Small alkali cations direct CO electroreduction to hydrocarbons rather than oxygenates

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Electrochemical carbon dioxide (CO2) reduction is key for sustainable chemicals and fuels.
• Achieving high selectivity for specific products like ethylene remains challenging.
• Understanding reaction mechanisms is crucial for optimizing CO2 electroreduction.

Purpose of the Study:

• To investigate the role of alkali cations in tuning CO2 electroreduction selectivity.
• To elucidate the mechanisms governing ethylene production.
• To enhance ethylene yield and energy efficiency through catalyst modification.

Main Methods:

• Operando Raman spectroscopy to study the electrolyte-catalyst interface.
• Computational simulations to understand cation-intermediate interactions.
• Antimony doping of copper catalysts to tune surface properties.

Main Results:

• Lithium ions (Li+) were found to promote ethylene production, unlike other alkali cations.
• Hydrated Li+ exhibits strong hydrogen bonding and weak cation-dipole interactions, suppressing hydrogenation on carbon.
• Antimony doping reduced the oxygen affinity of copper, suppressing undesirable intermediate formation.
• Achieved 79% ethylene faradaic efficiency and 39% energy efficiency in a membrane electrode assembly electrolyzer.

Conclusions:

• Alkali cation choice significantly impacts CO2 electroreduction pathways.
• Surface interactions at the electrolyte-catalyst interface are critical for selectivity.
• Combined strategies of cation selection and catalyst modification enable high-performance ethylene production.