Enhanced capacitive pressure sensing performance by charge generation from filler movement in thin and flexible PVDF-GNP composite films.

This study introduces an approach to overcome the limitations of conventional pressure sensors by developing a thin and lightweight composite film specifically tailored for flexible capacitive pressure sensors, with a particular emphasis on the medium and high pressure range. To accomplish this, we have engineered a composite film by combining polyvinylidene fluoride (PVDF) and graphite nanoplatelets (GNP) derived from expanded graphite (Ex-G). A uniform sized GNPs with an average lateral size of 2.55av and an average thickness of 33.74 av with narrow size distribution was obtained with a gas-induced expansion of expandable graphite (EXP-G) combined with tip sonication in solvent. By this precisely controlled GNP within the composite film, a remarkable improvement in sensor sensitivity has been achieved, surpassing 4.18 MPa-1 within the pressure range of 0.1 to 1.6 MPa. This enhancement can be attributed to the generation of electric charge from the movement of GNP in the polymer matrix. Additionally, stability testing has demonstrated the reliable operation of the composite film over 1000 cycles. Notably, the composite film exhibits exceptional continuous pressure sensing capabilities with a rapid response time of approximately 100 milliseconds. Experimental validation using a 3 × 3 sensor array has confirmed the accurate detection of specific contact points, thus highlighting the potential of the composite film in selective pressure sensing. These findings signify an advancement in the field of flexible capacitive pressure sensors that offer enhanced sensitivity, consistent operation, rapid response time, and the unique ability to selectively sense pressure.

In Situ Synthesis of a Bi2Te3-Nanosheet/Reduced-Graphene-Oxide Nanocomposite for Non-Enzymatic Electrochemical Dopamine Sensing.

Dopamine is a neurotransmitter that helps cells to transmit pulsed chemicals. Therefore, dopamine detection is crucial from the viewpoint of human health. Dopamine determination is typically achieved via chromatography, fluorescence, electrochemiluminescence, colorimetry, and enzyme-linked methods. However, most of these methods employ specific biological enzymes or involve complex detection processes. Therefore, non-enzymatic electrochemical sensors are attracting attention owing to their high sensitivity, speed, and simplicity. In this study, a simple one-step fabrication of a Bi2Te3-nanosheet/reduced-graphene-oxide (BT/rGO) nanocomposite was achieved using a hydrothermal method to modify electrodes for electrochemical dopamine detection. The combination of the BT nanosheets with the rGO surface was investigated by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry were performed to analyze the electrochemical-dopamine-detection characteristics of the BT/rGO nanocomposite. The BT/rGO-modified electrode exhibited higher catalytic activity for electrocatalytic oxidation of 100 µM dopamine (94.91 µA, 0.24 V) than that of the BT-modified (4.55 µA, 0.26 V), rGO-modified (13.24 µA, 0.23 V), and bare glassy carbon electrode (2.86 µA, 0.35 V); this was attributed to the synergistic effect of the electron transfer promoted by the highly conductive rGO and the large specific surface area/high charge-carrier mobility of the two-dimensional BT nanosheets. The BT/rGO-modified electrode showed a detection limit of 0.06 µM for dopamine in a linear range of 10-1000 µM. Additionally, it exhibited satisfactory reproducibility, stability, selectivity, and acceptable recovery in real samples.

Highly Water-Dispersible Graphene Nanosheets From Electrochemical Exfoliation of Graphite.

The electrochemical exfoliation of graphite has been considered to be an effective approach for the mass production of high-quality graphene due to its easy, simple, and eco-friendly synthetic features. However, water dispersion of graphene produced in the electrochemical exfoliation method has also been a challenging issue because of the hydrophobic properties of the resulting graphene. In this study, we report the electrochemical exfoliation method of producing water-dispersible graphene that importantly contains the relatively low oxygen content of <10% without any assistant dispersing agents. Through the mild in situ sulfate functionalization of graphite under alkaline electrochemical conditions using a pH buffer, the highly water-dispersible graphene could be produced without any additional separation processes of sedimentation and/or centrifugation. We found the resulting graphene sheets to have high crystalline basal planes, lateral sizes of several µm, and a thickness of <5 nm. Furthermore, the high aqueous dispersion stability of as-prepared graphene could be demonstrated using a multi-light scattering technique, showing very little change in the optical transmittance and the terbiscan stability index over time.

In situ exfoliation and modification of graphite foil in supercapacitor devices: a facile strategy to fabricate high-performance supercapacitors.

Graphite foils (GFs) are emerging as a new class of electrodes in supercapacitors (SCs) based on their light weight, and high electrical conductivity, although the surface area remains low. A novel method of, in situ electrochemical exfoliation and modification of GF in the assembled SCs, showed high energy density and power density of the SC devices.