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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. [ABSTRACT FROM AUTHOR]

Density functional calculations were performed on 15 functionalized graphene models to investigate the enhancement of quantum capacitance (CQ) by common dopant elements N, P, S, and O from biomaterials. Geometry optimizations and formation energy calculations demonstrated that the van der Waals radius and additional covalent bonds influenced the mechanical stress and formation energy, particularly due to the distortion of the graphene lattice caused by larger S or P atoms replacing carbon atoms. According to both the CQ and formation energy calculations, nitrogen emerged as the most promising doping element for enhancing CQ, followed by phosphorus, while sulfur showed a relatively lower contribution. Electron density profiles indicated that the improvement of CQ was facilitated by the lone pair electrons at the defects. The effects of dopants on electronic structures were further elucidated through CQ characteristics, resulting in the classification of functionalized graphene models into three types. The ‘graphitic’ type represented configurations that preserved most of the electronic structure of pristine graphene, while ‘p-type’ and ‘n-type’ represented those experienced the loss and gain of valence electrons, respectively. This electronic structure-based classification of doping provides valuable insights for future designs, enabling control over sintering and doping conditions in biomass-derived electrode materials for supercapacitors.

The effect of solvation on the free energy of reaction intermediates adsorbed on electrocatalyst surfaces can significantly change the thermochemical overpotential, but accurate calculations of this are challenging. Here, we present computational estimates of the solvation energy for reaction intermediates in oxygen reduction reaction (ORR) on a B-doped graphene (BG) model system where the overpotential is found to reduce by up to 0.6 V due to solvation. BG is experimentally reported to be an active ORR catalyst but recent computational estimates using state-of-the-art hybrid density functionals in the absence of solvation effects have indicated low activity. To test whether the inclusion of explicit solvation can bring the calculated activity estimates closer to the experimental reports, up to 4 layers of water molecules are included in the simulations reported here. The calculations are based on classical molecular dynamics and local minimization of energy using atomic forces evaluated from electron density functional theory. Data sets are obtained from regular and coarse-grained dynamics, as well as local minimization of structures resampled from dynamics simulations. The results differ greatly depending on the method used and the solvation energy estimates are deemed untrustworthy. It is concluded that a significantly larger number of water molecules is required to obtain converged results for the solvation energy. As the present system includes up to 139 atoms, it already strains the limits of computational feasibility, so this points to the need for a hybrid simulation approach where efficient simulations of much larger number of solvent molecules is carried out using a lower level of theory while retaining the higher level of theory for the reacting molecules as well as their near neighbors and the catalyst. The results reported here provide a word of caution to the computational catalysis community: activity predictions can be inaccurate if too few solvent molecules are included in the calculations. [ABSTRACT FROM AUTHOR]

Laser‐induced graphene (LIG) has attracted extensive attention owing to its facile preparation of graphene and direct engraving patterns for devices. Various applications are demonstrated such as sensors, supercapacitors, electrocatalysis, batteries, antimicrobial, oil and water separation, solar cells, and heaters. In recent years, doping has been employed as a significant strategy to modulate the properties of LIG and thereby improve the performance of LIG devices. Due to the patternable manufacture, controllable morphologies, and the synergistic effect of doped atoms and graphene, the doped LIG devices exhibit a high sensitivity of sensing, pseudocapacitance performance, and biological antibacterial. This paper reviews the latest novel research progress of heteroatom and nanoparticles doped LIG in synthesis, properties, and applications. The fabrications of LIG and typical doping approaches are presented. Special attention is paid to two doping processes of LIG: the one‐step laser irradiation method and the two‐step laser modification consisting of deposition, drop‐casting, and duplicated laser pyrolysis. Doped LIG applications with improved performance are mainly highlighted. Taking advantage of doped LIG's properties and device performances will provide excellent opportunities for developing artificial intelligence, data storage, energy, health, and environmental applications. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of the oxygen reduction reaction (ORR) is a major hurdle for the development of efficient fuel cells. The conventional Pt based catalysts being very expensive, development of noble metal free catalysts for accelerating the kinetics of ORR is highly important. Here, we explored the transition metal (Fe, Co, Ni and Cu) decorated over the nitrogen and phosphorous co-doped graphene as a single-atom catalyst for ORR. Among the four metal decorated systems considered, oxygen molecule is found to strongly interact with only Fe and Co systems while it was too weak with the Ni and Cu systems. Both the Fe and Co decorated systems were systematically investigated for their activity towards ORR through the four-electron reduction path. From the free energies calculated for all the intermediate reactions of ORR, Fe-decorated system was found to have lower overpotential as compared to that of the Co-decorated system indicating the former one as a better catalyst for ORR. [ABSTRACT FROM AUTHOR]

Developing stable and efficient catalysts for the electroreduction of nitrogen remains a huge challenge and single atom catalysts (SACs) are expected to achieve relatively high ammonia selectivity at low applied potential. Based on density functional theory calculations, the potential application of 27 single transition metal (TM = Sc-Zn, Y-Ag, Hf-Au) atoms supported by N(O)-dual-doped graphene (TM-O2N2/G) for the electroreduction of nitrogen is intensively investigated. At low nitrogen coverage, W(Mo, Nb, Ta)-O2N2/G are predicted to yield low ammonia selectivity (< 13%) at limiting-potential of −0.58, −0.53, −0.56, and −0.76 V starting from adsorbed nitrogen with side-on mode, respectively. With the increasing N2 coverage, the TM-O2N2/G is reconstructed as TM-(N2)2N2/graphene. The electroreduction of nitrogen proceeds from end-on adsorbed nitrogen molecule with high ammonia selectivity, and the limiting-potentials are theoretically predicted as −0.20, −0.40, −0.29, and −0.21 V on W(Mo, Nb, Ta)-(N2)2N2/G, respectively. It is suggested that utilizing the reorganization of local coordination environments of SACs by high coverage of reactant molecules under reaction condition can not only enhance the activity at lower limiting-potential but also improve the ammonia selectivity. [ABSTRACT FROM AUTHOR]

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.

