Atomically Dispersed Co₂ MnN₈ Triatomic Sites Anchored in N-Doped Carbon Enabling Efficient Oxygen Reduction Reaction.

Abstract

Atomically dispersed transition metal-nitrogen/carbon (M-N/C) catalysts have emerged as the most promising substitutes to the precious platinum counterparts toward the oxygen reduction reaction (ORR). However, the reported M-N/C catalysts are usually in the form of common M-N₄ moieties with only a single metal active site, and they suffer from insufficient activity. Herein, an unusual trinuclear active structure is elaborately developed with a nitrogen-coordinated single Mn atom adjacent to two Co atoms (Co₂ MnN₈ ) anchored in N-doped carbon as a highly efficient ORR catalyst via adsorption-pyrolysis of a bimetallic zeolitic imidazolate framework precursor. Atomic structural investigations and density functional theory (DFT) calculations reveal that Co₂ MnN₈ would experience a spontaneous OH binding to form Co₂ MnN₈ -2OH as the real active site, leading to a single electron-filled state in the <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><msub><mi>d</mi> <msup><mi>z</mi> <mn>2</mn></msup> </msub> <annotation>${\mathrm{d}}_{{z}^{2}}$</annotation></semantics> </math> orbital and an optimized binding energy of intermediates. Accordingly, the as-developed Co₂ MnN₈ /C exhibits an unprecedented ORR activity with a high half-wave potential of 0.912 V and outstanding stability, not only surpassing the Pt/C catalyst but also representing a new record for the Co-based catalyst.