Few-layer Graphene Sheets Research Articles

Few-layered graphene from cathodic exfoliation in binary solvents and application as a protective layer for lithium metal anodes

Electrochemical exfoliation is a top-down method recognized for its environmentally friendly and scalable approach for producing solution-processable graphene. Among its variation, cathodic exfoliation stands out for its potential in generating few-layer graphene with minimal defects. In this study, we developed a cathodic exfoliation method for graphite foil using a binary solvent system to produce graphene with a reduced number of layers. By employing a 0.1 M LiClO4 solution in a dimethyl sulfoxide and dimethyl carbonate solvents mixture at a 1:2 vol ratio, we enhanced the intercalation of solvated lithium ions into graphite, successfully exfoliating graphene with 5–6 layers. The exfoliated graphene exhibited a low defect density (ID/IG ∼0.05) and a C/O ratio of 33.2. Furthermore, when used as a coating on a separator, the exfoliated few-layered graphene (FLG) sheets demonstrated notable performance as a protective layer for Li metal anode in Li metal battery technology.

Thermophysical Profile of Industrial Graphene Water-Based Nanofluids.

The exceptional properties of high-grade graphene make it an ideal candidate for thermal dissipation and heat exchange in energy applications and nanofluid development. Here, we present a comprehensive study of few-layer graphene (FLG) nanofluids prepared in an industrial context. FLG nanofluids were synthesized through an ultrasound-assisted mechanical exfoliation process of graphite in water with a green solvent. This method produces FLG of high structural quality and stable nanofluids, as demonstrated by electron microscope, dynamic light scattering and ζeta potential analyses. Thermal conductivity measurements of FLG-based nanofluids were conducted in the temperature range of 283.15 K to 313.15 K, with FLG concentrations ranging from 0.005 to 0.200% in wt. The thermal conductivity of FLG nanofluids is up to 20% higher than water. The modeling of nanofluid thermal conductivity reveals that this enhancement is supported by the influence of the thermal resistance at the FLG interface, and the content, average dimensions and flatness of FLG sheets; this latter varying with the FLG concentration in the nanofluid. Additionally, the density and heat capacity of FLG suspensions were measured and compared with theoretical models, and the rheological behavior of FLG nanofluids was evaluated. This behavior is mainly Newtonian, with a weak 5% viscosity increase.

Graphene via Microwave Expansion of Graphite Followed by Cryo-Quenching and its Application in Electrostatic Droplet Switching.

Monoelemental atomic sheets (Xenes) and other 2D materials offer record electronic mobility, high thermal conductivity, excellent Young's moduli, optical transparency, and flexural capability, revolutionizing ultrasensitive devices and enhancing performance. The ideal synthesis of these quantum materials should be facile, fast, scalable, reproducible, and green. Microwave expansion followed by cryoquenching (MECQ) leverages thermal stress in graphite to produce high-purity graphene within minutes. MECQ synthesis of graphene is reported at 640 and 800 W for 10 min, followed by liquid nitrogen quenching for 5 and 90 min of sonication. Microscopic and spectroscopic analyses confirmed the chemical identity and phase purity of monolayers and few-layered graphene sheets (200-12 µm). Higher microwave power yields thinner layers with enhanced purity. Molecular dynamics simulations and DFT calculations support the exfoliation under these conditions. Electrostatic droplet switching is demonstrated using MECQ-synthesized graphene, observing electrorolling of a mercury droplet on a BN/graphene interface at voltages above 20 V. This technique can inspire the synthesis of other 2D materials with high purity and enable new applications.

