Why Is Methanol Formation Suppressed in CO₂ Reduction Over Copper Electrocatalysts?

Area of Science:

• Electrochemistry
• Catalysis
• Computational Chemistry

Background:

• Electrocatalytic CO2 reduction (CO2RR) offers a sustainable route to methanol (CH3OH) synthesis, contrasting with energy-intensive industrial methods.
• Copper (Cu) catalysts typically yield methane (CH4) and C2+ products, suppressing CH3OH formation in CO2RR.
• Understanding the intrinsic mechanisms governing product selectivity is crucial for advancing CO2RR.

Purpose of the Study:

• To elucidate the fundamental thermodynamic and kinetic factors responsible for the suppression of methanol formation during electrocatalytic CO2 reduction on Cu.
• To identify key intermediates and reaction pathways that dictate product selectivity.
• To propose a theoretical strategy for enhancing methanol selectivity in CO2RR.

Main Methods:

• Utilized constant-potential explicit solvent computational methods to systematically investigate reaction pathways.
• Compared thermodynamics and kinetics of C2+ products, CH4, and CH3OH formation.
• Analyzed 21 potential C-C coupling pathways and C1 product formation mechanisms.

Main Results:

• Identified nine C-C coupling pathways with significantly lower activation barriers than C1 products, indicating facile C2+ formation.
• Determined that the *CH2OH intermediate favors C-O bond cleavage to CH4 over hydrogenation to CH3OH, kinetically hindering methanol production.
• Simulated Faradaic efficiencies aligned with experimental trends, validating the proposed mechanism across different Cu surfaces and potentials.

Conclusions:

• The intrinsic suppression of methanol in CO2RR on Cu catalysts stems from the preferential C-O cleavage of the *CH2OH intermediate.
• A proposed strategy involves redirecting the reaction pathway via *COOH to *HCOO and stabilizing *CH2OH to promote hydrogenation to CH3OH.
• These findings provide a mechanistic basis for designing catalysts and conditions for selective methanol synthesis via CO2 electroreduction.