Mechanistic Insights into the Roles of Electrolyte Additives in Enhancing CO₂ Electroreduction Efficiency

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Electrolyte engineering is crucial for optimizing the competition between CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER).
• Understanding electrolyte-mediated interfacial mechanisms is key to enhancing CO2RR efficiency for CO production.
• Current strategies often lack fundamental mechanistic insights into electrolyte effects.

Purpose of the Study:

• To develop an environmentally friendly additive-assisted electrolyte engineering strategy for CO2RR.
• To investigate the role of polyethylene glycol (PEG) as an electrolyte additive in CO2RR on a gold (Au) electrode.
• To elucidate the underlying mechanisms responsible for enhanced CO2RR efficiency.

Main Methods:

• Comparative studies using polyethylene glycol (PEG), ethylene glycol (EG), and poly(ethylene glycol) dimethyl ether (PEGDME) as electrolyte additives.
• Electrochemical techniques including CO2RR and hydrogen evolution reaction (HER) measurements.
• Spectroscopic analyses (NMR, Raman) and electrochemical impedance spectroscopy (EIS).
• Computational simulations to understand interfacial interactions.

Main Results:

• Incorporating 40 vol % PEG into a 0.1 M NaHCO3 electrolyte increased CO Faradaic efficiency to 92% on a Au electrode, compared to 70% without additives.
• Comparative studies revealed that strong Na+ solvation by PEG and PEGDME is the primary factor for improved CO2RR efficiency.
• Hydrogen-bond network reconstruction was identified as a secondary contributing factor.

Conclusions:

• Additive-assisted electrolyte engineering using PEG is a simple and effective strategy to enhance CO2RR efficiency.
• The mechanism involves preferential Na+ solvation, which modulates the CO2RR pathway over HER.
• This work provides fundamental insights and a practical approach for designing electrolytes for efficient CO2 reduction.