One-step preparation of cobalt nickel oxide hydroxide@cobalt sulfide heterostructure film on Ni foam through hydrothermal electrodeposition for supercapacitors

Development of technologies or strategies to achieve efficient and low-cost electrode materials for high-performance supercapacitors is highly desirable in the field of renewable energy. In this study, a novel route for preparation of a two-phase film of 4Ni(OH)2·[email protected]9S8 on Ni foam was developed through chemical bath followed by hydrothermal electrodeposition, which was carried out by a one-step process in an autoclave. This strategy first grew nano-sheets of 4Ni(OH)2·NiOOH phase crystals (NiCo-OH) on Ni foam in the stage of elevating temperature, and then start to deposit Co9S8 phase species (CoS) onto the surface of NiC-oOH through hydrothermal electrodeposition during heat preservation, forming a cheek to cheek heterostructure. The resultant composite film as an electrode material for supercapacitors could deliver specific capacities of 1083.6 (2.709), 856.8 (2.142), 624.6 (1.562), 502.2 (1.256), 419.4 (1.049) and 279.2 (0.698) C·g−1 (C·cm−2) at 5, 10, 20, 30, 40 and 50 mA·cm−2, and long lifespan (no decay after 12,000 cycles), which is far higher than the single NiCo-OH film. The excellent capacitive performance is ascribed to the synergistic effect of NiCo-OH and CoS which could provide fast ion and electron conductions, respectively. When the NiCo-OH/CoS composite was utilized as the positive electrode material and active carbon as the negative material, an asymmetric supercapacitor device (ASC) was assembled and could achieve high specific capacitance (1.52 F·cm−2 at 5 mA·cm−2), good rate capability (a capacitance retention of 59% with an 10-fold increase in the discharge current density), high energy density (8.2 Wh·kg−1 (15.1 mWh·cm−3) at 542.8 W·kg−1 (111.1 mW·cm−3)), high power density (5440.2 W·kg−1 (1111.1 mW·cm−3) at 39.8 Wh·kg−1 (8.1 mWh·cm−3)) and excellent cycling stability (a capacitance retention of 85.5% after 12,000 cycles). The results prove that this novel strategy exhibits a promising prospect of direct fabrication of a heterostructure electrode with advantageous features, like convenience and time/cost saving, for high-performance supercapacitors.