Study on the preparation and mechanism of two-dimensional nanomaterials as plugging agents for oil-based drilling fluids

During the drilling of shale formations using oil-based drilling fluids (OBDFs), the infiltration of filtrate into formation micro-fractures is one of the primary causes of wellbore instability. Wellbore instability not only increases non-productive time during the drilling process but also significantly raises development costs. The key to addressing this issue is the development of nano plugging agents capable of effectively sealing formation micro-cracks. However, existing nano plugging agents suffer from poor dispersibility and mismatch with the scale of rock fractures under formation conditions. In this study, two-dimensional nano graphene oxide was synthesized via a redox method. XRD and Raman analyses confirmed the production of high-quality, few-layer two-dimensional graphene sheets. TEM analysis revealed that the synthesized high-reduction graphene oxide (R-GO) had an average lateral size of 2.16 μm, making it suitable for sealing formation micro-cracks. Performance tests demonstrated that R-GO maintained its non-aggregating and highly dispersible properties under formation conditions. Additionally, permeability reduction experiments showed that adding 0.25 %, 0.50 %, and 0.75 % R-GO resulted in permeability reduction rates of 29.12 %, 31.86 %, and 49.16 %, respectively. The conclusion is that R-GO, as a nano plugging agent for OBDFs, can form a dense sealing layer on the surfaces of shale nano-micro pores and fractures, thereby enhancing the stability of shale formations.

In Situ Polymer-Solution-Processed Graphene-PDMS Nanocomposites for Application in Intracranial Pressure Sensors.

Polydimethylsiloxane (PDMS) has emerged as a promising candidate for the dielectric layer in implantable sensors due to its exceptional biocompatibility, stability, and flexibility. This study introduces an innovative approach to produce graphene-reinforced PDMS (Gr-PDMS), where graphite powders are exfoliated into mono- and few-layer graphene sheets within the polymer solution, concurrently forming cross-linkages with PDMS. This method yields a uniformly distributed graphene within the polymer matrix with improved interfaces between graphene and PDMS, significantly reducing the percolation threshold of graphene dispersed in PDMS from 10% to 5%. As-synthesized Gr-PDMS exhibits improved mechanical and electrical properties, tested for potential use in capacitive pressure sensors. The results demonstrate an impressive pressure sensitivity up to 0.0273 kpa-1, 45 times higher than that of pristine PDMS and 2.5 times higher than the reported literature value. The Gr-PDMS showcases excellent pressure sensing ability and stability, fulfilling the requirements for implantable intracranial pressure (ICP) sensors.

Respiratory Toxicology of Graphene-Based Nanomaterials: A Review.

Graphene-based nanomaterials (GBNs) consist of a single or few layers of graphene sheets or modified graphene including pristine graphene, graphene nanosheets (GNS), graphene oxide (GO), reduced graphene oxide (rGO), as well as graphene modified with various functional groups or chemicals (e.g., hydroxyl, carboxyl, and polyethylene glycol), which are frequently used in industrial and biomedical applications owing to their exceptional physicochemical properties. Given the widespread production and extensive application of GBNs, they can be disseminated in a wide range of environmental mediums, such as air, water, food, and soil. GBNs can enter the human body through various routes such as inhalation, ingestion, dermal penetration, injection, and implantation in biomedical applications, and the majority of GBNs tend to accumulate in the respiratory system. GBNs inhaled and substantially deposited in the human respiratory tract may impair lung defenses and clearance, resulting in the formation of granulomas and pulmonary fibrosis. However, the specific toxicity of the respiratory system caused by different GBNs, their influencing factors, and the underlying mechanisms remain relatively scarce. This review summarizes recent advances in the exposure, metabolism, toxicity and potential mechanisms, current limitations, and future perspectives of various GBNs in the respiratory system.

