The Proximal Protonation Source in Cu-NH_x-C Single Atom Catalysts Selectively Boosts CO₂ to Methane Electroreduction

Area of Science:

• Heterogeneous Catalysis
• Electrocatalysis
• Materials Science

Background:

• Controlling active site coordination is key for catalyst performance in homogeneous catalysis.
• Heterogeneous single-atom catalysts (SACs) present challenges in precisely tuning the coordination environment.
• Copper SACs are promising for CO2RR but require optimized active sites.

Purpose of the Study:

• To develop a bottom-up strategy for constructing copper SACs with tunable N-site functional groups.
• To investigate the impact of proximal N-site functional groups (N-H vs. N-CH3) on CO2RR selectivity and activity.
• To elucidate the reaction mechanism for enhanced methane production.

Main Methods:

• Bottom-up synthesis of reduced graphene oxide supported copper SACs (rGO@Cu-N(Hx)-C).
• In situ protonation using N-H functional groups for CO2 reduction.
• Operando spectroscopic studies and theoretical calculations to analyze reaction pathways.
• Comparison with a -CH3 substituted counterpart (rGO@Cu-N-C).

Main Results:

• The N-H moiety in rGO@Cu-NHx-C acts as an in situ protonating agent, accelerating CO2 to methane conversion.
• Achieved a methane current density 2.42 times higher than the -CH3 substituted catalyst.
• Attained high methane faradaic efficiency (77.1%) via the favored *OCHO pathway.
• Demonstrated precise modulation of SACs for efficient and selective CO2 electroreduction.

Conclusions:

• The N-H functional group is crucial for enhancing CO2RR to methane through in situ protonation.
• The *OCHO pathway is energetically favored over the *CO pathway for methane production.
• This strategy enables rational design of SACs for targeted electrochemical CO2 reduction applications.