Electrodeposition of Nickel Nanostructures from Deep Eutectic Solvent / Water Mixtures

Supported nickel nanoparticles (NPs) are widely used as catalysts for fuel cells and electrosynthesis, as well as for biosensors and supercapacitors. These nanomaterials can be fabricated by multiple methods. However, electrodeposition offers several advantages since it permits the growth of the NPs directly on the support of interest and allows obtaining highly electroactive nanostructures [1]. In order to produce highly electroactive nanostructures, the electrochemical processes on the nanoscale need to be understood. In this context, Deep Eutectic Solvents (DESs) have generated great enthusiasm as a new generation of non-aqueous electrolytes. They offer plenty of advantages compared to traditional aqueous electrolytes or to highly expensive ionic liquids [2]. Moreover, by adding water to the DESs, the electrolyte behavior could be remarkably different. The ability of understanding the effect (and controlling the amount) of water in DES has been proven essential to tune the chemical nature of the electrodeposited Ni nanostructures, thereby obtaining highly electroactive NPs for a wide range of applications [3-4]. The electrodeposition of nickel nanostructures on glassy carbon was investigated in 1:2 choline chloride – urea (1:2 ChCl-U) DES containing different amounts of added water. By combining electrochemical techniques, with ex-situ FE-SEM, XPS, HAADF-STEM and EDX, the electrochemical processes occurring during nickel deposition and the effect of added water were better understood. At highly negative potentials, Ni growth is halted due to water splitting and the formation of a mixed layer of Ni/Ni(OH) 2(ads) [3]. Moreover, under certain conditions, the choline cations can also be (electro)chemically reduced at the electrode surface, blocking further 3D growth of the Ni NPs. Hence, a 2D crystalline Ni network can be formed in the inter-particle region, as depicted in the figure [5]. These novel nickel nanostructures can be of great interest for their electrocatalytic activity for different processes, such as the oxygen evolution reaction (OER). References: G-R. Li, H. Xu, X-F. Lu, J-X. Feng, Y-X. Tong, C-Y. Su. Nanoscale , 5 (2013) 4056-4069. E.L. Smith, A.P. Abbott, K.S. Ryder. Chemical Reviews , 114 (2014) 11060–11082. E.A. Mernissi Cherigui, K. Sentosun, P. Boockenooge, H. Vanrompay, S. Bals, H. Terryn, J. Ustarroz. The Journal of Physical Chemistry C , 121 (2017) 9337-9347. C. Du, B. Zhao, X-B. Chen, N. Birbilis, H. Yang. Scientific Reports , 6 (2016) 29225. E.A. Mernissi Cherigui, K. Sentosun, S. Bals, H. Terryn, J. Ustarroz. Manuscript in preparation (2017). Figure 1