Abstract
Cobalt oxide nanopowders are synthesized by the pyrolysis of aerosol particles of water solution of cobalt acetate. Cobalt nanopowder is obtained by subsequent reduction of obtained cobalt oxide by annealing under a hydrogen atmosphere. The average crystallite size of the synthesized porous particles ranged from 7 to 30 nm, depending on the synthesis temperature. The electrochemical characteristics of electrodes based on synthesized cobalt oxide and reduced cobalt oxide are investigated in an electrochemical cell using a 3.5 M KOH solution as the electrolyte. The results of electrochemical measurements show that the electrode based on reduced cobalt oxide (Re-Co3O4) exhibits significantly higher capacity, and lower Faradaic charge–transfer and ion diffusion resistances when compared to the electrodes based on the initial cobalt oxide Co3O4. This observed effect is mainly due to a wide range of reversible redox transitions such as Co(II) ↔ Co(III) and Co(III) ↔ Co(IV) associated with different cobalt oxide/hydroxide species formed on the surface of metal particles during the cell operation; the small thickness of the oxide/hydroxide layer providing a high reaction rate, and also the presence of a metal skeleton leading to a low series resistance of the electrode.
Highlights
Energy in the form of electricity generated from renewable resources such as wind, tidal and solar energy will contribute prominently and play an important role in our future energy demands by:(i) offering enormous potential for powering our future systems to overcome the concerns associated with the future energy shortage due to the anticipated doubling of world energy consumption within the 50 years [1] and (ii) the use of low—or even zero—emission energy sources to tackle the fundamental problems associated with the use of fossil fuels as the world strives to reduce greenhouse gas emissions
Along with different energy storage/conversion technologies such as lithium-ion batteries and fuel cells, which are well suited to absorbing/releasing energy over long charge/discharge times in a flat voltage fashion [2], supercapacitors are considered as an important class of energy storage technology which is intensively developed at the present day [1,3,4,5]
Energy storage/delivery in supercapacitors is based on the storage and release of electric charges and according to the mechanism of charge storage, supercapacitors are classified as three main types: (i) electrical double layer capacitors (EDLC) in which electric charges are stored electrostatically at the electrode/electrolyte interface where the electrode materials are predominantly carbonaceous materials, (ii) pseudocapacitors (PC) in which electric charges are stored Faradaically through fast reversible redox reactions on the surface/or in shallow depth of the active materials, and (iii) asymmetric supercapacitors (ASCs), which consist of a battery-type Faradaic electrode as an energy source and a capacitor-type electrode as a power source
Summary
Energy in the form of electricity generated from renewable resources such as wind, tidal and solar energy will contribute prominently and play an important role in our future energy demands by:. In order to increase the storage capacity of supercapacitors, composite electrodes based on carbon materials (activated carbon, carbon nanotubes, graphene, etc.), which provide a high specific surface area combined with heteroatoms or nanoparticles of metal oxides, which exhibit a pseudocapacitive effect are developed [34,35,36,37,38], utilizing graphene and achieving good dispersion might not be cost effective Further to these other approaches in which an oxide layer is coated on a metal plate using magnetron sputtering or electrodeposition techniques, the formation of transition metal oxide-based electrodes is practiced and applied in the manufacture of electrolytic capacitors [19,39,40,41,42,43]. This new and simple method of enhancing electrochemical activity is mainly related to the redox activity of electroactive material
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