Double linker MOF-derived NiO and NiO/Ni supercapacitor electrodes for enhanced energy storage

Metal-organic frameworks (MOFs)-derived nanomaterials have emerged as novel electrodes for electrochemical energy storage application. Herein, MOF-derived NiO and NiO/Ni composite electrodes have been successfully synthesized by a unique double-linker MOF-strategy involving a series of calcination procedures (400 °C, 500 °C and 600 °C). The introduction of calcination temperature influenced both the textural and electrochemical properties of the MOF-derived NiO/Ni-400 and NiO/Ni-500 composite electrodes obtained at 400 °C and 500 °C respectively, as well as the NiO-600 electrode produced at 600 °C. With the combined benefits of improved uniform pore-size distribution and electrical conductivity, the composite electrodes delivered an enhanced supercapacitor performance with specific capacitances of 104.6 mAg−1 (NiO/Ni-400) and 37.4 mAg−1 (NiO/Ni-500) compared with 28.5 mAg−1 for the NiO-600 electrode at the same current density. Interestingly, NiO/Ni retained about 90% of its original capacitance after 1000 cycles when measured in 3 M KOH electrolyte solution. Furthermore, the electrochemical kinetic analysis used to probe the energy storage mechanism revealed pseudocapacitive behaviors at all tested scan rates; with NiO/Ni contributing 67% of the total capacitance at a scan rate of 5 mV/s which increased to 87% at 100 mV/s. The results obtained confirm that the approach described in this study is promising for the design of MOF-based electrodes for energy storage applications.