Formation of highly porous NiCo2S4 discs with enhanced pseudocapacitive properties through sequential ion-exchange

In this work, we have developed a sequential chemically topotactic transformation strategy to fabricate highly porous thin NiCo2S4 discs with complex crisscross pore channels through sequential in situ ion-exchange. Starting from Co3O4 discs prepared by direct pyrolysis of solid Co-glycolate discs, complex porous Co3S4 and NiCo2S4 discs are obtained after the sequential ion-exchange reactions with S-2 and Ni2+ ions, respectively. Physicochemical and electrochemical investigations demonstrate that the as-derived NiCo2S4 discs with high electrical conductivity, ion-diffusion-derived large accessible surface area and pore volume present attractive pseudocapacitive properties including remarkably high capacitivity (908 F g(-1) at 3 A g(-1)), good rate capability (610 F g(-1) at 20 A g(-1)) and out-standing electrochemical stability with a capacitance retention of 82% after continuous cycling for 5000 cycles. Furthermore, a hybrid device using the NiCo2S4 discs and carbon-based composite as positive and negative electrodes, respectively, delivers a high energy density of 42.7Wh kg(-1) at a power density of 375 W kg(-1), suggesting that the NiCo2S4 discs could be a powerful electrode platform for advanced supercapacitors. (C) 2018 Elsevier Ltd. All rights reserved.