Mécanismes de croissance de nanostructures à base du sulfure de nickel pour les supercondensateurs

Abstract

The aim of this thesis is to prepare and characterize nickel sulfide films for application in supercapacitors. We used the spray pyrolysis technique to prepare these films because of its simplicity and low cost. In this work, we prepared two series of thin nickel sulfide films.  In the first serie, chloride nickel dehydrates 10−2M (NiCl2, 2H2O), and thiourea 2.10−2 M (S=C(NH2)2)) were used as precursors to prepare the nickel sulfide thin films. It was obtained from two solutions with different molarities; the mixture ([S]/[Ni]=2) was stirred for 3 hours at room temperature. The nickel sulfide thin films were performed on glass substrates (2x7 cm2) by spray pyrolysis method with heating at different substrate temperatures (523, 573 and 623K). The effect of deposition temperature (523, 573 and 623K) on structural, optical and electrical properties was investigated. The XRD diffraction shows that the prepared nickel sulfide at 523, 573 and 623K having an orthorhombic, hexagonal and hexagonal structure, which were Ni3S2, Ni17S18 and NiS2, respectively. The minimum value of crystallite size (45,9 nm) was measured of deposited film at 573K. The thin films prepared at 523 and 573K have an average transmittance about 20 %. The prepared Ni1S2 thin film at T=623 K has the lowest calculated optical band gap and Urbach energy. The Ni1S2 thin film also has the best calculated of the refractive index and the extinction coefficient. The FTIR spectrums of the nickel sulfide have various bands such as Ni-S, C-H, O-H, N–H and C-S. The maximum electrical conductivity is 4,29x105 (Ω.cm)-1 was obtained at 573K of the Ni17S18. The nickel sulfide thin films sprayed at 573K have good structural, optical and electrical properties.  The second serie: We prepared thin layers of nickel sulfide with a nickel precursorconcentration of 0.03, 0.05 and 0.07 mol/l at the substrate temperature of 300°C.We used thiourea (CS(NH2)2) and nickel nitrate (Ni(NO3)2.6H2O) as a source ofsulfur and nickel, respectively. After their elaboration, the films underwent various characterizations: structural, morphological, optical and electrical. The structural characterization shows that all the prepared thin films are poly crystalline and have a hexagonal structure according to ASTM sheet No. 98-064-6340 with preferential orientation on the plane (012). The crystallites size varied from 23.9 to 42.7 nm with an increase in the precursor’s concentration. Furthermore, the optical bandgap decreases from 1.07 to 0.96 eV. The elementary composition analysis confirmed the presence of Ni and S elements in the samples. Both scanning electron microscopy (SEM) and atomic force microscopy (AFM), revealed a homogenous crack-free and compact appearance in all scanned areas with spherical grains. Inaddition, the roughness of the films significantly increases with the increase of the precursor’s concentration. Finally, the film prepared with 0.05 M exhibits a highelectrical conductivity and capacitance ca. 1.97×103 S/cm and 115 µF/cm2, respectively, at room temperature. The above results showed that the films prepared in this study are very attractive asan electrode material for supercapacitors application.