Graphene-based supercapacitors for flexible and harsh environments application

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Determination of reliable resistance values for electrical double-layer capacitors

The power capabilities of supercapacitors are strongly influenced by their passive elements. Within this study, we investigate methods to address resistive components out of galvanostatic measurements and we compared literature methods with the aim to provide a guide to correctly exploit the resistance of supercapacitors. The impact of the sampling conditions of galvanostatic measurements is analyzed and related to electrochemical impedance spectroscopy. Further, a novel method based on the instantaneous power analysis is provided to get real-time information concerning the actual cell resistance during the measurement without altering the gal- vanostatic experiment. Measurements show that literature methods can provide values close to the series resistance, while the newly proposed power method results in a good estimate of the actual dissipative value

Performance study of a thin film cation exchange membrane on carbon electrode for supercapacitor application

In this work we report a green procedure for the infiltration of a SPEEK solution into a porous carbon electrode resulting in a thin-film cation exchange membrane. The electrodes have been investigated by a morphological point of view, showing the formation of a thin coating infiltrated into the porous carbonaceous matrix, while mechanical peeling of a tape demonstrated the adhesion of the proposed layer. The fabricated electrodes have been analyzed by electrochemical measurement. The 3-electrode cyclic voltammetry measurements allowed to verify the voltage window resulting in an improved negative potential, while the electrochemical impedance spectroscopy showed a reduction of the electrical resistance. The SPEEK electrode was used in a supercapacitor and deeply characterized by electrochemical analysis. The reported findings demonstrate for the first time the possibility to exploit a cation exchange material in thin film configuration for supercapacitor application with improved performance of the device and exclusively involving the use of nontoxic reagents

Pouch-sealing as an effective way to fabricate flexible dye-sensitized solar cells and their integration with supercapacitors

The scientific interest in integrated energy harvesting and storage (HS) devices has increased exponentially in the last decade since they represent an optimal solution to power portable electronic devices and low consuming Internet of Thing (IoT) sensor nodes. The integration of energy storage devices with photovoltaics can allow to avoid problems such as continuous battery replacement and periodic maintenance, reducing overall costs. In this context, dye sensitized solar cells (DSSCs) integrated with a supercapacitor represent the best choice in terms of lifetime, charge-discharge efficiency, and simplicity of connection avoiding electrical signal conditioning between the two devices. DSSCs have many similarities with supercapacitors, with the only aspect that remains uncovered being the sealing of the device. Herein we propose a common vacuum sealing technology for the integration of a supercapacitor and a DSSC made with shared current collectors, to maximize the integration between the two technologies. The HS device showed a maximum overall photon to electrical conversion and storage efficiency (OPECSE) of 6.10% under only 0.1 SUN illumination, thanks to the high photoconversion efficiency showed by the pouch sealed DSSC, equal to 6.62%. The HS device showed a high stability under bending condition and repeated photo-charge/discharge cycling

Morphological Characterization and Lumped Element Model of Graphene and Biochar Thick Films

Carbon based materials exhibit interesting mechanical, thermal and electrical properties which make them excellent contenders for use as fillers in composites as film. Graphene has been vastly used among the carbon-based materials. More recently eco-friendly carbon-based materials like biochar have emerged. The deployment of carbon-based materials in films needs to be studied since films are more versatile and permit the exploitation of electrical properties of such materials over circuits and systems. Typical circuits and systems exploiting electrical properties of novel materials perform a number of applications including sensing, detection, tunable devices and energy harvesting. In this paper, films composed of 9:1 graphene or biochar are deployed on a microstrip line. The morphological properties of graphene and biochar and their respective films are studied with Raman spectra and Field Emission Scanning Electron Microscope (FESEM). The electrical properties (four-point probe measurements and scattering parameter measurements) of the films. Low frequency measurements are used as starting point for circuit models estimating the lumped impedance of the films. From the morphological characterization it is shown that biochar films appear as granulates carbonaceous materials whereas graphene films contains several flakes forming a network. From the low frequency measurements and microwave characterization it is seen that graphene films are more conductive as compared to biochar films. In many applications, it is useful to know the surface impedance of the film since it varies on interaction with any external stimulus (variation of pressure, humidity, gas, etc.)

Flexible and High Temperature Supercapacitor Based on Laser-Induced Graphene Electrodes and Ionic Liquid Electrolyte, a De-rated Voltage Analysis.

Herein we report the fabrication and electrochemical characterization of a novel type of supercapacitor composed of laser-induced graphene (LIG) electrodes, achieved by the laser-writing of polyimide foils, and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as electrolyte. This combination allows the development of a flexible microsupercapacitor suitable for harsh environment application. The influence of several parameters is evaluated with the aim of maximizing the performance of the flexible pouch-bag devices, such as the laser-writing conditions, type of electrode layout and amount of nitrogen-doping. Among them, the laser writing conditions are found to strongly influence the areal capacitance allowing to achieve about 4 mF cm−2, as measured from the galvanostatic charge-discharge measurement at 10 µA cm−2, with a maximum operating potential range of 3 V at 25 °C. In order to probe the potential application of such device, i) flexible pouch architecture and ii) high temperature measurements (considering harsh environment field) are investigated. This type of flexible device exhibits energy and power density as high as 4.5 µWh cm−2 and 90.5 µW cm−2, respectively, high cycling stability as well as acceptable coulombic efficiency above 97% demonstrating good stability even at high bending condition (1.25 cm of bending radius). The electrochemical measurements increasing temperature up to 100 °C reveal a 300% of rise in capacitance and 43% of increment in energy density at de-rated voltage. The obtained energy storage performance are comparable to the best data ever reported for a microsupercapacitor for high temperature application. Moreover, a de-rated voltage analysis (DVA) is proposed as a safe procedure to characterize an energy storage device in an extended temperature range without compromising the system performances

PDMS/Polyimide Composite as an Elastomeric Substrate for Multifunctional Laser-Induced Graphene Electrodes

Laser-induced graphene (LIG) emerged as one of the most promising materials for flexible functional devices. However, the attempts to obtain LIG onto elastomeric substrates never succeed, hindering its full exploitation for stretchable electronics. Herein, a novel polymeric composite is reported as a starting material for the fabrication of graphene-based electrodes by direct laser writing. A polyimide (PI) powder is dispersed into the poly(dimethylsiloxane) (PDMS) matrix to achieve an easily processable and functional elastomeric substrate, allowing the conversion of the polymeric surface into laser-induced graphene (LIG). The mechanical and electrical properties of the proposed material can be easily tuned by acting on the polyimide powder concentration. The reported procedure takes advantage from the simple casting process, typical of silicone elastomer, allowing to produce electrodes conformable to any kind of shape and surface as well as complex three-dimensional structures. Electrochemical capacitors and strain gauges are selected as flexible prototypes to demonstrate the multifunctional properties of the obtained LIG on the PDMS/PI composite substrate