Porosity-Engineered CNT-MoS₂ Hybrid Nanostructures for Bipolar Supercapacitor Applications

Abstract

Bipolar supercapacitors that can store many fold higher capacitance in negative voltage compared to positive voltage are of great importance if they can be engineered for practical applications. The electrode material encompassing high surface area, better electrochemical stability, high conductivity, moderate distribution of pore size, and their interaction with suitable electrolytes is imperative to enable bipolar supercapacitor performance. Apropos of the aforementioned aspects, the intent of this work is to ascertain the effect of ionic properties of different electrolytes on the electrochemical properties and performance of a porous CNT-MoS2 hybrid microstructure toward bipolar supercapacitor applications. The electrochemical assessment reveals that the CNT-MoS2 hybrid electrode exhibited a two- to threefold higher areal capacitance value of 122.3 mF cm–2 at 100 μA cm–2 in 1 M aqueous Na2SO4 and 42.13 mF cm–2 at 0.30 mA cm–2 in PVA-Na2SO4 gel electrolyte in the negative potential window in comparison to the positive potential window. The CNT-MoS2 hybrid demonstrates a splendid Coulombic efficiency of ∼102.5% and outstanding stability with capacitance retention showing a change from 100% to ∼180% over 7000 repeated charging–discharging cycles.

Unconventional Synthesis of Metal (Ni, Co, Ag) Antimony Alloy Particles

“…Surprisingly, NiSb exhibits an ambipolar nature for supercapacitor applications, as shown in Figure a (CV at two distinct potential regions where the working electrode is either positive or negative). Ambipolar electrode materials play a vital role in enhancing the energy density of supercapacitors, even in symmetric cells where the two electrodes are identical, owing to their wide operating potential windows. − Here, NiSb shows two different electrochemical phenomena in the two distinct operating potential windows versus the Ag wire quasi-reference electrode. The intercalation and deintercalation of K + ions into/from NiSb occurs in the potential range of −1.1 to 0 V (negative electrode, abbreviated as −ve).…”

Engineered Two-Dimensional Transition Metal Dichalcogenides for Energy Conversion and Storage

“…vdW heterostructures, including TMD-graphene, TMD-MXene, and their hybrids with tailored morphology, have demonstrated exceptional supercapacitor capabilities. One way to address the drawbacks of TMDs, including their reduced conductivity and specific capacitance is to incorporate graphene and other carbon-based materials into the composite. − DFT calculations shows that the 1T-to-1T′ phase transition in MoS 2 is possible by the underneath CNT that can bring a very high quantum capacitance due to the large density of states near the Fermi level of 1T′ MoS 2 -CNT . The charge-transfer occurs from the carbon surface toward the 2H and 1T MoS 2 .…”

Preparation of Positive and Negative Composite Electrode Materials for High-Performance Aqueous Asymmetric Supercapacitor by a Sequential Two-Step Reaction

“…Compared to electrochemical double-layer (EDLC) materials, , redox-active organic electrode materials have received widespread attention due to their ability to undergo redox reactions and exhibit pseudocapacitance. − Redox-active organic electrode materials can be classified into two categories: p-doped type, including aniline, , pyrrole, and polyphenol, and n-doped type, just like anthraquinone, , naphthylimide, and peryleneimide. , These redox-active organic materials can offer advantages such as abundant pseudocapacitive sites, modifiable structure, low cost, and environmental friendliness. If appropriate organic electrode materials with different types of doping are selected to assemble asymmetric devices, one electrode is p-doping while the other is n-doping, which could provide high energy density. − However, the electrical conductivity of redox-active organic compounds has been limited by the degree of doping, resulting in the inability to utilize those advantages fully. Therefore, researchers have primarily focused on attaching organic materials to highly conductive carbon-based materials, such as activated carbon, carbon nanotubes, , and graphene , via π–π stacking, hydrogen bonding, and other noncovalent interactions. , To further increase the energy density, these composite electrode materials are utilized in the assembly of asymmetric devices. − For example, Jiao et al assembled asymmetric supercapacitors by fabricating redox-active PPA/rGO and GH-DN for the positive and negative electrodes, respectively.…”