Active catalysts with direct application in most of the relevant fields of Sustainable Chemistry are being widely demanded. Therefore, the design and synthesis of new metallic nanomaterials, outstanding metallic nanoparticles (NPs), becomes necessary. The use of new synthetic approaches is a useful path to better control the size, morphology and surface chemical composition of those nanostructured materials. The electrochemical deposition of a metal on the surface of an electrode using non-conventional solvents, such as ionic liquids and deep eutectic solvents (DES), emerges as a satisfactory alternative to the traditional methodologies.[1] In particular, choline chloride-based DES, using urea or glycerol and its derivatives as the DES hydrogen-bond donor, represent a new generation of bio-based green solvents, coming from renewable sources, and safe for the environment and human health.[2,3] Nitrogen management, either in urban wastewater treatment (where the main source of nitrogen comes as urea from urine) or in rural aquifers treatment (where nitrate contamination is significant due to the extensive use of fertilizers), represents one of the main challenges to be solved at present, as stated in H2020 objectives. In both cases, electrochemical water treatments by means of metallic electrocatalysts afford a suitable technology that is being widely applied, thanks to its greenness (no waste generation), simplicity, reliability and small physical footprint, to transform both contaminants into innocuous N2. In this communication, two model systems have been selected: i) Sn electrode for the electrocatalytic reduction of nitrate,[4] and ii) Ni electrode for the electrocatalytic oxidation of urea.[5] In particular, we present herein the synthesis of new Sn NPs and Ni NPs by electrochemical technologies, using different types of bio-based DES as the synthetic medium and the electrolyte. The selection and use of the most suitable DES were carried out through the study of their physical-chemical properties, such as conductivity, viscosity, polarity parameters, etc. The morphology, size and chemical composition of those new catalytic nanomaterials were fully characterized, and their electrocatalytic activity was evaluated through cyclic voltammetry and chronoamperometry. Finally, the morphological characteristics and performance of those nanoparticles electrosynthesized in DES have been compared with nanoparticles previously reported in the literature for denitrification and elimination of urea in water. References [1] R. Bernasconi, G. Panzeri, A. Accogli, F. Liberale, L. Nobili, L. Magagnin. Ionic Liquids: Electrodeposition from Deep Eutectic Solvents. Intech Open, London, 2017. [2] E. L. Smith, A. P. Abbott, K. S. Ryder. Chem. Rev. 2014, 114, 11060–11082. [3] A. Leal-Duaso, I. Favier, D. Pla, E. Pires, M. Gómez. ACS Sustainable Chem. Eng. 2021, 9, 6875–6885. [4] A. S. Fajardo, P. Westerhoff, C. M. Sanchez-Sanchez, S. Garcia-Segura. Appl. Catal. B: Environ. 2021, 281, 119465. [5] G. Ma, Q. Xue, J. Zhu, X. Zhang, X. Wang, H. Yao, G. Zhou, Y. Chen. Appl. Catal. B: Environ. 2020, 265, 1118567.