Supercapacitors – Nanocarbon Laboratory

22 Giugno 202516 Settembre 2025

Redox-Additive Gel Polymer Electrolyte Based on the Biodegradable Polymer Pectin for Supercapacitors with Enhanced Thermal Stability

The implementation of environmentally green materials in energy storage technologies is essential to ensure a fair and ethical transition to net zero. In this work, we present a gel electrolyte (GPE) based on pectin, a biodegradable natural biopolymer synthesized by using lithium chloride (LiCl) and potassium iodide (KI) as redox additives to enhance the performance of a supercapacitor. GPE shows enhanced thermal stability and flame retardancy, as confirmed by thermogravimetric and differential scanning calorimetry analysis. The optimized redox-additive GPE exhibits high flexibility and outstanding electrochemical properties including a high ionic conductivity (σ = 43 mS cm^–1) at room temperature and a wide stable potential window (∼2 V vs Ag/Ag⁺). The optimized GPE, with a redox additive and without, was tested with activated carbon electrodes derived from melon peel waste in symmetric supercapacitors. The addition of a redox additive to GPE films directly influences the performance of supercapacitors, leading to a 5 times increase in the specific capacitance (∼437 F g^–1) and specific gravimetric energy density (∼34 Wh kg^–1). The optimized supercapacitor exhibits stable cycling performance up to ∼8000 cycles by having an initial ∼31% fade in capacitance and a high Coulombic efficiency close to 99–100%.

27 Settembre 202416 Settembre 2025

Pre-treated biomass waste melon peels for high energy density semi solid-state supercapacitors

Semi-solid-state supercapacitors employing highly porous activated carbon (AC) electrodes are promising, cost-effective, and environmentally friendly energy storage devices with exceptional power performance. In this work, for the first time in literature, we report a comparative study on different pre-treatments made on melon waste starting precursor to produce hierarchical large surface area porous AC. Also, for the first time in our knowledge, a gel polymer electrolyte (GPE) consisting in lithium trifluoromethanesulfonate in ethylmethylimidazolium trifluoromethanesulfonate, with a high ionic conductivity (∼3.3 × 10⁻³ S cm⁻¹) and a working voltage window of ∼3.9 V vs Ag/Ag⁺, was used. The supercapacitors were electrochemically characterized with electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge tests. The working voltage window of the device was optimized in the range of 0–2.3V. Hydrothermally pre-treated AC-based supercapacitor is characterized by the best performance in terms of capacitance (∼161–170 F g⁻¹), specific energy (29–31.34 Wh kg⁻¹), and power density (839–860 W kg⁻¹) at 1 A g⁻¹. Supercapacitors based on ACs pre-treated via hydrothermal and ethanol soaking outperform devices based on simple chemically/physically ACs in rate performance, while hydrothermally pre-treated AC demonstrates superior stability over 8000 cycles, exhibits initial 15 % capacitance fading and coulombic efficiency close to 99–100 %.

12 Agosto 202416 Settembre 2025

High performance quasi-solid-state supercapacitor based on activated carbon derived from asparagus waste

Supercapacitors with carbon electrodes derived from biomass and utilizing gel polymer electrolytes are currently a focal point in the development of highly efficient, environmentally friendly, and cost-effective energy storage devices. In this study, we present porous activated carbon derived from asparagus waste, prepared through chemical activation with ZnCl₂ followed by physical activation with CO₂, as a high-performance electrode material for supercapacitors. The performance of electrodes has been discussed in comparison with supercapacitors employing both gel polymer electrolytes and conventional liquid electrolytes i.e. 7 M KOH. The flexible film of the gel polymer electrolyte exhibits noteworthy characteristics, including a high ionic conductivity of ∼6.3 mS cm⁻¹, and a high electrochemical stability window of ∼4.5 V. Supercapacitors prepared with this gel polymer electrolyte outperform supercapacitors with liquid electrolytes thanks to a broader electrochemical stability window, showing optimal charge-discharge performance, a specific capacitance of 160 F g⁻¹, a specific energy of 31 Wh kg⁻¹, and an effective power of 0.56 kW kg⁻¹. The superior rate performance is demonstrated by powering a LED for a substantial duration, highlighting the exceptional capabilities of the system. Additionally, the supercapacitor employing the gel polymer electrolyte displays an extended stability, sustaining approximately 10,000 charge-discharge cycles with only a modest initial fading of ∼16 % in specific capacitance and maintaining a high coulombic efficiency of ∼100 %.

