Our goal is to monitor lattice constant variation of Pt nanoparticles as a function of electrochemical potential in a fast regime (~10-20 kHz). We will monitor the evolution of the Bragg peaks as a function of potentials steps or by cycle the potentials (scan rate between 1 V/S 10V/s). The experiment will be performed either in the well established ID31 fuel cell, and/or in the ID31 liquid cell for grazing incidence diffraction.