Doping is a great strategy for tuning the characteristics of graphene-based nanomaterials. Phosphorous has a higher electronegativity as compared to carbon, whereas boron can induce p-type conductivity in graphene. This review provides insight into the different synthesis routes of phosphorous- and boron-doped graphene along with their applications in supercapacitors, lithium- ions batteries, and cells such as solar and fuel cells. The two major approaches for the synthesis, viz. direct and post-treatment methods, are discussed in detail. The former synthetic strategies include ball milling and chemical vapor discharge approaches, whereas self-assembly, thermal annealing, arc-discharge, wet chemical, and electrochemical erosion are representative post-treatment methods. The latter techniques keep the original graphene structure via more surface doping than substitutional doping. As a result, it is possible to preserve the features of the graphene while offering a straightforward handling technique that is more stable and controllable than direct techniques. This review also explains the latest progress in the prospective uses of graphene doped with phosphorous and boron for electronic devices, i.e., fuel and solar cells, supercapacitors, and batteries. Their novel energy-related applications will continue to be a promising area of study. [ABSTRACT FROM AUTHOR]

Graphene (G) has been a game-changer for conductive optical devices and has shown promising aspects for its implementation in the power industry due to its diverse structures. Graphene has played an essential role as electrodes, hole transport layers (HTLs), electron transport layers (ETLs), and a chemical modulator for perovskite layers in perovskite solar cells (PSCs) over the past decade. Nitrogen-doped graphene (N-DG) derivatives are frequently evaluated among the existing derivatives of graphene because of their versatility of design, easy synthesis process, and high throughput. This review presents a state-of-the-art overview of N-DG preparation methods, including wet chemical process, bombardment, and high thermal treatment methods. Furthermore, it focuses on different structures of N-DG derivatives and their various applications in PSC applications. Finally, the challenges and opportunities for N-DG derivatives for the continuous performance improvement of PSCs have been highlighted. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) detection and monitoring are necessary to prevent problems to human health. Therefore, the density functional theory was employed to examine the CO adsorption on metal clusters deposited on pristine and modified (defective and doped) graphene. First, the stability of Cu4 and Ni4 clusters deposited on pristine and modified graphene was determined. Then, the CO adsorption on metal clusters deposited on pristine and modified graphene was investigated. The interaction energies of the metal clusters deposited on modified graphene are higher than those supported on pristine graphene, which suggests that modified graphene materials are better support materials for these clusters. The metal clusters supported on graphene-based materials exhibit a good sensitivity toward the CO molecule. Therefore, these studied composites can be good candidates for CO detection. Metal clusters/modified graphene composites were investigated as CO sensors using the density functional theory [ABSTRACT FROM AUTHOR]

Supercapacitors are considered among the most promising electrical energy storage devices, there being a need to achieve the highest possible energy storage density. Herein small mixed Zn–Co metal oxide nanoparticles are grown on doped graphene (O‐, N‐ and, B‐doped graphenes). The electrochemical properties of the resulting mixed Zn–Co metal oxide nanoparticles (4 nm) grown on B‐doped graphene exhibit an outstanding specific capacitance of 2568 F g−1 at 2 A g−1, ranking this B‐doped graphene composite among the best performing electrodes. The energy storage capacity is also remarkable even at large current densities (i.e., 640 F g−1 at 40 A g−1). In contrast, larger nanoparticles are obtained using N‐ and O‐doped graphenes as support, the resulting materials exhibiting lower performance. Besides energy storage, the Zn–Co oxide on B‐doped graphene shows notable electrochemical performance and stability obtaining a maximum energy density of 77.6 W h Kg−1 at 850 W Kg−1, a power density of 8500 W Kg−1 at 28.3 W h Kg−1, and a capacitance retention higher than 85% after 5000 cycles. The smaller nanoparticle size and improved electrochemical performance on B‐doped graphene‐based devices are attributed to the higher defect density and nature of the dopant element on graphene. [ABSTRACT FROM AUTHOR]

Graphene has been widely investigated and applied in almost all areas of science and technology. Modulation of graphene properties is needed for its potential utilization in various applications. Chemical doping is one of the most attractive and efficient strategies to alter graphene properties. To date, substantial progress in this area has been reported, which needs to be thoroughly reviewed for its effective implementation in the development of commercial products in the days to come. This article presents a systematic, critical, and more informative review of the recent advancement in the chemical doping of graphene and its applications. Starting with a brief history along with the properties and synthesis of graphene, different experimental approaches to chemical doping and their outcomes reported so far are systematically documented. Further, extensive studies based on potential applications of doped graphene in various fields including light‐emitting diodes, photodetectors, solar cells, energy storage devices, sensors, and medical diagnoses are discussed and presented. Finally, the study is concluded with discussions on future prospective research work in this area. [ABSTRACT FROM AUTHOR]

In this study, the adsorption mechanism of glyphosate on pure graphene and Ti, Fe, Al and Ca atoms doped graphene surfaces is discussed in detail using the density functional theory. It is found that there is a degree adsorption of glyphosate on pure and metal atoms doped graphene surfaces through analyzing the adsorption energy, density of states, differential charge density, Mulliken population density. There are stronger adsorptions of glyphosate on atoms doped graphene surfaces than that on pure graphene surface. The strongest interaction is occurred when glyphosate on Ca doped graphene surface. This is because the-P=O…π,-COOH…π, and-OH…π non-covalent interactions are formed between glyphosate and pure graphene, whereas Metal-O “monodentate” and O-Metal-O “bidentate” covalent interactions are formed between glyphosate and doped graphenes. The results are hopeful to provide theoretical guidance for the application of graphene in environmental protection. [ABSTRACT FROM AUTHOR]

Based on the Lennard-Jones potential function, a theoretical model of atoms/ions interaction with finite-size (doped) graphene is presented to investigate the mechanical behaviors of atoms/ions adsorption and migration on the surface of finite-size boron, nitrogen and boron nitride doped graphene. The results show that boron, nitrogen and boron nitride doping can change the interaction between atoms/ions and graphene, and the type, position and domain size of doping elements have significant effects on the adsorption sites and adsorption energy of atoms/ions. The stable adsorption sites, adsorption heights and adsorption energy of atoms/ions on the surface of doped graphene can be controlled by regulating the doping elements. Meanwhile, boron, nitrogen and boron nitride doping can affect the energy period and energy barrier of atoms/ions migration on graphene surface. The proper design of boron, nitrogen and boron nitride doping position, size and distribution can effectively control the atom/ion migration behavior on graphene surface. This research work can provide a theoretical reference for atoms/ions carriers, molecular sieves and ion battery electrodes based on doped graphene and graphene heterostructures. [ABSTRACT FROM AUTHOR]

