Abstract
Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.
Highlights
Rising global population and the global energy crisis has led to concerns regarding electrical energy generation and consumption
Nanotechnology is an advancement in the field of technology that deals with manipulation and regulation of substances on a nanoscale measurement, employing scientific skills from a diverse biomedical and industrial approach (Soares et al 2018)
They used activated carbon as a negative electrode and NiCo2S4/Nickel sulfide (NiS) as a positive one. They used a supercapacitor of nickel cobaltite sulfide/nickel sulfide, which had a large active surface area with enhanced electrochemical characteristics such as, at 160 W kg−1 of power density, it exhibits an energy density value of 43.7 W h kg−1 and at Specific capacitance Energy density and power density
Summary
Rising global population and the global energy crisis has led to concerns regarding electrical energy generation and consumption. Additional focus areas include perovskite oxides, transition metals sulfides, carbon materials and conducting polymer materials, as materials that have been extensively and widely employed in the fabrication of supercapacitors to establish loopholes in some of these nanomaterials This would offer guidelines on how to design better energy storage devices with a higher power, density and sufficient storage ability. The partially substituting Co by the transition metals (i.e., Zn, Mn, Ni, and Cu) in the C o3O4 lattice leads to produce an inverse spinel structure, in which the external cation occupies the B-sites, while Co occupies both the A- and B-sites (Kim et al 2014) This presents effective channels for ion diffusion enrichment toward charge carriers (electrons or holes) that jump into the A-site and B-site for high electrical conduction (Liu et al 2018b). Several of these hold Β ions of one element in two valence states and should not be confused with the complex perovskite compounds which contain different elements in various valence states (Assirey 2019; Pan and Zhu 2016; Galasso 2013)
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