Edge‐Rich Fe−N₄ Active Sites in Defective Carbon for Oxygen Reduction Catalysis

Abstract

Controllably constructing nitrogen‐modified divacancies (ND) in carbon substrates to immobilize atomic Fe species and unveiling the advantageous configuration is still challenging, but indispensable for attaining optimal Fe−N−C catalysts for the oxygen reduction reaction (ORR). Herein, a fundamental investigation of unfolding intrinsically superior edge‐ND trapped atomic Fe motifs (e‐ND−Fe) relative to an intact center model (c‐ND−Fe) in ORR electrocatalysis is reported. Density functional theory calculations reveal that local electronic redistribution and bandgap shrinkage for e‐ND−Fe endow it with a lower free‐energy barrier toward direct four‐electron ORR. Inspired by this, a series of atomic Fe catalysts with adjustable ND−Fe coordination are synthesized, which verify that ORR performance highly depends on the concentration of e‐ND−Fe species. Remarkably, the best e‐ND−Fe catalyst delivers a favorable kinetic current density and halfwave potential that can be comparable to benchmark Pt−C under acidic conditions. This work will guide to develop highly active atomic metal catalysts through rational defect engineering.

Coordination Engineering of Single‐Atom Catalysts for the Oxygen Reduction Reaction: A Review

“…[ 114–120 ] Despite the above‐mentioned pyrrole‐type FeN 4 , most researchers still believe that the pyridinic‐N coordinated metal center is the active site. [ 1,86,121–126 ] In addition to the experimental evidences, general principles were also applied to guide the catalyst design. Cheng and co‐workers established a universal activity descriptor, [ 127 ] expressed as follows where θ d is the number of valence electrons in the metal d‐orbital, E M , E N , and E O/H are the electronegativity of the metal atom, nitrogen atom, and oxygen atom or hydrogen atom, respectively, n N is the number of nearest nitrogen atom around the metal atom, and α is the correction coefficient.…”

“…[114][115][116][117][118][119][120] Despite the above-mentioned pyrrole-type FeN 4 , most researchers still believe that the pyridinic-N coordinated metal center is the active site. [1,86,[121][122][123][124][125][126] In addition to the experimental evidences, general principles were also applied to guide the catalyst design. Cheng and co-workers established a universal activity descriptor, [127] expressed as follows…”

Defective Structures in Metal Compounds for Energy‐Related Electrocatalysis

“…Meanwhile, the controllable synthesis of defects is also beneficial for probing the structure–performance relationships, thus facilitating the rational design and fabrication of more efficient electrocatalysts for the target reactions. [ 47–49 ]…”

Atomic Level Dispersed Metal–Nitrogen–Carbon Catalyst toward Oxygen Reduction Reaction: Synthesis Strategies and Chemical Environmental Regulation

“…In the nitrogen‐containing modified defect catalysts, defects easily capture metal atoms to form a stable catalyst. [ 49‐52 ] The catalyst has a high density of active sites and a defective environment around the metal center and therefore exhibits excellent catalytic performance. [ 53 ] The defects can accurately determine the electronic structure and surface/interface properties of the catalyst, thereby adjusting the adsorption energy of intermediate substances by destroying the tiny original distribution and generating a new quantum equilibrium, thereby accelerating the kinetics of the electrocatalytic reaction.…”