Graphene Electrodes Research Articles

Laser Cutting Coupled with Electro-Exfoliation to Prepare Versatile Planar Graphene Electrodes for Energy Storage.

The study of planar energy storage devices, characterized by low-cost, high capacity, and satisfactory flexibility, is becoming a valuable research hotspot. Graphene, monolayer sp2 hybrid carbon atoms with a large surface area, always acts as its active component, yet there is a tension between its high conductivity and ease of implementation. Although the difficult-to-assemble graphene can easily achieve planar assemblies in its highly oxidized form (GO), the undesirable conductivity, even after proper reduction, still restricts its further applications. Here, a facile "Top-down" method has been proposed to prepare the graphene planar electrode via in situ electro-exfoliation of graphite supported on a piece of laser-cutting patterned scotch tape. Detailed characterizations have been performed to study its physiochemical property evolution during electro-exfoliation. The obtained flexible graphene planar electrodes show decent energy storage performance, e.g., 40.8 mF cm-2 at a current density of 0.5 mA cm-2 and an 81% capacity retention at a current density of 8 mA cm-2 for the optimized sample G-240. Their high conductivity also makes it possible to couple them with other redox-active materials through electrodeposition to improve their performance, e.g., ferrocene-functionalized mesoporous silica film (Fc-MS), MnO2, and polyaniline (PANI). The highest capacity was achieved with the PANI functionalized sample, which achieved a 22-fold capacity increase. In a word, the versatility, practicality, and adaptability of the protocol to prepare the planar graphene electrode proposed in this work make it a potential candidate to meet the continuously growing energy storage demands.

Spin dependent molecular junction with graphene electrodes as a thermoelectric nanodevice

Using Green's function method, spin-resolved thermoelectric quantum transport is examined in a molecular junction composed of a phenalene molecule connected to two external graphene leads with and without magnetic exchange potential application on the scattering region. Two different configurations of the system are considered: perpendicular and parallel leads. Theoretical results show that the application of the external exchange potential separates the Seebeck coefficients of different spin states and dramatically increases the coefficients. Furthermore, the temperature gradient between the left and right parts of the system generates a current of nanoAmpere order of magnitude even in the absence of a bias voltage. With the exchange potential, the current is spin-resolved and increased up to 50 times in comparison to the absence of the exchange potential. According to the results, the system acts as a spin filter at some specific chemical potential. Moreover, the current dramatically increases in parallel configuration compared to the perpendicular arrangement. Consequently, the proposed molecular device, with adjustable parameters and a magnificent Seebeck coefficient, can be a promising alternative to ordinary thermoelectric structures in the design of the new generation of thermal spintronic devices.

Do specific ion effects influence the physical chemistry of aqueous graphene-based supercapacitors? Perspectives from multiscale QMMD simulations

Whether or not specific ion effects determine the charge storage properties of aqueous graphene and graphite-based supercapacitors remains a highly debated topic. In this work we present a multiscale quantum mechanics – classical molecular dynamics (QMMD) investigation of aqueous mono- and divalent salt electrolytes in contact with fully polarizable charged graphene sheets. By computing both the electrochemical double layer (EDL) and quantum capacitance we observe a constant electrode specific capacitance with cationic radii and charge. Counterintuitively, we determine that a switch in the cation adsorption mechanism from inner to outer Helmholtz layers leads to negligible changes to the EDL capacitance, this appears to be due to the robust electronic structure of the graphene electrodes. However, the ability of ions (such as K+) with a relatively low hydration free energy to penetrate the inner Helmholtz plane and adsorb directly on the electrode surface is found to slow their diffusion parallel to the interface. Ions in the outer Helmholtz layer are found to have higher diffusivity at the surface due to their position in ion channels between water layers. Our results show that surface effects such as the surface polarization and the partial dehydration and local structuring of ions on the surface underpin the behaviour of cations at the interface and add a vital new perspective on trends in ion mobilities seen under confinement.

