Elucidating the Donor/Acceptor Regulatory Mechanism for CO₂ Electroreduction

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Copper-nitrogen (Cu-Nx) active sites show promise for electrochemical CO2 reduction reaction (CO2RR).
• Systematic modulation of CO2RR activity in these catalysts remains challenging.

Purpose of the Study:

• To investigate the relationship between CO2RR activity and electron density at the Cu-N4 center.
• To design and synthesize substituted copper phthalocyanines (CuPc-R) with varying electronic properties.

Main Methods:

• Synthesis of CuPc-R with electron-withdrawing/donating groups.
• Electrochemical characterization to determine CO2RR activity and selectivity.
• Density Functional Theory (DFT) calculations and in situ spectroscopy.

Main Results:

• A positive shift in ligand reduction potential correlated with increasing Hammett constants was observed.
• CO2RR to methane (CH4) activity showed a near-linear relationship with the Hammett constant.
• CuPc-Cl4 exhibited maximum CH4 Faradaic efficiency (FECH4) of 73.7% and current density (jCH4) of -147.4 mA cm-2.

Conclusions:

• Decreased electron density at the Cu-N4 center, induced by strong electron-withdrawing groups, suppresses competing hydrogen evolution reaction (HER).
• This electronic tuning effectively promotes CH4 selectivity in CO2RR.
• Substituted copper phthalocyanines offer a viable strategy for enhancing CO2RR performance.