Regulation of high value-added carbon nanomaterials by DC arc plasma using graphite anodes from spent lithium-ion batteries

With the extensive use of lithium-ion batteries (LIBs), neglecting to recycle graphite anodes from LIBs leads to environmental pollution and the waste of graphite resources. Thus, developing an efficient and environment-protecting approach to reusing spent graphite anodes is necessary. Here, high value-added graphene sheets (GS), carbon nanohorns (CNHs), fluorine-doped CNHs (F-CNHs), and amorphous carbon nanoballs (ACNs) were prepared from spent graphite anodes of LIBs via DC arc plasma. In order to control the conversion of spent graphite anodes into various carbon nanomaterials, the growth mechanism of carbon nanomaterials is investigated by quenching rate. Benefiting from the extremely high quenching rates (>1.8 × 106 K/s) produced by DC arc plasma, the particle size of the prepared ACNs and CNHs is small and evenly distributed. The CNHs show a “dahlia-like” structure, and the number of graphene layers is only 3–8. Furthermore, the structural transformation mechanism of carbon nanomaterials is researched by deposition temperature. The ACNs, few-layer GS, and CNHs produced by the high quenching rates are unstable and prone to structural transformation. When these carbon nanomaterials are deposited on the cathode surface and cathode holder, the ACNs, “dahlia-like” CNHs, and GS undergo processes of fusing and overlaying at high temperatures, respectively, resulting in the agglomeration and increased particle size of ACNs and “seed-like” CNHs. Meanwhile, the GS is bent and converted into carbon nanocages (CBCs). Overall, the carbon nanomaterials prepared using spent anodes from LIBs by arc plasma are a facile, environment-friendly, and economical strategy to achieve high value-added utilization of the graphite.

Superlubricity and Stress-Shielding of Graphene Enables Ultra Scratch-Resistant Glasses.

Glasses, when subjected to scratch loading, incur damages affecting their optical and mechanical integrity. Here, it is demonstrated that silica glasses protected with mechanically exfoliated few-layer graphene sheets can exhibit remarkable improvement in scratch resistance. To this extent, the friction and wear characteristics of silica glasses with exfoliated graphene using atomic force microscopy (AFM) are explored. The friction forces recorded during AFM scratch tests of the graphene-glass surfaces at multiple loads exhibit ∼98% reduction compared to that of the bare silica glass, with the friction coefficient falling in the superlubricity regime. This dramatic reduction in friction achieved by the graphene sheets results in significantly lower wear of the graphene-glass surfaces postscratching. Further investigations employing atomistic simulations reveal that the stress-shielding mechanism is due to the reduced deformation of graphene-glass surfaces, thereby curtailing the overall damage. Altogether, the present work provides a new fillip toward the development of glasses with enhanced scratch resistance exploiting two-dimensional coatings.

Low-temperature green synthesis of few-layered graphene sheets from pomegranate peels for supercapacitor applications

Graphene presents practical applications in energy storage devices, especially supercapacitors. However, mainstream synthesis of graphene includes toxic chemical usage, which threatens the environment. With the recent attention shift to synthesizing nanomaterials from agro-waste due to their easy availability, cost-effectiveness, and, most importantly, their environmental friendliness, we present, in this work for the first time, a novel and green synthesis of few-layered graphene sheets using pomegranate peels as a precursor at a low temperature of 80 °C. The surface morphology and microstructural properties are determined by Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), and the electrical properties determined by Hall Effect Measurement. The application as a supercapacitor is also examined using Cyclic Voltammetry (CV), Charge–Discharge Cycling (GCD), and Electrochemical Impedance Spectroscopy (EIS). The resulting supercapacitor delivers an areal capacitance of 3.39 mF{cm}^{-2} at a current density of 15.6 μA {cm}^{-2}, making our synthesized graphene a good choice for electrochemical storage devices.

(Invited) Tuning Optoelectronic and Chiroptical Properties of Carbon Dots Based Hybrids

