Plasma treatment of nafion membranes: Understanding the trade-off between surface modification and electrochemical degradation

Abstract

Nafion is a polymer commonly used in electrochemical devices due to its excellent ionic conductivity. In applications such as proton-exchange membranes for fuel cells (PEMFCs) and ionomeric polymer metal composites (IPMCs), the interfacial properties are critical to device performance. Several studies use plasma treatment to modify the Nafion surface aiming for adhesion improvement through nanoroughness, however, most of them neglect the effects of this treatment on the membrane chemical structure and electrochemical performance. This work comprehensively investigates the Nafion properties, evaluating chemical, morphological, and electrochemical modifications trhough relevant characterization methods. Atomic force (AFM) and scanning electron microscopies (SEM) showed increased nanoroughness with plasma treatment time. Also, Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses showed fluorine and sulfur abstraction, associated with side chain breakage. This effect was prejudicial to the water uptake and decreased the ionic conductivity, measured by Electrochemical Impedance Spectroscopy (EIS), from 140.8 to 1.0 μS cm−1 in the plasma-treated Nafion. Also, an applied electrochemical device was prepared and confirmed the ionic transport reduction using plasma-treated Nafion. This phenomenon is crucial for electrochemical devices, as fewer ionic channels remain on the treated membrane surface reducing water absorption, ionic conductivity, and charge density.