Fe-N-Carbon aerogel catalyst for oxygen reduction reaction

Proton exchange membrane fuel cell (PEMFC)s are an excellent energy conversion device for wide application of hydrogen, especially for portable or transportation applications. To reduce the total cost of these devices, recent non-precious-metal catalysts (NPMCs) have shown promises in replacing platinum-based catalysts. Among NPMCs, iron-nitrogen-carbon (Fe-N-C) catalysts subclass are the most mature. These catalysts are characterized by nitrogen coordinated iron ions acting as active centers. Numerous studies have focused on promoting their catalytic performance and exploring their oxygen reduction reaction (ORR) mechanism. Despite being less performant than Pt/C, the activity difference can be offset by ca. 3-10 times thicker cathodes. Nevertheless, in such configuration, mass transport limitations become predominant and need to be optimized. Carbon aerogels are an ideal candidate to synthesize Fe-N-C catalysts with excellent mass transport properties thanks to their tridimensional open texture,tailored pore size distribution from micro to macropores and good electrical conductivity. Herein, we synthesized Fe-N-C aerogel catalysts from resorcinol (R)-formaldehyde (F)-melamine (M) hydrogel and iron precursors using “one pot” sol-gel method followed by CO2supercritical drying and post heat treatments (N2and NH3atmospheres). The impacts of the synthesis parameters on catalytic activity and mass transport properties have been investigated. We show that the iron precursors as well as additive ligands affect the catalytic activity. We also demonstrate that chemical parameters, especially pH and melamine content in the sol, can greatly change the morphology of Fe-N-C aerogels and control their mass transport properties. Comparison between results obtained in RDE setup and in PEMFC will be presented.