Improvement of the pseudocapacitive performance of cobalt oxide-based electrodes for electrochemical capacitors

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

Efficient recovery annealing of the pseudocapacitive electrode with a high loading of cobalt oxide nanoparticles for hybrid supercapacitor applications

Electrochemical pseudocapacitors, along with batteries, are the essential components of today’s highly efficient energy storage systems. Cobalt oxide is widely developing for hybrid supercapacitor pseudocapacitance electrode applications due to its wide range of redox reactions, high theoretical capacitance, low cost, and presence of electrical conductivity. In this work, a recovery annealing approach is proposed to modify the electrochemical properties of Co(3)O(4) pseudocapacitive electrodes. Cyclic voltammetry measurements indicate a predominance of surface-controlled redox reactions as a result of recovery annealing. X-ray diffraction, Raman spectra, and XPES results showed that due to the small size of cobalt oxide particles, low-temperature recovery causes the transformation of the Co(3)O(4) nanocrystalline phase into the CoO phase. For the same reason, a rapid reverse transformation of CoO into Co(3)O(4) occurs during in situ oxidation. This recrystallization enhances the electrochemical activity of the surface of nanoparticles, where a high concentration of oxygen vacancies is observed in the resulting Co(3)O(4) phase. Thus, a simple method of modifying nanocrystalline Co(3)O(4) electrodes provides much-improved pseudocapacitance characteristics

ZnO-CoO Nanopowders for Asymmetric Supercapacitors

Zn1-xCoxO nanopowders were obtained by chemical bath deposition followed by thermal annealing. The structure and morphology of the samples were studied by X-ray diffraction analysis and scanning electron microscopy. Raman spectra were studied at room temperature using a Solver Spectrum (NT-MDT) spectrometer with laser excitation at 473 nm. Depending on the synthesis conditions, nanopowders with an average size of 1-2 nm were obtained. It was shown that while chemical precipitation from a solution of zinc nitrate allows to obtain zinc oxide, and chemical precipitation from a solution of cobalt nitrate results in cobalt hydroxocarbonate, the presence of zinc and cobalt in equal molar concentrations inhibits the growth of both zinc oxide and cobalt hydroxocarbonate. The growth mechanism in the case of equal molar concentrations of zinc and cobalt in the growth solution changes dramatically. The resulting material is transformed by annealing in air into ZnCo2O4 oxide. However, it can be easily transformed by annealing at 350 °C in hydrogen atmosphere into a ZnO-CoO solid solution having a ZnO-type hexagonal lattice. The obtained fine powder of ZnO-CoO solid solution has an average crystallite size of 1-2 nm, depending on the conditions of preparation, and optical absorption spectra indicate the presence of doubly charged cobalt Co2+, which is in a tetrahedral environment. XRD and Raman results show that a single-phase Zn0.5Co0.5O solid solution is obtained, which consists of a hexagonal phase of the ZnO type. Electrodes from the obtained material showed a high specific capacity

EFFECT OF SYNTHESIS METHOD PARAMETERS ON THE PHOTOCATALYTIC ACTIVITY OF TUNGSTEN OXIDE NANOPLATES

A simple chemical bath deposition method has been developed to study the formation of nanoplate morphology of tungsten oxide. The obtained materials were characterized by field emission scanning electron microscopy, transmission electron microscopy, x-ray diffractometry, Raman spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the resulting samples was further evaluated by degradation of Rhodamine B under light irradiation. It was found that both synthesis parameters and morphology affected the tungsten oxide photocatalytic activity. Tungsten oxide nanoplates obtained by a simple chemical bath deposition method have demonstrated a higher specific area and higher photocatalytic activity compared to the nanopowders obtained by the hydrothermal metho