Conventional versus Unconventional Oxygen Reduction Reaction Intermediates on Single Atom Catalysts

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• The oxygen reduction reaction (ORR) is crucial for energy technologies like fuel cells and metal-air batteries.
• Understanding ORR mechanisms is key to designing efficient electrocatalysts.
• Single-atom catalysts (SACs) on nitrogen-doped graphene (NG) offer tunable electronic properties for ORR.

Purpose of the Study:

• To investigate conventional and unconventional ORR mechanisms on M@NG (M = Sc-Zn, Pt) using DFT.
• To identify stable reaction intermediates and their impact on electrocatalytic activity.
• To determine promising SACs for efficient ORR.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Analysis of various adsorption geometries for O2 intermediates.
• Thermodynamic overpotential and limiting potential calculations.

Main Results:

• Unconventional *O2 intermediates (superoxo complexes) are often more stable than conventional ones.
• M@NG systems predominantly follow unconventional pathways, except for Cr@NG and Cu@NG where both compete.
• Conventional mechanisms yield lower overpotentials than unconventional ones.
• Transition metals with fewer d-electrons show lower activity due to higher overpotentials.

Conclusions:

• Cobalt on nitrogen-doped graphene (Co@NG) is a promising SAC, favoring the conventional mechanism with low overpotential (0.38 V) and limiting potential (0.85 V).
• Copper on nitrogen-doped graphene (Cu@NG) is the second-best candidate.
• Catalyst design should consider both conventional and unconventional ORR pathways for optimal performance.