This thesis work focuses on the development of a new microporous structure for PEMFC gas diffusion layers. The development of new materials for PEM fuel cells is a necessity to improve the power density provided by actual cell, to reduce the cost of materials and the price of the system. PEMFCs have problems with the distribution of liquid water inside the cell, particularly in its porous

layers. The microporous layer is one of the porous layers whose role is to optimize the water distribution. Developing a new micro-porous structure can provide additional information on the parameters influencing water management in the cell and provide a path to improving the fuel cell performance. As part of the PEPR (Priority Research Program and Equipment) H2 PEMFC95 project, the CEA Departments of IRAMIS (Saclay) and Hydrogen for Transport (LITEN-DEHT Grenoble) will collaborate on the development of Optimized and innovative GDLs based on carbon nanotubes, more suitable for the defined operating conditions. Aligned CNT mats have indeed demonstrated their effectiveness as a microporous layer [1]. The performance is at least similar to the best state-of-the-art gas diffusion layer depending on the conditions, and up to 30% improvement in power density could be achieved, without any hydrophobic treatment. For this thesis subject, we propose to continue the development of these diffusion layers integrating CNTs for their interest in terms of stability with respect to oxidation and their hydrophobicity by producing microporous layers with variable porosity. The objective is to substitute them for GDL while improving understanding of its role and, in general, of transport phenomena in a PEMFC core. To do this, the work has two parts. A materials section with manufacturing aspects and characterization of functional properties and an electrochemistry section with fuel cell measurements