficient electrocatalyst were synthesized via controlled thermal annealing using a mixture of graphene oxide, nickel nitrate and uric acid. The synthesized Ni−NGr catalyst presented excellent electrocatalytic performance for ethanol, glucose and glycerol oxidation, stemming from the synergistic effects of nickel and N‐graphene. The electrocatalytic activity was enhanced by the high surface area and nitrogen‐based active sites of pyridinic and graphitic N in doped graphene. These N‐moieties enhanced the accessibility of active sites while preventing agglomeration of nickel nanoparticles on the doped graphene surface. The hybrid electrocatalyst performances were significantly improved and are suited for electrooxidation application in fuel cells.

Changes to the dissociation barrier of H2 due to buckling induced by a chemisorbed hydrogen on a doped graphene surface

An effectiveway of enhancing hydrogen storage on adsorbent materials can be induced by the hydrogen spill-over mechanism, although to date there is no general consensus which satisfactorily explains the mechanism. In this work, a possible reaction path to explain hydrogen adsorption is shown. Density-functional calculations were used to study the dissociation of molecular hydrogen near to a stressed region, as a consequence of chemisorbed hydrogen at the graphene-nitrogen surface. We found that as a result of the buckling induced by the chemisorbed hydrogen, the dissociation barrier of molecular hydrogen diminished by 0.84 eV. The chemisorbed hydrogen is the final state in the spill-over mechanism on a graphene-nitrogen decorated with palladium clusters. This effect helps to create hydrogen nanoislands that may change the diffusion and detrapping of H. An electronic structure analysis suggests that these systems occasionally present metallic or semiconductor behavior. Graphical Abstract Hydrogen dissociation and adsorption process via buckling defect.

Methanol decomposition reactions over a boron-doped graphene supported Ru-Pt catalyst.

The decomposition of methanol is currently attracting research attention due to the potential widespread applications of its end products. In this work, density functional theory (DFT) calculations have been performed to investigate the adsorption and decomposition of methanol on a Ru-Pt/boron doped graphene surface. We find that the most favorable reaction pathway is methanol (CH3OH) decomposition through O-H bond breaking to form methoxide (CH3O) as the initial step, followed by further dehydrogenation steps which generate formaldehyde (CH2O), formyl (CHO), and carbon monoxide (CO). The calculations illustrate that CH3OH and CO groups prefer to adsorb at the Ru-top sites, while CH2OH, CH3O, CH2O, CHO, and H2 groups favor the Ru-Pt bridge sites, indicating the preference of Ru atoms to adsorb the active intermediates or species having lone-pair electrons. Based on the results, it is found that the energy barrier for CH3OH decomposition through the initial O-H bond breaking is less than its desorption energy of 0.95 eV, showing that CH3OH prefers to undergo decomposition to CH3O rather than direct desorption. The study provides in-depth theoretical insights into the potentially enhanced catalytic activity of Ru-Pt/boron doped graphene surfaces for methanol decomposition reactions, thereby contributing to the understanding and designing of an efficient catalyst under optimum conditions.

Dissociative Adsorption of Molecular Hydrogen on BN-Doped Graphene-Supported Aluminum Clusters

The present work, demonstrates dissociative adsorption of molecular hydrogen on supported and unsupported aluminium clusters (Aln, n=4 - 8, 13) using Density Functional Theory based calculations. The studies reveal that the presence of a BN doped graphene surface support reduces the dissociative adsorption barrier of the bond in molecular hydrogen on even atom clusters. In particular, supported Al6 demonstrates a barrier-less dissociative adsorption towards the H2 molecule. These results demonstrate the excellent potential of supported Al nanoparticles for hydrogen storage and also the potential of doped graphene systems are catalyzing supports.

