Electrochemical CO2 reduction
is a promising approach
to obtain sustainable chemicals in energy conversion. Improving the
selectivity of CO2 reduction toward a particular C2 product such as ethylene remains a significant challenge.
Herein, we report a series of imidazolium hexafluorophosphate compounds
as surface modifiers for planar Cu foils to boost the Faradaic efficiency
(FE) of ethylene from 5 to 73%, which is among the highest reported
using polycrystalline Cu. The modified electrodes are convenient to
prepare. The structure–function study demonstrates that varying
the alkyl or aromatic substituents on the imidazolium nitrogen atoms
has significant effects on the morphology of the deposited films and
the product selectivity of CO2 reduction. Experimental
FEC≥2, FEC2H4, ln(FEC≥2/FECH4
), and ln(FEC2H4
/FEC2H5OH) values show generally
linear relationships with FEH2
while using different
imidazolium modifiers, suggesting that factors governing proton reduction
may also be directly related to both overall C≥2 generation and ethylene selectivity. This work presents an effective
and practical way in tailoring the active sites of metallic surface
for selective CO2 reduction.