Multiscale structural engineering of atomically dispersed FeN₄ electrocatalyst for proton exchange membrane fuel cells

Atomically dispersed iron–nitrogen–carbon (Fe–N–C) catalysts have emerged as the most promising alternative to the expensive Pt-based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs), however suffer from low site density of active Fe-N₄ moiety and limited mass transport during the catalytic reaction. To address these challenges, we report a three-dimensional (3D) metal–organic frameworks (MOF)-derived Fe–N–C single-atom catalyst. In this well-designed Fe–N–C catalyst, the micro-scale interconnected skeleton, the nano-scale ordered pores and the atomic-scale abundant carbon edge defects inside the skeleton significantly enhance the site density of active Fe-N₄ moiety, thus improving the Fe utilization in the final catalyst. Moreover, the combination of the above mentioned micro- and nano-scale structures greatly facilitates the mass transport in the 3D Fe–N–C catalyst. Therefore, the multiscale engineered Fe–N–C single-atom catalyst achieves excellent ORR performance under acidic condition and affords a significantly enhanced current density and power density in PEMFC. Our findings may open new opportunities for the rational design of Fe–N–C catalysts through multiscale structural engineering.