Graphene Electrodes Research Articles

Uranium capture by a layered 2D/2D niobium phosphate/holey graphene architecture via an electro-adsorption and electrocatalytic reduction coupling process.

As an energy-efficient and eco-friendly technique, capacitive deionization (CDI) has shown great potential for uranium (U(VI)) capture recently. However, extracting U(VI) with high kinetics, capacity and selectivity remains a major challenge due to the current surface active sites-based material and co-existing ions in aqueous solution. Here we rationally designed a layered 2D/2D niobium phosphate/holey graphene (HGNbP) electrode material, and originally demonstrated its efficient U(VI) capture ability via an electro-adsorption and electrocatalytic reduction coupling process. The less-accumulative loose layered architecture, open polycrystalline construction of niobium phosphate with active phosphate sites, and rich in-plane nano-pores on conductive graphene nanosheets endowed HGNbP with fast charge/ion transport, high electroconductivity and superior pseudocapacitance, which enabled U(VI) ions first to be electro-adsorbed, then physico-chemical adsorbed, and finally electrocatalysis reduced/deposited onto electrode surface without the limitation of active sites under a low potential of 1.2V. Based on these virtues, the HGNbP exhibited a fast adsorption kinetics, with a high removal rate of 99.9% within 30min in 50mgL-1 U(VI) solution, and a high adsorption capacity up to 1340mgg-1 in 1000mgL-1 U(VI) solution. Furthermore, the good recyclability and selectivity towards U(VI) were also realized.

Understanding molecular and electrochemical charge transfer: theory and computations.

Electron, proton, and proton-coupled electron transfer (PCET) are crucial elementary processes in chemistry, electrochemistry, and biology. We provide here a gentle overview of retrospective and currently developing theoretical formalisms of chemical, electrochemical and biological molecular charge transfer processes, with examples of how to bridge electron, proton, and PCET theory with experimental data. We offer first a theoretical minimum of molecular electron, proton, and PCET processes in homogeneous solution and at electrochemical interfaces. We illustrate next the use of the theory both for simple electron transfer processes, and for processes that involve molecular reorganization beyond the simplest harmonic approximation, with dissociative electron transfer and inclusion of all charge transfer parameters. A core example is the electrochemical reduction of the S2O82- anion. This is followed by discussion of core elements of proton and PCET processes and the electrochemical dihydrogen evolution reaction on different metal, semiconductor, and semimetal (say graphene) electrode surfaces. Other further focus is on stochastic chemical rate theory, and how this concept can rationalize highly non-traditional behaviour of charge transfer processes in mixed solvents. As a second major area we address ("long-range") chemical and electrochemical electron transfer through molecular frameworks using notions of superexchange and hopping. Single-molecule and single-entity electrochemistry are based on electrochemical scanning probe microscopies. (In operando) scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are particularly emphasized, with theoretical notions and new molecular electrochemical phenomena in the confined tunnelling gap. Single-molecule surface structure and electron transfer dynamics are illustrated by self-assembled thiol molecular monolayers and by more complex redox target molecules. This discussion also extends single-molecule electrochemistry to bioelectrochemistry of complex redox metalloproteins and metalloenzymes. Our third major area involves computational overviews of molecular and electronic structure of the electrochemical interface, with new computational challenges. These relate to solvent dynamics in bulk and confined space (say carbon nanostructures), electrocatalysis, metallic and semiconductor nanoparticles, d-band metals, carbon nanostructures, spin catalysis and "spintronics", and "hot" electrons. Further perspectives relate to metal-organic frameworks, chiral surfaces, and spintronics.

Silver nanoparticles - laser induced graphene (Ag NPs - LIG) hybrid electrodes for sensitive electrochemical-surface enhanced Raman spectroscopy (EC-SERS) detection.

This paper presents a novel approach for the fabrication of low cost Electrochemical-Surface Enhanced Raman Scattering (EC-SERS) sensing platforms. Laser Induced Graphene (LIG) electrodes were readily fabricated by direct laser writing of polyimide tapes and functionalized with silver nanoparticles (Ag NPs) to obtain hybrid Ag NPs - LIG electrodes suitable for EC-SERS analysis. Detection was achieved by coupling a handheld potentiostat with a Raman spectrograph, enabling measurement of SERS spectra of target analytes generated during voltage sweeps in the 0.0 to -1.0 V interval range. The sensing capabilities of the fabricated system were first tested with model molecule 4-aminobenzenethiol (4-ABT). Following sensitive detection of 4-ABT, EC-SERS analysis of food contaminant melamine in milk and antibiotic difloxacin hydrochloride (DIF) in river water was demonstrated, achieving sensitive detection of both analytes without pre-treatment steps. The easiness of fabrication, versatility of design, rapid analysis time and potential miniaturization of the system make Ag NPs - LIG electrodes suitable for a large range of in situ applications in the field of food monitoring and for environmental analysis.

