Self-sacrifice Template Formation of Hollow Hetero-Ni 7 S 6 /Co 3 S 4 Nanoboxes with Intriguing Pseudo-capacitance for High-performance Electrochemical Capacitors

Herein, we report a simple yet efficient self-sacrifice template protocol to smartly fabricate hollow hetero-Ni 7 S 6 /Co 3 S 4 nanoboxes (Ni-Co-S NBs). Uniform nickel cobalt carbonate nanocubes are first synthesized as the precursor via solvothermal strategy, and subsequently chemically sulfidized into hollow heter-Ni-Co-S NBs through anion-exchange process. When evaluated as electrode for electrochemical capacitors (ECs), the resultant hetero-Ni-Co-S NBs visually exhibit attractive pesudo-capacitance in KOH just after continuously cyclic voltammetry (CV) scanning for 100 cycles. New insights into the underlying energy-storage mechanism of the hollow hetero-Ni-Co-S electrode, based on physicochemical characterizations and electrochemical evaluation, are first put forward that the electrochemically induced phase transformation gradually occurrs during CV sweep from the hetero-Ni-Co-S to bi-component-active NiOOH and CoOOH, which are the intrinsic charge-storage phases for the appealing Faradaic capacitance (~677 F g −1 at 4 A g −1 ) of hollow Ni-Co-S NBs at high rates after cycling. When further coupled with negative activated carbon (AC), the AC//hetero-Ni-Co-S asymmetric device with extended electrochemical window of 1.5 V demonstrates high specific energy density of ~31 Wh kg −1 . Of significance, we strongly envision that hollow design concept and new findings here hold great promise for enriching synthetic methodologies, and electrochemistry of complex metal sulfides for next-generation ECs.