Sulfidation of CoAl-layered double hydroxide on Ni foam for high-performance supercapacitors

Abstract The transition-metal sulfides (CoAl-S) as supercapacitor electrode materials were fabricated onto Ni foam via a simple and cost-effective two-step hydrothermal route. The sulfidation treatment significantly improved the electrical conductivity and accelerated the ion diffusion rate for the materials. By adjusting the S2−/Co2+ molar ratio during the sulfidation process, it was found that the CoAl-S8 sulfide with a 3D and loosely interconnected network mesoporous structure on the Ni foam was gained at S2−/Co2+ molar ratio of 8.0, and exhibited the highest specific capacitance. Benefiting from the unique network structural feature to facilitate active sites exposure and facile charge transfer, the optimized CoAl-S8 material displayed an enhanced specific capacitance of 575.3 C g−1 (1150.6 F g‒1) at 1.0 A g‒1 and cycling stability with 97.8 % capacitance retention after 1000 cycles at 5.0 A g‒1 in the three-electrode system. Furthermore, the as-fabricated CoAl-S8//AC device delivered outstanding energy densities of 55.31 and 32.91 Wh kg−1 at a power density of 749.97 and 7498.48 W kg−1, respectively, and excellent rate capability and outstanding long-term cycle stability (92.45 % of the initial value at 5 A g−1 after 10 000 cycles). This facile synthesis strategy provided a useful clue in designing novel and effective electrode materials for supercapacitors.