Epoxy-rich Fe Single Atom Sites Boost Oxygen Reduction Electrocatalysis.

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrocatalysts are vital for efficient energy conversion and storage.
• Single-atom catalysts offer superior metal utilization and tunable electronic properties, presenting an alternative to precious metals.
• Understanding the precise role of different species at anchoring sites in single-atom catalysts remains a challenge.

Purpose of the Study:

• To develop and investigate novel iron single-atom catalysts (Fe1/NSOC) incorporating sulfur and oxygen functional groups for enhanced oxygen reduction reaction (ORR) performance.
• To elucidate the atomic-level mechanisms responsible for the improved catalytic activity.

Main Methods:

• Synthesis of Fe single-atom catalysts with sulfur and oxygen functional groups (Fe1/NSOC).
• Electrochemical characterization, including half-wave potential measurements.
• Spectroscopic analysis to probe the catalyst's electronic structure and composition.
• Density functional theory (DFT) calculations to model catalytic mechanisms.

Main Results:

• Fe1/NSOC achieved a high half-wave potential of 0.92 V vs. RHE, outperforming commercial Pt/C and Fe single-atom catalysts on nitrogen-doped carbon (Fe1/NC).
• Spectroscopic data indicated sulfur groups induce epoxy groups near FeN4S2 centers, modulating the electronic structure of iron.
• DFT calculations confirmed that sulfur and epoxy groups optimize the Fe active site's charge and facilitate the rate-limiting step (OH* removal).

Conclusions:

• Fe1/NSOC demonstrates superior ORR electrocatalytic activity compared to existing benchmarks.
• The synergistic effect of sulfur and epoxy groups is crucial for enhancing the electronic properties and catalytic kinetics of iron single-atom catalysts.
• This work provides fundamental insights into the design principles for highly efficient non-precious metal electrocatalysts.