Effect of catalyst ink composition on the performance of carbon aerogel based Fe-N-C catalyst for the oxygen reduction reaction

Abstract

Application of Fe N C catalysts faces two main challenges. The initial performance loss during first hours of HT PEMFC operation of membrane electrode assembly (MEA) containing Fe N Cs as cathode catalyst is much higher compared to Pt/C based MEAs. This originates mainly from carbon corrosion and Fe demetalation. Moreover, the lower volumetric activity of Fe N Cs compared to Pt/C demands thicker catalyst layers, which can cause mass transport limitations. These challenges need to be overcome to use Fe N C catalysts in the HT PEMFC cathode. To minimize mass transport limitation and increase the volumetric activity porous carbon aerogels (CA) are a promising candidate for incorporation of Fe-Nx sites. The Fe N CA catalyst is produced via CA support-based synthesis including impregnation with Fe and N containing precursor, two pyrolysis steps and an acid leaching. Different catalyst ink suspensions with varied compositions of catalyst material, ethanol or 2-propanol, water and NafionTM are produced and investigated using RRDE setup to gain insights on activity and selectivity. The experiments are conducted at room temperature in diluted phosphoric acid to investigate the impact of phosphates on the activity. The results are compared to a commercial Fe N C (PMF-0011904, Pajarito Powder) catalyst. The outcomes from electrochemical and physical evaluations will provide insights into the importance of optimizing the catalyst ink for Fe N CA material. The results are important for further catalyst ink optimization for Fe N CA GDE manufacturing and their investigation under HT PEMFC conditions in a GDE half-cell setup.