Doped Graphene Research Articles

Effects of graphene doping on shape stabilization, thermal energy storage and thermal conductivity properties of PolyHIPE/PEG composites

The development of clean and renewable energy sources has been necessitated by the ever-increasing energy consumption, increasing environmental degradation caused using fossil fuels and concerns over the rise in CO2 spreading. Functional phase change materials (PCMs)' energy storage capacity is appealing owing to their environmental friendliness, superior thermal energy storage (TES) capacity, and capability to improve energy efficiency. A series of hierarchical porous high internal phase emulsion polymer (PolyHIPE) materials with high PCM impregnation capacity were synthesized in this investigation. It has been achieved to encapsulate 80 % by mass of polyethylene glycol (PEG) into the PolyHIPE structure. However, the efficiency of energy storage and conversion systems is affected by a wide variety of factors; one of them is poor thermal conductivity. The development of carbon-based materials like graphene is particularly promising in the disciplines of energy storage and conversion. With this intention, the synthesis of composite PCMs in which the heat conductivity has been enhanced with graphene at three different ratios (wt% 3, 5, and 10) has been performed, conducting comprehensive investigations. The produced composite PCMs have an energy storage capability of over 120 J·g−1 and high thermal and structural stability. In the polyHIPE/graphene structures produced in the absence PCM, the thermal conductivity value exhibits a notable enhancement of up to 125 % due to the increased amount of graphene compared to the polyHIPE material. Following the impregnation of PolyHIPE@Graphene with PEG, it was observed that the thermal conductivity value improved by up to 51.2 % in comparison to PCM. The addition of graphene also gradually shortened the heat storage-release time. In short, herein a series of PCM composites with high energy storage capacity, capable of trapping different PCMs within their structure, has been proposed for TES applications. The manufactured composite PCMs have the potential to be used for a wide range of things, like maintaining the temperature of batteries and photovoltaic solar cells, packaging perishable foods, and providing thermal comfort in textiles and medicinal materials.

An ultra-sensitive detection of Melamine in milk using Rare-earth doped Graphene Quantum Dots- Synthesis and Optical Spectroscopic approach

This work focuses on a rapid and sensitive spectroscopic approach for detecting melamine in food products based on rare-earth Terbium-doped Graphene Quantum Dots (Tb-GQDs) synthesized using microwave and simple chemical conjugation methods. Citric acid and diethylene triamine (DETA) are the precursors of synthesizing GQDs. Terbium, a rare earth element with exceptional fluorescence properties, is doped onto the surface of the GQD to obtain dual photoemission with a broad spectral window and to provide excellent photo-stable characteristics. The as-synthesized Tb-GQDs were characterized using various spectroscopic and microscopic techniques. The synthesized Tb-GQD were spherical with a size of around 6 nm, showing approximately a quantum yield of 52 %, concerning the Standard-Quinine sulfate quantum yield of 54 %. Further, Tb-doped GQDs act as a fluorescent probe, were used to detect and quantify the concentration of melamine (0––5 µM) used as an adulterant in milk and milk products and obtained a maximum detection limit of 0.31 µM. This work concludes that the reported dual emitting Tb-GQDs provide a sensitive and effective platform for detecting melamine in real-time samples, especially in milk, and show promising potential in food industries.

Modification of advanced low-dimensional nanomaterials towards high performance CO2 adsorption: an interpretative state-of-the-art review

Abstract Carbon capture continues to gain attention from researchers especially in light of alarming increase of greenhouse gases in the atmosphere in the recent decades. Among the available carbon capture technologies, both of physical and chemical adsorption is favourably seen with various applicable adsorbents successfully introduced. Such promising CO2 adsorbent candidates include low-dimensional nanomaterials such as graphene, carbon nanotubes (CNTs) and fairly new MXenes. In this review, we will be covering the effects of various types of modifications and functionalization of these materials in enhancing the CO2 adsorption capacities. This includes functionalization with oxygenated and protic functional groups, heteroatoms doping, defect engineering and surface modification. It is observed that doping of graphene, amine-functionalization of CNTs and surface termination modification of MXenes are some of the most widely researched strategies. Since MXenes are a recent addition in the field of CO2 capture, we also covered some fundamental theoretical findings to introduce this new 2D nanomaterial to the readers. With this review, we aim to provide a better understanding on how modifications and functionalization process help to improve CO2 uptake in order to help synthesis of high-performance adsorbents in the future.

Advancing the pressure sensing performance and biocompatible of conductive rGO/PEDOT/PDMS composite film for simple and efficient pressure sensor

Recently, the demand for superior wearable strain sensors has been growing steadily with the widespread application of stretchable electronics. Based on polydimethylsiloxane (PDMS) and poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate, it has good compatibility with graphene doping. Herein, an uncomplicated and capable pressure sensor based on PEDOT/PDMS-wrapped free-standing reduced graphene oxide (rGO) was devised and manufactured. The graphene-containing composite conductor exhibits superb electrical conductivity, resilience, and piezoresistive effect, and surprisingly exhibits excellent antibacterial capabilities and cycling constancy. The fast response and recovery times of this pressure sensor are below 9 and 21 ms, respectively. The magnitude of current changes did not fluctuate significantly after 10 000 cycles of use, which indicates the great dependence of the sensor. Strain sensors as one of primary demand is that composite conductors are attached straight to the mortal skin (joints, elbows and knees) for actual-time monitoring.

Electronic and vibrational spectra of substitutional pair-defects of Boron and Nitrogen atoms in graphene and graphane

The substitutional doping of graphene and related materials with Boron (B) and/or Nitrogen (N) atoms can be effectively used to tailor their properties for specific applications. In this paper, we investigate the energetics, electronic structures and vibrational spectra of substitutional pair-defects in graphene and graphane. The structural distortions in the vicinity of BN pair-defects are small as compared to the distortions in the vicinity of BB or NN pair-defects. The BB (NN) pair-defects in graphene and graphane transform them into p (n) semiconductors. However, the BN pair-defects doped graphene and graphane are intrinsic semiconductors. The Raman and IR spectra of above mentioned pair-defects have unique features, which can be used to identify these defects in graphene as well as graphane structures.

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.