Nonpyrolytic Fe‐N‐C/Fe2O3 heterostructure with RuO2‐like OER Activity Synthesized via Polyacrylonitrile‐derived Conjugated Pyridinic‐nitrogen‐carbon Sheet

Abstract

Pyrolytic single Fe atom‐nitrogen‐carbon materials (Fe‐N‐C) and their derivatives are excellent catalysts for electrochemical oxygen reduction reactions. However, they exhibit poor oxygen evolution reaction (OER) activity due to non‐optimal Fe‐O* bonding. This limitation is overcome via electronic structure modulation (i.e., tuning the heteroatom type, concentration, and location within Fe’s n ≥ 1 coordination sphere). However, the methods used are complex and energy‐intensive (i.e., 1000 to 1200°C) raising concerns about reproducibility and cost. This study introduces a method for synthesizing nonpyrolytic Fe‐N‐C/Fe2O3 composites with similar electronic structure modulation as pyrolytic Fe‐N‐C and OER activity akin to commercial RuO2. The methodology involves doping low‐melting hydrated Fe‐salts in electrospun polyacrylonitrile nanofiber to catalyze its transformation into conjugated pyridinic‐N‐rich graphite‐like sheets (i.e., N‐C) at 300°C. N‐C chelate effectively with oxygen‐vacant (Ov)‐rich Fe atoms derived from Fe2O3 NPs resulting in Fe‐N‐C/Fe2O3 heterostructures. The Fe2O3 coupling effectively tunes Fe‐N‐C’s electronic structure via Ov modulation. Consequently, the Fermi and d‐orbital energy levels are optimized leading to partial filling of the antibonding states, optimal Fe‐O* bonding, high electrochemically active surface area, and OER activity. Because Fe‐N‐C/Fe2O3 is synthesized at 300 oC using well‐established techniques, its complexity and cost are favorable compared to pyrolytic Fe‐N‐C materials.