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

Amorphous cobalt sulfide (designated as ) nanoparticles were first synthesized in the unique interface under mild hydrothermal treatment for . Electrochemical tests revealed that the high energy density accompanied by good power properties (a specific capacitance of obtained at ) was delivered by the as-synthesized only after continuous voltammetry (CV) cycles in 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 in the KOH solution is proposed as follows: During continuous CV cycling in the KOH solution, the phase transformation of as-prepared nanoparticles is slowly electrochemically induced into whiskerlike around their surfaces, and it is the electrochemical reconstruction of whiskerlike on their surfaces, rather than nanoparticles themselves, that are responsible for their good energy-storage properties in the alkaline KOH electrolyte.