Supercapacitor with Carbon/MoS2 Composites

Abstract

Transition metal dichalcogenides (TMDs) with a two-dimensional character are promising electrode materials for an electrochemical capacitor (EC) owing to their unique crystallographic structure, available specific surface area, and large variety of compounds. TMDs combine the capacitive and faradaic contribution in the electrochemical response. However, due to the fact that the TMDs have a strong catalytic effect of promoting hydrogen and oxygen evolution reaction (HER and OER), their usage in aqueous ECs is questioned. Our study shows a hydrothermal l-cysteine–assisted synthesis of two composites based on different carbon materials—multiwalled carbon nanotubes (NTs) and carbon black (Black Pearl-BP2000)—on which MoS2 nanolayers were deposited. The samples were subjected to physicochemical characterization such as X-ray diffraction and Raman spectroscopy which proved that the expected materials were obtained. Scanning electron microscopy coupled with electron dispersive spectroscopy (SEM/EDS) as well as transmission electron microscopy images confirmed vertical position of few-layered MoS2 structures deposited on the carbon supports. The synthetized samples were employed as electrode materials in symmetric ECs, and their electrochemical performance was evaluated and compared to their pure carbon supports. Among the composites, NTs/MoS2 demonstrated the best electrochemical metrics considering the conductivity and capacitance (150 Fg−1), whereas BP2000/MoS2 reached 110 Fg−1 at a current load of 0.2 Ag−1. The composites were also employed in a two-electrode cell equipped with an additional reference electrode to monitor the potential range of both electrodes during voltage extension. It has been shown that the active edge sites of MoS2 catalyze the hydrogen evolution, and this limits the EC operational voltage below 1 V. Additional tests with linear sweep voltammetry allowed to determine the operational working voltage for the cells with all materials. It has been proven that the MoS2/carbon composites possess limited operating voltage, that is, comparable to a pure MoS2 material.

Operando Monitoring of Local pH Value Changes at the Carbon Electrode Surface in Neutral Sulfate-Based Aqueous Electrochemical Capacitors

“…This problem can be tackled in two ways: by either increasing the operating cell voltage ( U ) and/or the specific capacitance ( C ), as these are the parameters that govern the energy stored in the device, as given by In electrochemical capacitors, the choice of a solvent is of utmost importance, as it governs the maximum voltage of the system. Currently, capacitors that operate in an organic medium as an electrolyte solution, mainly based on acetonitrile or propylene carbonate as solvents, , are the most widely used and commercialized, as the use of these media allows for a high, undisrupted voltage operation of up to 2.7 V. − However, these solvents pose several important drawbacks such as high toxicity, flammability, and price, which can greatly hinder further implementations in both industry and research settings. − The use of an aqueous medium proves to be a much better and greener alternative; however, it is characterized by a narrow voltage window of ∼1.23 V , due to the decomposition of water, which, in turn, limits the energy stored by the device. − Although numerous studies have been done on the topic, progress related to research based on the enhancement of the operating voltage of aqueous electrolytes is undoubtedly lacking, and much of the focus is directed toward the development of high-capacitance electrode materials . To increase operating voltage, potential ranges of both negative and positive electrodes must be considered, such as ­(where U is the operating voltage, Δ E + and Δ E – being the potential ranges of positive and negative electrodes, respectively).…”

High-Potential Aqueous Asymmetric Supercapacitor Based on 2D Molybdenum Disulfide and Vanadium Pentoxide Electrodes

“…Different types of materials like carbon-derived materials, metal oxides, sulfides, − and conducting polymers , were used as positive and negative electrodes to construct the ASC. Among these, transition metal dichalcogenide (TMD)-based materials − and transition metal oxides (TMOs) − are getting more and more attention in recent years because of their high surface area, better mechanical strength, high energy density, availability of a large variety of compounds, and so on. However, the successful demonstration of these materials in the fabrication of high-power supercapacitors, especially using the aqueous electrolyte, was very scarce.…”

“…However, the low electrical conductivity of MoS 2 holds back its electrochemical performance to an extent . On the other hand, some of the recent studies show that the composite electrodes of MoS 2 with carbon-based material would effectively enhance the electrical conductivity and electrochemical performances. ,− Similarly, vanadium pentoxide (V 2 O 5 ) is one of the TMOs that garnered huge interest as a pseudocapacitive electrode material in SCs due to its 2D layered structure, variable oxidation state, high specific capacity, low cost, ease of availability, environmental friendliness, and better safety. − However, there are very few studies on the utilization of V 2 O 5 for asymmetric SC fabrication. − …”

Facile synthesis and effect of thermal treatment on MoO3−x@MoS2 (x = 0, 1) bilayer nanostructure: toward photoelectrochemical applications

“…In recent years, molybdenum sulfide (MoS 2 ), a metal dichalcogenide, has emerged as a versatile material for diverse applications, including photodetector [1][2][3], light-emitting diode [4,5], gas sensor [6][7][8], supercapacitor [9,10], field effect transistor [11,12], photoelectrochemical or hydrogen evolution reaction (HER) [13][14][15][16][17][18][19], photocatalysis [20], Li-battery [21,22], and environmental treatment [23,24]. The two-dimensional (2D) MoS 2 nanoflake structure exhibits a pseudo-quantum confinement effect, which gives rise to superior properties such as high carrier mobility, fast photoexcited electron-hole pair separation/transfer, adjustable energy bandgap, and robust thermal stability [1,7,[25][26][27].…”