Abstract Supercapacitors are considered among the most promising electrical energy storage devices, there being a need to achieve the highest possible energy storage density. Herein small mixed Zn–Co metal oxide nanoparticles are grown on doped graphene (O‐, N‐ and, B‐doped graphenes). The electrochemical properties of the resulting mixed Zn–Co metal oxide nanoparticles (4 nm) grown on B‐doped graphene exhibit an outstanding specific capacitance of 2568 F g−1 at 2 A g−1, ranking this B‐doped graphene composite among the best performing electrodes. The energy storage capacity is also remarkable even at large current densities (i.e., 640 F g−1 at 40 A g−1). In contrast, larger nanoparticles are obtained using N‐ and O‐doped graphenes as support, the resulting materials exhibiting lower performance. Besides energy storage, the Zn–Co oxide on B‐doped graphene shows notable electrochemical performance and stability obtaining a maximum energy density of 77.6 W h Kg−1 at 850 W Kg−1, a power density of 8500 W Kg−1 at 28.3 W h Kg−1, and a capacitance retention higher than 85% after 5000 cycles. The smaller nanoparticle size and improved electrochemical performance on B‐doped graphene‐based devices are attributed to the higher defect density and nature of the dopant element on graphene.

A first-principles theoretical study employing auxiliary density functional theory was performed to investigate the stability and catalytic activity of Pt4−nNin (n = 0–3) clusters supported on pyridinic N3-doped graphene (PNG) nanoflakes. First, the stability of the tetrahedral Pt4−nNin (n = 0–3) clusters supported on PNG nanoflakes was investigated. After, the O adsorption on Pt4−nNin (n = 0–3) clusters supported on PNG nanoflakes was studied as prototype systems to investigate the catalytic activity of PtNi alloy clusters supported on PNG nanoflakes for the oxygen reduction reaction (ORR). The computed interaction energy between the Pt4−nNin (n = 1–3) clusters and the PNG nanoflakes is higher than the one of the Pt4 cluster supported on the PNG nanoflake. According to the obtained oxygen adsorption energies, Pt4−nNin (n = 1–3) alloy clusters supported on PNG nanoflakes could be better candidates for the ORR than the Pt4 cluster supported on PNG nanoflakes. [ABSTRACT FROM AUTHOR]

In this work, a hydrothermal technique was adopted in obtaining a hybrid composite of cobalt-nickel oxalate (CoNi(C 2 O 4) 2 ·nH 2 O) and doped electrochemically exfoliated graphene (EEG) as supercapacitor electrodes. Extensive characterisation by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) technique, X-ray diffraction (XRD) and Raman spectroscopy revealed a sheet-like morphology of the doped-EEG integrated with CoNi(C 2 O 4) 2 ·nH 2 O nanoparticles. XPS analysis confirmed the presence of nitrogen, phosphorus, and sulphur in the EEG at low concentrations. The Raman vibration bands displayed the characteristic features of CoNi(C 2 O 4) 2 ·nH 2 O and EEG in the composite. The hybrid composite electrode evaluated in a half-cell configuration using a 3 M KOH aqueous electrolyte exhibited notable electrochemical performance with a maximum specific capacity of 139.2 mAh g−1 (corresponding to 955.7 F g−1 gravimetric capacitance) at a 1.0 A g−1 current density. The electrodes were also continuously cycled for over 4500 constant charging-discharging steps and demonstrated about 86 % retention in capacity at 10.0 A g−1. The exhibited performance is linked to the high electrically conductive multi-atom doped EEG, and the CoNi(C 2 O 4) 2 ·nH 2 O/EEG composite's high specific surface area, which significantly contributes to the overall electrode's electrochemical stability when compared to the pristine CoNi(C 2 O 4) 2 ·nH 2 O electrode. This makes the CoNi(C 2 O 4) 2 ·nH 2 O/EEG composites suitable material electrodes for hybrid supercapacitor applications. • A hybrid composite of cobalt-nickel oxalate and doped electrochemically exfoliated graphene was synthesised. • The as-synthesised composite electrode exhibited notable electrochemical performance and good long-term cycling stability. • A hybrid cobalt-nickel oxalate/graphene composite is a suitable material electrode for hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

The effects of substitutional doping by nitrogen and phosphorus of graphene with mono and di-vacancies are investigated on its structural and electronic properties. The consequences of subsequent doping with silicon, and atomic tuning of coordination environment of silicon are systematically analyzed. The appearance of localized states near the Fermi level of modified graphenes leads to significant enhancement of quantum capacitance and stored charges of modified graphenes. Thus, the synergistic effects of defects and dopants are expected to be useful for design considerations of graphene-based supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Aluminum–sulfur (Al−S) batteries of ultrahigh energy‐to‐price ratios are a promising energy storage technology, while they suffer from a large voltage gap and short lifespan. Herein, we propose an electrocatalyst‐boosting quasi‐solid‐state Al−S battery, which involves a sulfur‐anchored cobalt/nitrogen co‐doped graphene (S@CoNG) positive electrode and an ionic‐liquid‐impregnated metal–organic framework (IL@MOF) electrolyte. The Co−N4 sites in CoNG continuously catalyze the breaking of Al−Cl and S−S bonds and accelerate the sulfur conversion, endowing the Al−S battery with a shortened voltage gap of 0.43 V and a high discharge voltage plateau of 0.9 V. In the quasi‐solid‐state IL@MOF electrolytes, the shuttle effect of polysulfides has been inhibited, which stabilizes the reversible sulfur reaction, enabling the Al−S battery to deliver 820 mAh g−1 specific capacity and 78 % capacity retention after 300 cycles. This finding offers novel insights to design Al−S batteries for stable energy storage. [ABSTRACT FROM AUTHOR]