Nanoflowers on Microporous Graphene Electrodes as a Highly Sensitive and Low-Cost As(III) Electrochemical Sensor for Water Quality Monitoring

In this work, we report a low-cost and highly sensitive electrochemical sensor for detecting As(III) in water. The sensor uses a 3D microporous graphene electrode with nanoflowers, which enriches the reactive surface area and thus enhances its sensitivity. The detection range achieved was 1-50 ppb, meeting the US-EPA cutoff criteria of 10 ppb. The sensor works by trapping As(III) ions using the interlayer dipole between Ni and graphene, reducing As(III), and transferring electrons to the nanoflowers. The nanoflowers then exchange charges with the graphene layer, producing a measurable current. Interference by other ions, such as Pb(II) and Cd(II), was found to be negligible. The proposed method has potential for use as a portable field sensor for monitoring water quality to control hazardous As(III) in human life.

Tunable Interferometric Effects between Single-Molecule Suzuki-Miyaura Cross-Couplings.

Parallel two molecular bridges loaded with a palladium catalyst were integrated into separate pairs of graphene electrodes in the same device. Based on the complete description of the one-palladium catalytic pathway by single-molecule electrical spectroscopy, this setup enables the mapping of the cross-correlation between different catalysts and demonstrates the emergent complexity in the extrapolation from single molecule to ensemble. The anticorrelation behaviors at the time scale of two individual catalysts in sufficiently close proximity were revealed in the Suzuki-Miyaura cross-coupling. Further experimental evidence demonstrates that the long-range electric dipole-dipole interaction induced by solvent leads to the destructive interferometric effect of two catalysts. In contrast, the cooperative coupling of the elementary step between two catalysts affords a local acceleration. This new form of reaction dynamics measurement via focusing on multiple molecules with single-event resolution holds great promise to build a bridge between single molecule and ensemble.

A High-Linearity Glucose Sensor Based on Silver-Doped Con A Hydrogel and Laser Direct Writing

A continuous glucose monitoring (CGM) system is an ideal monitoring system for the blood glucose control of diabetic patients. The development of flexible glucose sensors with good glucose-responsive ability and high linearity within a large detection range is still challenging in the field of continuous glucose detection. A silver-doped Concanavalin A (Con A)-based hydrogel sensor is proposed to address the above issues. The proposed flexible enzyme-free glucose sensor was prepared by combining Con-A-based glucose-responsive hydrogels with green-synthetic silver particles on laser direct-writing graphene electrodes. The experimental results showed that in a glucose concentration range of 0-30 mM, the proposed sensor is capable of measuring the glucose level in a repeatable and reversible manner, showing a sensitivity of 150.12 Ω/mM with high linearity of R2 = 0.97. Due to its high performance and simple manufacturing process, the proposed glucose sensor is excellent among existing enzyme-free glucose sensors. It has good potential in the development of CGM devices.

The Role of the Precursor on the Electrochemical Performance of N,S Co-Doped Graphene Electrodes in Aqueous Electrolytes

The introduction of pillared agents or dopants to the graphene used as the electroactive material in supercapacitor electrodes can be an efficient way to facilitate ion transfer, mitigate re-stacking, and improve electrochemical performance. We evaluated the effect of different precursors containing nitrogen (N) and sulfur (S) atoms to dope graphene flake (GF) lattices. The electrochemical performance of the doped GF was assessed in 1 M KOH and 1 M Na2SO4 electrolytes. N- and S-doped GF flakes were synthesized via mechanochemical synthesis, also known as ball milling. After being ground, the materials were calcined under N2. The physicochemical characterization of the materials evidenced the co-doping of both S and N into the graphene backbone, as corroborated by the results of Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). As shown by the results, the nature of the precursors influences the ratio of S and N in the doped graphene flakes and, consequently, the response of the electroactive electrode material. The co-doping obtained using 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole revealed a specific capacitance of 48 F.g−1 at 1.0 A∙g−1 and over 90% capacitance retention after 10,000 cycles at 10.0 A∙g−1 in Na2SO4.

