Three-Dimensional Binder Free Co-MOF@Co3O4/Ni Nanostructured Electrode for High Performance Supercapatteries
Authors: Mohanty Ankita , Mohanty Smita , Nayak Sanjay Kumar , Ramadoss Ananthakumar 
Published: May 2020

Inflating energy consumption of modern society demands sustainable energy storage device. Optimization of energy along with power density is the major concern for a sustainable energy storage device. Different types of materials are used for both supercapacitors and batteries. Usually carbon based materials are used as electric double layer capacitor (EDLC) and transition metal oxide and conducting polymers are used as pseudocapacitive type materials[1]. Transition metal oxides like Co3O4 [2] , NiCo2O4 [3]and Bi2O3[4] etc. are used as battery type materials. Hybridization of both battery and supercapacitor type materials can give high specific capacitance as well as high specific surface area and conductivity thus maximizing both energy density and power density of the electrode material. Metal organic frameworks (MOFs) are consisting of covalent bonds between transition metal ions and organic linkers containing carboxylic groups or imidazole groups[5]. These novel materials can provide very high specific surface area, good tailorability, and appreciable aspect ratio etc. A number of literature on MOF based energy storage device material are fabricated by binder method [6]. Use of binder lessens the conductivity and the active surface area of the electrode material. If a transition metal oxide is formed directly on a conducting substrate and over that, a MOF is formed then the morphology of the entire electrode will not only provide three-dimensional nanostructure but also high surface area, porosity and appreciable aspect ratio. Therefore, this approach can be proved as a highly fruitful for the synthesis of an excellent supercapattery device.
In this work, an approach to synthesize a three-dimensional binder-free electrode material based on cobalt-metal organic frameworks (Co-MOF) grown over cobalt oxide is adopted. Cobalt oxide is grown over nickel sheet (Co3O4/Ni) via hydrothermal process followed by solvothermal process for the formation of Co-MOF@Co3O4/Ni using trimesic acid as organic linker. The structural, morphological and compositional confirmation was accomplished through X-ray diffraction (XRD) analysis, Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) analysis, respectively. The image delivers a three-dimensional micro-flower structure embedded with multidimensional polygons with good porosity and high specific surface area (Fig. 1). Herein the cobalt oxide forms a three-dimensional micro flower structure and the growth of MOF over that adds extra porosity, surface area and stability. The electrochemical characterization was accomplished through cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) analysis using a three electrode system in 1M KOH solution. The Co-MOF@Co3O4/Ni binder-free electrode showed a battery type behavior i.e. redox peaks in both CV and GCD curve. The specific capacity obtained from cyclic voltammetry analysis was 539 mC/cm2 at scan rate of 5mV/s. This binder free and three-dimensional porous architecture electrode avoids the use of extra additive and provide large specific surface area and porosity for the easy access of electrolyte ions and charge storage and better electrical conductivity for the fast electron transportations. Hence, this novel three-dimensional binder-free Co-MOF@Co3O4/Ni electrode can be proved as an excellent candidate for supercapattery device.
The detailed experimental results and discussion will be presented in the meeting.

Acknowledgements:

This research work is financially assisted by the Department of Science and Technology-Inspire (DST-Inspire) Fellowship (IF170869), by Govt. of India.

References:

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Figure 1