Advances in the research of carbon electrodes for perovskite solar cells.

Perovskite solar cells (PSCs) were first proposed in 2009. They have the advantages of low cost, a simple manufacturing process and excellent photoelectric performance. PSC electrodes are mainly made from precious metals such as gold and silver. Still, the cost of precious metals is high and they react with the other components of the PSCs, resulting in the poor stability of the photovoltaic device. Using carbon as an electrode material can both reduce the cost and significantly improve the stability of the photovoltaic device. However, the poor interface contact between the carbon electrode and perovskite and carbon electrode resistance results in poor photovoltaic device photoelectric performance. Finding a way to successfully utilize carbon as an alternative electrode material is a key step toward moving PSCs from the laboratory to industrialization. This paper reviews the application of carbon black, graphite, graphene, carbon nanotubes (CNTs) and composite carbon electrode in PSCs, focusing on progress in the research of doping, structure, interface modification and the production process.

A New Program of Voltammetry Experiment Teaching Based on Laser-Scribed Graphene Electrode

A New Program of Voltammetry Experiment Teaching Based on Laser-Scribed Graphene Electrode

In Vivo Voltammetric Imaging of Metal Nanoparticle-Catalyzed Single-Cell Electron Transfer by Fermi Level-Responsive Graphene.

Metal nanomaterials can facilitate microbial extracellular electron transfer (EET) in the electrochemically active biofilm. However, the role of nanomaterials/bacteria interaction in this process is still unclear. Here, we reported the single-cell voltammetric imaging of Shewanella oneidensis MR-1 at the single-cell level to elucidate the metal-enhanced EET mechanism in vivo by the Fermi level-responsive graphene electrode. Quantified oxidation currents of ~20 fA were observed from single native cells and gold nanoparticle (AuNP)-coated cells in linear sweep voltammetry analysis. On the contrary, the oxidation potential was reduced by up to 100 mV after AuNP modification. It revealed the mechanism of AuNP-catalyzed direct EET decreasing the oxidation barrier between the outer membrane cytochromes and the electrode. Our method offered a promising strategy to understand the nanomaterials/bacteria interaction and guide the rational construction of EET-related microbial fuel cells.

Single-step electropolymerization on a printed sensor towards a conductive thin film polymer for the simultaneous determination of drug metabolites: 5-aminosalicylic acid and sulfapyridine.

Amino acid conductive polymers can easily form a thin film on a sensor surface by an electrochemical process. Therefore, we are pioneers in reporting the electropolymerization of L-methionine on the surface of a screen-printed graphene electrode to obtain a disposable electrochemical sensor for determining drug metabolites (5-aminosalicylic acid (5-ASA) and sulfapyridine (SPD)) of sulfasalazine (SSZ) simultaneously. In this work, the developed sensor was facilely created through a single step of electropolymerization under mild conditions (0.1 M phosphate buffer pH 7.0) using cyclic voltammetry. Important parameters in the synthesis process were systematically investigated followed by surface composition and morphology studies. Then, analytical performances, comprising sensitivity, selectivity, stability, reproducibility, and sample preparation, were carefully evaluated. Under optimal conditions, the proposed methodology demonstrated a highly sensitive and selective simultaneous detection of 5-ASA and SPD with wide linear dynamic ranges of 1-50 μM and 80-250 μM and low detection limits of 0.60 and 0.57 μM for 5-ASA and SPD, respectively. To evaluate the potential of the designed sensor, it was successfully applied by simultaneously determining 5-ASA and SPD in real human urine samples on the same day (intra-day study) and on three different days (inter-day study).

A conformal van der Waals graphene coating enabled high-performance piezo-ionic sensor for spatial, gesture, and object recognition

Highly electrically conductive (16 ohm sq−1) and conformal van der Waals graphene electrodes were synthesized on piezo-ionic materials. Such electrodes enhanced the piezo-ionic output to 90.3 mV and distinguished soft and hard objects.

Graphene-interfaced flexible and stretchable micro-nano electrodes: from fabrication to sweat glucose detection.

