Electrochemically Induced Phase Transformation and Charge-Storage Mechanism of Amorphous CoS[sub x] Nanoparticles Prepared by Interface-Hydrothermal Method

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Abstract
Amorphous cobalt sulfide (designated as CoSxCoSx ) nanoparticles were first synthesized in the unique H2O∕CS2H2O∕CS2 interface under mild hydrothermal treatment for 48h48h . Electrochemical tests revealed that the high energy density accompanied by good power properties (a specific capacitance of 650Fg−1650Fg−1 obtained at 4Ag−14Ag−1 ) was delivered by the as-synthesized CoSxCoSx only after continuous 240cyclic240cyclic voltammetry (CV) cycles in 2M2M KOH aqueous solution, which was in sharp contrast with its poor supercapacitive performance at the initial CV cycles. The energy-storage mechanism of the nanosized CoSxCoSx in the KOH solution is proposed as follows: During continuous CV cycling in the KOH solution, the phase transformation of as-prepared CoSxCoSx nanoparticles is slowly electrochemically induced into whiskerlike Co(OH)2Co(OH)2 around their surfaces, and it is the electrochemical reconstruction of whiskerlike Co(OH)2Co(OH)2 on their surfaces, rather than CoSxCoSx nanoparticles themselves, that are responsible for their good energy-storage properties in the alkaline KOH electrolyte.

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