Maximizing the Active Site Densities of Single-Atomic Fe-N-C Electrocatalysts for High-Performance Anion Membrane Fuel Cells

Abstract

Iron- and nitrogen-doped carbon (Fe-N-C) catalysts have received significant attention owing to their high oxygen reduction reaction (ORR) activities, which are comparable to those of state-of-the-art Pt/C catalysts. This high ORR activity originates from the atomically dispersed Fe coordinated with the nitrogen atom (Fe-N-x) active site. Increasing the Fe-N-x active site density can enhance the ORR activity. In this study, we suggest a facile and effective method for maximizing the active site densities using a simple ZnCl2 activation method. ZnCl2 activation was applied to the metal organic framework-derived Fe-N-C catalyst that exhibits superior ORR activity compared to Pt/C and a recently reported nonprecious metal catalyst. Through various electrochemical analyses, we confirmed that this activity originates from the effectively increased active site density. The anion-exchange membrane fuel cell (AEMFC) performance was measured to confirm practical applicability, and we obtained a significantly high performance of 1076 mA cm(-2) at 0.6 V, which is significantly higher than the currently reported performance of carbon-based Fe-N-C AEMFC cathode catalysts. We demonstrate the potential of our strategy for applications in various carbon-based materials that can be used for the development of high-efficiency electrochemical energy devices.