Uncovering the Nonmonotonic Relationship between Total Activity and Single-Atom Density for Oxygen Reduction...

Area of Science:

• Catalysis
• Materials Science
• Electrochemistry

Background:

• Single-atom catalysts (SACs) are crucial for reactions like oxygen reduction (ORR).
• High density of single-atom sites is generally pursued to maximize catalyst activity.
• Interactions between adjacent single atoms at high densities are often overlooked.

Purpose of the Study:

• To investigate the nonmonotonic relationship between single-atom density and catalytic activity.
• To understand the impact of proximity effects on the intrinsic activity of single-atom sites.
• To provide insights for designing high-performance SACs with optimal site densities.

Main Methods:

• Theoretical calculations were employed to model catalyst behavior.
• Experimental validation was performed using cobalt-embedded carbon as a model SAC for ORR.
• Analysis focused on the influence of interatomic distances on ORR energetics.

Main Results:

• A nonmonotonic relationship between ORR activity and single-atom density was observed.
• Proximity effects, such as hydrogen bonding and steric hindrance, were identified as key factors.
• Intrinsic activity decreased when the distance between neighboring cobalt sites fell below approximately 0.5 nm.
• Both total and mass activities of Co-SACs exhibited turning points with increasing single-atom density.

Conclusions:

• The common assumption of monotonically increasing activity with site density is challenged.
• Optimal single-atom densities are crucial for maximizing catalyst performance.
• This finding guides the rational design of advanced SACs by considering inter-site interactions.