We have demonstrated a simple solvothermal strategy (reaction at 220 oC) to synthesize very stable monodispersed cubic rock salt structure CoO with cube/rectangular morphology and spinel Co3O4 nanocrystals with sphere and hexagonal platelet morphology depending on the presence or absence of surfactant or change in reaction time. [1] The sizes of the as prepared CoO nanocrystals were found to be in 15-35 nm and Co3O4 nanospheres were found to be in 30-35 nm range. The dimensions of hexagonal platelets are 3-4 μm in diameter and ~100 nm in thickness.

The structure, morphology, composition, optical absorption and surface area/pore volume distribution of the cobalt oxide samples were characterized using X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectrometry, scanning electron microscopy, UV-Vis spectrometry and BET adsorption isotherm. Electrochemical performance of the synthesized materials (all CoO and Co3O4 samples) was evaluated using Cyclic Voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Galvanostatic charge-discharge (GCD) measurements of Co3O4 samples were carried out in two electrode cell assembly (Co3O4/KOH/Co3O4).

In the present work we have obtained ~476 F/g specific capacitance for the Co3O4 hexagonal platelet with very high energy and power density of 42.3 Wh kg-1 and 1.56 kW kg-1 respectively at a high current density of 0.5 Ag-1 without utilizing any large area support. [2] This suggest that the present Co3O4 is a improved metal oxide and exhibit better performance compared to other metal oxides like MnO2, TiO2, SnO2 etc. and can be utilized for supercapacitor device fabrication. The overall electrochemical values and performance of our hexagonal Co3O4 platelet particles as pseudocapacitive material are excellent over most of the other reported Co3O4 micro/nano-structures and these observed better electrochemical properties are attributed to the layered platelet structural arrangement of the hexagonal platelet and the presence of exceptionally high numbers of regularly ordered pores.

References:

K. Deori and S. Deka, CrystEngComm, 2013, 15, 8465-8474.

K. Deori, S. K. Ujjain, R. K. Sharma and S. Deka, ACS Appl. Mater. Interfaces, in press, DOI: dx.doi.org/10.1021/am4027482

Sasanka Deka

University of Delhi

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