Local Chemical Environment Governs Anode Processes in CO₂ Electrolyzers

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• The development of efficient CO2 electrolysis relies on stable and abundant anode catalysts.
• Iridium (Ir) is a common anode catalyst, but its scarcity motivates research into alternatives.
• Nickel (Ni) is abundant and used in alkaline water electrolysis, prompting its investigation for CO2 electrolysis.

Purpose of the Study:

• To compare the operational stability and performance of Iridium (Ir) and Nickel (Ni) anodes in CO2 electrolysis.
• To identify the degradation mechanisms of Nickel anodes under CO2 electrolysis conditions.

Main Methods:

• Electrolyzer cell testing with Ir and Ni anodes.
• Analysis of anolyte chemistry and anode surface under operational stress.

Main Results:

• Iridium anodes demonstrated stability under CO2 electrolysis conditions.
• Nickel anodes exhibited rapid degradation, leading to premature cell failure.
• Degradation mechanisms for Ni anodes include anolyte pH decrease and localized high carbonate concentrations.

Conclusions:

• Nickel is not a suitable direct replacement for Iridium anodes in CO2 electrolysis in its current form.
• The observed degradation mechanisms, particularly pH decrease, are critical challenges for Ni anode stability in recirculating anolyte systems.