Coupled Electron–IonTransfer Drives NickelNanofilm Formation at a Water-Free Deep Eutectic Solvent/Oil Interface

Nickel nanofilms were prepared at an ethaline/toluene interface, which is a water-free deep eutectic solvent (DES)/oil (O) interface, where the absence of water enables a unique environment for interfacial redox chemistry. When NiCl42– in ethaline was contacted with decamethylcobaltocene (DMCc) in toluene at the liquid/liquid interface, nickel nanoparticles nucleated and subsequently assembled into two-dimensional networks that developed into continuous nanofilms floating at the interface. Liquid/liquid electrochemistry and post-reaction UV–vis spectroscopy measurements revealed that the reduction of NiCl42– proceeds spontaneously through a coupled electron–ion transfer pathway, in which the electron transfer between NiCl42– and DMCc is balanced by the ion transfer of generated DMCc+ from the O phase to the DES phase. This charge-compensated, spontaneous ET–IT mechanism demonstrates that water-free DES/O interfaces can serve as functional soft templates for substrate-free base metal nanofilm fabrication.