Epoxy‐rich Fe Single Atom Sites Boost Oxygen Reduction Electrocatalysis

Abstract

Electrocatalysts for highly efficient oxygen reduction reaction (ORR) are crucial for energy conversion and storage devices. Single‐atom catalysts with maximized metal utilization and altered electronic structure are the most promising alternatives to replace current benchmark precious metals. However, the atomic level understanding of the functional role for each species at the anchoring sites is still unclear and poorly elucidated. Herein, we report Fe single atom catalysts with the sulfur and oxygen functional groups near the atomically dispersed metal centers (Fe1/NSOC) for highly efficient ORR. The Fe1/NSOC delivers a half‐wave potential of 0.92 V vs. RHE, which is much better than those of commercial Pt/C (0.88 V), Fe single atoms on N‐doped carbon (Fe1/NC, 0.89 V) and most reported nonprecious metal catalysts. The spectroscopic measurements reveal that the presence of sulfur group induces the formation of epoxy groups near the FeN4S2 centers, which not only modulate the electronic structure of Fe single atoms but also participate the catalytic process to improve the kinetics. The density functional theory calculations demonstrate the existence of sulfur and epoxy group engineer the charges of Fe reactive center and facilitate the reductive release of OH* (rate‐limiting step), thus boosting the overall oxygen reduction efficiency.

Axially Modified Square-Pyramidal CoN4–F1 Sites Enabling High-Performance Zn–Air Batteries

“… For O K-edge spectra, Co-FNC exhibits more apparent π* C–O–C and σ* C–O peaks than Co-NC, indicating partial retention of C–O–C structure during CVD process, favoring 4e – ORR (Figure S16). , In Co K-edge XANES spectra, the absorption edge of Co-FNC slightly shifts to higher energy relative to Co-NC, suggesting a more positive valence of the Co atom (Figure S17, inset). In Co-NC, the slight decrease in the oxidation state of the Co species can be attributed to the presence of small Co particles.…”

“…Recently, metal–nitrogen–carbon (M–N–C, M = Fe and Co, etc.) catalysts with metal–nitrogen coordination (M–N 4 ) hold huge potential in advanced materials field, due to the maximum atom utilization, adjustable electronic and coordination structure. , Among many, Co–N–C is currently the most promising candidate to replace Pt catalyst applied in ZABs with the advantage of natural abundance, encouraging ORR activity, and inertness to Fenton reaction . Unfortunately, owing to the weak adsorption energy of ORR intermediates on CoN 4 sites, the electrocatalytic performance of Co–N–C is rather poor, leading to low cell efficiency .…”

Unified ORR mechanism criteria via charge–spin–coordination of Fe functional units

“…(2) there is plenty of room for improvement in the dynamic balance of catalytic activity and stability. [20][21][22][23][24][25] Complex working conditions cause irreversible phenomena such as aggregation, dissolution and phase transition of Fe components, and also induce structural damage to carbon supports. These malignant reconstructions are largely limiting the practical application of degradation of the Fe-based catalyst.…”

Boron in the Second Coordination Sphere of Fe Single Atom Boosts the Oxygen Reduction Reaction

“…To this end, it is highly desirable to introduce another ORR site in the second coordination sphere of the M 1 N 4 system for adsorbing oxygen-containing intermediates. With the efforts of various research groups, the manipulation of second coordination sphere in single atoms has been recognized as a powerful strategy for upgrading the electrocatalytic performance. − Experimentally, introducing sulfur (S) , or phosphorus (P) atoms in the second coordination sphere of Fe single atom has been proven to significantly enhance its catalytic performance toward ORR. In the catalysis of ORR over M 1 N 4 , boron (B) as an ideal foreign atom can provide additional active sites in the second coordination sphere, which is attributed to the coordination effect between the empty 2p orbital of B atom and the electron-rich oxygen-containing intermediates. − More importantly, the doped B sites in the nitrogen-doped carbon structure (BNC) are weakly adsorbed to oxygen-containing intermediates, in contrast to those of the M 1 N 4 sites.…”