In this study, the interactions of magnesium (Mg) atom and Mg(001) surface with different metal-atom-doped graphene were investigated using a density functional theory (DFT) method. For the interactions of magnesium with Al-, Mn-, Zn-, and Zr-doped and intrinsic graphene, it was found that the magnesium atoms were physisorbed into the hollow sites of the intrinsic graphene with only the smallest interaction energy (approximately −1.900 eV). However, the magnesium atoms tended to be chemisorbed on the doped graphene, which exhibited larger interaction energies and charge transfers. Additionally, the Zn-doped graphene displayed the largest interaction energy with the Mg atom (approximately −3.833 eV). For the interactions of Mg(001) with Al-, Mn-, Zn-, and Zr-doped and intrinsic graphene (intrinsic and doped graphene/Mg interface), doped atoms interacted with a Mg layer to make graphene wrinkle, resulting in a higher specific surface area and better stability. Mg–C chemical bonds were formed at the Al-, Zn-, and Zr-doped interface, and Mg–Mn chemical bonds were formed at the Mn-doped interface. This study provided the fundamental research for future research into doped atoms on graphene reinforced magnesium matrix composites. [ABSTRACT FROM AUTHOR]

Developing cheap and earth-abundant electrocatalysts with high activity and stability for oxygen reduction reactions (ORRs) is highly desired for the commercial implementation of fuel cells and metal-air batteries. Tremendous efforts have been made on doped-graphene catalysts. However, the progress of phosphorus-doped graphene (P-graphene) for ORRs has rarely been summarized until now. This review focuses on the recent development of P-graphene-based materials, including the various synthesis methods, ORR performance, and ORR mechanism. The applications of single phosphorus atom-doped graphene, phosphorus, nitrogen-codoped graphene (P, N-graphene), as well as phosphorus, multi-atoms codoped graphene (P, X-graphene) as catalysts, supporting materials, and coating materials for ORR are discussed thoroughly. Additionally, the current issues and perspectives for the development of P-graphene materials are proposed. [ABSTRACT FROM AUTHOR]

A novel carbon-based material was synthesized by chemical doping of Iodine (I2) into multilayer graphene (MLG) using photolysis method. Elemental analysis using Energy Dispersive X-ray (EDX) determined low amount of Iodine doping in the graphene. Raman spectroscopy demonstrated increase in number of layers of graphene. Iodine doped graphene (I-MLG) showed a sharp reduction in resistance when exposed to NO2 gas at room temperature. It demonstrated sensing response of 69% for 100 ppm of gas in just 16 seconds at room temperature. When compared with other gases and vapours, I-MLG showed selective sensing towards NO2 gas by reduction in resistance during exposure. Hybrid Material displayed reversible sensing but recovery after the removal of NO2 gas source took 1380 seconds. An electric field assisting sensor element was fabricated to lower the recovery time to 156 seconds after applying negative gate voltage of −15V. Sensing and recovery mechanisms of I-MLG along with effect of electric field are presented. [ABSTRACT FROM AUTHOR]

The exploration and development of different carbon nanomaterials happening over the past years have established carbon electrodes as an important electrocatalyst for oxygen reduction reaction. Metal-free catalysts are especially promising potential alternatives for replacing Pt-based catalysts. This article describes recent advances and challenges in the three main synthesis manners (i.e., pyrolysis, hydrothermal method, and chemical vapor deposition) as effective methods for the production of metal-free carbon-based catalysts. To improve the catalytic activity, heteroatom doping the structure of graphene, carbon nanotubes, porous carbons, and carbon nanofibers is important and makes them a prospective candidate for commercial applications. Special attention is paid to providing an overview on the recent major works about nitrogen-doped carbon electrodes with various concentrations and chemical environments of the heteroatom active sites. A detailed discussion and summary of catalytic properties in aqueous electrolytes is given for graphene and porous carbon-based catalysts in particular, including recent studies performed in the authors' research group. Finally, we discuss pathways and development opportunities approaching the practical use of mainly graphene-based catalysts for metal–air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

Doping of the graphene lattice with transition-metal atoms resulting in a high magnetic anisotropy energy (MAE) is an important goal of materials research owing to its potential application in spintronics. In this article, using spin-polarized density functional theory including spin–orbit coupling, we examined the magnetic properties of graphene with vacancy defects, both bare and nitrogen-decorated, and doped by Cr, Mn, and Fe transition-metal single atom (TM-SA) and two different TM atoms simultaneously. The adsorption of a second TM atom on an already embedded TM atom, i.e., the formation of upright TM dimers, was also considered. It is found that the graphene-mediated coupling between TM dopants can significantly increase MAE compared to that of SA impurities. While the MAE of TM-SA did not exceed 2 meV, it was enhanced to −23 meV for Cr and Fe simultaneously embedded into two separated double-vacancy (DV) defects and to a remarkably high value of 119.7 meV for two upright Fe–Mn dimers bound to two separate DVs, considerably exceeding the sum for individual TM-SAs. The latter MAE corresponds to a blocking temperature of 34 K assuming a relaxation time of 10 years. The origin of the enhanced MAE is discussed in relation to the spin excitations at the Fermi level and changes in d-derived states accompanying the rotation of the magnetization between in-plane and out-of-plane directions. We demonstrate that the presence of partially occupied degenerate states at the Fermi level favors its formation. The stability of the systems is also discussed. The computational findings are supplemented by an atomic-resolution characterization of an incidental Mn impurity bonded to four carbon atoms, whose localized spin matches expectations as measured using core-level electron energy-loss spectroscopy. Conducting TM-doped graphene with robust magnetic features offers prospects for the design of graphene-based spintronic devices. [ABSTRACT FROM AUTHOR]

In the present study, monazite-type strontium chromate (SrCrO 4) as a ternary metal oxide was prepared by the sol-gel method. Nitrogen and sulfur co-doped graphene decorated with SrCrO 4 nanocrystals was synthesized successfully, and the electrochemical hydrogen storage performance of the SrCrO 4 and its relative nanocomposites also were investigated by chronopotentiometry (CHP) technique. The effect of doped graphene as a substrate of the SrCrO 4 sample on the improvement of the electrochemical hydrogen storage performance was considered as well. The SrCrO 4 -nitrogen and sulfur co-doped graphene (SrCrO 4 /NSG) displayed the highest discharge capacity in comparison to SrCrO 4 -reduced graphene oxide (SrCrO 4 /rGO), SrCrO 4 calcined at 1000 °C (SrCrO 4 (1000)) and SrCrO 4 calcined at 800 °C (SrCrO 4 (800)). Also, increasing the hydrogen storage capacity of the samples by repeating the cycles indicated the excellent cycle stability of the nanoparticles. In monazite-type structures, oxygen vacancies can be created by thermal treatment. Creating oxygen vacancies can improve redox reactions, which increase the conductivity of the samples and hydrogen storage capacity. [Display omitted] • Strontium chromate has monoclinic monazite-type structure. • Graphene nanocomposites have received much attention as electrode materials for hydrogen storage. • The (SrCrO 4 /NSG) exhibited the highest discharge capacity in comparison to (SrCrO 4 /rGO), (SrCrO 4 (1000)) and (SrCrO 4 (800)). [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials are becoming common consumer products due to their outstanding charge carrier ability, high specific surface area, high thermal stability, and great potential for environmental decontamination. Properties of graphene-based materials can be enhanced by doping with elements. Boron and phosphorus are major dopants for graphene, graphene oxide, and graphene quantum dots. Phosphorous has higher electron-donating ability than carbon, which induces n-type conductivity to graphene, whereas boron doping results in p-type conductivity. Doping with boron and phosphorous enhances surface area and defects in graphene materials, this aids in tuning their properties. Doping creates a band gap in graphene that facilitates photocatalytic applications. This review presents emerging applications of boron- and phosphorous-doped graphene and graphene quantum dots as sensors, adsorbents, photocatalysts, and electrocatalysts for detecting and remediating contaminants. [ABSTRACT FROM AUTHOR]

