COMEHTE

The necessary reduction of greenhouse gases emissions, as a worldwide concern, should more than ever motivate us to find alternatives to fossil resources as well as adapted energy conversion processes. Among others, fuel cells will play a strategic role during the energy transition to come, and are likely to become a key player in the future energy mix. Proton Exchange Membrane Fuel Cells (PEMFC) are no doubt the most versatile (polyvalent) since they can meet many needs, across a wide range of power (from mW for portable applications to MW for stationary through dozens of kW for transport). In 2012, PEMFCs accounted for 88% of the shipments (457,000 units) and 41% of the megawatts shipped (166.7 MW). A major concern in PEMFC development, especially in the transport sector, is to increase their operation temperature above 100°C while decreasing the relative humidity conditions. Today, the operating temperature is still limited by the electrolyte used in the membrane-electrodes assemblies (MEAs). In COMEHTE, we propose to take benefit from clays hygroscopic properties to develop new composite membranes based on microfibrous sepiolite and tubular halloysite. These clays will be functionalized in order to direct the membrane morphology at the nanoscale, i) to make them proton conductive (addition of acid groups) and ii) to favor the interaction with Nafion®, the host matrix (addition of fluorinated groups). The particular elongated morphology of such clays will participate to improving the mechanical strength of the composite membrane. This approach will be coupled with the development of active nanofibre reinforcements to further improve the membrane mechanical resistance and with the incorporation of radical scavengers to limit the membrane degradation. The composite materials will also be used as the proton conductor in catalytic layers so as to optimize the membrane-electrode interface. Chemical functionalization, plasma activation and thermal complexation will be studied as three complementary routes to modify raw materials. Silane based precursors will be used to efficiently react with the numerous hydroxyl groups covering both inner and outer surfaces of the selected clays. Neutral or reactive plasma will be applied either to create reactive radicals to favor the chemical post-functionalization or to directly functionalize the treated clays. Thermal complexation will notably help dispersing the loads in the polymer matrix. Dedicated characterizations will be performed so as to identify the proper treatment routes and to select the most promising composites. The selection will be realized on different criteria such as the ion exchange capacity, the proton conductivity, the swelling, the thermomechanical resistance or the thermochemical stability. The selected materials will then be used to prepare membrane-electrodes assemblies (MEAs) from membranes and electrodes developed in the project. MEAs will be tested in severe conditions (intermediate temperature and low relative humidity, accelerated stress tests) in comparison to reference MEAs. The most promising MEAs will finally be tested in short stack configuration, following automotive test cycles.