Unintended cation crossover influences CO₂ reduction selectivity in Cu-based zero-gap electrolysers.

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Membrane electrode assemblies are key for CO2 electrolysis but suffer from cathode pore precipitation due to cation crossover.
• Anion exchange membranes often exhibit imperfect ion exclusion, allowing cation migration from the anolyte.

Purpose of the Study:

• To investigate the influence of anolyte concentration on cation crossover in CO2 electrolyzers.
• To understand the effect of cation crossover on copper catalyst behavior and product selectivity.

Main Methods:

• Systematic variation of anolyte ionic strength (KOH or KHCO3).
• Operando X-ray absorption spectroscopy (XAS) and quasi in situ X-ray photoelectron spectroscopy (XPS) to analyze copper surface speciation.
• Analysis of CO2 electrolysis product selectivity (CO vs. C2+ products).

Main Results:

• Anolyte concentration directly affects alkali metal cation (K+) crossover.
• Increased cation crossover correlates with a switch in selectivity towards C2+ products (e.g., C2H4).
• Dilute anolytes yield mixed Cu+/Cu0 surface species, while concentrated anolytes result in exclusively Cu0 species.

Conclusions:

• Cation crossover significantly influences copper catalyst performance and selectivity in catholyte-free CO2 electrolysis.
• Anolyte concentration is a critical parameter affecting reaction pathways, including C-C coupling.
• Understanding and controlling cation effects are essential for designing stable and selective CO2 electrolyzers.