Oriented Electrostatic Effects on O₂ and CO₂ Reduction by a Polycationic Iron Porphyrin

Area of Science:

• Electrochemistry
• Catalysis
• Energy Conversion

Background:

• Next-generation energy technologies require efficient chemical-to-electrical energy conversion.
• Molecular catalysts with atomically positioned electrostatic motifs can stabilize charged intermediates.
• An iron porphyrin with cationic groups has shown promise for oxygen reduction (ORR) and carbon dioxide reduction (CO2RR).

Purpose of the Study:

• To investigate the catalytic activity of individual atropisomers of a metalloporphyrin.
• To understand the role of atomically positioned charge in ORR and CO2RR.
• To determine the impact of electrostatic environment on reaction kinetics and thermodynamics.

Main Methods:

• Synthesis and isolation of four individual atropisomers of an iron porphyrin.
• Electrochemical evaluation of each atropisomer for ORR and CO2RR.
• Analysis of turnover frequencies and overpotentials for each reaction.

Main Results:

• All four atropisomers effectively catalyzed both ORR and CO2RR at fast rates and low overpotentials.
• Maximum turnover frequencies varied significantly among isomers: 60-fold for ORR and 5-fold for CO2RR.
• Specific isomers (αβαβ for ORR, αααα for CO2RR) exhibited the highest activity and overpotential.

Conclusions:

• Atomically positioned charge plays a complex role in multistep electrochemical transformations.
• High charge density, rather than precise orientation, is crucial for optimizing thermodynamics and kinetics.
• This study provides novel insights into electrostatic control in molecular electrocatalysis.