Switching CO2 electroreduction selectivity between CO and HCOOH on poly(ionic liquid)-Ag hybrids

Abstract

The electrocatalytic conversion of CO2 into CO and HCOOH is highly attractive due to its potential high energy efficiency. In this study, the selectivity switching from CO to HCOOH on Ag sites was achieved by finely fabricating poly(ionic liquid)-silver (PIL-Ag) hybrids containing alkyl chains. The length of the alkyl chain influenced the structure of Ag sites with different intrinsic activity of *COOH and *H (and thereby *OCHO) formation, as well as the mass transfer behavior of CO2 and H2O. During acidic CO2RR at –300 mA cm–2, Ag@PIL-C(4)-0.5 demonstrated a high Faradaic efficiency ratio of HCOOH to CO (FEHCOOH/FECO = 1.45), while Ag@PIL-C(6)-0.5 favored the production of CO. By contrast, Ag@PIL-C(12)-0.5, which possessed low activities and poor mass transfer, exhibited a high apparent FEHCOOH/FECO ratio of 1.35. Experiment combined mechanism studies demonstrated that the higher enrichment of *H versus *CO2 intermediates at the Ag sites is beneficial for *OCHO formation. In light of this point, the FEHCOOH/FECO ratio increased from 0.15 to 0.87 with a low FEH2 (<5.0%) on Ag@PIL-C(6)-2.0, which has high activity and good mass transfer of CO2, by increasing the current density from –100 mA cm–2 to –600 mA cm–2.