Synergistic effects of Ni particles within Co-BDC MOF (Ni@Co-BDC) for high-performance supercapacitors

A cobalt-BDC metal organic framework has been synthesized using a simple solvothermal approach, followed by nickel electrodeposition, resulting in a Ni@Co-BDC framework for supercapacitor application. Characterizations of Co-BDC MOF and Ni@Co-BDC MOF have been made through morphological, structural, and electrochemical studies. The BET analysis reveals a high surface area, 89 m2 g- 1, and the average pore diameter, 20.8 nm for CoBDC MOF. The surface morphology confirms closely packed (0.2-1 mu m) microrods having porosity in Co-BDC MOF while the porosity is decreased in Ni@Co-BDC MOF. The crystallinity of both the MOFs was ascertained by XRD. The EIS spectra show a decrease in charge transfer resistance for Ni@Co-BDC MOF 2.5 Omega compared to Co-BDC MOF 3.5 Omega. This suggests that the electrodeposited nickel particle grew in the pores of Co-BDC MOF and had a strong interaction with the it-electrons of phenyl rings, leading to the formation of holes in the linker, causing high conductivity of Ni@Co-BDC MOF. Moreover, the ability to hold charge increased by maximizing use of active electrode species (hole in each linker molecule), resulting in decreased intrinsic resistance of Co-BDC MOF and facilitating effective ion diffusion path enhancing specific capacitance and cyclic stability. This helped to attain an outstanding specific capacitance of 1152 F g- 1 at 1 mV s- 1, increased rate capability, and retained 84 % of its capacitance even after 3000 cycles. An asymmetric supercapacitor device constructed with Ni@Co-BDC and activated carbon, operated in complementary potential window-0.5 to 1 V in 3 M KOH, delivered substantial energy density, 67.2 Wh kg- 1, and power density, 624.9 W kg- 1. Also, the energy density remained 62 % of the initial value at maintained power density of 992.6 W kg- 1.