Weakening origin of hydrogen bond in ionic liquid at the electrified interface

Abstract

Hydrogen bonds (HBs) widely exist in applications ranging from biology to electrochemistry, where quantifying HB at the electrochemical interface poses significant challenges. Herein, we propose an approach to quantitatively decouple the electrostatic and van der Waals interactions of HBs in ionic liquids (ILs) by injecting electrons into the electrode interface. The charging process showed that the order of obtaining electrons is molybdenum disulfide > graphene > IL > boron nitride. Interestingly, the preferentially charged cations would lead to a direct reduction of coulombic interactions in HBs; in contrast, the charged substrate would repel the anion and weaken HBs indirectly. Infrared (IR) spectrum and covalent change analysis verified the charging-induced direct and indirect decoupling processes. Moreover, the energy analysis indicates that the electrostatic terms account for ~50% of HBs. These results on the weakening origin of HBs can guide the molecular design of ILs toward high-performance electrochemical applications.