Abstract
Ion-exchange membranes (IEMs) represent a key component in various electrochemical energy conversion and storage systems. In this study, electrochemical impedance spectroscopy (EIS) was used to investigate the effects of structural changes of anion exchange membranes (AEMs) on the bulk membrane and interface properties as a function of solution pH. The variations in the physico/electrochemical properties, including ion exchange capacity, swelling degree, fixed charge density, zeta potentials as well as membrane and interface resistances of two commercial AEMs and cation exchange membranes (CEMs, as a control) were systematically investigated in different pH environments. Structural changes of the membrane surface were analyzed by Fourier transform infrared and X-ray photoelectron spectroscopy. Most notably, at high pH (pH > 10), the membrane (Rm) and the diffusion boundary layer resistances (Rdbl) increased for the two AEMs, whereas the electrical double layer resistance decreased simultaneously. This increase in Rm and Rdbl was mainly attributed to the deprotonation of the tertiary amino groups (-NR2H+) as a membrane functionality. Our results show that the local pH at the membrane-solution interface plays a crucial role on membrane electrochemical properties in IEM transport processes, particularly for AEMs.
Highlights
Ion exchange membranes (IEMs) have been successfully applied in various water and energy systems [1,2]
anion exchange membranes (AEMs) were contrary with those measured in the alkaline condition
It was was parameters in AEMs were contrary with those measured in the alkaline condition
Summary
Ion exchange membranes (IEMs) have been successfully applied in various water and energy systems [1,2]. The properties of the IEM system are affected by the physical properties of the membrane such as fixed charge density and ion exchange capacity, and by the operating conditions such as flow rate, electrolyte concentration, pH, and temperature. The influence of membrane surface properties and physicochemical characteristics (e.g., morphology and charge distribution) [27] and the effect of operational conditions (e.g., flow rate, electrolyte concentration and temperature) on IEM systems have been widely investigated by EIS [23,26,27,28]. The obtained results are valuable towards the development of highly well as interface resistance and capacitance, were studied in a 0.5 M NaCl solution with efficient ionpH exchange processes for are application intowards water/waster treatment (e.g.,of highly a varying (2~12).membrane. ED) asand well as energy conversion and storage systems (e.g., CO2/H2O electrolyzers)
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