Signature of Proton–Hole Transfer in Hydrogen-Bonded Solids at 10 K

Abstract

Although proton transport in water ice is well understood, proton–hole transfer (PHT) involving proton abstraction by anions remains less explored. This study investigates PHT in H₂S and NH₃ solids at low temperatures, aiming to determine whether these solids exhibit negative charge transport similar to that in ice. In H₂S and NH₃ solids at 10 K, surface HS^– and NH₂^– anions in hydrogen-bonded systems trigger negative current flow, providing a clear signature of PHT. This negative current is controlled by electron flow and 193 nm ultraviolet irradiation, which generates HS^– and NH₂^– anions on the solid surfaces. In bilayer H₂S/H₂O and NH₃/H₂O solids, a significant negative current is observed only in the NH₃/H₂O solid, which is attributed to the exothermic proton abstraction by NH₂^– from H₂O at the bilayer interface, a process not available for H₂S on ice. This study is the first to demonstrate PHT-induced electrochemical behavior in hydrogen-bonded solids other than ice.