Two-Dimensional Bimetallic Zn/Fe-Metal-Organic Framework (MOF)-Derived Porous Carbon Nanosheets with a High Density of Single/Paired Fe Atoms as High-Performance Oxygen Reduction Catalysts

Abstract

Developing efficient non-precious-metal catalysts to accelerate the sluggish oxygen reduction reaction (ORR) is highly desired but remains a great challenge. Herein, using 2D bimetallic Zn/Fe-MOF as the precursor and g-C3N4 as the nitrogen source and stabilizer, porous carbon nanosheets doped with large amounts of single/paired Fe atoms (3.89 wt %) and N (10.28 wt %) are successfully prepared. It is found that the addition of g-C3N4 plays a key role in achieving a high loading of Fe single/paired atoms, and the 2D nanosheet structure gives the materials a high surface area and highly porous structure, resulting in outstanding ORR catalytic activity in both alkaline and acidic solutions. Our optimal sample achieved half-wave potentials in alkaline and acid media of up to 0.86 and 0.79 V (vs reversible hydrogen electrode (RHE)), respectively, values 20 mV higher than a commercial Pt/C catalyst in an alkaline medium and only 60 mV lower than Pt/C in an acidic medium. Moreover, its ORR durability was superior to that of commercial Pt/C in both electrolytes. We found that almost all the doped Fe in the sample existed as single or paired atoms coordinated with N. This work may provide an effective strategy for preparing high-performance catalysts bearing single/paired atoms by using MOFs as precursors.

Single‐Atom and Dual‐Atom Electrocatalysts Derived from Metal Organic Frameworks: Current Progress and Perspectives

“… (A) SEM and HAADF‐STEM images of the Fe/N‐PCN catalyst. Reproduced with permission [122] . Copyright 2020, American Chemistry Society.…”

“…[118][119][120][121] Recently, Liao and co-workers reported single/paired Fe atoms on porous carbon nanosheet (Fe/N-PCNs) for ORR using a 2D Zn/Fe-MOF as a precursor with the assistance of g-C 3 N 4 ( Figure 15A). [122] The Zn 2 + extend the distance of Fe atoms in the MOF and g-C 3 N 4 also served as stabilizer to prohibit the aggregation of Fe atoms. The HAAD-STEM image indicated the Reproduced with permission.…”

“…Metal-organic frameworks (MOFs)-derived atomic electrocatalysts have demonstrated great potentials in various electro- Reproduced with permission. [122] Copyright 2020, American Chemistry Society. (B) Illustration for the controllable preparation of the CoÀ NÀ C-x catalysts with varied active site structures.…”

Synthesis and Performance of MOF-Based Non-Noble Metal Catalysts for the Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells: A Review

“…Another Fe-based electrocatalyst (Fe/N-PCNs) prepared using g-C 3 N 4 as a nitrogen source was reported by Zheng et al [ 73 ], who first synthesized g-C 3 N 4 by the thermal decomposition of urea at 550 °C and then prepared a Zn/Fe-MOF via a hydrothermal reaction between Zn(NO 3 ) 2 ·6H 2 O, FeSO 4 ·7H 2 O, and 1,4,5,8-naphthalenetetracarboxylic anhydride as an organic ligand. Finally, the mixture of g-C 3 N 4 and Zn/Fe-MOF was heated under Ar at 950 °C for 1 h (the best conditions found by the authors) to afford Fe/N-PCNs.…”

Fe/Co Containing N‐Doped Hierarchical Porous Carbon Microcuboids and Microcylinders as Efficient Catalysts for Oxygen Reduction Reaction

“…The specific surface area and the porous structure of the carbon supports which determine the accessible part of active sites and the transport properties of ORR‐relevant species are also important for the electrocatalytic activity [19] . A lot of work has been devoted to the synthesis of carbon supports with specific morphologies, such as nanotubes, [20] nanosheets, [21] nanodisks, [22] etc. Metal‐organic hybrid materials are commonly used as precursors for the synthesis of M−N−C catalysts [23–25] .…”