Hydronium-Induced Switching between CO₂ Electroreduction Pathways.

Area of Science:

• Electrochemistry
• Catalysis
• Computational Chemistry

Background:

• CO2 electroreduction catalysts are often categorized by their product selectivity.
• Silver is a highly selective catalyst for CO production in aqueous electrolytes.
• The role of the reaction environment in determining catalyst selectivity is not fully understood.

Purpose of the Study:

• To investigate whether product selectivity is an intrinsic property of the catalyst or influenced by the reaction environment.
• To explore the role of hydronium ions in CO2 electroreduction pathways.
• To demonstrate the ability to tune catalyst selectivity through electrolyte manipulation.

Main Methods:

• Density Functional Theory (DFT) calculations to model reaction pathways and activation energy barriers.
• Experimental CO2 electroreduction using a silver catalyst in aqueous electrolytes with varying hydronium concentrations (neutral vs. highly alkaline).

Main Results:

• DFT simulations revealed that hydronium ions significantly lower the activation barrier for CO formation by facilitating oxygen hydrogenation.
• Removing hydronium ions increased the oxygen hydrogenation barrier and decreased the carbon hydrogenation barrier, favoring formate production.
• Experimental results showed a selectivity switch from CO to over 50% formate when using a silver catalyst in highly concentrated KOH, limiting hydronium concentration.

Conclusions:

• Catalyst selectivity in CO2 electroreduction is not an intrinsic property but a result of the combined catalyst and reaction environment.
• Hydronium ion concentration is a critical factor influencing transition state kinetics and determining favored reaction pathways.
• Electrolyte engineering offers a powerful strategy to control and tune CO2 electroreduction product selectivity.