Pseudocapacitance of Mesoporous Spinel-Type MCo(2)O(4) (M = Co, Zn, and Ni) Rods Fabricated by a Facile Solvothermal Route

[Image: see text] We present the structural properties and electrochemical capacitance of mesoporous MCo(2)O(4) (M = Co, Zn, and Ni) rods synthesized by a facile solvothermal route without necessity to use templates. The Brunauer–Emmett–Teller specific surface areas of these mesoporous rods are found to be about 24, 54, and 62 m(2) g(–1) with major pore diameters of about 31, 15, and 9 nm for MCo(2)O(4), M = Co, Zn, and Ni, respectively. X-ray photoelectron spectroscopy and X-ray diffraction studies reveal the phase purity of the samples with a predominant spinel-type crystal structure. The spinel crystal structure with lattice parameters of 8.118, 8.106, and 8.125 Å is obtained for MCo(2)O(4), M = Co, Zn, and Ni, respectively. The transmission electron microscopy study reveals that the mesoporous rods are built by self-assembled aggregates of nanoparticles which are well-interconnected to form stable mesoporous rods. The electrochemical capacitor performance was investigated by means of cyclic voltammetry, galvanostatic charge/discharge cycling, and impedance spectroscopy in a three-electrode configuration. As a result, the spinel-type MCo(2)O(4) rods exhibit high specific capacitances of 1846 F g(–1) (CoCo(2)O(4)), 1983 F g(–1) (ZnCo(2)O(4)), and 2118 F g(–1) (NiCo(2)O(4)) at a scan rate of 2 mV/s. Furthermore, the mesoporous spinel-type metal oxides show desirable stability in alkaline electrolyte during long-term cycling with excellent cycling efficiency.