Hybrid Composite Based on Porous Cobalt‐Benzenetricarboxylic Acid Metal Organic Framework and Graphene Nanosheets as High Performance Supercapacitor Electrode

Abstract

Poor electrical conductivities, structural instabilities and long synthesis procedures, limit the application of metal organic frameworks (MOFs) in energy storage systems. In the present work, we synthesize a cobalt‐benzene tricarboxylic acid based MOF (CoBTC MOF) via two different approaches i. e. solvothermal route and mechanochemical grinding for its utility in energy storage. When characterized structurally and electrochemically, the CoBTC MOF synthesized by mechanochemical method is found to be superior because of large surface area, enhanced porosity/diffusion process through MOF and structural robustness along with less time requirement. Further, its hybrid composite with graphene nanosheets (CoBTC MOF/GNS) was prepared for its performance as a supercapacitor material. The characterization reveals the formation of sandwich structure where CoBTC MOF rods (thickness ranging from 0.5 to 2 μm) are placed in between GNS. This arrangement has resulted into high specific capacitance of 608.2 F.g−1 at current density of 0.25 A.g−1 in 1 M KOH electrolyte along with excellent capacitance retention up to 94.9% after 2000 charge/discharge cycles. Also, a symmetric supercapacitor has been assembled for practical application of CoBTC MOF/GNS which demonstrates specific capacitance of 183.2 F.g−1 with high energy density and power density of 49.8 Wh.kg−1 and 1025.8 W.kg−1 respectively, along with 92.1% retention of initial capacitance after 5000 charge‐discharge cycles.

Fabrication of an Advanced Symmetric Supercapattery Based on Nanostructured Bismuth‐Cobalt‐Zinc Ternary Oxide Anchored on Silicon Carbide Hybrid Composite Electrode

“…From the Nyquist plots, each impedance spectrum has two major components— a small arc and the linear part—which are distributed among the high‐frequency and low‐frequency regions, respectively. The diameter of arc is the measure of charge transfer resistance ( R ct ) which is originated from the geometry and conductivity of electrode/electrolyte interface . To achieve the ideal capacitive behavior of the material, the diameter of the arc should be small and the linear part of the Nyquist plot should be nearly parallel to Y ‐axis (also known as imaginary axis).…”

“…The diameter of arc is the measure of charge transfer resistance (R ct ) which is originated from the geometry and conductivity of electrode/electrolyte interface. [38] To achieve the ideal capacitive behavior of the material, the diameter of the arc should be small and the linear part of the Nyquist plot should be nearly parallel to Y-axis (also known as imaginary axis). In this study, the pristine SiC exhibited smallest arc at high-frequency region among all, suggesting high conducting ability of this material with R ct value of 1.32 Ω. Conversely, pristine BiCoZnO nanoparticles showed poor conductivity among all with the highest R ct value of 6.12 Ω.…”

Synthesis of Metal Organic Frameworks by Ball-Milling

“…In addition, long-term ball milling may also cause the MOF structure to collapse, lose its periodic structure, and become amorphous [84,85], which is difficult to achieve in a solution phase reaction. The ball milling method can also make it more convenient to combine MOFs and other materials to form binary or even multiple composite materials [18,[86][87][88][89][90][91][92][93], such as GO/MOFs composites [94][95][96][97][98][99] Cu-BTC with truncated octahedral shape, and showed significantly reduction of reaction time and effectively improvement of yield [78].…”

Supercapacitor electrodes based on metal‐organic compounds from the first transition metal series

“…For SCs based on monometallic organic compounds, cobalt is the most commonly used metal in the first transition metal series 25,27,50,67,69,72,73,97‐134 . Summarized in Tables 3 and 4 are the electrode and SC performances of cobalt‐organic compounds and their composites ( 12 ‐ 92 ).…”

“…Cobalt polycarboxylate MOFs are the most popular cobalt‐organic compounds as electrode materials in SCs 25,27,50,67,72,73,97,99‐116,132 . H 2 BDC (Figure 4A) is one of the most typical polycarboxylate ligands and has been widely used to fabricate SC electrodes based on Co‐MOFs and their composites ( 13 ‐ 16 , 18 , 19 , 25 ).…”