Ternary (molybdenum disulfide/graphene)/carbon nanotube nanocomposites assembled via a facile colloidal electrostatic path as electrocatalysts for the oxygen reduction reaction: Composition and nitrogen-doping play a key role in their performance

Nanocomposites have garnered attention for their potential as catalysts in electrochemical reactions vital for technologies like fuel cells, water splitting, and metal-air batteries. This work focuses on developing three-dimensional (3D) nanocomposites through aqueous phase exfoliation, non-covalent functionalization of building blocks with surfactants and polymers, and electrostatic interactions in solution leading to the nanocomposites assembly and organization. By combining molybdenum disulfide (MoS2) layers with graphene nanoplatelets (GnPs) to form a binary 2D composite (MoS2/GnP), and subsequently incorporating multiwalled carbon nanotubes (MWNTs) to create ternary 3D composites, we explore their potential as catalysts for the oxygen reduction reaction (ORR) critical in fuel cells. Characterization techniques such as X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction elucidate material composition and structure. Our electrochemical studies reveal insights into the kinetics of the reactions and structure-activity relationships. Both the (MoS2/GnP)-to-MWNT mass ratio and nitrogen-doping of GnPs (N-GnPs) play a key role on the electrocatalytic ORR performance. Notably, the (MoS2/N-GnP)/MWNT material, with a 3:1 mass ratio, exhibits the most effective ORR activity. All catalysts demonstrate good long-term stability and methanol crossover tolerance. This facile fabrication method and observed trends offer avenues for optimizing composite electrocatalysts further.

Energy storage performance of 2D MoS2 and carbon nanotube heterojunctions in symmetric and asymmetric configuration

Excellent cyclic stability and fast charge/discharge capacity demonstrated by supercapacitors foster research interest into new electrode materials with 100% cycle life and high specific capacitance. We report an improvement in the electrochemical performance of MoS₂/multiwalled carbon nanotubes (MWCNT) nanohybrid and intensively explored its performance in symmetric and asymmetric supercapacitor (ASC) assembly. The symmetric assembly of MoS₂/MWCNT exhibits capacitance of around 274.63 F g^-1 at 2 A g^-1 with higher specific energy/power outputs (20.70 Wh kg^-1/1.49 kW kg^-1) as compared to the supercapacitor based on pristine MoS₂ (5.82 Wh kg^-1/1.07 kW kg^-1). On the other hand, a unique all-carbon-based ASC assembled with MoS₂/MWCNT and VSe₂/MWCNT composite with K₂SO₄ as electrolyte delivers the highest energy density of 32.18 Wh kg^-1 at a power density of 1.121 kW kg^-1 with exceptional cycling stability and excellent retention of about 98.43% even after 5000 cycles. These outstanding results demonstrate the excellent electrochemical properties of both symmetric and asymmetric systems with high energy density and performance, which further enable them to be a potential candidate for supercapacitor applications.

Advanced materials and technologies for supercapacitors used in energy conversion and storage: a review

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Highly Dispersible Hexagonal Carbon-MoS2 -Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors

MoS₂ , a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS₂ -carbon was successfully synthesized through an l-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS₂ flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m²  g^-1 , a total pore volume of 0.677 cm³  g^-1 , and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g^-1 (0.12 F cm^-2 ) at a constant current density of 0.1 A g^-1 ; thus suggesting that hollow carbon-MoS₂ -carbon nanoplates are promising candidate materials for supercapacitors.

Few layered MoS2 grown on pencil graphite: a unique single-step approach to fabricate economical, binder-free electrode for supercapacitor applications

While all reports on supercapacitors are based on electrodes that are fabricated either using expensive, complex fabrication techniques or multiple steps based synthesis routes, the current work is the first report of one-step hydrothermally grown MoS₂ on pencil graphite electrode (PGE) for ultra-high performance supercapacitor application. Field emission scanning electron microscope images revealed MoS₂ micro-flower like structure containing interwoven nanosheets whereas chemical characterizations data confirmed the successful growth of few layered (>4 layers) MoS₂ on PGE. The performance of the electrode was optimized using various grades of pencil, and it was found that the areal capacitance of the MoS₂ grown on 1H PGE(7178.8 mF cm^-2) was about 3.4 and 4.1 folds greater than those of the MoS₂ grown on 2B, 6H PGE at the same current density respectively. This low cost, binder-free MoS₂ based PGE paves a novel way towards the advancement of affordable electrodes for energy storage-conversion and bioanalytical applications.

A review of recent progress in molybdenum disulfide-based supercapacitors and batteries

This article reviews the recent progress in molybdenum disulfide-based supercapacitors and batteries.