Effect of microwave on the nanowire morphology, optical, magnetic, and pseudocapacitance behavior of Co <inf>3</inf>O <inf>4</inf>

In the context of immense control of synthesis methods on the structural and functional characteristics of the materials, nanowire morphologies of Co 3O 4 are synthesized in conventional reflux and microwave-assisted methods, under homogeneous precipitation conditions. The Co 3O 4 sample synthesized by the conventional reflux method consists of randomly distributed thin nanowires while the microwave reflux method generates higher-dimensional and arranged Co 3O 4 nanowires. The surface area and pore structural analysis of the Co 3O 4 samples show significant difference in their meso- and macroporosity as well as specific surface area, due to differently crystallized products. The UV-Vis-DRS study shows crystallite size dependent optical transitions and band gaps. The magnetic study illustrates finite size effect and low temperature ferromagnetism in both samples; the lower-dimensional nanowires being more ferromagnetic than the higher-dimensional Co 3O 4 nanowires. Due to smaller crystallite size and more accessible surface sites, the Co 3O 4 sample synthesized by the conventional reflux method shows better charge storage, high Coulombic efficiency, and enhanced rate response during the pseudocapacitance studies. However the Co 3O 4 sample synthesized using the microwave-assisted method shows better high rate cyclic stability due to its more rigid orientated nanowire structure. Further, the Ragone plot exhibits considerably higher energy and power densities of lower-dimensional Co 3O 4 nanowires. Broadly, this study reveals that, under nonhydrothermal homogeneous precipitation conditions, the conventional reflux synthesized lower-dimensional Co 3O 4 nanowires bear superior surface properties than the microwave synthesized higher-dimensional Co 3O 4 nanowires, for electrochemical supercapacitor applications. © 2011 American Chemical Society.