Direct Air Capture-Compatible Azolate and Amino Acid Ionic Liquids for Electrochemical CO₂ 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.