Catalyst gradient for cathode active layer of proton exchange membrane fuel cell

The experimental use of catalyst gradients within the active layer of a PEM FC cathode allows studying the influence of the location effect of Pt nanop articles on cathode performances. The catalyst gradient effect quantitative ly and qualitatively depends on porosity: it is stronger for non-porous act ive 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 p referential location of Pt nanoparticles close to the gas diffusion layer s ide in non-porous active layers and close to the proton exchange membrane s ide in porous active layers. In the latter case, better performances are ob served. Therefore, the optimisation of catalyst utilisation is obtained wit h thin porous active layers and with preferential location of Pt nanopartic les close to the proton exchange membrane side. These experimental results are confirmed by modelling both diffusion and ionic ohmic drop within activ e layers with catalyst gradients. (C) 2000 Elsevier Science Ltd. All rights reserved.