Flexible and stretchable wearable electronic devices have received tremendous attention for their non-invasive and personal health monitoring applications. These devices have been fabricated by integrating flexible substrates and graphene nanostructures for non-invasive detection of physiological risk biomarkers from human bodily fluids, such as sweat, and monitoring of human physical motion tracking parameters. The extraordinary properties of graphene nanostructures in fully integrated wearable devices have enabled improved sensitivity, electronic readouts, signal conditioning and communication, energy harvesting from power sources through electrode design and patterning, and graphene surface modification or treatment. This review explores advances made toward the fabrication of graphene-interfaced wearable sensors, flexible and stretchable conductive graphene electrodes, as well as their potential applications in electrochemical sensors and field-effect-transistors (FETs) with special emphasis on monitoring sweat biomarkers, mainly in glucose-sensing applications. The review emphasizes flexible wearable sweat sensors and provides various approaches thus far employed for the fabrication of graphene-enabled conductive and stretchable micro-nano electrodes, such as photolithography, electron-beam evaporation, laser-induced graphene designing, ink printing, chemical-synthesis and graphene surface modification. It further explores existing graphene-interfaced flexible wearable electronic devices utilized for sweat glucose sensing, and their technological potential for non-invasive health monitoring applications.

Tuning quantum capacitance in 2D graphene electrodes: the role of defects and charge carrier concentration

Electrochemical oxidation of a graphene monolayer results in a G-band shift in the micro-Raman spectrum and an increase in the quantum capacitance, resulting from an increase in the number and density of defects and charge carrier concentration in the graphene structure.

MnO2-decorated highly porous 3D-printed graphene supercapacitors for photosynthetic power systems

3D printed graphene electrodes decorated with nanoporous MnO2 and thylakoid membranes isolated from spinach leaves enable more efficient harvesting and storage of photosynthetic electrons produced from photosynthesis in thylakoid membranes.

Regulation and mechanism of graphene electrode bending on negative differential resistance of 2-phenylpyridine molecular devices

Combining non-equilibrium Green’s function with density functional theory, we study the electronic transport properties of the molecular devices comprised of 2-phenylpyridine and zigzag graphene nanoribbon (ZGNR) electrodes. The <i>I-V</i> characteristics and transmission coefficients under external voltage biases are analyzed, and the results show that the negative differential resistance (NDR) is effectively adjusted by the bending of ZGNR electrode, which reduces the peak voltage (<i>V</i><sub>p</sub>) and increases the peak-valley ratio (PVR) of the device. When the electrode bending angle is 15°, the PVR of device M2 is a maximum value of 12.84 and <i>V</i><sub>p</sub> is 0.1 V, which is low enough for practical applications. The transmission spectra, the density of states and the real-space scattering state distribution at <i>E</i><sub>f </sub> of device under zero bias explain that the weaker coupling between the molecules and the electrodes is caused by the bending of the ZGNR electrode, which might be responsible for the adjustability of NDR. The analysis shows that the bending of the electrode changes the electronic structure between the 2-phenylpyridine molecule and the ZGNR electrode, and then changes the wave functions overlap between them, the coupling between the molecule and the electrodes gets weaker. An external bias can induce the level to shift. The transmission coefficient for the weaker coupling between the molecules. The electrodes can fluctuate wildly from level to level, and large NDR effect under very low bias is obtained with the variation of external bias. Therefore, for highly symmetric molecular devices, the electronic transport properties can be effectively adjusted by changing the coupling between the central molecule and the electrodes. Our investigations indicate that the 2-phenylpyridine molecular device with ZGNR electrodes may have potential applications in the field of low-power dissipation molecules device.

Electrochemical inactivation of enteric viruses MS2, T4, and Phi6 using doped laser-induced graphene electrodes and filters

Titanium suboxide-doped laser-induced graphene holds great potential to inactivate model enteric viruses MS2, T4, and Phi6. The mechanism of inactivation was recognized as the combination of electric field-induced effects and electrooxidation.

Screen printing and laser-induced flexible sensors for the simultaneous sensitive detection of uric acid, tyrosine, and ascorbic acid in sweat.

A wearable sweat sensor, which could continuously monitor biomolecules related to the human physiological state, is emerging as a promising piece of health surveillance equipment. However, current sensors cannot simultaneously achieve a detection performance that equates to that of traditional sensors and satisfactory mechanical strength. Herein, a wearable sweat sensor with excellent detection performance and mechanical stability is designed and fabricated. Based on the integration of laser-induced graphene electrodes and a screen printing technique, this wearable sweat sensor could realize both the separate and simultaneous detection of uric acid (UA), tyrosine (Tyr), and ascorbic acid (AA) with high sensitivity. Good UA sensing performance in artificial sweat could be maintained even after 20 000 bends. In addition, the sensor can operate well in the wearing state or in a complex bovine whole blood sample. For the detection of human sweat, the changes in UA concentration after a purine-rich meal are continuously monitored and the results are in accordance with the corresponding serum UA detection results tested with a commercial serum UA meter. These results suggest its application potential in health monitoring for both gout patients and healthy humans.

