Structured Electrodes Induce Local pH as a Primary Determinant of CO₂ Reduction Selectivity.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Highly structured electrodes can improve catalytic performance, but their complex surfaces complicate understanding selectivity.
• The carbon dioxide reduction (CDR) reaction's selectivity is influenced by the electrode's microenvironment.

Purpose of the Study:

• To investigate the role of electrode microstructure in enhancing carbon dioxide reduction selectivity.
• To compare the performance of photolithographically fabricated gold microwire (MW) electrodes with planar electrodes for CO2 reduction.

Main Methods:

• Fabrication of gold microwire (MW) and planar electrodes using photolithography.
• Electrochemical measurements to determine faradaic efficiency for CO2 reduction to CO (FE(CO)).
• In situ confocal microscopy with a ratiometric pH sensor to map local pH at the electrode-solution interface.

Main Results:

• MW electrodes exhibited enhanced FE(CO) compared to planar electrodes.
• A local pH gradient at the electrode-solution interface was identified as the cause of enhanced selectivity.
• Normalization for local pH revealed similar FE(CO) dependence for both MW and planar electrodes.

Conclusions:

• Electrode microstructure, specifically the local pH gradient it creates, is crucial for enhancing CDR selectivity.
• The observed selectivity is governed by the bicarbonate/carbonate (HCO3-/CO32-) equilibrium.
• Understanding and controlling the electrode-solution interface microenvironment is key for designing efficient CDR catalysts.