In this study, the adsorption mechanism of glyphosate on pure graphene and Ti, Fe, Al and Ca atoms doped graphene surfaces is discussed in detail using the density functional theory. It is found that there is a degree adsorption of glyphosate on pure and metal atoms doped graphene surfaces through analyzing the adsorption energy, density of states, differential charge density, Mulliken population density. There are stronger adsorptions of glyphosate on atoms doped graphene surfaces than that on pure graphene surface. The strongest interaction is occurred when glyphosate on Ca doped graphene surface. This is because the P=O…π, -COOH…π and -OH…π non - covalent interactions are formed between glyphosate and pure graphene, whereas Metal - O "monodentate" and O - Metal - O "bidentate" graphenes. The results are hopeful to provide theoretical guidance for the application of graphene in environmental protection. [ABSTRACT FROM AUTHOR]

The interaction of graphene with water molecules under an applied electric field is not thoroughly understood, yet this interaction is important to many thermal, fluidic, and electrical applications of graphene. In this work, the effect of electrical doping of graphene on water adsorption is studied through adsorption isotherms and current–voltage (IV) characterizations as a function of the Fermi level. The water adsorption onto graphene increases by ≈15% and the doping levels increase by a factor of three with a gate‐to‐graphene voltage of +20 or −20 V compared to 0 V for sub‐monolayer adsorption. This change in uptake is attributed to the increase in density of state of graphene upon electrical‐doping, which changes the Coulombic and van der Waals interactions. The water adsorption onto graphene is either n‐ or p‐doping depending on the applied gate‐to‐graphene voltage. The ambi‐doping nature of water onto graphene is due to the polar nature of water molecules, so the doping depends on the orientation of the water molecules. [ABSTRACT FROM AUTHOR]

Abstract An in situ coupling strategy to prepare Co9S8/S and N dual-doped graphene composite (Co9S8/NSG) has been proposed. The key point of this strategy is the function-oriented design of organic compounds. Herein, cobalt porphyrin derivatives with sulfo groups are employed as not only the coupling agents to form and anchor Co9S8 on the graphene in situ, but also the heteroatom-doped agent to generate S and N dual-doped graphene. The tight coupling of multiple active sites endows the composite materials with fast electrochemical kinetics and excellent stability for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The obtained electrocatalyst exhibits better activity parameter (ΔE = 0.82 V) and smaller Tafel slope (47.7 mV dec−1 for ORR and 69.2 mV dec−1 for OER) than commercially available Pt/C and RuO2. Most importantly, as electrocatalyst for rechargeable Zn–air battery, Co9S8/NSG displays low charge–discharge voltage gap and outstanding long-term cycle stability over 138 h compared to Pt/C–RuO2. To further broaden its application scope, a homemade all-solid-state Zn–air battery is also prepared, which displays good charge–discharge performance and cycle performance. The function-oriented design of N4-metallomacrocycle derivatives might open new avenues to strategic construction of high-performance and long-life multifunctional electrocatalysts for wider electrochemical energy applications.

It is believed that HOOO. radicals play a key role in atmospheric and environmental chemistry as well as in biological oxidation reactions. In the present contribution, we aim to understand the ability of graphene to scavenge HOOO. radicals by studying the adsorption of HOOO. radical on the pristine and doped (B-doped, N-doped and (B,N)-codoped) graphene using density functional theory (DFT) calculations. It is found that mechanisms of adsorption of HOOO. radical on the pristine and N-doped graphene involve physisorption whereas those on the B-doped and (B,N)-codoped graphene involve chemisorption. The interaction between the pristine graphene and HOOO. radical is found to be weaker than that between doped graphene and HOOO. radical. Our calculations demonstrate that both the pristine and doped-graphene studied here can scavenge the HOOO. radicals. However, the B- and N-doped graphene can do this job more effectively. [ABSTRACT FROM AUTHOR]

Fluorine emission from domestic wastewater is a major cause of severe environmental issues. In this paper, the density functional theory has been used to reveal the adsorption properties of F− ions and HF molecules on intrinsic graphene, B-doped graphene, and Al-doped graphene. Throughout the analysis of band structure, geometric structure, adsorption energy, charge transfer, charge density, density of states, and frontier orbital, we can find that the adsorption of F− ions and HF molecules on intrinsic graphene and HF molecules on B-doped graphene is weak, and it is only physical adsorption. When F− ions and HF molecules are adsorbed on Al-doped graphene and F− ions adsorbed on B-doped graphene, the adsorption energy, charge transfer, and charge density greatly increase, and the adsorption distance significantly decreases, and there exist obvious hybridizations by analyzing the charge density and density of states. We can also find that Al-doped graphene is more sensitive to F− ions after comparing the variation of band gap. The work conducted in this research provides a theoretical guidance for the application of fluorine sensors based on graphene. [ABSTRACT FROM AUTHOR]

In this study, the interactions of magnesium (Mg) atom and Mg(001) surface with different metal-atom-doped graphene were investigated using a density functional theory (DFT) method. For the interactions of magnesium with Al-, Mn-, Zn-, and Zr-doped and intrinsic graphene, it was found that the magnesium atoms were physisorbed into the hollow sites of the intrinsic graphene with only the smallest interaction energy (approximately −1.900 eV). However, the magnesium atoms tended to be chemisorbed on the doped graphene, which exhibited larger interaction energies and charge transfers. Additionally, the Zn-doped graphene displayed the largest interaction energy with the Mg atom (approximately −3.833 eV). For the interactions of Mg(001) with Al-, Mn-, Zn-, and Zr-doped and intrinsic graphene (intrinsic and doped graphene/Mg interface), doped atoms interacted with a Mg layer to make graphene wrinkle, resulting in a higher specific surface area and better stability. Mg–C chemical bonds were formed at the Al-, Zn-, and Zr-doped interface, and Mg–Mn chemical bonds were formed at the Mn-doped interface. This study provided the fundamental research for future research into doped atoms on graphene reinforced magnesium matrix composites.

