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Öğe Flexible Electrospun PVDF Piezoelectric Nanogenerators with Electrospray-Deposited Graphene Electrodes(Springer, 2023) Unsal, Omer Faruk; Altin, Yasin; Bedeloglu, Ayse CelikToday, there is a great demand for the development of portable, lightweight, flexible, and stable devices that produce and store energy to provide the power that wearable electronics and smart textile materials need. For this purpose, in recent years, researchers have focused on the development of nanofiber-based nanogenerators that have high surface areas thanks to their nanofibrous structures. Therefore, this study presents the development of piezoelectric nanogenerators made of poly(vinylidene fluoride) (PVDF) nanofibers and graphene-based flexible electrodes via electrospray deposition (ESD) technique using electrospinning devices. First, graphene oxide (GO) was electrosprayed onto the PVDF-nanofiber surface, then, the coated GO layer was reduced by chemical treatment to obtain reduced-GO (rGO) and to increase the electrical conductivity. With the ESD technique, it has been observed that graphene oxide nanosheets successfully wrapped on the nanofibers without agglomerating, and this effect was further enhanced by the reduction process. The effect of different thicknesses of graphene electrodes on the efficiency of nanogenerators was investigated. As a result, a maximum peak-to-peak voltage of 1.00 V was produced by a rGO-sprayed nanofiber-based nanogenerator, while 0.688 V was obtained with pure PVDF nanofibers. Also, voltage-per-gram analysis showed that the output voltage was directly related to the electrode morphology and thickness.Öğe Graphene oxide modified carbon fiber reinforced epoxy composites(Walter De Gruyter Gmbh, 2020) Altin, Yasin; Yilmaz, Hazal; Unsal, Omer Faruk; Bedeloğlu, AyşeThe interfacial interaction between the fiber and matrix is the most important factor which influences the performance of the carbon fiber-epoxy composites. In this study, the graphitic surface of the carbon fibers was modified with graphene oxide nanomaterials by using a spray coating technique which is an easy, cheap, and quick method. The carbon fiber-reinforced epoxy matrix composites were prepared by hand layup technique using neat carbon fibers and 0.5, 1 and 2% by weight graphene oxide (GO) modified carbon fibers. As a result of SEM analysis, it was observed that GO particles were homogeneously coated on the surface of the carbon fibers. Furthermore, Young's modulus increased from 35.14 to 43.40 GPa, tensile strength increased from 436 to 672 MPa, and the elongation at break was maintained around 2% even in only 2% GO addition.Öğe Nanofiber mat-based highly compact piezoelectric-triboelectric hybrid nanogenerators(Budapest Univ Technol & Econ, 2023) Unsal, Omer Faruk; Bedeloglu, Ayse CelikStudies on energy generation devices for necessary energy needs have been an increasing trend all over the world as the kinds and quantities of consumer gadgets have increased. Researchers have been studying nanogenerators for the last 15 years in response to this demand. The three main reasons for these studies are increased output power, application to con-sumer items, and mechanical stability. Hybrid nanogenerators, on the other hand, are a method of combining at least two en-ergy conversion mechanisms, hence reducing the need for a single conversion mechanism. In this context, while triboelec-tric-piezoelectric combination hybrid nanogenerators are the most popular hybrid nanogenerator class, they have several drawbacks, such as non-compact and unstable structures. As a result, for the first time, a small hybrid polymer-nanofiber-based hybrid nanogenerator concept with high output voltage and current is disclosed in this study. A hybrid nanofibrous structure was created using an electrospinning apparatus with double and triple nozzles. As a result of the periodic-compression test, the resulting nanogenerators produced a maximum voltage density of 5350 V/m2 and a current density of 5454 A/m2. By hand tapping, the resulting master unit was able to light up 119 LEDs and charge a commercial capacitor up to 0.9 V.Öğe Poly(vinylidene fluoride) nanofiber-based piezoelectric nanogenerators using reduced graphene oxide/polyaniline(Wiley, 2020) Unsal, Omer Faruk; Altin, Yasin; Bedeloğlu, AyşeRecently, piezoelectric nanogenerators have received great interest as they can convert waste mechanical and radiative energy to electricity and can be used in self-energy generating systems and sensor technologies. In this study, electrospun poly(vinylidene fluoride) (PVDF) nanofiber-based piezoelectric nanogenerators with reduced graphene oxide (rGO), polyaniline (PANI), and PANI-functionalized rGO (rGOPANI) have been developed. Two different types of nanofiber mats were produced: First, rGO- and rGOPANI-doped PVDF nanofiber mats and second, rGO, PANI and rGOPANI-spray-coated PVDF nanofiber mats that have worked as nanogenerators' electrodes. Then, characterizations of samples were performed in terms of piezoelectricity, Fourier transform infrared (FTIR) spectrophotometric, X-ray diffractions (XRD), and scanning electron microscopy analyses. FTIR and XRD results confirmed that piezoelectric beta-crystalline phase of PVDF occurred after the electrospinning process. Besides, maximum output voltages were obtained as 7.84 and 10.60 V for rGO-doped PVDF and rGOPANI-coated PVDF nanofiber mats, respectively. As a result, the doped nanofibers were found to be more successful due to the higher device accuracy in sensor technologies compared with spray-coated samples. However, spray-coating method proved to be more suitable technique for the production of nanogenerators on an industrial scale in terms of fast and large-scale applicability. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48517.Öğe Three-Dimensional Piezoelectric-Triboelectric Hybrid Nanogenerators for Mechanical Energy Harvesting(Amer Chemical Soc, 2023) Unsal, Omer Faruk; Bedeloglu, Ayse C. elikThis study presents experimental results on the production,characterization,and applications of three-dimensionally designed piezoelectric-triboelectrichybrid nanogenerators. The hybrid nanofiber mats were manufacturedusing poly(vinylidene fluoride) and thermoplastic polyurethane asthe piezoelectric and triboelectric counter materials, respectively,by the simultaneous electrospinning process. Surface-engineering agentssuch as poly(vinylpyrrolidone), reduced graphene oxide nanoplates(rGO NPs), and zinc oxide nanowires (ZnO NWs) were utilized in three-dimensionaldecoration stages. The nanofiber surfaces were roughened using thesacrifice method, followed by the application of electrospraying andhydrothermal growth techniques to decorate the nanofibers with rGONPs and ZnO NWs, thereby enhancing the device. The resulting hybridnanogenerators were subjected to periodic compression via an appliedforce, resulting in a 75.0% increase in voltage density and a 169.23%increase in current density compared to the neat hybrid nanogenerator,thanks to the surface roughening treatment. Furthermore, the decorationsof rGO NPs and ZnO NWs on the nanofibers contributed to a 271.80%increase in voltage density and a 230.77% increase in current density,reaching values of 2.35 kV/m(2) and 3.40 mA/m(2), respectively. The nanogenerators were also tested in various applications,including energy storage, device powering, and textile sensors, todemonstrate their practicality.