Dispersion corrected density functional study of CO oxidation on pristine/functionalized/doped graphene surfaces in aqueous phase

The catalytic oxidation of CO by molecular oxygen (O2) over graphene, epoxy functionalized graphene and sulphur doped graphene surface is investigated theoretically by employing dispersion corrected Density Functional Theory. The adsorption of O2 and CO molecules over the pristine, functionalized and doped graphene surface has been compared. The channel for oxidation of CO to CO2 is elucidated in detail in the presence of aqueous solvent. Computations suggest that catalytic cycle of CO oxidation is initiated through the ER-mechanism, with the formation of a carbonate intermediate, the second pre-adsorbed CO reacts with the carbonate intermediate through LH-mechanism whereby, two CO2 molecules are released and adsorption surface becomes available for the subsequent reaction. The activation barrier for CO oxidation is considerably lowered in the case of oxidation over functionalized 12.45kcal/mol and doped 14.52kcal/mol graphene surface in comparison to the observed barrier of 23.98kcal/mol for the pristine graphene.

DFT study on Al-doped defective graphene towards adsorption of elemental mercury

In this paper, we use the density functional theory to study the adsorption of mercury on the surface of intact, defective and doped graphene respectively. The results show that the adsorption energies of the elemental mercury on the intact and defective graphene surface are −0.220ev and −0.342ev, which belongs to physisorption process; while the energy on the surface of Al-doped graphene is −0.57ev, which is a chemisorption process. Besides, the adsorption energy of Hg atom on the doped graphene surface grows as the number of Al atom grows. However, when increasing the number of Al-doped on the defective position, the adsorption of Hg will be affected. The best number of Al-doped on the single defective site is one.

Selective AuCl3 doping of graphene for reducing contact resistance of graphene devices

Low contact resistance between metal-graphene contacts remains a well-known challenge for building high-performance two dimensional materials devices. In this study, CVD-grown graphene film was doped via AuCl3 solution selectively only to metal (Ti/Au) contact area to reduce the contact resistances without compromising the channel properties of graphene. With 10mM-AuCl3 doping, doped graphene exhibited low contact resistivity of ∼897Ωμm, which is lower than that (∼1774Ωμm) of the raw graphene devices. The stability of the contact resistivity in atmospheric environment was evaluated. The contact resistivity increased by 13% after 60days in an air environment, while the sheet resistance of doped graphene increased by 50% after 30 days. The improved stability of the contact resistivity of AuCl3-doped graphene could be attributed to the fact that the surface of doped-graphene is covered by Ti/Au electrode and the metal prevents the diffusion of AuCl3.

A Comparative Density Functional Study of Hydrogen Peroxide Adsorption and Activation on the Graphene Surface Doped with N, B, S, Pd, Pt, Au, Ag, and Cu Atoms

The adsorption of the hydrogen peroxide (H2O2) molecule, which is known as the common form of reactive oxygen species in living cells, was investigated theoretically over pure graphene and heteroatom- (nitrogen-, boron-, and sulfur-) and metal-atom- (silver-, gold-, copper-, palladium-, and platinum-) doped graphene surfaces using the density functional theory (DFT) method. This study involved the optimization of pure and doped graphene surfaces, adsorption of the gas molecule on top of the doped atoms and neighboring carbon atoms, and analysis of the behavior of the gas molecule over the various adsorption sites. First-principles calculations revealed that the copper-doped and silver-doped graphene surfaces are the most thermodynamically favorable surfaces for the direct formation of water molecules. Moreover, the sulfur-doped surface exhibits a superior performance among the heteroatom-doped surfaces. Additionally, the gap between the orbital energies of the system was found to have an effect on the sur...

Density functional theory study of elemental mercury adsorption on boron doped graphene surface decorated by transition metals

Decoration of Pd4-A (square planar) on B-doped graphene significantly promotes Hg0 adsorption, a single site of Pd4 cluster on BDG could strongly adsorb up to six Hg atoms.

A First Principles study on Boron-doped Graphene decorated by Ni-Ti-Mg atoms for Enhanced Hydrogen Storage Performance.

We proposed a new solid state material for hydrogen storage, which consists of a combination of both transition and alkaline earth metal atoms decorating a boron-doped graphene surface. Hydrogen adsorption and desorption on this material was investigated using density functional theory calculations. We find that the diffusion barriers for H atom migration and desorption energies are lower than for the previously designed mediums and the proposed medium can reach the gravimetric capacity of ~6.5 wt % hydrogen, which is much higher than the DOE target for the year 2015. Molecular Dynamics simulations show that metal atoms are stably adsorbed on the B doped graphene surface without clustering, which will enhance the hydrogen storage capacity.