Abstract
It is well-known that in neutral and acidic aqueous electrolytes, MoS2 monolayers can store charges by adsorption of cations on to the electrode-electrolyte interface as its analog of graphene. Restricted by its low conductivity and the charge storage mechanism, the electrochemical performance of MoS2 monolayer supercapacitor electrode is not satisfactory. It is reported here that water bilayers absorbed on MoS2 monolayers can be involved in charge storage. One proton of each absorbed water molecule can intercalate/de-intercalate the water bilayers during charging/discharging in the alkaline aqueous electrolyte. For two water molecules are present for every Mo atom, the water bilayers can endow MoS2 monolayers an ultrahigh specific capacitance. In this paper, 1T phase MoS2 nanosheets with three monolayers were synthesized by hydrothermal reaction. It presents a specific capacitance of 1120 F g−1 at a current density of 0.5 A g−1 in KOH. As it is assembled with active carbon into a hybrid supercapacitor, the device has an energy density of 31.64 Wh kg−1 at a power density of 425 W kg−1, and gets a specific capacitance retention of 95.4% after 10,000 cycles at 2 A g−1.
Highlights
Accessible surface atoms, near-surface atoms of pseudocapacitance materials are involved in energy storage process
The phenomenon reported in this paper is sure to expand the application of MoS2 nanosheets in electrochemical energy storage
The specific capacitance presents a very high value of 78.82 F g−1 at a current density of 0.5 A g−1, corresponding to an energy density of 31.64 Wh kg−1 at a power density of 425 W kg−1, which is comparable to the Nickel hydroxide related composite electrodes in reports (Table S1)[8,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75]
Summary
Accessible surface atoms, near-surface atoms of pseudocapacitance materials are involved in energy storage process. The capacitor electrode composed of 1T-MoS2 monolayers presented impressive electrochemical performance and very high capacitance[26] It has been reported and evidenced by X-ray diffraction for decades that as MoS2 monolayers are in aqueous solution, a new phase is obtained where two water monolayers are present and sandwich the MoS2 monolayers[37,38]. The electrode materials composed of self-assembled rose-like metallic 1T phase MoS2 nanosheets present a very high specific capacitance (1120 F g−1) at 0.5 A g−1. This is the highest value for pure MoS2 as far as we know. The phenomenon reported in this paper is sure to expand the application of MoS2 nanosheets in electrochemical energy storage
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