Double Metal Ions Synergistic Effect in Hierarchical Multiple Sulfide Microflowers for Enhanced Supercapacitor Performance

In this paper, the design, synthesis, and measurement of a new and hierarchically structured series of Ni_xCo_1–xS_1.097 electroactive materials are reported. The materials were synthesized through an ion-exchange process using hierarchically structured CoS_1.097 as precursors, and a strategy utilizing the synergistic effect of double metal ions was developed. Two complementary metal ions were used to enhance the performance of electrode materials. The specific capacitance of the electroactive materials was continuously improved by increasing the nickel ion content, and the electric conductivity was also enhanced when the cobalt ion was varied. Experimental results showed that the nickel ion content in Ni_xCo_1–xS_1.097 could be adjusted from x = 0 to 0.48. Specifically, when x = 0.48, the composite exhibited a remarkable maximum specific capacitance approximately 5 times higher than that of the CoS_1.097 precursors at a current density of 0.5 A g^–1. Furthermore, the specific capacitance of Ni_0.48Co_0.52S_1.097 electrodes that were modified with reduced graphene oxide could reach to 1152 and 971 F g^–1 at current densities of 0.5 and 20 A g^–1 and showed remarkably higher electrochemical performance than the unmodified electrodes because of their enhanced electrical conductivity. Thus, the strategy utilizing the synergistic effect of double metal ions is an alternative technique to fabricate high-performance electrode materials for supercapacitors and lithium ion batteries.