Carbon dots (CDs) are a rising star in carbon nanomaterials due to their easy preparation and numerous potential applications. With a diameter from a few to tens of nanometers, and a tunable structure, composition, and morphology, they integrate the merits of water solubility, low biological toxicity, and diversity of opto-electronic properties. Commonly, they are categorized into different subgroups, where graphene quantum dots (GQDs) and carbon nanodots (CNDs) can be found. GQDs are two-dimensional nanoparticles of one or few-layer graphene sheets formed during the exfoliation processes of graphitic materials, whereas CNDs are amorphous nanoparticles fabricated from easily affordable organic precursors, natural products, or waste.In recent years, we have set-up methodologies for the synthesis of GQDs and CNDs, carried out a detailed characterization of the obtained structures, and explored the modulation of properties by chemical modification of these carbon nanostructures, as part of the objectives of our research.Special attention was dedicated to customize the optoelectronic properties of GQDs and CNDs, and to investigate the electronic communication in related functional materials.1 Both, electron-donor and electron-acceptor character of GQDs and CNDs, make their charge-transfer chemistry rather versatile. Charge-separated states are observed in the photoexcitation of CNDs previously endowed with electron-donating extended tetrathiafulvalenes (exTTF) or electron-accepting 11,11,12,12-tetracyano-9,10-anthra-p-quinodimethanes (TCAQ).In a different approach, the top-down synthesis of chiral GQDs by covalent functionalization of GQDs with chiral ligands has been explored.2 Chirality can actually be transferred to a supramolecular structure built with pyrene molecules, where the chiral-GQDs/pyrene ensembles show a characteristic chiroptical response depending on the configuration of the organic ligands introduced on the GQDs structure. Furthermore, amide hydrogen bonding and π-π stacking interactions could drive the self-aggregation process to construct supramolecular polymers at the nanoscale (Figure).Within this contribution, we will present and discuss the most recent advances on the use of CDs in our group. References a) Ferrer-Ruiz, A.; Scharl, T.; Haines, P.; Rodríguez-Pérez, L.; Cadranel, A.; Herranz, M. A.; Guldi, D. M.; Martín, N. Angew. Chem. Int. Ed. 2018, 57, 1001-1005; b) Scharl, T.; Ferrer-Ruiz, A.; Saura-Sanmartín, A.; Rodríguez-Pérez, L.; Herranz, M. A.; Martín, N.; Guldi, D. M. Chem. Commun., 2019, 55, 3223-3226; c) Ferrer-Ruiz, A.; Scharl, T.; Rodríguez-Pérez, L.; Cadranel, A.; Herranz, M. A.; Martín, N.; Guldi, D. M. J. Am. Chem. Soc. 2020, 142, 20324−20328.a) Vázquez-Nakagawa, M.; Rodríguez-Pérez, L.; Herranz, M. A.; Martín, N. Chem. Commun., 2016, 52, 665-668, b) Vázquez-Nakagawa, M.; Rodríguez-Pérez, L:, Martín, N.; Herranz, M. A.; Angew. Chem. Int. Ed., 2022, 61, e202211365. Figure 1

One pot green synthesis of few-layer graphene (FLG) by simple sonication of graphite and Azardirachta Indica resin in water for high-capacity and excellent cyclic behavior of rechargeable lithium-ion battery

A simple, green, and eco-friend route is employed for the preparation of few-layer graphene using Azardirachta Indica resin (AZIr) in water. In addition, the preparation of the solvent (AZIr) for the exfoliation of graphene involves various steps, including vacuum filtration and surface tension optimization by the capillary rise method. It has been demonstrated that the 4 h sonication effectively exfoliated graphite to form a Few-Layer Graphene (FLG) sheet. Structural, morphological, and surface topographical analysis were performed using X-ray diffraction, Raman spectrum, FTIR spectrum, atomic force microscopy, and Scanning electron microscope. The as-prepared FLG was demonstrated as anode material for lithium-ion batteries¸ exhibiting a high initial capacity of 464 mAh g−1 at 0.1C and excellent cyclic performance of 527 mAh g−1 at 200th cycle with 100 % capacity retention. The maximum capacity of 281 mAh g−1 was achieved when tested at a high current rate of 10C. These results suggest that few-layer graphene is a promising material for high-performance Li-ion battery applications.

