The effect of mechanical vibration on Platinum (Pt) particle agglomeration and growth in the catalyst layer of a Membrane Electrode Assembly (MEA) for a Proton Exchange Membrane Fuel Cell (PEMFC) was investigated. A series of experiments were conducted using a 300-h accelerated test with potential cycling and transmission electron microscopy (TEM). Each of the 300-h accelerated tests used different constant mechanical vibration conditions (frequency and acceleration). It was observed that the average diameter of Pt particles under vibration is 10% smaller than the ones that were under no vibration conditions. The Pt particles in the order of 2-2.5 nm in the pristine state have grown to approximately 6 nm (after 300-h accelerated test without vibration condition) and to approximately 5.47 nm (after 300 h accelerated test under 1 g 20 Hz vibration condition). (C) 2012 Elsevier B.V. All rights reserved.