Electrodeposition of NiO Films and Inverse Opal Organized Layers from Polar Aprotic Solvent-Based Electrolyte

The implementation of polar aprotic organic solvents remains almost unexplored for the direct electrochemical deposition (ECD) of nickel oxide dense or mesoporous thin films and organized macroporous structures. In the present work, the electrochemical deposition of this oxide in dimethyl sulfoxide (DMSO) medium by cathodic reduction of nickel nitrate hexahydrate is investigated. The electrochemical phenomena involved in the deposition process have been analyzed by cyclic voltammetry (CV). It is shown that the ECD process occurs below -0.80 V/SCE. The gas atmosphere for the deposition and salt dissolution was found important parameters for the electroactivity of the system and the best conditions for ECD have been defined. Raman spectroscopy has shown the direct NiO deposition. Moreover, the crystallization and higher ordering occuring through thermal annealing has been followed by the 2-magnon Raman band of NiO. The difficulty of obtaining well-crystallized pure phase without metallic nickel was stressed by the X-ray diffraction study and thermogravimetry of the layers. We have shown that annealing the sample at 450 degrees C resulted in oxidation and crystallization and in the formation of a mesoporous morphology. The electrochemical activity and electrochromism of the layers has been investigated by CV in alkaline aqueous solution. Finally, we have prepared opal inverse organized structures with a perfectly defined macropore organization and size using a macrosphere polystyrene template. It has illustrated the high interest of the present electrodeposition technique for the preparation of nickel oxide layers with enhanced properties for advanced applications. (C) 2016 Elsevier Ltd. All rights reserved.