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The authors regret the omission of one of the affiliations of the author Jon Ustarroz from the original manuscript. The correct affiliations for this paper are as shown. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Electrodeposition is an important technology for several applications such as the fabrication of metallic coatings, elaboration of semiconductor thin films for photovoltaics and synthesis of nanomaterials. Compared to physical vapor deposition techniques (e.g. sputtering), electrodeposition is especially interesting for large area surface treatments at the industrial scale, due to its versatility and low cost. Furthermore, electrodeposition permits the growth of the nanostructures directly on the substrate of interest and allows obtaining highly electroactive nanostructures [1]. Over the last few years Deep Eutectic Solvents (DESs) have generated great enthusiasm as a new generation of non-aqueous electrolytes. They offer plenty of advantages, such as high thermal stability and broad electrochemical window compared to aqueous solutions. Furthermore, DESs are less toxic and their preparation is less demanding and more cost-effective than this of Room Temperature Ionic Liquids (RTILs) [2]. In the present work,we investigated the electrodeposition of nickel on both glassy carbon (GC) and low carbon steel substrates from 1:2 choline chloride – urea DES (1:2 ChCl-U). The GC was used to generate supported nanostructures. Alternatively, the Ni films were sought after when using steel substrates. In both cases, by combining electrochemical techniques, such us cyclic / linear sweep voltammetry and chronoamperommetry, with ex-situ characterization, like FE-SEM, XPS, STEM, EDX and EELS, the electrochemical processes occurring during nickel deposition were better understood. Special attention was given to the interaction between the solvent and the electrodeposited nickel phase. This interaction has been shown to be very different from that in the aqueous solutions [3-4] [1] G-R. Li, H. Xu, X-F. Lu, J-X. Feng, Y-X. Tong, C-Y. Su, Electrochemical synthesis of nanostructured materials for electrochemical energy conversion and storage. Nanoscale, 5 (2013), 4056-4069. [2] E.L. Smith, A.P. Abbott, K.S. Ryder, Deep eutectic solvents (DESs) and their applications. Chemical Reviews, 114, (2014), 11060–82. [3] J.A. Hammons, T. Muselle, J. Ustarroz, M. Tzedaki, M. Raes, A. Hubin, et al., Stability, Assembly, and Particle/Solvent Interactions of Pd Nanoparticles Electrodeposited from a Deep Eutectic Solvent, The Journal of Physical Chemistry C. 117 (2013) 14381–14389. [4] E.A. Mernissi Cherigui, P. Bouckenooge, K. Sentosun, H. Vanrompay, S. Bals, H. Terryn, J. Ustarroz, Electrodeposition of Nickel Nanostructures from Deep Eutectic Solvents, Manuscript in Preparation. (2016).

Supported nickel nanoparticles 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 nanoparticles (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, such as high stability at higher temperatures and broad electrochemical window compared to aqueous solutions. Furthermore, DESs are easier to prepare, less toxic and much cheaper than room temperature ionic liquids (RTILs) [2]. A recent approach, based on using carbon coated TEM grids as electrochemical electrodes, was developed in our group in order to study, at the nano-scale, the electrodeposited structures directly from the supporting substrate [3]. In this work, we used this approach to study the electrodeposition of nickel nanostructures from 1:2 choline chloride – urea DES (1:2 ChCl-U). By combining electrochemical techniques, such us cyclic / linear sweep voltammetry and chronoamperommetry, with ex-situ characterization, like FE-SEM, XPS, STEM, EDX and EELS, the electrochemical processes occurring during nickel deposition were better understood. Special attention was given to the interaction between the solvent and the electrodeposited nickel phase. In the frame of this investigation, a large population of small crystalline nickel nanostructures (< 20-50 nm) was obtained within a wide range of deposition parameters. Interestingly, we have found evidences that support the presence of an interaction between the DES and the growing nickel NPs that could lead to a self-limiting growth mechanism [4]. Indeed, the nanostructures obtained are formed by aggregated nanoclusters of few nanometers in diameter [5]. These results show that metal electrodeposition from DESs can be of great interest to produce nanostructures with electrocatalytic properties in a controllable and efficient way. [1] G-R. Li, H. Xu, X-F. Lu, J-X. Feng, Y-X. Tong, C-Y. Su, Electrochemical synthesis of nanostructured materials for electrochemical energy conversion and storage. Nanoscale, 5 (2013), 4056-4069. [2] E.L. Smith, A.P. Abbott, K.S. Ryder, Deep eutectic solvents (DESs) and their applications. Chemical Reviews, 114, (2014), 11060–82. [3] J. Ustarroz, J.A. Hammons, T. Altantzis, A. Hubin, S. Bals, H. Terryn, A generalized electrochemical aggregative growth mechanism. Journal of the American Chemical Society, 135 (2013), 11550–11561. [4] J.A. Hammons, T. Muselle, J. Ustarroz, M. Tzedaki, M. Raes, A. Hubin, et al., Stability, Assembly, and Particle/Solvent Interactions of Pd Nanoparticles Electrodeposited from a Deep Eutectic Solvent, The Journal of Physical Chemistry C. 117 (2013) 14381–14389. [5] E.A. Mernissi Cherigui, P. Bouckenooge, K. Sentosun, H. Vanrompay, S. Bals, J. Ustarroz, H. Terryn, Electrodeposition of Nickel Nanostructures from Deep Eutectic Solvents, Manuscript in Preparation. (2016).