NiO morphology dependent optical and electrochemical properties

NiO is a material of large applicative potential in high power density and long cycling life batteries [1-2], because of its supercapacitor properties [3]. However, NiO properties can be strongly morphologydependent [4] and it is crucial to control the synthesis conditions in order to obtain superior performing materials. Here, morphology dependent properties of NiO have been investigated by exploring different synthesis conditions. Ni(OH)2, NiO precursor, was synthesized by hydrothermal method, employing 4 different bases: NH3, (CH3CH2)3N, NaOH or (NH2)2CO. The synthesis products were, then, characterized by XRD and FTIR and calcined at two different temperatures, 400°C and 600°C. The obtained NiO samples, also characterized by XRD, show different morphologies, some being nanometric, others flower-like micrometric, as determined by Scanning Electron Microscopy. In Figure 1 two microscopies are reported of one nanometric and one micrometric sample. Figure 1 SE micrographies of NiO obtained by different synthesis procedure: a) with NH3 and calcined at 400°C, magnification 200K x, b) with NH3 and calcined at 400°C, magnification 20K x. The optical properties of the different samples were probed by reflectance spectroscopy. Kubelka-Munk theory allowed an estimation of the absorption coefficient of NiO powders. Furthermore, screen-printed electrodes were modified with the different types of NiO in several buffers and probed with respect to [Fe(CN)6)]3- detection using cyclic voltammetry. We observed morphology-dependent extinction coefficients as well as amperometric responses of the different electrodes. [1] T. Ya, A. Jain, S.K. Tripathi, Mater. Sci. Eng. B, 2014, 183, 54. [2] K. Xiao, J.W. Li, G.F. Chen, Z.Q. Liu, N. Li, Y.Z. Su, Electrochim. Acta 2014, 149, 341. [3] R.Y. Li, T.T. Yang, Z.J. Li, Electrochim. Acta, 2015, 152, 530. [4] Y. Yang, Y. Liang, Z. Zhang, Y. Zhang, H. Wu, Z. Hu, J. Alloys Comp. 2016, 658, 621.