In English

In presented work we have reported that polyvinylpyrrolidone (PVP) is suitable organic solvent for mechanical exfoliation of crystalline graphite to graphene in aqueous solution through kitchen blender technique. Morphological, structural and optical, properties of graphene samples were characterized by scanning electron microscopy, Raman scattering and UV-Visible spectroscopy. Scanning electron microscopy demonstrates folded morphology of graphene flakes with ~4 nm thickness. Raman scattering was revealed the high-quality graphene with low levels of defects after the exfoliation process of graphite/PVP dispersions. The G band at ~1582 cm−1 on Raman spectra is related with stretching vibrations of carbon atoms. The broadening of the G band is not observed, that indicated on absence of the basal plane defects in the graphene structure, which can be introduced during exfoliation by the kitchen blender. The ratio of the intensity of 2D and G bands equal to 1.66 (I2D/IG>1) and the value of 2D band full width at half maximum is 79.88 cm–1, indicated a few-layer graphene (FLG) structure. The defects quantity identified by the intensity ratio of the D and G bands, ID/IG is 0.18, significantly lower than that reported for graphene oxide with basal plane defects (> 1) and for sonication dispersed graphene (~ 0.6). The graphene dispersions were characterized by UV–Vis spectroscopy, minimum transmittance observed at around 270 nm is attributed to the π→π* transitions of aromatic C–C bonds in graphene. The optical transmittance minimum and the overall high transmittance decreasing values observed between 270 and 800 nm strongly suggest the presence of two-dimensional material in the dispersion, thus confirming the successful exfoliation of graphite to graphene by blending. We demonstrate the simple and nontoxic method to product high-quality FLG sheets, free from defects, using a kitchen blender and eco-friendly polyvinylpyrrolidone as an organic exfoliant.

Graphene-based field-effect transistor using gated highest-k ferroelectric thin film

We report a graphene-based highest-k ferroelectric field-effect transistor (GFE-FET) in which few-layer graphene sheets (FLGS) act as a channel layer and highest-k ferroelectric like barium zirconium titanate/barium calcium titanate (BZT/BCT) acts as an insulating gate layer. The electrochemical and sol-gel method has been used to prepare the used good quality FLGS and excellent BZT/BCT ferroelectric materials. SEM, XRD, UV–Vis, FTIR, and Raman spectroscopy measurements were done to characterize the produced materials. In order to evaluate the mobility of the fabricated GFE-FET, FET was fabricated with BZT/BCT gate and FLGS on top of it as conducting channel. The resultant field-effect mobility obtained from the fabricated GFE-FET is approximately ∼1.72 × 104 cm2V–1s−1 with 103 on/off ratio. These results ensure potential applications in some future high-speed electronic devices.

Inducing SERS activity at graphitic carbon using graphene-covered Ag nanoparticle substrates: Spectroelectrochemical analysis of a redox-active adsorbed anthraquinone.

Graphitic carbon electrodes are central to many electrochemical energy storage and conversion technologies. Probing the behavior of molecular species at the electrochemical interfaces they form is paramount to understanding redox reaction mechanisms. Combining surface-enhanced Raman scattering (SERS) with electrochemical methods offers a powerful way to explore such mechanisms, but carbon itself is not a SERS activating substrate. Here, we report on a hybrid substrate consisting of single- or few-layer graphene sheets deposited over immobilized silver nanoparticles, which allows for simultaneous SERS and electrochemical investigation. To demonstrate the viability of our substrate, we adsorbed anthraquinone-2,6-disulfonate to graphene and studied its redox response simultaneously using SERS and cyclic voltammetry in acidic solutions. We identified spectral changes consistent with the reversible redox of the quinone/hydroquinone pair. The SERS intensities on bare silver and hybrid substrates were of the same order of magnitude, while no discernible signals were observed over bare graphene, confirming the SERS effect on adsorbed molecules. This work provides new prospects for exploring and understanding electrochemical processes in situ at graphitic carbon electrodes.

