Influence of the synthesis parameters on the proton exchange membrane fuel cells performance of Fe–N–C aerogel catalysts

Abstract

Fe–N–C aerogel catalysts were prepared by sol–gel polycondensation of resorcinol, melamine and formaldehyde precursors in the presence of FeCl 3 salt, followed by supercritical drying and thermal treatments. The effect of the mass ratio of precursors on the microstructure, iron speciation and oxygen reduction reaction (ORR) performance of the Fe–N–C aerogels was investigated by N 2 sorption, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy, CO chemisorption and rotating disk electrode in acidic medium. The best ORR performance (activity and mass transport) was obtained by an optimum balance between pore structure and active Fe-N x species. Through acid washing, the durability of the catalyst was further improved by eliminating unstable and inactive species, particularly iron nanoparticles and iron carbide. From the CO chemisorption and turnover-frequency value, the surface sites were comparable with the highest values reported in literature. Finally, Fe–N–C aerogel catalyst was implemented a in membrane–electrode assembly with an active area of 25 cm 2 and tested in single cell, emphasizing the importance of the ink formulation on the performance. • Optimum balance between pore texture and active FeNx species for best ORR performance. • Better mass-transport properties due to higher mesopore volume in the Fe–N–C catalyst. • XAS and 57 Fe Mössbauer spectroscopies identified FeN x and Fe-inorganic species. • Acid washing treatment eliminates the unstable and inactive Fe-inorganic species. • Need to adapt the ink formulation to the catalyst texture for high performance MEAs.