26 Maggio 202216 Settembre 2025

Asymmetric supercapacitors based on nickel decorated graphene and porous graphene electrodes

Thermal exfoliation of graphite oxide is a scalable way to produce macroscopic amount of defective graphene-based compounds with high specific surface area, ideal as electrode materials in high-performance electrochemical supercapacitors. In order to increase the stored energy, defective graphene has been decorated with Ni nanoparticles without exposing the system to air. During the first charge cycle in an aqueous electrolyte (KOH 3.5 M), Ni anchored to graphene proved to easily convert to Ni(OH)₂ at the nanoscale and hence to reversibly assume Ni²⁺ and Ni³⁺ valence during cyclic voltammetry, through its conversion to NiOOH. Such reversible faradaic mechanism led to a one order of magnitude increase of the specific capacitance of electrodes, reaching up to 1900 F/g at 2 mV/s in KOH 3.5 M. An asymmetric supercapacitor was obtained by coupling a pure graphene negative electrode with a Ni decorated graphene positive one. The supercapacitor, operating with aqueous electrolyte, was successfully cycled in the 0–1.5 V voltage range, reaching a maximum specific energy of 37 Wh/kg and a maximum specific power of 5 kW/kg. The devices displayed good reversibility and retained 72% of the specific energy over 10 thousand of cycles. Such promising results disclose to possible industrial implementation of graphene-based supercapacitors, for a wide range of energetic application.

31 Gennaio 202118 Febbraio 2021

In situ decoration of laser-scribed graphene with TiO2 nanoparticles for scalable high-performance micro-supercapacitors

Graphene-based miniaturized supercapacitors, obtained via laser conversion of suitable precursors, have been attracting recent attention for the production of energy storage small-scale devices. In this work, a one-pot synthesis of TiO₂ nanoparticles embedded in porous graphene-based electrodes has been obtained with the LightScribe® technology, by converting the precursor materials through the absorption of a DVD burner infrared laser light. Enhanced electrochemical performance of devices has been achieved thanks to the combination of faradic surface reactions, arising from metal oxide nanoparticles, with the conventional electrochemical double layer capacitance, arising from porous graphene. Micro-supercapacitors, consisting of TiO₂-graphene electrodes, have been tested by investigating two hydrogel polymer electrolytes, based on polyvinyl alcohol/H₃PO₄ and polyvinyl alcohol/H₂SO₄, respectively. Specific areal capacitance up to 9.9 mF/cm² are obtained in TiO₂-graphene devices, corresponding to a volumetric capacitance of 13 F/cm³ and doubling the pristine graphene-based device results. The micro-supercapacitors achieved specific areal energy and specific areal power of 0.22 μWh/cm² and 39 μW/cm², along with a cyclability greater than 3000 cycles. These high-performance results suggest laser-scribed TiO₂-graphene nanostructures as remarkable candidates in micro-supercapacitors for environment-friendly, large-scale and low-cost applications.

6 Maggio 201918 Febbraio 2021

Super-activated biochar from poultry litter for high-performance supercapacitors

We report on the preparation of a novel hierarchically-porous super-activated carbon originating from organic waste with specific surface area exceeding 3000 m2/g, obtained starting from biochar derived by the pyrolysis of poultry litter. The chemical activation process proved to be efficient to remove the majority of impurities other than carbon, stabilizing a highly porous hierarchical structure with local graphene-like morphology. The presence of P and S with concentration below 0.1 wt% distinguishes this activated carbon from the usual ones obtained from vegetal sources. Thanks to these features, the obtained porous compound demonstrated to behave as an excellent electrode material for high-performance symmetric supercapacitors, reaching high specific capacitance up to 229 (13) F/g. Remarkably, the devices also supply high current density of 10 A/g without using any conducting additives and display high power density and reliability. Moreover, these optimal performances have been obtained operating by using simple eco-friendly electrolytes, like KOH and Na2SO4 aqueous solutions. The availability, the biocompatibility and the inexpensiveness of the starting materials, together with the low environmental impact of the electrolyte, suggest possible large-scale applications for such devices, for example in the field of transportation or in renewable energy-grids, but also in the field of bio-medicine.