Fullerene Transformed into a 3-D Structure of Nitrogen-Doped Few-Layer Graphene Sheets: Growth and Field Emission Properties

3-D-structured nitrogen-doped few-layer graphene sheets (3-D NFLGs) have been prepared using a fullerene C60 precursor combined with a microwave excited nitrogen plasma process. A deep understanding of the growth mechanism and regulating of morphology that can adjust the field emission properties is crucial for its widespread application. In this work, the detailed growth process and microstructure and the field emission properties of the as-synthesized vertical aligned 3-D NFLGs were studied. The growth of the 3-D NFLGs can be divided into three steps: evaporation of the C60, opening of the C60, and formation of the 3-D NFLGs. The growth process and morphology of the materials can be neatly regulated by changing the evaporating temperature of the C60, electron temperature of the plasma, and substrate temperature through our self-designed reaction equipment. Interestingly, the vertical 3-D NFLGs grew at a limited microwave power and nitrogen pressure and could be divided into three different morphological features, reflected in their distribution uniformity, interparietal distance, number of layers, and crystallinity, which exhibited different field emission properties. Additionally, the 3-D NFLGs were all in situ doped with ∼4% nitrogen atoms from nitrogen gas during the growth process, while different compositions of the nitrogen atoms were reflected in the graphitic N increasing with increasing nitrogen pressure. Furthermore, the field emission measurements show that the as-obtained vertical 3-D NFLGs exhibited the lowest turn-on electric field (1.30 V/μm@10 μA/cm2) and threshold field (2.1 V/μm@1 mA/cm2) at the M1 morphology and the highest stability at the M3 morphology. Remarkable field emission performance was obtained for the 3-D NFLGs with M2 morphology, showing their great potential for field emission applications.

Production of graphene-derivatives using organic molecules for supercapacitors and beyond

Graphene is rapidly expanding for applications ranging from nanoelectronics to space exploration. A material with such enormous potential requires a variety of synthesis methods. Here, we report a library of relatively sustainable redox-active organic molecules for the reduction of graphene oxide (GO) namely N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), 7,7,8,8-tetracyanoquinodimethane (TCNQ), ferrocene (Ferro), and decamethylferrocene (DFerro). Among them, the reduction of GO using TMPD starts even with simple hand-shaking for just a few minutes. By controlling the sonication time under ambient conditions, one can control the electronic properties of the reduced graphene oxide (rGO). The resulting free-standing films delivered a capacitance of 185 F/g when tested them as supercapacitor electrodes. We also demonstrated that TMPD can exfoliate graphite into few-layer graphene sheets with simple sonication. We further show that under mild heating, these molecules can serve as dopants during the reduction process to produce nitrogen-doped graphene. Our results may guide researchers to explore sustainable organic molecules for the large-scale production of graphene-based materials for diverse applications.

Nanocomposite Hydrogels Containing Few-Layer Graphene Sheets Prepared through Noncovalent Exfoliation Show Improved Mechanical Properties

Hydrogels show great potential as soft materials for biomedical applications and flexible devices. However, conventional hydrogels exhibit poor mechanical strengths owing to the presence of water in their polymer networks. Therefore, improving the mechanical properties of hydrogels by controlling the chemical and physical structures that affect their macroscopic behaviors is a challenging issue. In this study, we developed a nanocomposite (NC) hydrogel that harbors exfoliated few-layer graphene sheets through noncovalent interactions. The bifunctional polymer PImQ, which contains both aromatic and cationic groups, was found to enable the direct exfoliation of graphite to few-layer graphene through π–π interactions in 2.7% yield. The poly(acrylamide)-based NC hydrogel containing the PImQ/graphene composite as a nanofiller shows a 3.4-fold increase in tensile stress compared with the hydrogel without the nanofiller. The introduction of the PImQ/graphene nanocomposite also increases the fracture stress of the NC hydrogel through cation–π and π–π interactions. The improved mechanical properties of the NC hydrogel result from the synergistic effects of the chemical crosslinking of the polymer network and the physical crosslinking of the polymer/graphene nanofiller.

