Acid Strength Effects on Dimerization during Metal-Free Catalytic Dioxygen Reduction

Area of Science:

• Catalysis
• Electrochemistry
• Organic Chemistry

Background:

• Developing earth-abundant catalysts for the oxygen reduction reaction (ORR) is crucial for sustainable energy and industrial processes.
• Transition metal catalysts are widely used but raise environmental and cost concerns.

Purpose of the Study:

• To report a novel transition metal-free dicationic organocatalyst for ORR.
• To investigate the influence of acid-base properties on the ORR mechanism using this catalyst.

Main Methods:

• Electrochemical and spectrochemical studies of the organocatalyst in acetonitrile.
• Utilized halogenated acetic acid derivatives with a wide pKa range (12.65–20.3).

Main Results:

• A kinetically relevant peroxo dimer intermediate formed under electrochemical conditions with all tested acids.
• Under spectrochemical conditions, strong acids reduced the dimer's kinetic contribution, while weaker acids remained limited by dimer equilibrium.

Conclusions:

• The study provides mechanistic insights into metal-free ORR catalysis.
• Catalyst performance can be tuned by balancing redox activity and molecular unsaturation with intermediate pKa, similar to metal-based systems.