A Tunable Single-Molecule Light-Emitting Diode with Single-Photon Precision.

A robust single-molecule light-emitting diode (SM-LED) with high color purity, linear polarization, and efficiency tunability is prepared by covalently integrating one fluorescent molecule into nanogapped graphene electrodes. Furthermore, single-molecule Förster resonance energy transfer from the electroluminescent center to different accepters is achieved through rational molecular engineering, enabling construction of a multicolor SM-LED. All these characterizations are accomplished in the photoelectrical integration system with high temporal/spatial/energy resolution, demonstrating the capability of the single-photon emission of SM-LEDs. The success in developing high-performance SM-LEDs inspires the development of the next generation of commercial display devices and promises a single-photon emitter for use in quantum computation and quantum communication.

Electrochemical Performance of Potassium Bromate Active Electrolyte for Laser-Induced KBr-Graphene Supercapacitor Electrodes

In this paper, we have reported a low-concentration active electrolyte of KBrO3 for the supercapacitor’s application. The electrochemical processes were carried out in two concentrations of KBrO3 with 0.2 and 0.4 M. Additionally, we have reported a novel strategy for doping graphene during its fabrication process with a potassium bromide (KBr) solution. The chemical doping of graphene with KBr improved the electrochemical properties of graphene used as supercapacitors. HRTEM images confirmed the multi-layer graphene obtained by CO2 laser based on polyimide. The effect of KBr on the graphene lattice has been studied using Raman spectroscopy. The two electrodes of graphene and KBr-doped graphene were subjected to the electrochemical properties study as a supercapacitor by electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge techniques. The results exhibited the successful method of graphene doping and the stability of using KBrO3 as a suitable electrolyte for electrochemical processes with this lower molarity. The specific capacitance of the pristine graphene capacitor in 0.2 M of KBrO3 was 33 Fg−1, while this value increased up to 70 Fg−1 for KBr-doped graphene in 0.4 M of KBrO3. The specific capacity in mAhg−1 has also increased twofold. The results exhibited the possibility of using KBrO3 as an electrolyte. The supercapacitor performance almost showed good stability in the life cycle.

Molecular insights into the electric double-layer structure at a polymer electrolyte-electrode interface

Polymer electrolyte-based electric double-layer supercapacitors (EDLCs) have been increasingly studied for flexible, wearable, and multifunctional energy storage applications. Although the phenomenon that electrode materials present significantly lower EDL capacitances in polymer electrolytes than in liquid electrolytes has been widely observed, it has not been well studied and explained. Here we present the molecular dynamics simulation of a representative polymer electrolyte-based EDLC to reveal the atomic structure of such a polymer electrolyte-electrode interface for the first time. The polymer electrolyte composed of polyethylene oxide and lithium perchlorate is simulated between graphene electrodes and compared with an aqueous electrolyte-based system with the same lithium salt. We find that the polymer-based system shows unique EDL structures in the inner and outer Helmholtz layers that are not seen in the aqueous one. Statistical analyses along with ab initio calculations show that the disparities mainly come from the different interaction strengths between ions, polymer or water molecules, and graphene electrodes. Despite these disparities, the intrinsic interfacial capacitances calculated from various simulated charge states of different EDLCs show very close values. Combined with experimental measurements, we conclude that the reduced capacitances with polymer electrolytes reported in the literature come from the poor interface between electrode and electrolyte, which can be significantly improved through proper thermal treatments.

