Institute of Fundamental Technological Research

Carbon/graphene quantum dots are 0D fluorescent carbon materials with sizes ranging from 2 nm to around 50 nm, with some attractive properties and diverse applications. Different synthesis routes, bandgap variation, higher stability, low toxicity with tunable emission, and the variation of physical and chemical properties with change in size have drawn immense attention to its potential application in different optoelectronics-based materials, especially advanced light-emitting diodes and energy storage devices. WLEDs are a strong candidate for the future of solid-state lighting due to their higher luminance and luminous efficiency. High-performance batteries play an important part in terms of energy saving and storage. In this review article, the authors provide a comparative analysis of recent and ongoing advances in synthesis (top-down and bottom-up), properties, and wide applications in different kinds of next-generation light-emitting diodes such as WLEDs, and energy storage devices such as batteries (Li-B, Na-B) and supercapacitors. Furthermore, they discuss the potential applications and progress of carbon dots in battery applications such as electrode materials. The authors also summarise the developmental stages and challenges in the existing field, the state-of-the-art of carbon/graphene quantum dots, and the potential and possible solutions for the same.

carbon dots, graphene quantum dots, white-LED, supercapacitors, Na-ion batteries, Li-ion batteries

In the present article, an ionic liquid-based polymer gel electrolyte was synthesized by using poly(vinylidene fluoride-co-hexafluo-ropropylene) (PVdF-HFP) as a host polymer. The electrolyte films were synthesized by using the solution casting technique. The as-prepared films were free-standing and transparent with good dimensional stability. Optimized electrolyte films exhibit a maximum room-temperature ionic conductivity of σ = 8.9 × 10^−3 S·cm^−1. The temperature dependence of the prepared polymer gel electrolytes follows the thermally activated behavior of the Vogel–Tammann–Fulcher equation. The total ionic transference number was ≈0.91 with a wider electrochemical potential window of 4.0 V for the prepared electrolyte film which contains 30 wt % of the ionic liquid. The optimized films have good potential to be used as electrolyte materials for energy storage applications.

ionic liquid, polymer gel electrolytes, solution casting technique, transference number

In the present studies, the effect of ionic liquid 1-Ethyl-2,3-dimethylimidazoliumtetrafluoroborate (EDiMIM)(BF4) on ionic conductivity of gel polymer electrolyte using poly(vinylidene fluoride-co-hexafluoropropylene) [PVdF(HFP)] and magnesium perchlorate [Mg(ClO4)2] as salt was investigated. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 8.4 × 10^–3 S cm^−1. The optimized composition reflects Vogel-Tammann-Fulcher (VTF) behavior in the temperature range of 25 °C to 100 °C. The X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy studies confirm the uniform blending of ionic liquid, polymer, and salts along with the enhanced amorphous nature of the optimized system. Dielectric and modulus spectra studies provide the information of electrode polarization as well as dipole relaxation properties of polymeric materials. The optimized electrolyte system possesses a sufficiently large electrochemical window of the order of 6.0 V with stainless steel electrodes.

gel polymer electrolyte, ionic liquid, ionic conductivity, temperature dependence, supercapacitors

In the present study sodium ion conducting polymer blend electrolytes has been prepared using poly (vinylidene fluoride – hexafluoro – propylene) (PVdF-HFP), poly (methyl methacrylate) (PMMA), and sodium thiocyanate (NaSCN) salt by solution-cast technique. The highest ionic conductivity of the optimized blend polymer electrolyte system [PVdF(HFP)-PMMA (4:1)] (20 wt%)-[NaSCN (1 M)] (80 wt%) has been found to be 4.54 × 10^−2 S cm^−1 at room temperature. The temperature dependence conductivity plot shows the Arrhenius behaviour and its activation energy calculated from the plot were found to be 0.13 eV. The structural and morphological studies of polymer blend electrolyte were investigated by XRD, SEM and FTIR spectroscopy. Complex formation between polymer and salt has been confirmed by these studies. The thermal properties of optimized electrolyte system were examined by differential scanning calorimetry (DSC) techniques. The ionic transport number was calculated using d.c polarization techniques and was found to be 0.92, which shows that electrolyte system is predominantly ionic in nature. The electrochemical potential window of optimized polymer blend electrolyte was tested and observed to be ~2.8 V.

polymer blends electrolyte, solution cast technique, sodium ion, FTIR, DSC

In the present studies, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), ionic liquid {1-Ethyl-3-methylimidazolium bromide} (EMIM)(Br), and magnesium perchlorate Mg(ClO4)2 as salt were used to synthesize free standing electrolyte films by using solution cast technique. The prepared electrolyte films were investigated by using various structural and electrochemical techniques like scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) as well as ionic and temperature dependence studies. It has been observed that addition of ionic liquid significantly increases the properties like ionic conductivity, thermal stability, transparency etc. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 2.05 × 10^−2 S cm^−1 which is suitable for device fabrication point of view. The optimized electrolyte films are suitable for supercapacitor application.

gel polymer electrolytes, ionic liquid, solution cast technique, supercapacitors

Almondshell-basedchemicallytreatedandactivated nanoporous charcoal powder (AS(T)) has been successfully prepared by chemical activation method using potassium hydroxide (KOH) as an activating agent. The as-synthesized AS(T)wassystematicallycharacterizedbyvarioustechniques like N2 adsorption, scanning electron microscopy (SEM), Xray diffraction, and thermogravimetric analysis. The AS(T)based nanoporous activated charcoal is tested as an electrode material with ionic liquid-based polymer gel electrolyte for electrochemical double-layer capacitors (EDLCs). EDLCs prepared from AS(T) exhibit specific capacitance of 986.3 mF cm−2 (equivalent to single-electrodespecific capacitance of 563.6 F g−1). The energy density of 62.8 Wh kg−1 and power density of 2.1 kW kg−1 have been observed for nanoporous AS(T)-based EDLCs.

Almond shell, Nanoporous carbon, Ionicliquid, Electrochemical double-layer capacitor

Low cost with high specific capacitance and energy density is the critical and main requirement for practical supercapacitors. In the present work, nano porous activated carbon having specific surface area of 400 m2 g-1 from sugarcane waste (bagasse) has been synthesized and characterized as an electrode material for supercapacitor applications using ionic liquid based polymer gel electrolytes. The fabricated cell shows the overall specific capacitance of 372 mF cm-2 which is equivalent to single electrode specific capacitance of 248 F g-1. The corresponding energy and power density of 16.3Wh kg-1 and 1.66 kWkg-1 were achieved for EDLCs.