Ideally Pseudocapacitive Behavior of Amorphous Hydrous Cobalt-Nickel Oxide Prepared by Anodic Deposition

Abstract

Binary hydrous cobalt-nickel oxide with an amorphous structure ͑denoted as a-(Co ϩ Ni)(OH) 2 •nH 2 O͒ anodically deposited from a CoCl 2 •6H 2 O ϩ NiCl 2 •6H 2 O solution with its Co:Ni ratio of 4:6 and pH 8.0 exhibited a very large pseudocapacitance of ca. 730 F g Ϫ1 in 1 M NaOH. The electrochemical reversibility of this material was examined at various charging-discharging currents in 1 M NaOH with different temperatures. This binary hydrous oxide exhibiting ideally pseudocapacitive behavior ͑i.e., high reversibility, high specific capacitance, and high power property͒ has been demonstrated to be a potential candidate for the application of electrochemical supercapacitors. The morphology and rough nature of this deposit were demonstrated through means of atomic force microscopy. © 2002 The Electrochemical Society. ͓DOI: 10.1149/1.1448184͔ All rights reserved. Energy storage systems delivering very high pulse power for limited time intervals with an acceptable capacitance are generally called supercapacitors. These electrochemical systems have been demonstrated to be promising devices for improving the service life of batteries.1,2 The supercapacitors usually consist of highly porous materials ͑e.g., active carbon͒ with very high specific surface area or electroactive materials with several oxidation states/structures within the potential window of solvent decomposition. 1,3,4 The former devices are also called double-layer capacitors because of the storage of charge within the electrical double layer at the electrodeelectrolyte interface. On the other hand, the latter are generally called pseudocapacitors since faradaic processes at/within the electroactive materials exhibit capacitive-like responses.Amorphous hydrous oxides prepared by several techniques ͑e.g., sol-gel, electrochemical, and chemical precipitation methods͒ usually exhibit relatively large pseudocapacitance and good reversibility.3-8 Moreover, cheaper precursors as well as reliable and easy-control techniques for preparing the electroactive materials with good capacitive characteristics have attracted much attention. Because transition metal oxides ͑e.g., oxides of Co, Ni, Mn, Mo, V, Cr, W, Re, etc.͒ and conducting polymers have several oxidation states or structures that lead to redox transitions within the potential region of water decomposition, 1,3,7-13 energy ͑i.e., pseudocapacitance͒ can be stored within the reversible redox transitions of these electroactive materials. Because the performance of an electrochemical ͑EC͒ supercapacitor is mainly determined by the electrochemical characteristics of the superficial electroactive species, 1,[3][4][5][6] the electrochemical reversibility as well as the pulse power property of these potential candidates should be examined systematically.Hydrous cobalt and nickel oxides prepared by the sol-gel or electrochemical techniques have been proposed to be suitable materials for the application of EC supercapacitors.10,11 However, the sol-gel technique is relatively complicated and the electrochemical pr...

Supercapacitive Properties of Co-Ni Mixed Oxide Electrode Adopting the Nickel Foam as a Current Collector

“…Comparing these with the shapes of some voltammograms from other reports, 21,[26][27][28] the CV shapes at low scan rate (e.g., 10-50 mV s ) are very close to that of a nickel oxide/ carbon nanotube electrode 26 and a Co-Ni oxide/Ni mesh electrode, 27 in which the oxidation and reduction peaks appear at near 0.4 and 0.2 V, respectively. These redox peaks may correspond to the formation of nickel hydroxide at the surface of nickel oxide by the following reaction 29,30 in an aqueous KOH solution:…”

“…21,27 As well, larger oxidation and reduction peaks with the potential shifts in positive and negative directions, respectively, may originate from the nickel foam current collector itself (see Figure 1(b)), resulting in a similar CV pattern with increasing scan rate. Moreover, the effect of the nickel foam substrate may be enhanced at the higher scan rate because the redox reaction occurs more actively on the surface of nickel foam when charging and discharging at a high current rate.…”

“…Nickel oxide, 9-13 cobalt oxide, [14][15][16][17][18][19] and Co-Ni mixed oxide 20,21 have been studied as alternative electrode materials to RuO 2 . Nickel oxide was seen as a possibility to improve the capacitance and to enhance charge-storage capability by the control of surface morphology.…”

“…such that the redox transition of Ni(OH) 2 /NiOOH can be suppressed by mixing the cobalt oxide 21 in the high potential range in which an oxygen evolution reaction may occur:…”

Synthesis and Characterization of Pure CoO and Ni-doped CoO-NiO-SiO2 Nanocomposites Using Sol-Gel Technique

“…Nickel and cobalt oxide shows p-type semiconducting behavior similar to intrinsic spinel cobalt oxide 4 . Our interest in nickel cobalt oxide is due to their enormous uses like as electrode material in batteries 5 in solar cells 6 , a heterogeneous optical recording media 7 , super capacitor 8 , sensors or optical limiters, switches 9 and in flat panel displays etc. The spinel oxide of nickel-cobalt has well documented and established applications in electrochemistry.…”