Chemically coupled 0D-3D hetero-structure of Co9S8-Ni3S4 hollow spheres for Zn-based supercapacitors

Abstract As one of the most promising supercapacitor electrode materials, transition metal sulfides (TMSs) with unique hollow structural features and multiple functional compositions have attracted tremendous interest in the scientific community. Herein, by rationally design a Ni-LDH@Co-BTC yolk-shelled-structure as a template, we successfully fabricate a chemically coupled 0D-3D hetero-structure of Co9S8-Ni3S4 hollow spheres (Co9S8-Ni3S4 HS). During the sulfidation process, the free Co2+ ions derived from the hydrolysis Co-BTC core are anchored by S-rich hierarchical Ni3S4 hollow microsphere shell and further reacted with emerging S2− ion from the hydrolysis of TAA to form the chemically coupled Co9S8 and Ni3S4. The optimized Co9S8-Ni3S4 HS-13 shows prominent supercapacitor performance (239.30 mAh g−1 (1723 F g−1) at 1 A g−1) and excellent cycling stability (94.7 % capacitance retention after 3000 cycles). The as-fabricated Co9S8-Ni3S4 HS-13//rGO-Zn hybrid Zn-based supercapacitor presented a high energy density of 381.63 Wh kg−1 at 1.67 kW kg−1 and excellent cycling durability (91.7 % capacitance retention after 5000 cycles). Then, through the ex-situ XPS measurements, the energy storage mechanism of the Co9S8-Ni3S4 HS-13//rGO-Zn device is proved to be a novel double ions (OH− and Zn(Ⅱ)) intercalation/deintercalation reaction.