• Energy Research

Supercapacitors (SCs) are considered a promising alternative to batteries to power up portable and wearable devices. Among different categories of materials for SCs, carbon nanofibers (CNFs) are particularly appealing for their electrochemical, morphological, and mechanical properties, coupled with the ease of synthesis. Electrospinning is a simple and low‐cost technique to prepare the polymer‐based precursors for CNFs, allowing to obtain fibers with a tunable morphology and a diameter in the nanometer range. However, even if electrospun CNFs were intensely studied over the years, in the literature there is a lack of information regarding the optimization of the thermal treatment to prepare bare CNFs with high specific capacitance (C s). Herein, a systematic study on the optimization of the stabilization and carbonization temperatures for electrospun CNFs prepared from polyacrylonirtile is reported, achieving a maximum C s of 49 F g−1 at 0.5 A g−1 in a symmetrical SC device based on 1 m H2SO4 electrolyte. Aspects related to the specific surface area, nitrogen doping, and carbon microstructure are examined concerning the different thermal treatments, allowing to define structure–property–function relationships in these capacitive nanoarchitectures.

Bi2S3 has gained considerable attention as a semiconductor for its versatile functional properties, finding application across various fields, and liquid phase exfoliation (LPE) serves as a straightforward method to produce it in nano-form. Till now, the commonly used solvent for LPE has been N-Methyl-2-pyrrolidone, which is expensive, toxic and has a high boiling point. These limitations drive the search for more sustainable alternatives, with water being a promising option. Nonetheless, surfactants are necessary for LPE in water due to the hydrophobic nature of Bi2S3, and organic molecules with amphoteric characteristics are identified as suitable surfactants. However, systematic studies on the use of ionic surfactants in the LPE of Bi2S3 have remained scarce until now. In this work, we used sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS) and sodium hexadecyl sulfonate (SHS) as representative species and we present a comprehensive investigation into their effects on the LPE of Bi2S3. Through characterizations of the resulting products, we find that all surfactants effectively exfoliate Bi2S3 into few-layer species. Notably, SDBS demonstrates superior stabilization of the 2D layers compared to the other surfactants, while SHS becomes the most promising surfactant for obtaining products with high yield. Moreover, the resulting nano-inks are used for fabricating films using spray-coating, reaching a fine tuning of band gap by controlling the number of cycles, and paving the way for the utilization of 2D Bi2S3 in optoelectronic devices.

MoS2 and WS2 have gathered significant attention due to their tunable properties and wide range of applications. Liquid‐phase exfoliation (LPE) is a facile method to prepare 2D MoS2 and WS2. Currently, the principally employed solvents for LPE of MoS2 and WS2 are expensive and toxic, and have high boiling points. These drawbacks encourage to find more sustainable alternatives to the liquid medium used for the preparation of 2D material inks. Water is the best option, but surfactants are necessary for LPE in water, since MoS2 and WS2 are hydrophobic. Organic molecules with amphoteric character such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium hexadecyl sulfonate (SHS) are selected as suitable candidates for the role. However, the study of these surfactants used in LPE is barely systematically reported. In this work, a detailed investigation is presented on their impact on the LPE of MoS2 and WS2, which are representatives of transition‐metal dichalcogenides. By characterizing and qualifying the products from average number of layers, it is found that all the surfactants work efficiently to exfoliate MoS2 and WS2 into few layers, and SHS stabilizes the 2D layers better than the other two. However, in terms of yield and relative surfactant concentration, a real trade‐off is not identified between maximized quantity of exfoliated materials and minimized surfactant concentration, which prompts to select the colloidal ink based on the specific further needs for processing.

2D materials are interesting flat nanoplatforms for the implementation of different electrochemical processes, due to the high surface area and tunable electronic properties. 2D transition metal dichalcogenides (TMDs) can be produced through convenient top-down liquid-phase exfoliation (LPE) methods and present capacitive behaviour that can be exploited for energy storage applications. However, in their thermodynamically stable 2H crystalline phase, they present poor electrical conductivity, being this phase a purely semiconducting one. Combination with conducting polymers like polyaniline (PANI), into nanohybrids, can provide better properties for the scope. In this work, we report on the preparation of 2D WS2@PANI hybrid materials in which we exploit the LPE TMD nanoflakes as scaffolds, onto which induce the in-situ aniline polymerization and thus achieve porous architectures, with the help of surfactants and sodium chloride acting as templating agents. We characterize these species for their capacitive behaviour in neutral pH, achieving maximum specific capacitance of 160 F/g at a current density of 1 A/g, demonstrating the attractiveness of similar nanohybrids for future use in low-cost, easy-to-make supercapacitor devices.