Developing cheap and earth-abundant electrocatalysts with high activity and stability for oxygen reduction reactions (ORRs) is highly desired for the commercial implementation of fuel cells and metal-air batteries. Tremendous efforts have been made on doped-graphene catalysts. However, the progress of phosphorus-doped graphene (P-graphene) for ORRs has rarely been summarized until now. This review focuses on the recent development of P-graphene-based materials, including the various synthesis methods, ORR performance, and ORR mechanism. The applications of single phosphorus atom-doped graphene, phosphorus, nitrogen-codoped graphene (P, N-graphene), as well as phosphorus, multi-atoms codoped graphene (P, X-graphene) as catalysts, supporting materials, and coating materials for ORR are discussed thoroughly. Additionally, the current issues and perspectives for the development of P-graphene materials are proposed.

The electronic properties of the interface between metallic doped zigzag graphene nanoribbons and perfect graphene nanoribbons are investigated. The density functional based tight-binding approach and a non-equilibrium Green function method are employed for our calculations. The atoms of Ni, Co, and Fe are used as doping atoms. The graphs of current–voltage, density of states, electron density, transmission spectrum, and rectification ratio are obtained. The results show that the bond lengths around the atoms of Ni, Co, and Fe are increased. Moreover, it is observed that for the graphene-based nanodevice the curves of current–voltage are linear and symmetric when no impurity exists and with the effect of impurities the curves are non-linear and asymmetric. While Ni, Co, and Fe impurities are applied into the systems we found that the maximum electron densities are located around the impurities of Ni and the current is decreased. The density of states and transmission spectrum are also examined for different systems. It is found that for certain amount of energies some resonances occur for the current, and the atoms at the edge of nanoribbon are mostly responsible for the transfer of the electrons. The obtained results can be of interest for the construction of nanoelectronic devices and can have practical applications. [ABSTRACT FROM AUTHOR]

Making use of synergy and introducing defects can effectively regulate the electronic structure of carbon nanomaterials, which is of great importance for achieving desired electrochemical performance. Herein, we report a facile protocol for preparing S, N-doped graphene with simultaneous ferroferric oxide functionalization (Fe 3 O 4 -SNG), which is then used as support to anchor Pt nanoparticles for catalyzing the anodic reaction of direct methanol fuel cells (DMFCs), the promising portable power sources that have small environmental footprint, compact system design, and higher volumetric energy density compared with existing technologies. The functionalization by Fe 3 O 4 as well as S and N doping increases the defect level in graphene, and also affect the subsequent growth of Pt particles, leading to formation of Pt nanoparticles with worm-like morphology on the surface of Fe 3 O 4 -SNG support (Pt/Fe 3 O 4 -SNG). The electrochemical evaluations show that the worm-like Pt nanoparticles anchored on Fe 3 O 4 -SNG have larger electrochemically active surface areas and enhanced specific activities for methanol oxidation reaction (MOR) due to their strong electronic interaction with the supports, which also promotes the oxidative removal of the intermediate poisoning products formed during methanol electrooxidation, thereby improving the long-term stability of the Pt catalyst. Image 1 • A facile protocol for preparing the Fe 3 O 4 -functionalized S, N co-doped graphene. • The Fe 3 O 4 -functionalized S, N co-doped graphene is used to support Pt particles. • The Pt particles supported on functionalized graphene have worm-like morphologies. • The worm-like Pt particles exhibit good performance for methanol electrooxidation. [ABSTRACT FROM AUTHOR]

Conjugated microporous polymers (CMPs) as emerging porous materials with diverse structures and tunable building‐units have attracted much attention in the electrochemical field. Herein, we designed phthalocyanine‐porphyrin‐based conjugated microporous polymers as precursors for fabrication of Co, Fe, N tri‐doped graphene composites towards oxygen reduction and evolution reaction (ORR/OER). As expected, the elements cobalt and iron are well dispersed in graphene carbon and interact with the nitrogen sites, thereby providing extra electrocatalytic active sites and enhancing its overall conductivity. Benefiting from its unique design and structure, the obtained catalyst affords a superior bifunctional catalytic activity with a positive onset potential of 0.957 V for ORR, and a low overpotential of 0.36 V for OER. More attractively, the CoFeNG is employed as an air cathode catalyst in Zn‐air batteries, showing a maximum current density of 215 mA cm−2 and good cycle stability for 20000 s. The rational design of phthalocyanine‐porphyrin‐based derivatives provides a feasible route for the construction of high‐performance ORR/OER catalysts. [ABSTRACT FROM AUTHOR]

Tetrachlorodibenzodioxin (TCDD) is one of the most famous dioxin families that is hazardous to humans and the environment. Designing cheap and novel catalysts for its detecting and removing is an essential need for the environment. In this work, DFT + VdW is used to investigate the potentiality of proposed catalysts in adsorbing and dissociating TCDD. P-type and N-type charge carrier effects on the adsorption process are modeled by doping of B/Al and N/P atoms in the graphene. Al-doped graphene, with − 1.27 eV adsorption energy, has the highest possibility to adsorb TCDD. P-type dopants have higher interactions with TCDD in comparing with N-type dopants. Introducing positive and negative charges on the studied complexes shows that in all complexes, the driving force of complexation is π-π stacking except for the Al-doped graphene. Dissociative adsorption studies show that unlike literature data, chlorine atoms on the surface of studied catalysts are not dissociated from TCDD, and instead, C–O bonds in TCDD are dissociated symmetrically and asymmetrically. Data show that Al-doped graphene is the best catalyst for symmetrical dissociation, and pure graphene is the best one for asymmetrical dissociation of TCDD. [ABSTRACT FROM AUTHOR]