High-performance self-powered ultraviolet photodetector in SnO2 microwire/p-GaN heterojunction using graphene as charge collection medium

• Using a facile vapor transport deposition method, the samples of SnO 2 microwires were synthesized individually self-catalyzed by a fast and simple CVD method. By combining p-type GaN substrate, a single SnO 2 microwire heterojunction photodetector working in the ultraviolet wavelengths was constructed. • By replacing the top electrodes from ITO to monolayer graphene, enhanced ultraviolet photoresponses were obtained, which exhibiting a peak responsivity 223.7 mA/W, detectivity ∼ 6.9 × 10 12 Jones, high EQE of 77%, and a fast response speed (rising/decaying times ∼ 18/580 μs) at 360 nm light illumination when the device is operated in self-driven mode. Our results suggest that the graphene transparent electrodes can not only allow the majority of the incident light to reach the contact area but also offer an easy carrier transport channel when the electron-holes were separated. • In particular, the microscopic photoresponse mechanism of the fabricated n-SnO 2 microwire/p-GaN heterojunction photodetector that using monolayer graphene as charge collection medium was studied. The Schottky-potential is formed by the built-in electric-field from graphene to the SnO 2 wire. The built-in field is in the same direction as the original SnO 2 /GaN built-in electric field, which was similar to the reverse voltage applied to the heterojunction. Therefore, the net built-in field toward the SnO 2 /GaN heterointerface can be increased, resulting in the increment of the carrier collection efficiency through graphene as a charge collection medium. Graphene monolayer has been extensively applied as a transparency electrode material in photoelectronic devices due to its high transmittance, high carrier mobility, and ultrafast carrier dynamics. In this study, a high-performance self-powered photodetector, which is made of a SnO 2 microwire, p-type GaN film, and monolayer graphene transparent electrode, was proposed and fabricated. The detector is sensitive to ultraviolet light signals and illustrates pronounced detection performances, including a peak responsivity ∼ 223.7 mA W –1 , a detectivity ∼ 6.9 × 10 12 Jones, fast response speed (rising/decaying times ∼ 18/580 μs), and excellent external quantum efficiency ∼ 77% at 360 nm light illumination without external power supply. Compared with the pristine SnO 2 /GaN photodetector using ITO electrode, the device performances of responsivity and detectivity are significantly increased over 6 × 10 3 % and 3 × 10 3 %, respectively. The performance-enhanced characteristics are mainly attributed to the high-quality heterointerface of n-SnO 2 /p-GaN, the highly conductive capacity, and the unique transparency of graphene electrodes. Particularly, the built-in potential formed at the SnO 2 /GaN heterojunction interface could be strengthened by the Schottky potential barrier derived from the graphene electrode and SnO 2 wire, enhancing the carrier collection efficiency through graphene as a charge collection medium. This work is of great importance and significance to developing excellent-performance ultraviolet photodetectors for photovoltaic and optoelectronic applications in a self-powered operation manner.

Facile and Tunable Synthesis of Nitrogen-Doped Graphene with Different Microstructures for High-Performance Supercapacitors

Heteroatom-doped graphene is of great interest for energy storage applications due to its improved local electronic structures compared with undoped graphene. However, a tunable method for the preparation of heteroatom-doped graphene with a special microstructure is still worth developing. Herein, a novel nitrogen-doped graphene with different microstructures is facilely synthesized via an in situ interlamination self-assembling method that employs the in situ formed Fe3(PO4)2 and organoamine as the catalyst and carbon source, respectively. By tuning the alkyl chain length in organoamine, octylamine and dodecylamine, bubble-like and sheet-like nitrogen-doped graphene are obtained, respectively. In three-electrode supercapacitor tests, besides the double-layer capacitance, the as-prepared graphene electrode material indeed exhibits pseudocapacitance due to the N-rich feature, delivering a good rate capability (166 F g–1 at 20 A g–1) and cyclic performance (96% capacitance retention over 20,000 cycles at 20 A g–1). More importantly, the symmetrical supercapacitor studies reveal the promising practicality due to the achieved excellent energy and power densities together with long-term cyclability. Thereby, this work establishes a new milestone for the facile synthesis of heteroatom-doped graphene with a desired microstructure for energy storage and other applications.

Publisher's Note: “Fabrication of interdigitated electrodes of graphene oxide/silica by femtosecond laser-induced forward transfer for sensing applications” [J. Appl. Phys. 133, 053103 (2023)

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On the Road to the Frontiers of Lithium-Ion Batteries: A Review and Outlook of Graphene Anodes.

Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started withand then the approaches to improve its electrochemical performanceare comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggregation, fast electrons/ions transportation, and optimal solid electrolyte interphase are discussed, demonstrating the close connection between the surface structure and electrochemical activity of graphene. Second, graphene derivatives anodes prepared by heteroatom doping and covalent functionalization are outlined, which show great advantages in boosting the Li storage performances because of the additionally introduced defect/active sites for further Li accommodation. Furthermore, binder-free and free-standing graphene electrodes arepresented,exhibiting great prospects for high-energy-density and flexible LIBs. Finally, the remaining challenges and future opportunities of practically available graphene anodes for advanced LIBs are highlighted.

Bubble Up Induced Graphene Microspheres for Engineering Capacitive Energy Storage

AbstractTranslating the material merits of graphene to practical supercapacitor devices is critical for promoting capacitive energy storage, but is challenging due to the limited scalability in fabricating high‐performance graphene electrode films. Here, we demonstrate a method for fabricating graphene microsphere films, formed by the bubble‐induced destruction and agglomeration of the self‐assembled toplayer of mixed graphene oxide and exfoliated graphene over an adequately heated solution. The microspheres have compact, randomly distributed graphene flakes, endowing the films with a high bulk density (0.92 g cm−3) and ion conductivity to allow ultrahigh charge/discharge current densities of up to 1,000 A g−1 in an ionic liquid. The stack cell with an areal mass loading of 10 mg cm−2 exhibits an excellent energy density of 83.4 Wh L−1, superior to the state‐of‐the‐art carbon‐based supercapacitors, and approaching that of lead‐acid batteries. More importantly, a meter‐scale film is fabricated within half a minute by a developed roll‐to‐roll process, demonstrating the enormous potential of these films in the industrial manufacturing of supercapacitors. Furthermore, the film electrode is infilled with an ionogel electrolyte and assembled into an all‐solid‐state, flexible device with durable flexibility and multiple optional outputs, demonstrating the potential of these supercapacitors for powering flexible electronic devices.

Investigation of fiber laser-induced porous graphene electrodes in controlled atmospheres for ZnO nanorod-based NO2 gas sensors

This study aims to develop fiber laser-induced graphene (LIG) on polyimide films fabricated under a chamber with air, vacuum, or nitrogen atmospheres. Moreover, ZnO nanorods with a large specific surface area were synthesized by a facile and low-cost hydrothermal method. The ZnO nanorod sensing solution was drop-cast on the LIG surface with porous structures as a sensing layer for the NO2 gas sensor. The characteristics of the LIGs and ZnO nanorods including the surface morphology, elemental content, crystal structure, elemental composition, and chemical bond were investigated. The ZnO gas sensor with LIG electrodes fabricated in air has outstanding sensing performance in a high response (251.71 %), fast response and recovery times (9.5 s and 8.3 s, respectively), and response stability at a NO2 concentration of 1000 ppb. In addition, the ZnO gas sensor with LIG electrodes fabricated in vacuum has an excellent sensitivity. Based on the ZnO nanorod/LIG-based NO2 gas sensor with a high response and sensitivity, the proposed gas sensors can be combined with the Internet of Things and widely used in real-time detecting harmful gases.

Paper-based electrochemical sensor for simultaneous detection of salivary Δ⁹-tetrahydrocannabinol and thiocyanate to differentiate illegal cannabis smokers

