Oxide based supercapacitors: II-other oxides

As discussed in the last chapter, oxides exhibit strong pseudocapacitive effect, thus making them promising candidates as electrodes of supercapacitors. Besides manganese oxides, various other oxides and complex oxides, such as V2O5 [1-3], Fe2O3 [4, 5], Fe3O4 [6-8], Co3O4 [9], NiO [10], CuO [11, 12], ZnO [13, 14], WO₃ [15], MoO₃ [16], RuO₂ [17-20], NiCo₂O₄ [21-23] and ferrites [24-26], have been developed in various forms, such as pure oxides, nanohybrids and nanocomposites, with outstanding electrochemical performances as electrodes of supercapacitors. From the morphology point of view, they can be presented as nanoparticles, nanowires, nanorods, nanotubes, nanosheets, nanoneedles, nanoflakes and nanoflowers, which can be developed by using different methods, including hydrothermal, solvothermal, chemical precipitation, chemical bath deposition, sol-gel, electrodeposition and microwave assisted synthetic routes. They have also been incorporated with other components, such as CNTs, graphenes and conductive polymers, to form 0D-3D nanostructured materials. However, due to the space limitation, this chapter only covers Co₃O₄ [9] and NiO [10], as well as their corresponding complex oxide NiCo₂O₄ [21-23], as representatives.