Self-assembled Zn-functionalized Ni-MOF as an efficient electrode for electrochemical energy storage

Zinc-functionalized nickel metal-organic framework (Zn/Ni-MOF) was grown directly on nickel foam (NF) and used as an efficient binder-free electrode for supercapacitor application. The structural characteristics of the composite materials were analyzed by different analytical techniques. The results obtained revealed flower-decorated ball-shape microstructures were obtained from Zn functionalization of the surface of Ni-MOF micro-sheets, with a relatively larger surface area and unique pore characteristics. The electrochemical performance measured using a 3 M KOH electrolyte solution indicated that Zn-doped Ni-MOF containing Zn/Ni in the ratio 1:2 (ZNN1) exhibited the optimum performance. ZNN1 revealed good rate capability with a maximum specific capacitance of 391 Fg(-1) at a current density of 1 Ag(-1 )and retained about 70% of its initial capacitance at 10 Ag-1. The electrode also possessed maximum energy and power density of 12 Wh kg(-1) and 2000 Wkg(-1), respectively, with a high cycling stability of 85% after 5000 cycles. The enhanced electrochemical performance of ZNN1 was attributed to the increase in the surface area and electrical conductivity of Ni-MOF occasioned by incorporation of an optimum concentration of Zn dopant. The charge storage mechanism was predominantly controlled by the diffusion process, which suggests that the method employed in this study is promising for the fabrication of pseudocapacitive materials.