Cu2ZnSnS4 QDs anchored 2-D few-layer graphene bridge enhanced photo induced charge carrier transport behavior for high efficient kesterite photovoltaic cell

Quaternary chalcogenide Cu2ZnSnS4 (CZTS) is a promising absorber for photovoltaic cell application due to its excellent properties like natural abundancy, non-toxic material incorporation, high absorption coefficient ∼104 cm−1 and tuneable band gap energy of 1.4–1.6 eV. However, still there is a huge gap of efficiency between the market oriented Si based photovoltaic device and kesterite device as it is hindered by poor charge carrier mobility. To improve the carrier mobility of semiconducting CZTS material, incorporation of highly conducting material like graphene would be helpful. The incorporation of graphene into CZTS enhances the separation and transfer of charge carriers in an efficient way inhibiting recombination. In this present work, the photovoltaic performance of solution processed single phase kesterite CZTS QDs anchored on electro-chemically prepared few-layer graphene sheet (FLGS) as active layer has been reported. The QD decoration has been carried out by a simple, scalable, environment friendly solution based approach without surface modifications and post-sulphurization treatment. The prepared hybrid structure demonstrates significant increase in photocurrent and optical absorbance indicates the fast charge carrier transport behaviour. The power conversion efficiency (PCE) of fabricated hybrid CZTS QDs-FLGS photovoltaic cell with device configuration of Mo/CZTS QDs-FLGS/CdS/ZnO/Al approached ∼7.64% (for 2.5 wt% FLGS loading) with short circuit current density (Jsc) of 19.07 mAcm−2, superior to individual CZTS QDs (∼6.11% PCE and 15.6% Jsc).

Electrical and Structural Characterization of Few-Layer Graphene Sheets on Quartz.

Despite the impressive performance and incredible promise for a variety of applications, the wide-scale commercialization of graphene is still behind its full potential. One of the main challenges is related to preserving graphene’s unique properties upon transfer onto practically desirable substrates. In this work, few-layer graphene sheets deposited via liquid-phase transfer from copper onto a quartz substrate have been studied using a suite of experimental techniques, including scanning electron microscopy (SEM), Raman spectroscopy, admittance spectroscopy, and four-point probe electrical measurements. SEM measurements suggest that the transfer of graphene from copper foil to quartz using the aqueous solution of ammonium persulfate was accompanied by unintentional etching of the entire surface of the quartz substrate and, as a result, the formation of microscopic facet structures covering the etched surface of the substrate. As revealed by Raman spectroscopy and the electrical measurements, the transfer process involving the etching of the copper foil in a 0.1 M solution of (NH4)2S2O8 resulted in its p-type doping. This was accompanied by the appearance of an electronic gap of 0.022 eV, as evidenced by the Arrhenius analysis. The observed increase in the conductance of the samples with temperature can be explained by thermally activated carrier transport, dominating the scattering processes.

Electronic Tuning of Core-Shell CoNi Nanoalloy/N-Doped Few-Layer Graphene for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

The discovery of highly efficient, durable, and affordable bifunctional ORR/OER electrocatalysts is of great significance for the commercialization of rechargeable metal-air batteries. Herein, we synthesized uniformly sized CoNi alloy nanoparticles encapsulated with N-doped few-layer graphene (N-FLG) sheets via pyrolysis of a CoNi dual metal-organic framework precursor. The developed CoNi/N-FLG catalyst exhibited excellent oxygen reduction activity (comparable to a commercial 20 wt % Pt/C catalyst) and outstanding oxygen evolution activity (superior to a commercial 20 wt % IrO2/C catalyst), thus enabling efficient bifunctional oxygen electrocatalysis and stability when applied in prototype rechargeable zinc-air batteries. The remarkable electrochemical properties of CoNi/N-FLG originate from its unique core-shell structure and favorable electron penetration effects, thereby optimizing the adsorption/desorption strengths of intermediates formed during the oxygen reduction and oxygen evolution reactions.