Direct Air Capture-Compatible Azolate and Amino Acid Ionic Liquids for Electrochemical CO ₂ Reduction to CO on a Silver Cathode

Direct air capture (DAC) compatible ionic liquids (ILs) are attractive for integrating CO2 capture and conversion due to their high CO2 solubility at low partial pressures, tunable chemisorption mechanisms, low volatility, and wide electrochemical windows. However, very few ILs have high CO2 uptake at DAC conditions (420 ppm CO2), and even fewer have been evaluated for chemical compatibility and mechanistic continuity for combined capture and electrochemical CO2 reduction (eCO2RR). We demonstrate that two representative DAC-capable ILs, [P4444][Val] (amino acid-based) and [P66614][5-Me-Imd] (azolate-based), exhibit favorable electrochemical reduction behavior. CO and H2 were the dominant gas-phase products by GC, while 1H and 13C NMR confirmed negligible liquid-phase HCOOH. Chronoamperometry at moderate applied potentials (−2.0 to −2.5 V vs Ag/AgCl) in a two-compartment H-cell with a Ag coated carbon paper as the working electrode yielded steady-state current densities of ∼10 mA cm−2 with CO FE of 96% for [P4444][Val] and 95% for [P66614][5-Me-Imd], highlighting the role of viscosity and chemically absorbed CO2-IL species to provide highly selective CO formation while suppressing H2 evolution.