Graphene-based nanomaterials have potential as electrocatalysts for the oxygen reduction reaction (ORR) due to their unique physical and chemical properties. In this study, the mechanism of the ORR on M–N3 (M = Mn, Fe, Co, Ni, Cu) co-doped graphene with defects is investigated using dispersion-corrected density functional theory (DFT) computations. The results show that Mn-N3-Gra, Co-N3-Gra, and Ni-N3-Gra are more thermodynamically stable than Fe-N3-Gra and Cu-N3-Gra. Only Mn-N3-Gra exhibits some catalytic activity at pH < 11.327 while M-N3-Gra (M = Fe, Co, Ni, and Cu) are not suitable ORR catalysts. Under acidic conditions at pH = 0, the overpotentials of the optimal 4e− catalytic path are 0.56 V, 0.849 V, and 0.381 V for Mn-N3-Gra, Co-N3-Gra, and Ni-N3-Gra, respectively. These values are consistent with experimental results. These results indicate that Ni-N3-Gra, the optimal catalyst in this study, is comparable with Pt. The M-N3-Gra (M = Fe, Cu) catalysts cannot promote ORR under acid conditions. [ABSTRACT FROM AUTHOR]

In order to design biosensors, it is quite necessary to have an insight upon the nature of interaction between the modified nucleic bases (MNBs) and carbonaceous materials. This study is focussed upon the interaction of the various doped graphene models like graphene (GR), aluminium doped graphene (AlG), sulphur doped graphene (SG), nickel doped graphene (NiG), chromium doped graphene (CrG) and germanium doped graphene (GeG) with MNBs (caffeine, hypoxanthine, uric acid and xanthine) by employing the electronic structure calculations and the associated methodology. All the geometries considered in this study (MNBs and graphene models) were initially optimized at M06-2X/6-31+G** basis set without any constraints followed by the single point energy calculation at three different and well established methods using the Gaussian 09 software package. A detailed comparison of the interaction energy is accomplished in this study. The interaction energy values were further corrected for the basis set superposition error. The theory of atoms in molecules analysis is also performed in detail, which showcases the bond critical points, Laplacian and various other parameters of interest. The variation of frontier molecular orbitals, i.e., highest occupied molecular orbital–lowest unoccupied molecular orbital gap for different models of graphene have been discussed in detail upon the adsorption of MNBs. Among the doped graphene models, the graphene model doped with Cr seems to be more suitable for the application of sensors, also it is found that the MNBs interact primarily via π – π interaction. The results highlight that the CrG can act as a sensor for the detection of MNBs. [ABSTRACT FROM AUTHOR]

The influence of boron (B), nitrogen (N), oxygen (O), and sulfur (S) doping on enhancing quantum capacitance were investigated through a series of the surface-doped trilayer graphene structures by using density functional theory (DFT) calculations. The quantum capacitance of monolayer models was enhanced through a single doping, a triple doping, and a vacancy defect. Our calculations suggested that the layer interactions within the trilayer models decreased the quantum capacitance but increased the stability of the doped structures. Interestingly, in the case of sulfur dopants with significantly larger atomic size than carbon, the stacking layers induced a surface distortion that could avoid the steric clashes with stacking layers and enhanced the stability. In conclusion, this work provided more realistic models of modified carbon-based electrodes for supercapacitors with more accurate information from the combined effects of doping and stacking layers. • This work provided more realistic models of modified carbon-based electrodes considering the effects of stacking layers. • Stacking layers decreased the quantum capacitance as peaks in density of state (DOS) profiles were averaged out. • Distortion of sulfur doped stacking layers enhanced both stability and quantum capacitance. [ABSTRACT FROM AUTHOR]

A theoretical study was performed to reveal ability of doped-graphene nanoadsorbents for COCl 2 uptake. • Doped-graphene (AG) nanosheets are excellent adsorbents for the COCl 2 uptake. • COCl 2 induces remarkable changes in the electronic properties of the adsorbents. • TiG and CrG are efficient adsorbents at low and high COCl 2 concentrations. • CrG and MnG show efficient adsorption and electronic response in aerobic conditions. • New materials for capture/filtration of COCl 2 are proposed. A density functional theory study was performed to analyse the interaction of COCl 2 onto A-doped graphene nanosheets (AG, where A: Al, Si, Ti, Cr, Mn, Fe). Adsorption configurations, adsorption energies, electronic properties, and the interaction in a co-adsorption regime were characterised in detail for all the adsorbent-adsorbate complexes. The results show that these materials are excellent COCl 2 adsorbents, with adsorption energies of up to 1.1 eV/molecule and remarkable changes in the electronic properties. The changes in the adsorption stability in a co-adsorption regime indicates that TiG and CrG are efficient adsorbents at low and high relative COCl 2 concentrations; while, AlG, MnG and FeG will be efficient only at low relative COCl 2 concentrations, where the adsorption stability per COCl 2 molecule significantly decreases with respect to the single adsorption. Otherwise, the COCl 2 adsorption and electronic response in aerobic environments was found to be suitable only for CrG and MnG, where the electronic response is based on the recognition of the [COCl 2 ]δ+–dopant–[O 2 ]δ− intermediate. This work allows to propose new graphene-based materials for the adsorption, filtration, and/or collection of toxic COCl 2. [ABSTRACT FROM AUTHOR]

Abstract The binding configurations of the nitrogen have a great influence on the performance of the doped graphene-based lithium ion batteries anode, while the mechanism of lithium storage is still unclear. In this paper, the binding configuration of the nitrogen is controlled in doped graphene by introducing little sulfur atoms to produce more proportion of graphite nitrogen, which have an excellent cyclic performance with delivering 589 mAh g−1 at 5 A g−1 after 1000 cycles in the lithium ion batteries anode. What's more, the kinetics is improving with higher lithium ion diffusion coefficient and a smaller impedance of charge-transfer compared to the samples which do not regulated the binding configurations of the nitrogen. The characteristic electronic structure of graphite nitrogen is considered to reveal the lithium storage mechanism. Consequently, this work can provide a new insight for regulating binding configurations of nitrogen to improving lithium storage kinetics of the doping graphene electrodes. Graphical abstract Image 1 Highlights • The binding configurations of nitrogen are controlled by a facile method. • The kinetics mechanism of lithium storage for graphite nitrogen is revealed. • The material affords a high capacity of 589 mAh g−1 after 1000 cycles at 5 A g−1. [ABSTRACT FROM AUTHOR]

