Ammonium Cation-Promoted CO₂ Electroreduction on Au in Acidic Media

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Electrochemical reduction of carbon dioxide (CO2) in acidic media is crucial for mitigating carbonate formation.
• Protons in acidic media can enhance hydrogen evolution reaction (HER), necessitating strategies to promote CO2 reduction reaction (CO2RR) while suppressing HER.

Purpose of the Study:

• To investigate the effectiveness of ammonium (NH4+) cations as promoters for CO2 electrolysis on gold (Au) catalysts in acidic media.
• To compare the performance of NH4+ with alkali metal cations (Na+, K+) in enhancing CO2RR activity and suppressing HER.

Main Methods:

• Electrochemical experiments were conducted using Au catalysts in acidic media with different cations (NH4+, Na+, K+).
• CO2RR activity and HER selectivity were measured.
• Computational estimations of local pH and adsorption energies were performed.

Main Results:

• NH4+ cations demonstrated a 3-fold improvement in CO2RR activity compared to Na+ and K+.
• The enhanced activity is attributed to NH4+'s superior electrostatic stabilization of CO2 adsorption, the rate-limiting step.
• NH4+ cations were found to mitigate interfacial pH swings during CO2RR.
• The cation effect was independent of the size of the Au nanocatalysts.

Conclusions:

• NH4+ cations are more effective promoters for CO2 electrolysis on Au in acidic media than alkali metal cations.
• The study advances the understanding of nonmetal cation effects on CO2RR.
• This work presents a viable cation strategy for enhancing CO2 electrolysis efficiency.