Impact of Aerogel Modification for Fe-N-C Activity and Stability towards Oxygen Reduction Reaction in Phosphoric Acid Electrolyte

Abstract

Resorcinol-formaldehyde based carbon aerogel (CA) has been tailored to meet the requirements as a Fe-N-C carbon support, aiming to provide sufficient, inexpensive cathode catalysts for high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). Therefore, different treatments of the aerogel are explored for optimal pore structure and incorporation of surface functionalities, which are crucial for Fe-N-C synthesis and electrochemical performance. Fe-N-Cs of differently modified aerogel are investigated in phosphoric acid electrolyte. The results show that HNO3 treatment for 5 h yields the Fe-N-C with highest mass activity and selectivity, attributed to the highest amount of nitrogen functionalities revealed by energy dispersive X-ray spectroscopy (XPS) and proper Fe-Nx site formation. HNO3 oxidation for 2 h leads to Fe-N-C with slightly lower oxygen reduction reaction (ORR) activity and selectivity. In contrast, the Fe-N-C synthesized from CA with H3PO4 treatment shows negligible ORR activity. The feasibility of one-step activation and carbonization treatment with K2CO3 and, for the first time, with K2CO3 and melamine is proven as the obtained Fe-N-Cs exhibit promising ORR activity. The results are compared with the commercial Fe-N-C PMF-014401. This study contributes to the advancement of cost-efficient HT-PEMFCs by optimizing Fe-N-C catalyst properties.