The role of copper decorating poly(1,8-diaminonaphthalene)/graphene electrodes as a catalyst in the determination of nitrite

. Electroactive poly(1,8-diaminonaphthalene) is known to have a high affinity for metal ions thanks to amine and imine groups in the polymer chain. However, electrochemical sensors based on pristine P(1,8-DAN) have a major drawback concerning its poor electrical conductivity. To solve this problem, recently P(1,8-DAN) has been modified with some advanced nanomaterials such as carbonaceous materials or different metallic elements. In this research, we reported the synthesis and electrochemical characterization of a poly(1,8-diaminonaphthalene)/graphene composite film capable of adsorbing Cu2+ ions towards the application of nitrite sensing. P(1,8-DAN) was directly electropolymerized on graphene-coated glassy carbon electrode by a potential cycling between –0.15 and +0.95 V (vs. SCE) at a scan rate of 0.05 V/s, in aqueous solution containing 1.0 M HClO4 and 1.0 mM monomer 1,8-DAN,. The adsorption of Cu2+ ions onto the P(1,8-DAN) thin film was caried out in 0.1 M Cu(NO3)2 solution at 80 oC, followed by electrochemically redution to metal Cu0 by applying -0.4 V. The obtained copper decorating poly(1,8-diaminonaphthalene)/graphene (Gr/P(1,8-DAN)-Cu) electrodes acted as a catalyst in the enhancement of electrochemical signal for the determination of nitrite. The linear voltammetric response to the nitrite concentration was observed by a square wave voltammetric technique in the range of 0.69 to 1.12 mM with a detection limit of 0.13 mM. The results open up the path for designing other nitrite sensing based on our novel approach.

Synergistic effect between the graphene electrodes and the BiFeO3-BaTiO3 composite to overcome the limit of capacitance in eco-friendly supercapacitors made with a seawater electrolyte

To reduce the contamination of the water/soil by wasted polyethylene (generated by daily products), we propose here the fabrication of efficient and flexible supercapacitors (SCs) using recycled polyethylene (PE) from toothpaste tubes. A graphene ink was printed on the PE to make it conductive and the capacitive performance of the SCs was enhanced by adding to their electrodes a BiFeO3/BaTiO3 (BF/BT) ceramic. The devices made without the BF/BT showed a maximum capacitance and energy density of 312.4 F g−1 and 62.4 Wh kg−1, respectively. Moreover, the devices made with BF/BT and PVA/H3PO4 gel-electrolyte, presented a capacitance and energy density of 721.8 F g−1 and 144.6 Wh kg−1, respectively. This last device had 130% more capacitance than that without BF/BT. In order to make an eco-friendly SC, we substituted the PVA/H3PO4 electrolyte with seawater and obtained a capacitance and energy density of 563.7 F g−1 and 112.7 Wh kg−1, respectively. This last value of capacitance is ≈ 22% lower than that for the device made with PVA/H3PO4, but we avoid the toxicity of the acidic electrolyte for the environment. Interestingly, the SC devices reported here maintained a voltage of 0.6–1.05 V after 10 h of steady discharge. Absorbance, XPS and Raman techniques demonstrated the presence of oxygen vacancies, Ti4+/ Ti3+, Bi3+/ Bi2+ and Fe3+/ Fe2+ species (redox centers) on the SC electrodes made with BF/BT and PVA/H3PO4, but only the oxygen vacancies and Bi3+/ Bi2+ species were found in the SC electrodes fabricated with BF/BT and seawater. Thus, the lower performance of the devices made with seawater is associated to the absence of certain redox centers that contributed to the charge storage. Overall, the results of this investigation demonstrated that efficient SCs can be fabricated from recycled plastics and innocuous components (BF/BT and seawater) for wearable technologies, benefiting in this way the environment.

Highly efficient detection of ofloxacin in water by samarium oxide and β-cyclodextrin-modified laser-induced graphene electrode

We developed a new electrochemical sensor that detects ofloxacin (OFL) in water by depositing β-cyclodextrin (β-CD) and samarium oxide nanoparticles (Sm2O3 NPs) onto a laser-induced graphene (LIG) electrode. Scanning electron microscopy, Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, contact angle measurements, and electrochemical impedance spectroscopy were used to characterize β-CD/Sm2O3 NPs/LIG electrodes. Our results showed that the improved electrochemical activity is due to the excellent electrocatalytic performance of Sm2O3 NPs, improving electron transfer efficiency. The deposition of β-CD improves electrode hydrophilicity and increases the adsorption capacity of OFL on the electrode surface. The synergistic effect of two modification compositions can promote OFL detection. The enhanced adsorption energy and improved electron transfer characteristics were also confirmed by density functional theory calculations. Under optimal detection conditions, the sensor achieves a wide linear range (0.01 ∼ 1.0 μmol/L and 1.0 ∼ 120 μmol/L) and a low detection limit (0.005 μmol/L) with good anti-interference ability and stability. This sensor has also been successfully applied to the detection of OFL in tap water and lake water. These results show that the developed sensor is a promising step towards rapid in situ detection of OFL in water environments.

