The goal of this project is to perform an in-situ structural, morphological and compositional characterization of bimetallic electrocatalytic nanoparticles (NPs) both at the nanometer and the atomic scale. We will synthesize bimetallic NPs electrochemically and/or through colloidal chemistry, by tuning the ratio of different elements including Pt, Ni, Ag, Cu and Sn. The coexistence of different materials on the same nano-object increases its functionalities because the individual properties of each component can be present on a single NP, and even more interestingly, opens the way to the discovery of new properties stemming from an interaction between the different materials. However, only little is known about the changes occurring at the nanometer and atomic scale when electrocatalytic NPs are exposed to aggressive chemical environments. Therefore, we will perform in-situ Transmission Electron Microscopy (TEM) experiments using dedicated holders which can operate at elevated temperatures, pressures and in liquid environments. The proposed research will be of great benefit since it can unravel the reasons for the occurrence of dynamic changes in the catalyst surface, which in turn can also drastically alter the performance and reliability of the catalysts.