Template-assisted synthesized MoS2/polyaniline hollow microsphere electrode for high performance supercapacitors

Designed fabrication of MoS2 hollow structures with different geometries and the comparative investigation toward capacitive properties

Hollow MoS2 cubes and spheres were synthesized by a one-step hydrothermal method with the hard template method. The structure and morphology were characterized, and their electrochemical properties were studied. It is concluded that the specific capacitance of the hollow MoS2 cubes (335.7 F g-1) is higher than that of the hollow MoS2 spheres (256.1 F g-1). The symmetrical supercapacitors were assembled, and the results indicate that the specific capacitance of the device composed of hollow MoS2 spheres (32.9 F g-1) is slightly lower than that of the hollow MoS2 cube (37.4 F g-1) device. Furthermore, the symmetrical supercapacitor (MoS2-cube//MoS2-cube) provides a maximum energy density of 4.93 W h kg-1, which is greater than that of the symmetrical capacitor (MoS2-sphere//MoS2-sphere, 3.65 W h kg-1). This may indicate that hollow molybdenum disulfide cubes with substructures have more efficient charge transfer capabilities and better capacitance characteristics than hollow spheres. After 8000 cycles, the coulombic efficiency of the two symmetrical capacitors is close to 100%. The capacity retention of the MoS2 sphere device (95.2%) is slightly higher than that of the MoS2 cube device (90.1%). These results show that the pore structure, specific surface, and active site of MoS2 with different hollow structures have a greater impact on its electrochemical properties.

Strategies for Advanced Supercapacitors Based on 2D Transition Metal Dichalcogenides: From Material Design to Device Setup

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Pt/MoS2/Polyaniline Nanocomposite as a Highly Effective Room Temperature Flexible Gas Sensor for Ammonia Detection

A Pt/MoS2/polyaniline (Pt/MoS2/PANI) nanocomposite is successfully synthesized by the hydrothermal process combined with the in situ polymerization method, and then Pt particles are decorated on its surface. The Pt/MoS2/PANI nanocomposite is deposited on a flexible Au-interdigitated electrode of a polyimide (PI) film. The flexible sensor exhibits a higher response value and fast response/recovery time to NH3 at room temperature (RT). It results in 2.32-fold and 1.13-fold improvement in the gas-sensing response toward 50 ppm NH3 compared to those of PANI and MoS2/PANI-based gas sensors. The detection limit is 250 ppb. The enhancement sensing mechanisms are attributed to the p-n heterojunction and the Schottky barrier between the three components, which has been confirmed by the current-voltage (I-V) curves. A satisfactory selectivity to NH3 against trimethylamine (TMA) and triethylamine (TEA) is obtained according to density functional theory (DFT), Bader's analysis, and differential charge density to illustrate the adsorption behavior and charge transfer of gas molecules on the surface of the sensing materials. The sensor retains the excellent sensing response value even under high relative humidity and sensing stability at higher bending angle/numbers to NH3 gas. Hence, Pt/MoS2/PANI can be regarded as a promising sensing material for high-performance NH3 detection at room temperature applied in flexible wearable electronics.

Recent progress in 2D hybrid heterostructures from transition metal dichalcogenides and organic layers: properties and applications in energy and optoelectronics fields

Atomically thin transition metal dichalcogenides (TMDs) present extraordinary optoelectronic, electrochemical, and mechanical properties that have not been accessible in bulk semiconducting materials. Recently, a new research field, 2D hybrid heteromaterials, has emerged upon integrating TMDs with molecular systems, including organic molecules, polymers, metal-organic frameworks, and carbonaceous materials, that can tailor the TMD properties and exploit synergetic effects. TMD-based hybrid heterostructures can meet the demands of future optoelectronics, including supporting flexible, transparent, and ultrathin devices, and energy-based applications, offering high energy and power densities with long cycle lives. To realize such applications, it is necessary to understand the interactions between the hybrid components and to develop strategies for exploiting the distinct benefits of each component. Here, we provide an overview of the current understanding of the new phenomena and mechanisms involved in TMD/organic hybrids and potential applications harnessing such valuable materials in an insightful way. We highlight recent discoveries relating to multicomponent hybrid materials. Finally, we conclude this review by discussing challenges related to hybrid heteromaterials and presenting future directions and opportunities in this research field.

