Melamine-assisted synthesis of cobalt–nickel coordination polymers as electrode materials for supercapacitors

Coordination polymers (CPs) and/or metal–organic frameworks (MOFs) are new active materials for supercapacitors (SC). In this study, by solvothermal route, we conduct the melamine-assisted synthesis of bimetallic CPs (Co–Ni CPs) with controllable structures. The concentration of melamine plays an important role in the morphology of Co–Ni CPs, and the CPs can be turned from microspheres to nanorods. The Co–Ni CPs are used as electrode materials for SC. The spherical Co–Ni–CP-M exhibits the highest capacitances of 677 F g−1 and 585 F g−1 at current densities of 1 A g−1 and 10 A g−1, respectively, indicating an outstanding rate capability in a three-electrode system with 2.0 M KOH electrolyte. Furthermore, the Co–Ni–CP-M//active carbon device shows superior long-term cycling stability, i.e., approximately 92.6% of the initial capacitance can be retained after 10,000 cycles at 10 A g−1 in 2.0 M KOH electrolyte. In addition, the asymmetric SC device achieves an excellent energy density of 28.35 W h kg−1 at a power density of 700 W kg−1.