The experimental use of catalyst gradients within the active layer of a PEMFC cathode allows studying the influence of the location effect of Pt nanoparticles on cathode performances. The catalyst gradient effect quantitatively and qualitatively depends on porosity: it is stronger for non-porous active layers than for porous ones. The origin of the catalyst gradient effect is not the same according to porosity: oxygen diffusion is a rate limiting step for non-porous active layers, while ionic-ohmic drop is limiting for porous ones. Thus, the catalyst utilisation efficiency increases with the preferential location of Pt nanoparticles close to the gas diffusion layer side in non-porous active layers and close to the proton exchange membrane side in porous active layers. In the latter case, better performances are observed. Therefore, the optimisation of catalyst utilisation is obtained with thin porous active layers and with preferential location of Pt nanoparticles close to the proton exchange membrane side. These experimental results are confirmed by modelling both diffusion and ionic ohmic drop within active layers with catalyst gradients.