Cannabis smoking is on the rise as a result of cannabis legalization across the world. The intake of cannabis by smoking has an impact on the mental health of smokers and intimates. Therefore, rapid monitoring of illicit cannabis use via direct saliva samples is necessary. The Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and thiocyanate (SCN) level in saliva can be an effective biomarker to differentiate between cannabis and non-cannabis smokers such as cannabis ingestion, cigarette smokers, and healthy people. In this work, there is a development of an electrochemical sensor, “copper-phthalocyanine-modified screen-printed graphene electrodes (CuPc/SPGE),” for the concurrent determination of Δ⁹-THC and SCN using differential pulse voltammetry. Furthermore, the applicability of the CuPc/SPGE sensor was verified by simultaneously measuring Δ⁹-THC and SCN in saliva samples. The results from the developed sensor were similar to those obtained by high-performance liquid chromatography. This proposed sensor represents a first step in the differentiation of illegal cannabis smokers using the correlation between the contents of Δ⁹-THC and SCN in saliva, with features of rapidity, simplicity, low cost, and disposability.

Molecular understanding of the Helmholtz capacitance difference between Cu(100) and graphene electrodes.

Unraveling the origin of Helmholtz capacitance is of paramount importance for understanding the interfacial structure and electrostatic potential distribution of electric double layers (EDL). In this work, we combined the methods of ab initio molecular dynamics and classical molecular dynamics and modeled electrified Cu(100)/electrolyte and graphene/electrolyte interfaces for comparison. It was proposed that the Helmholtz capacitance is composed of three parts connected in series: the usual solvent capacitance, water chemisorption induced capacitance, and Pauling repulsion caused gap capacitance. We found the Helmholtz capacitance of graphene is significantly lower than that of Cu(100), which was attributed to two intrinsic factors. One is that graphene has a wider gap layer at interface, and the other is that graphene is less active for water chemisorption. Finally, based on our findings, we provide suggestions for how to increase the EDL capacitance of graphene-based materials in future work, and we also suggest that the new understanding of the potential distribution across the Helmholtz layer may help explain some experimental phenomena of electrocatalysis.

Hybrid graphene electrode for the diagnosis and treatment of epilepsy in free-moving animal models

Various electrophysiological and imaging techniques have been studied for the diagnosis and treatment of epilepsy. In particular, electrocorticography (ECoG) provides valuable information that can guide clinical treatment of patients with epilepsy. Currently, it is necessary to define the clinical benefits of ECoG in free-moving animals for the treatment of epilepsy. Here, we present the results of simultaneous recordings of multiple cortical sites and responsive neurostimulations for epilepsy treatment carried out in free-moving rats. In this study, we developed a high-density, flexible electrode array comprising graphene/Au/graphene that stably wraps onto the cortex surface of a living rat brain, exhibiting a superior signal-to-noise ratio. The hybrid graphene multichannel electrode successfully detected brain signals with high-throughput spatiotemporal resolution and substantially suppressed pilocarpine-induced epileptic discharges and behavior. Simultaneous recording and neurostimulation in awake animals can lead to a fundamental change in the treatment of medically intractable epilepsy.

Laser Reduced Graphene Oxide Electrode for Pathogenic Escherichia coli Detection.

Graphene-based materials are of interest in electrochemical biosensing due to their unique properties, such as high surface areas, unique electrochemical properties, and biocompatibility. However, the scalable production of graphene electrodes remains a challenge; it is typically slow, expensive, and inefficient. Herein, we reported a simple, fast, and maskless method for large-scale, low-cost reduced graphene oxide electrode fabrication; using direct writing (laser scribing and inkjet printing) coupled with a stamp-transferring method. In this process, graphene oxide is simultaneously reduced and patterned with a laser, before being press-stamped onto polyester sheets. The transferred electrodes were characterized by SEM, XPS, Raman, and electrochemical methods. The biosensing utility of the electrodes was demonstrated by developing an electrochemical test for Escherichia coli. These biosensors exhibited a wide dynamic range (917-2.1 × 107 CFU/mL) of low limits of detection (283 CFU/mL) using just 5 μL of sample. The test was also verified in spiked artificial urine, and the sensor was integrated into a portable wireless system driven and measured by a smartphone. This work demonstrates the potential to use these biosensors for real-world, point-of-care applications. Hypothetically, the devices are suitable for the detection of other pathogenic bacteria.