Theories for Electrolyte Effects in CO₂ Electroreduction.

Area of Science:

• Electrochemistry
• Catalysis
• Renewable Energy

Background:

• Electrochemical CO2 reduction (eCO2R) converts waste CO2 into valuable chemicals using renewable electricity, crucial for net-zero emissions.
• Catalyst and electrolyte optimization are key research areas for enhancing eCO2R activity.
• Electrolyte composition can influence eCO2R activity by orders of magnitude.

Purpose of the Study:

• To review theories explaining electrolyte effects on electrochemical CO2 reduction (eCO2R).
• To elucidate the mechanisms by which cations, anions, and pH influence eCO2R.
• To identify challenges and future directions for predictive electrolyte design.

Main Methods:

• Review of theoretical models and experimental observations concerning electrolyte effects in eCO2R.
• Analysis of cation effects (e.g., alkali metals) on reaction intermediates and interfacial pH.
• Examination of anion and pH influences on proton donation, active site blocking, and local environment tuning.

Main Results:

• Electrolytes impact eCO2R via field effects on intermediates, proton donor modulation, anion adsorption, and homogeneous reactions.
• Alkali metal cations (Cs+ > K+ > Na+ > Li+) enhance activity through stabilization and pH buffering.
• Electrolyte pH significantly alters eCO2R activity (several orders of magnitude) by shifting interfacial fields and changing proton sources.

Conclusions:

• Current models rationalize observed trends but lack general predictive power for electrolyte design.
• Challenges include simulating dynamic catalyst-electrolyte interfaces and understanding multi-scale interplay (kinetics, mass transport).
• Advancements in ab initio dynamic models and coupled mass transport are needed for accurate interface understanding and predictive electrolyte design.