In recent decades, finding a solution to replace metal catalysts with inexpensive and available elements has been investigated extensively. Carbon nanomaterials doped with heteroatom such as (N, B and S) which do not have any metal content can provide sustainable materials with a remarkable electrocatalytic activity that can compete with their metal counterparts. Doped graphene has been considered as an electrode material for oxygen reduction reaction, supercapacitor and Li-ion batteries. In this present account, co-doped graphene with nitrogen and sulfur was studied in order to investigate their electrochemical hydrogen storage performance. The dual doped sample was prepared via a simple hydrothermal method, using thiourea as a nitrogen and sulfur source. The nitrogen and sulfur co-doped graphene (NSG) showed excellent electrical conductivity and electrochemical performance compared with the nitrogen doped graphene (NG) and graphene oxide (GO). Doping graphene with foreign atoms is a method to create a semiconducting gap in it and can act as an n-type semiconductor, therefore the electrochemical performance is remarkable when used as an electrode. According to the results by increasing the electrical conductivity of graphene, the storage capacity of hydrogen was increased. The discharge capacity of GO after 20 cycles was increased from 653 mAh/g to 1663 mAh/g (5.88 wt% hydrogen) and 2418 mAh/g (8.55 wt% hydrogen) in single doped graphene (NG) and co-doped graphene (NSG), respectively. The prepared samples were characterized via X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Brunauer-Emmet-Teller analysis (BET), vibration sample magnetometer (VSM) and infrared spectrum (FT-IR). • Doped graphene can act as a metal-free electrocatalyst. • The nitrogen and sulfur co-doped graphene (NSG) showed excellent electrochemical performance. • Compared with the nitrogen doped graphene (NG) and graphene oxide (GO). • The discharge capacity of NSG was increased to 2418 mAh/g. [ABSTRACT FROM AUTHOR]

The capability of nickel, cobalt and iron doped graphene nanosheets (GNSs) for adsorption of ozone, sulfur dioxide and nitrogen dioxide molecules are scrutinized by means of density functional theory calculations. The molecular electrostatic potential, adsorption energy and charge transfer of these gas molecules on metal doped GNS are studied. The high negative adsorption energy values exhibit that the nickel, cobalt and iron dopant atoms can remarkably enhance the interaction of molecules with doped GNS. The range of adsorption energy is − 1.45 to − 4.56 eV for the most stable complexes. Also, ozone can be dissociated on Fe doped GNS. The results indicated that the iron doped GNS is the most effective for adsorbing ozone, nitrogen dioxide and sulfur dioxide molecules. After adsorption of these molecules, the energy gaps of the doped GNSs are decreased in all complexes. This investigation shows that doped GNSs based nanomaterials can be helpful for controlling and capturing of harmful gases. [ABSTRACT FROM AUTHOR]

Abstract We demonstrate a facile hydrothermal synthesis of the interconnected porous NiCo 2 O 4 nanosheets for hybrid supercapacitor applications. The as-synthesized NiCo 2 O 4 nanosheets show a high specific capacitance of 3137 F g−1 at a current density of 2 A g−1, which is much greater than 1916 and 1251 F g−1 of Co 3 O 4 and NiO, respectively. Interestingly, the total specific capacitance of the NiCo 2 O 4 is almost close to the sum of the specific capacitance of the NiO and Co 3 O 4. Furthermore, a hybrid supercapacitor is configured with the NiCo 2 O 4 nanosheets and the nitrogen- and sulfur-codoped reduced graphene oxide as the positive and negative electrodes, respectively. This hybrid supercapacitor delivers a maximum energy density of 33.64 W h kg−1 at a power density of 1196 W kg−1 and excellent long-term cyclic stability over 12,000 charge/discharge cycles at the enlarged voltage window of 1.5 V. The remarkable supercapacitive performances of the hybrid device are attributed to the interconnected porous structure of NiCo 2 O 4 nanosheets and three-dimensional continuous macropores of codoped reduced graphene oxides. Graphical abstract Image 1 Highlights • The interconnected porous NiCo 2 O 4 nanosheets are synthesized. • The NiCo 2 O 4 shows high capacitances of 3137 and 2420 F g−1 at 2 and 20 A g−1. • The HSC consists of NiCo 2 O 4 nanosheets and 3D N,S-rGO. • The HSC delivers a maximum energy density of 33.64 W h kg−1. • The HSC exhibits the outstanding cyclic stability and Coulombic efficiency. [ABSTRACT FROM AUTHOR]

Abstract Application of lithium-sulfur battery is still hindered by the poor cycling life, rapid capacity decay and severe self-discharge, which are mainly caused by the well-known dissolving and shuttling effects. Thus, a systematic investigation including perfect graphene, nitrogen doped graphene, iron and nitrogen co-doped graphene as anchor materials for sulfur cathodes in lithium sulfur battery are performed, in order to search new chemical functional graphene with good electrocatalysis and shuttling suppression abilities. Our results reveal that iron and nitrogen co-doped graphene monolayer is a good anchoring material, in which the Li S Fe N four-membered ring structure ensures the stability of adsorption structure and allows adsorption energy of the adsorption structure to be in the suitable range. The effect of the four-membered ring mainly contributes by the strong binding between Fe and S coming from magnetic catalytic absorption. Moreover, the Fe N 4 @graphene can promote the fully discharge of lithium polysulfides benefiting from the low decomposition energies of Li 2 S and Li 2 S 2 on its surface and the catalytic effect of 3 d electrons of doped iron. PDOS demonstrates essential role of iron in rending Fe S bond with strong anchoring. Our research unravels anchor effect of FeN 4 @graphene in lithium sulfur batteries and provides invaluable theoretical guidance for high-performance lithium sulfur batteries. Highlights • Systematic investigation of chemical functional graphene as anchor materials for sulfur in Li-S battery. • The effect of the four-membered ring is mainly due to the strong binding of Fe-S caused by magnetic catalytic adsorption. • FeN 4 @graphene can promote the fully discharge of lithium polysulfide. The decomposition energies of Li 2 S n on FeN 4 @graphene is low due to the catalytic effect of 3 d electrons of doped iron. [ABSTRACT FROM AUTHOR]