Self‐Sacrificing Template Synthesis of Carbon Nanosheets Assembled Hollow Spheres with Abundant Active Fe–N4O1 Moieties for Electrocatalytic Oxygen Reduction

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 21
• Main Authors: Ma, Fei‐Xiang, Liu, Zheng‐Qi, Zhang, Guobin, Fan, Hong‐Shuang, Du, Yue, Zhen, Liang, Xu, Cheng‐Yan
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 24.05.2023
• Subjects: Carbon; Chelation; Chemical reduction; Cyanuric acid; Electrocatalysts; Fe–N–C; Fine structure; hollow structures; Mass transfer; Maximum power density; Melamine; Metal air batteries; Microspheres; Nanosheets; Nanotechnology; oxygen reduction; Oxygen reduction reactions; single‐atom catalysts; Structural analysis; Thickness; Zinc-oxygen batteries
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202207991

Single‐atom Fe–N–C (Fe1–N–C) materials represent the benchmarked electrocatalysts for oxygen reduction reaction (ORR). However, single Fe atoms in the carbon skeletons cannot be fully utilized due to the mass transfer limitation, severely restricting their intrinsic ORR properties. Herein, a self‐sacrificing template strategy is developed to fabricate ultrathin nanosheets assembled Fe1–N–C hollow microspheres (denoted as Fe1/N‐HCMs) by rational carbonization of Fe3+ chelating polydopamine coated melamine cyanuric acid complex. The shell of Fe1/N‐HCMs is constructed by ultrathin nanosheets with thickness of only 2 nm, which is supposed to be an ideal platform to isolate and fully expose single metal atoms. Benefiting from unique hierarchical hollow architecture with highly open porous structure, 2 nm‐thick ultrathin nanosheet subunits and abundant Fe–N4O1 active sites revealed by X‐ray absorption fine structure analysis, the Fe1/N‐HCMs exhibit high ORR performance with a positive half‐wave potential of 0.88 V versus the reversible hydrogen electrode and robust stability. When served as air‐cathode catalysts with ultralow loading mass of 0.25 mg cm−2, Fe1/N‐HCMs based Zn–air batteries present a maximum power density of 187 mW cm−2 and discharge specific capacity of 806 mA h gZn−1 in primary Zn–air batteries, all exceeding those of commercial Pt/C. A self‐sacrificing template strategy is developed to fabricate 2 nm‐thick nanosheets assembled Fe1–N–C hollow microspheres (Fe1/N‐HCMs) with highly open porous architecture, which is supposed to fully expose the catalytic active sites to boost the oxygen reduction reaction. Unlike the general Fe–N4 configuration in most reported Fe1–N–C catalysts, the active sites in Fe1/N‐HCMs have been identified as Fe–N4O1 configuration.