The formation of Cu and Pt nanoparticles in an imidazolium-based ionic liquid was followed by UV-Visible spectroscopy. The different growth processes, autocatalytic first order and oriented second order, for Cu and Pt, respectively, is attributed to the different chemical nature of the metal particles surface. Stabilization through layering of the particles surface by the ionic liquid has an important impact on the use of noble and non-noble metal nanoparticles in energy conversion systems such as fuel cells and CO2 electrocatalytic reduction to useful fuels. (C) The Author(s) 2017. Published by ECS. All rights reserved.