The CCL is the most limiting component in terms of performance and durability, mainly due to the conditions in which the ORR occurs along with its sluggish kinetic. This is also the least understood component compared to GDL or membrane. The fundamental reasons of, and the relative contribution of the phenomena (kinetic or transport) on, performance limitations of CCL are still currently under discussion. We aim at better understanding the relationships between the composition/structure of CCL made of Pt based NP supported on Carbon, their effective transport properties/limitations and finally the overall fuel cell performance. This is a prerequisite to a rational design of effective CCL which will allow to make highly efficient and durable MEA with low platinum loading. Thus, our ambition is to bring new knowledge on the: 1/microstructure of the CCL, 2/ correlation between transport properties of CCL and its components (Platinum, Carbon, Ionomer), 3/ local conditions in CCL during operation, 4/ performance limitations induced by transport phenomena, 5/modelling of transport phenomena in CCL.