Nonpyrolytic Fe−N−C/Fe2O3 Heterostructure with RuO2‐Like OER Activity Synthesized via Polyacrylonitrile‐Derived Conjugated Pyridinic‐Nitrogen‐Carbon Sheet

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 °C using well‐established techniques, its complexity and cost are favorable compared to pyrolytic Fe−N−C materials. A method of synthesizing nonpyrolytic Fe−N−C materials with OER activity akin to commercial RuO2 is presented. The method involves catalyzing polyacrylonitrile's transformation into N−C at 300 °C using low‐melting hydrated Fe‐salts, resulting in the formation of Fe−N−C/Fe2O3 heterostructures. Fe2O3 modulates the electronic structure of Fe−N−C via oxygen vacancy tuning enabling optimal Fe−O* bonding, high electroactive surface area, and OER activity.