Appropriate Acid Etching to Obtain Defect‐Rich and Porous Zeolitic‐Imidazolate‐Framework‐Derived Undercoordinated Fe‐NC Catalysts Toward Boosted Oxygen Reduction Reaction

Iron‐nitrogen‐carbon (Fe‐NC) catalysts, particularly those with Fe‐N 4 coordination moieties, are the most promising alternatives to commercial Pt@C for oxygen reduction reaction (ORR) in green energy conversion. The acid etching strategy is an effective and simple strategy to break the symmetric coordination of Fe‐N 4 on the carbon substrate to further enhance the activity. Herein, a superior Fe‐NC catalyst with undercoordinated Fe‐N 2 moieties was produced through a concentration‐controlled acid etching strategy, following an underlying quantitative indicator (I D /I G ) to regulate its defect degree accurately. Due to the defect‐rich and porous carbon structure to accelerate the mass transfer, this Fe‐N 2 catalyst exhibited an admirable half‐wave potential (E 1/2 ) of 0.85 V RHE versus 0.87 V RHE for commercial Pt@C, and a better stability and a higher limiting current density (−6.3 mA cm −2 ) in alkaline conditions, outperforming the other involved Fe‐NCs and the Pt@C. This work provides an acid etching strategy to accurately control the defect degree and break the symmetrical Fe‐N 4 coordination structure of Fe‐NCs for enhancing the ORR activity.