A comprehensive review of carbon nanotube-based metal oxide nanocomposites for supercapacitors

Energy storage is one of the challenging technical issues for the society to the transition to renewable energy. Effective energy storage devices are typically added to balance supply and demand to facilitate this firming of renewable energy. Supercapacitor will be a great choice for energy storage as well as electrochemical phenomena for its high-power density and stable retention rate with a wide range of cycling numbers. Carbon nanotube (CNT) and metal-based composites has some unique properties which are distinguishable from others, for instance, the superior electrochemical interaction of the metal oxides with the CNTs, the establishment of a highly porous 3-dimensional framework through CNT entanglement, that further allows the rapid and efficient movement of ions to the productive surfaces of the elements of the nanocomposite, and the elevated strength of CNT@metal oxides. This review discusses how the electrochemical performance in terms of specific capacitance (SPc), energy density, power density, and the number of cycle capacitance retention changes after introducing different kinds of metal oxide with CNTs. However, nanocomposites with different materials have demonstrated high power density but low energy density known as pseudocapacitance behavior. Therefore, present challenges and prospects and where upcoming research has to be focused are discussed here. •Recent CNT-based nanocomposite supercapacitor electrodes have been studied in detail.•There have been discussions on operating principles and many key synthesis approaches.•The performance of supercapacitor electrodes is improved.•Analysis has been done on the relative performance of several supercapacitor electrodes.