Ionic Transfers across rGO/Fluorine-Free Ionomer Film Interfaces Studied by Electrogravimetric Methods

Fluorine-free ionic conductive polymers are required for many applicative domains such as energy storage and conversion. In this context, polymerized ionic liquid crystals (PILCs) are of interest as they may form nanostructured channels favoring ion conduction. In this work, a sulfonated PILC membrane was designed as a single-ion conducting material and studied with nonconventional electrogravimetric techniques to gain insight into the ionic behavior at the electrode/electrolyte interface. To this end, a reduced graphene oxide (rGO)/PILC bilayer exposed to a H₂SO₄ electrolyte was constructed and compared with a rGO/Nafion bilayer system, which served as a state-of-the-art reference. First, adding a thin layer of such polymers onto the rGO surface was found to increase its gravimetric capacitance. Then, the nonconventional ac-electrogravimetric method demonstrated cation selectivity (Donnan's effect) in bilayers and revealed strong mechanistic differences between PILC and Nafion regarding proton diffusion. Therefore, ac-electrogravimetry proves to be a robust technique to characterize ion selectivity and related interfacial mechanisms in ionic exchange membranes.