Reimagining acidic CO₂ electroreduction via anion-mediated proton transfer

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Acidic CO2 electroreduction (CO2RR) is a promising carbon-negative technology for chemical synthesis.
• The competing hydrogen evolution reaction (HER) and salt precipitation from high cation concentrations hinder CO2RR efficiency and durability.
• Current strategies rely on high cation concentrations (e.g., K+) to suppress HER, leading to operational challenges.

Purpose of the Study:

• To develop an anion engineering strategy for acidic CO2RR that avoids high cation concentrations and salt precipitation.
• To elucidate the role of anion hydrolysis in proton transfer dynamics and its impact on CO2RR and HER selectivity.
• To establish a new paradigm for electrolyte design in acidic CO2RR systems.

Main Methods:

• Utilized mass spectrometry, spectroscopic techniques, and theoretical calculations to investigate proton transfer mechanisms.
• Employed anion engineering by varying anion hydrolysis tendency in acidic electrolytes.
• Tested non-hydrolyzable chloride anions (Cl-) in low cation concentration (0.2 M K+) acidic conditions (pH 1).

Main Results:

• Hydrolyzable anions were found to promote HER by facilitating proton transfer through protonated species and strengthened hydrogen-bond networks.
• Achieved highly selective CO2RR with 87.3% Faradaic efficiency under strong acidic conditions (pH 1) using non-hydrolyzable Cl- at low K+ concentration.
• Demonstrated that anion hydrolysis tendency is a critical factor influencing electrocatalytic performance in acidic CO2RR.

Conclusions:

• Anion engineering offers a novel approach to optimize acidic CO2RR, shifting focus from cation concentration to anion properties.
• This strategy effectively suppresses HER and prevents salt precipitation, enhancing electrolyzer durability and CO2RR selectivity.
• The findings establish anion hydrolysis tendency as a key descriptor for designing advanced electrolytes for efficient CO2 electroreduction.