Ionic liquids/metal reactivity: on the origins of cation–anion synergy to form stable grafted molecules

• In situ XPS; • In situ PM-IRRAS; • Rational design of ionic liquids; • Interfacial reactivity. • Molecular origins of ionic liquid synergisms. In this work, the reactivity between a Cu single crystal (110) and an alkylammonium ionic liquid – the ethylammonium nitrate (EAN) – was investigated by in situ X-ray photoelectron spectroscopy (XPS) and polarization modulation infrared reflectance absorbance spectroscopy (PM-IRRAS). EAN molecules were successfully deposited in the UHV XPS chamber at different surface coverages and the results revealed the strong nitrate anion and ammonium cation reactivity towards the Cu (110) single crystal. In addition, important variations in the anion reactivity towards the Cu single crystal was shown when the cation nature was changed (comparison of EAN, sodium nitrate and ammonium nitrate). In fact, PM-IRRAS results revealed that such variations in reactivity arise from different nitrate orientation towards the substrate, confirming, at the molecular level, the presence of the so-called cation–anion synergy. These findings provide fundamental prospects enabling more thought-through designs of task specific and environmentally friendly ionic liquids for broader applications, including electrocatalysis and heterogeneous catalysis.