Stretching-insensitive stretchable and biocompatible triboelectric nanogenerators using plasticized PVC gel and graphene electrode for body-integrated touch sensor

Triboelectric nanogenerators (TENG) can generate strong electrical signals even with low frequencies and weak forces, thus research has been conducted to use them as wearable, body-attachable, and body-embeddable devices using biomechanical energies. For this reason, the TENG components, such as dielectric materials and electrodes, should be stretchable. A stretchable and biocompatible single electrode TENG based on plasticized polyvinyl chloride (PVC) gel with a graphene electrode is fabricated. PVC gel is a suitable stretchable TENG dielectric material owing to its high stretchability, dielectric constant, and tribo-negative properties, and graphene is a highly conductive electrode. Graphene and PVC gel-based stretchable and biocompatible TENGs display excellent electrical outputs (48 V, 2.5 μA, and 0.49 W/m2). The electrical resistance range of the electrode which does not affect the TENG output performance, and a stretching-insensitive TENG with approximately 50% stretching rate is successfully demonstrated through this study. In addition, both PVC gel and graphene are biocompatible. These stretching-insensitive and biocompatible TENGs may be used as a self-powered touch sensor that can be integrated into the human body.

An On-Chip Microscale Vacuum Chamber with High Sealing Performance Using Graphene as Lateral Feedthrough.

On-chip microscale vacuum chambers with high sealing performance and electrical feedthroughs are highly desired for microscale vacuum electronic devices and other MEMS devices. In this paper, we report an on-chip microscale vacuum chamber which achieves a high sealing performance by using monolayer graphene as lateral electrical feedthrough. A vacuum chamber with the dimensions of π × 2 mm × 2 mm × 0.5 mm is fabricated by anodically bonding a glass chip with a through-hole between two Si chips in a vacuum, after monolayer graphene electrodes have been transferred to the surface of one of the Si chips. Benefiting from the atomic thickness of monolayer graphene, the leak rate of Si-glass bonding interface with a monolayer graphene feedthrough is measured at less than 2 × 10-11 Pa·m3/s. The monolayer graphene feedthrough exhibits a minor resistance increase from 22.5 Ω to 31 Ω after anodic bonding, showing good electrical conductance. The pressure of the vacuum chamber is estimated to be 185 Pa by measuring the breakdown voltage. Such a vacuum is found to maintain for more than 50 days without obvious degradation, implying a high sealing performance with a leak rate of less than 1.02 × 10-16 Pa·m3/s.

Plasmon-enhanced Graphene/4H–SiC /graphene metal-semiconductor-metal ultraviolet photodetector: Concept and optimization

In this paper, a hybrid approach that combines a light trapping formalism and a metaheuristic optimization approach is suggested to enhance speed and sensing capabilities of a thin film/4H–SiC photodetector (PD). To overcome the shadowing problem, interdigitated electrodes made of graphene are employed. Besides, Ag nanoparticles are inserted to enhance photon absorption in the 4H–SiC active area. To avoid the complexity of considering all randomly deposited nanoparticles, the Maxwell-Garnet theory-based dielectric method is employed. The impact of plasmonic engineering factors on the photodetector characteristics is studied. By using embedded Ag nanoparticles and highly transparent graphene electrodes, the proposed device exhibits a maximum responsivity of 269.6 mA/W, a high photocurrent to dark current ratio (PDCR) of 1.7 × 106, a linear-dynamic-range (LDR) of 272 dB, a response time τ = 13.45 μs, and a detectivity of 5.4 × 1013 Jones. In addition, the suggested model is regarded as a fitness function to be used for a Multi Objective Genetic Algorithm (MOGA) optimization method which optimizes the sensing ability of the device and its speed. The optimized design discloses optimum performances in terms of responsivity (564.5 mA/W), PDCR (3.75 × 106), LDR (301 dB), and detectivity (1.25 × 1014 Jones). Also, it balances the compromise between sensing performance and response time (τ = 4.7 μs). Our results show that using an efficient light trapping formalism and a metaheuristic optimization technique, it is possible to notably improve the photodetector sensitivity.