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The effects of electrolytes on the electrochemical performance of nickel cobaltite-titania nanotubes composites as electrochemical capacitors were evaluated. Four types of electrolytes were selected to assess their effects on the prepared composites, namely aqueous electrolytes of 1.0 M KCl, 1.0 M HCl, 1.0 M KOH; and an organic electrolyte, 0.27 M tetra-n-butylammonium tetrafluoroborate (TBATFB) ionic liquid salt in acetonitrile. The composites performed better in 1.0 M HCl and 1.0 M KOH, than in 1.0 M KCl and 0.27 M TBATFB, which suggested that aqueous electrolytes with non-neutral pH would improve the specific areal capacitance values of the composites. Results have shown optimal performance in 1.0 KOH, which endowed the composite with excellent rate capability up to 200 mV s−1. Cyclic voltammogram of the composite analysed in 1.0 M KOH produced a leaf-shaped like profile, with higher current densities towards more positive potentials. Charge-discharge analyses in 1.0 M KOH has shown that the composite possessed specific areal capacitance of up to 214.76 µF cm−2 when it was evaluated at the current density of 350 µA cm−2. The composite also retained up to 97.79% of its specific areal capacitance when current density was increased to 400 µA cm−2. This material has demonstrated potential application for electrochemical capacitors through its facile fabrication technique. [ABSTRACT FROM AUTHOR]

Precious metal oxides exhibit impressive characteristics that caught worldwide attention due to their promising capacitive performance, excellent electrochemical stability and low resistance, and these metal oxides have been extensively employed in supercapacitor application. This type of supercapacitors is known as redox supercapacitors or pseudocapacitors which applied faradaic process in storing energy in their systems. Thus, new materials with impressive electrochemical performance are highly demanded. In this aspect, cobaltite system with spinel structure has been the subject of intense research due to its established applications in electrochemistry. Besides, carbonaceous materials like activated carbons, carbon nanotubes, graphites, graphenes and fullerenes utilize electric double-layer capacitance whereby energy is stored by charge separation at an electrode/electrolyte interface. With greater development conducted on metal oxides and carbonaceous materials for supercapacitor application, introduction of hybrid and composite electrodes comprise of these two types of materials have been well received. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured synthesis of nickel–cobalt oxide/activated carbon composite by adapting a co-precipitation protocol was revealed by transmission electron microscopy. X-ray diffraction analysis confirmed that nickel–cobalt oxide spinel phase was maintained in the pure and composite phases. Cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy were employed to elucidate the electrochemical properties of the composite electrodes in 1.0 M KCl. The specific capacitance which was the sum of double-layer capacitance of the activated carbon and pseudocapacitance of the metal oxide increased with the composition of nickel–cobalt oxide before showing a decrement for heavily-loaded electrodes. Utilisation of nickel–cobalt oxide component in the composite with 50 wt. % loading displayed a capacitance value of ∼59 F g−1. The prepared composite electrodes exhibited good electrochemical stability. [Copyright &y& Elsevier]

Abstract: NiCo2O4 and NiMn x Co2−x O4−y (x ≤1.0) have been synthesized by a co-precipitation method, and the effects of Mn substitution for Co on the microstructural and electrochemical properties pertaining to the supercapacitor applications have been studied. Spinel structure is retained when a quarter of Co of the spinel is substituted with Mn (i.e., x =0.5), where the Mn ions predominantly occupy the octahedral sites of the spinel lattice. The presence of Mn significantly suppresses crystal growth upon thermal treatment but tends to cause severe crystallite agglomeration. Electrodes of the materials exhibit nearly ideal electrochemical capacitor behavior in neutral electrolyte solution (1M KCl(aq)). Mn substitution greatly enhances the specific capacitance of the spinel, giving gravimetric and superficial specific capacitances of ca. 110Fg−1 and ca. 380μFcm−2, respectively for x =0.5 powder. The capacitance enhancement is attributed to the facile charge-transfer characteristic of the Mn ions, as revealed by in situ X-ray absorption near-edge structure analysis. [Copyright &y& Elsevier]