Dr.João C. Coelho

Graphene and its composites have attracted much attention for applications in energy storage systems. However, the toxic solvents required for the exfoliation process have hampered the exploitation of its properties. In this work, graphene dispersions are obtained via liquid phase exfoliation (LPE) of graphite in cyrene, an environmentally friendly solvent with solubility parameters like those of N-methyl-2-pirrolidone. The obtained dispersions with a concentration of 0.2 mg ml−1 comprised multilayered graphene sheets with lateral sizes in the hundreds of nanometers, as confirmed by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Mixing the obtained dispersions with ethanol made it possible to collect the graphene, which was redispersed in 2-Propanol. This active material was used to fabricate supercapacitor electrodes using a scalable spray deposition method on carbon nanotube (CNT) current collectors with the aid of vinyl masks. The device, tested with a PVA/LiCl gel electrolyte, achieved a specific capacitance of 3.4 mF cm−2 (0.015 mA cm−2). In addition, the devices show excellent cycling stability (>10 000 cycles at 0.5 mA cm−2) and good mechanical properties, losing less than 10% of initial capacitance after 1000 bending cycles. This work demonstrates the adaptability of liquid-phase exfoliation to produce graphene sustainably, providing the proof-of-concept for further 2D materials processing and green microsupercapacitor (MSC) fabrication. © 2025 The Author(s). Published by IOP Publishing Ltd.

Gel polymer electrolytes (GPEs) are regarded as a promising alternative to conventional electrolytes, combining the advantages of solid and liquid electrolytes. Leveraging the abundance and eco-friendliness of cellulose-based materials, GPEs were produced using methyl cellulose and incorporating various doping agents, either an ionic liquid (1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [Pyr14][TFSI]), its polymeric ionic liquid analogue (Poly(diallyldimethylammonium bis(trifluoromethylsulfonyl)imide) [PDADMA][TFSI]), or an anionically charged backbone polymeric ionic liquid (lithium poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino) sulfonyl) imide] LiP[STFSI]). The ion dynamics and molecular interactions within the GPEs were thoroughly analyzed using Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Heteronuclear Overhauser Enhancement Spectroscopy (HOESY), and Pulsed-Field Gradient Nuclear Magnetic Resonance Diffusion (PFG-NMR). Li+ transference numbers (tLi+) were successfully calculated. Our study found that by combining slow-diffusing polymeric ionic liquids (PILs) with fast-diffusing lithium salt, we were able to achieve transference numbers comparable to those of liquid electrolytes, especially with the anionic PIL, LiP[STFSI]. This research highlights the influence of the polymer′s nature on lithium-ion transport within GPEs. Additionally, micro supercapacitor (MSC) devices assembled with these GPEs exhibited capacitive behavior. These findings suggest that further optimization of GPE composition could significantly improve their performance, thereby positioning them for application in sustainable and efficient energy storage systems. © 2024 The Author(s). ChemSusChem published by Wiley-VCH GmbH.

Laser-induced graphene (LIG) is widely used to fabricate microsupercapacitors (MSCs) on various sustainable substrates, such as wood, cork, and lignin. However, the fabrication of MSCs, especially high energy density devices on paper, has rarely been reported. In this work, LIG electrodes are fabricated on wax-coated paper, followed by electrochemical deposition of manganese oxide (MnO2). The obtained LIG/MnO2 supercapacitors exhibit a maximum areal capacitance of 86.9 mF cm−2, while a device with pristine LIG electrodes exhibit a capacitance of 9.1 mF cm−2, both measured at a current density of 0.1 mA cm−2. In addition, the supercapacitor exhibits good cycling stability, retaining 80% of its initial capacitance after 1000 charge/discharge cycles at a current density of 1 mA cm−2. Notably, the LIG/MnO2 supercapacitor exhibits an exceptionally high energy density of 7.3 µWh cm−2 at a power density of 38.8 µW cm−2. In summary, a simple, fast, scalable, reproducible, and energy-efficient fabrication method is represented using electrochemical deposition of manganese oxide on paper-based laser-induced graphene, which are natural, abundant, and sustainable materials, paving the way for large-scale production of environmentally friendly supercapacitors.

Laser-induced graphene (LIG) is as a promising material for flexible microsupercapacitors (MSCs) due to its simple and cost-effective processing. However, LIG-MSC research and production has been centered on non-sustainable polymeric substrates, such as polyimide. In this work, it is presented a cost-effective, reproducible, and robust approach for the preparation of LIG structures via a one-step laser direct writing on chromatography paper. The developed strategy relies on soaking the paper in a 0.1 M sodium tetraborate solution (borax) prior to the laser processing. Borax acts as a fire-retardant agent, thus allowing the laser processing of sensitive substrates that other way would be easily destroyed under the high-energy beam. LIG on paper exhibiting low sheet resistance (30 Ω sq−1) and improved electrode/electrolyte interface was obtained by the proposed method. When used as microsupercapacitor electrodes, this laser-induced graphene resulted in specific capacitances of 4.6 mF cm−2 (0.015 mA cm−2). Furthermore, the devices exhibit excellent cycling stability (> 10,000 cycles at 0.5 mA cm−2) and good mechanical properties. By connecting the devices in series and parallel, it was also possible to control the voltage and energy delivered by the system. Thus, paper-based LIG-MSC can be used as energy storage devices for flexible, low-cost, and portable electronics. Additionally, due to their flexible design and architecture, they can be easily adapted to other circuits and applications with different power requirements. Graphical Abstract: [Figure not available: see fulltext.] © 2022, The Author(s).

The development of new and more accurate fabrication technologies has, in the past few years, boosted interest in advanced device manufacturing. 2D materials, thanks to their diverse properties and dispersibility in liquid carriers, constitute a rich toolbox for ink-based applications. However, the lack of standardized production methods offering a good compromise between performance and affordability has so far been a limiting factor for the application of 2D inks. In this Review, we provide a comprehensive description of the steps involved in device fabrication for different applications, from material selection and ink formulation to printing strategies and device assembly. We conclude with a critical overview of the main scientific and technical limitations currently faced by 2D inks and the related printing technologies, and discuss their market penetration and implementation stage. © 2022, Springer Nature Limited.