Decoupling Product Selectivity in Electrocatalytic CO₂ Reduction by Steering the Interfacial Water Structure.

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Controlling electrochemical CO2 reduction reaction (CO2RR) pathways is crucial for efficient catalysis.
• Silver (Ag) catalysts typically favor carbon monoxide (CO) production.
• Developing strategies to tune catalyst selectivity is a key challenge.

Purpose of the Study:

• To demonstrate a method for steering silver's selectivity towards formic acid (HCOOH) instead of CO.
• To investigate the role of interfacial water structure in CO2RR selectivity.
• To establish a link between water structure and HCOOH formation.

Main Methods:

• Utilized poly(diallyldimethylammonium chloride) (PDDA) in an alkali-metal-cation-free acidic electrolyte.
• Engineered a hydrophobic interface promoting "free-like" water (f-H2O).
• Employed operando spectroscopy, isotope labeling, electrochemical analysis, and density functional theory (DFT) simulations.

Main Results:

• Demonstrated a direct, quantitative correlation between f-H2O abundance and HCOOH selectivity.
• Identified a distinct mechanistic channel for HCOOH formation via *H + CO2 hydrogenation in f-H2O-rich environments.
• Showed that f-H2O promotes HCOOH selectivity, overriding Ag's intrinsic CO selectivity.

Conclusions:

• Tuning interfacial water structure is a powerful strategy to control CO2RR pathways.
• Hydrophobic interfaces with f-H2O favor HCOOH formation over CO.
• This approach offers rational control over CO2RR selectivity, moving beyond intrinsic catalyst properties.