NiO Pseudocapacitance and Optical Properties: Does The Shape Win?

Abstract

In the present paper, we investigate the effects of alkali and operational temperature on NiO capacitive and optical properties. The NiO samples were prepared by a straightforward, surfactant-free hydrothermal synthesis, employing Ni(NO3)2 and either urea or moderately sterically hindered triethylamine (TEA). The syntheses were followed by calcinations at either 400 or 600 °C. NiO samples were characterized by XRD, scanning electron microscopy, and nitrogen adsorption isotherms. The optical properties were investigated by reflectance spectroscopy, and the pseudocapacitance was studied by cyclic voltammetry and galvanostatic charge charge-discharge measurements. We found that the synthesis with TEA yielded nanoflowers whereas the morphology of the synthesis with urea varied with the calcination temperature and resulted in nanoparticles or nanoslices at calcination temperatures of 400 and 600 °C, respectively. The NiO samples prepared at a lower temperature displayed a favorable combination of surface area and porosity that allowed for high performance with capacitances of 502 and 520 F g−1 at a current density of 1 A g−1 for nanoflowers and nanoparticles, respectively. The band gaps of all the samples were compatible with the estimated nanoparticle sizes. Finally, we used the synthesized NiO samples for the preparation of screen-printed electrodes (SPEs) modified by drop-casting and probed them against a [Fe(CN)6]3−/4− probe.

Room Temperature Syntheses of ZnO and Their Structures

“…Their properties can be varied in different ways, by doping [19,20], capping, and controlling the structure, shape, and size with bottom-up and top-down approaches [21][22][23][24][25][26][27][28]. The types of synthesis include sol-gel methods, hydrothermal synthesis, solvothermal synthesis, and electrospinning [29][30][31][32][33][34][35]. Among the oxides, ZnO has been thoroughly investigated because of its properties, such as a wide band gap (~3.35 eV) with a high exciton binding energy of (~60 meV), wurtzite crystal structure, piezoelectric properties, and relatively low cost [36,37], which make it a suitable candidate for energy conversion/storage, high-performance electronics, photocatalysis, sensors, solar cells, and supercapacitors [38][39][40][41][42].…”

NiO Grained-Flowers and Nanoparticles for Ethanol Sensing

“…No other peaks of other phases or impurities were detected. The assigned reflections correspond to a face centered cubic crystalline structure, quite often achieved upon calcination of a hydrothermally synthesized Ni-containing precursor and common to all the NiO-based sensors of comparison in this paper [15,[17][18][19][20][21][22][23][24][27][28][29][30][31][32]. The full width at half maximum was used to estimate the average size, through the Scherrer formula, D = K λ / β cos (θ), where K is a constant (ca.…”

“…Therefore, several types of sensors have been developed based on metal oxides, conducting polymers carbon nanostructured materials, and porous materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Among metal oxides, NiO is a p-type semiconductor with a wide band gap (3.0-4.0 eV) [15][16][17] and supercapacitor properties extensively applied in electrochemical devices, lithium ion batteries, and dye-sensitized photocathodes [18]. The efficiency of the applications is often morphology-related and different shapes of NiO have varied responses, modulated through the combination of porosity and surface area.…”

Optically Controlled Supercapacitors: Functional Active Carbon Electrodes with Semiconductor Particles

“…Applications have also been proposed for the future digital micro-grid [ 10 , 11 ] and optical modulators [ 12 ]. Though much effort has been invested in the material, chemistry and electrical properties of batteries [ 13 ], and of S-C [ 14 , 15 , 16 ], surprisingly little research has been devoted to optoelectronic effects in S-C [ 17 ]. Here, carbon-based, optically controlled S-C that exhibit electrical double-layer behavior are described.…”