High Capacitive Antimonene/CNT/PANI Free-Standing Electrodes for Flexible Supercapacitor Engaged with Self-Healing Function

In virtue of the high electrochemical activity and inherent flexibility, polyaniline (PANI) is an ideal electrode material for flexible supercapacitors (SCs). However, in practical applications, the inevitable agglomeration of PANI leads to low capacitance, poor rate performance, and cycling stability. Here, antimonene (Sb) nanosheets with ultrathin thickness, excellent mechanical strength, and flexibility are introduced into the carbon nanotube (CNT) framework for PANI electrodeposition via simple vacuum filtration, which enables the continuous and uniform growth of PANI. The resultant free-standing Sb/CNT/PANI electrode can thus exhibit a high specific capacitance of 578.57 F g^-1 together with a high rate capability. Besides, thanks to the introduction of Sb nanosheets, the agglomeration of PANI during the electrodeposition is improved, which correspondingly alleviates the structural deterioration of PANI during repeated charge/discharge. Thus, the flexible SC assembled by Sb/CNT/PANI electrodes demonstrates both an impressive specific capacitance of 416 F g^-1 and outstanding cycling stability over 12 000 cycles. Moreover, this SC device can have a practical self-healing function by employing self-healable polyurethane. The facile strategy reported herein sheds light on the design of high-performance flexible SCs, catering to the needs of portable and wearable electronics.

Synergistically modified WS2@PANI binary nanocomposite-based all-solid-state symmetric supercapacitor with high energy density

WS2@PANI nanocomposite prepared by hydrothermal and physical blending method shows remarkably high specific capacitance and energy density while retaining excellent cyclic stability.

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.

Preparation of a polymer nanocomposite via the polymerization of pyrrole : biphenyldisulfonic acid : pyrrole as a two-monomer-connected precursor on MoS2 for electrochemical energy storage

We prepared a poly(pyrrole : biphenyldisulfonic acid : pyrrole (Py:BPDSA:Py)) nanocomposite of molybdenum disulfide (MoS₂), P(Py:BPDSA:Py)-MoS₂, with high crystallinity. The composite is synthesized by oxidative polymerization of Py:BPDSA:Py as a two-monomer-connected precursor (TMCP) linked by ionic bonding on a molybdenum disulfide (MoS₂) monolayer. The chemical, structural and morphological characterization of this composite is confirmed by Raman spectroscopy, FT-IR, X-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), and scanning electron microscopy (SEM). The crystal structure is analysed by X-ray diffraction (XRD) and high-voltage electron microscopy (HVEM), which shows a face-centered cubic (FCC) crystal structure for the composite. Nitrogen adsorption-desorption isotherms show an improved specific surface area (91.3 m² g^-1). The electrochemical properties of the composite with a unique crystal structure and a large specific surface area are analysed through cyclic voltammetry (CV), which shows a specific capacitance of 681 F g^-1 demonstrating that the composite can be used as an efficient electrode active material for electrochemical energy storage systems.

Research Progress on Applications of Polyaniline (PANI) for Electrochemical Energy Storage and Conversion

Conducting polyaniline (PANI) with high conductivity, ease of synthesis, high flexibility, low cost, environmental friendliness and unique redox properties has been extensively applied in electrochemical energy storage and conversion technologies including supercapacitors, rechargeable batteries and fuel cells. Pure PANI exhibits inferior stability as supercapacitive electrode, and can not meet the ever-increasing demand for more stable molecular structure, higher power/energy density and more N-active sites. The combination of PANI and other active materials like carbon materials, metal compounds and other conducting polymers (CPs) can make up for these disadvantages as supercapacitive electrode. As for rechargeable batteries and fuel cells, recent research related to PANI mainly focus on PANI modified composite electrodes and supported composite electrocatalysts respectively. In various PANI based composite structures, PANI usually acts as a conductive layer and network, and the resultant PANI based composites with various unique structures have demonstrated superior electrochemical performance in supercapacitors, rechargeable batteries and fuel cells due to the synergistic effect. Additionally, PANI derived N-doped carbon materials also have been widely used as metal-free electrocatalysts for fuel cells, which is also involved in this review. In the end, we give a brief outline of future advances and research directions on PANI.