Enhancing Active Site Density in Fe-NC Electrocatalysts via 2D Structural Engineering for Efficient Oxygen Reduction

Abstract

Enhancing the active site density of metal-nitrogen-carbon (M-NC) catalysts is critical for improving their oxygen reduction reaction (ORR) performance in proton exchange membrane fuel cells (PEMFCs). In this study, we report a two-dimensional (2D) Fe-NC sheet catalyst designed to maximize active site exposure through structural engineering. Unlike conventional three-dimensional (3D) Fe-NC catalysts, the 2D Fe-NC sheet exhibits a significantly higher surface area and increased Fe-N4 site density, leading to enhanced ORR kinetics. The expanded electrochemical interface and improved active site accessibility contribute to superior site utilization and mass transport properties. Electrochemical evaluations confirm that the 2D Fe-NC sheet outperforms its 3D counterpart in ORR activity, demonstrating higher half-wave potential and turnover frequency. Furthermore, PEMFC single-cell tests reveal that the 2D Fe-NC sheet achieves comparable performance to previously reported M-NC catalysts, particularly when combined with 3D structures to mitigate aggregation effects. This study highlights the importance of morphology engineering in optimizing M-NC catalysts for efficient PEMFC applications.