Synthesis of free-standing metal sulfide nanoarrays via anion exchange reaction and their electrochemical energy storage application

Metal sulfides are an emerging class of high-performance electrode materials for solar cells and electrochemical energy storage devices. Here, a facile and powerful method based on anion exchange reactions is reported to achieve metal sulfide nanoarrays through a topotactical transformation from their metal oxide and hydroxide pre-forms. Demonstrations are made to CoS and NiS nanowires, nanowalls, and core-branch nanotrees on carbon cloth and nickel foam substrates. The sulfide nanoarrays exhibit superior redox reactivity for electrochemical energy storage. The self-supported CoS nanowire arrays are tested as the pseudo-capacitor cathode, which demonstrate enhanced high-rate specific capacities and better cycle life as compared to the powder counterparts. The outstanding electrochemical properties of the sulfide nanoarrays are a consequence of the preservation of the nanoarray architecture and rigid connection with the current collector after the anion exchange reactions. Arrays of various metal sulfide nanostructures are obtained via a shape-reserved transformation directly from their oxide or hydroxide pre-forms induced by a versatile anion exchange reaction method. The obtained metal sulfide nanostructures demonstrate much improved pseudocapacitor performance compared to sulfides in other forms.