Method for determining ion exchange membrane resistance for electrodialysis systems

Ion transport resistance is an important characteristic of ion exchange membranes. It is not a constant but is influenced by among other things the salt concentration in the external solution. A vast number of publications investigated the membrane resistance; however, the use of different methods leads to different results. Different approaches and possible flaws are discussed and a method for measuring membrane resistance is developed, evaluated, and described. It is shown that this method can be used in a wide concentration range of 0.001–5 M NaCl. The method is based on electrical impedance spectroscopy within an electrochemical cell containing four electrodes. An AC is applied on two work electrodes, while two thin platinum iridium wires are used as reference electrodes to evaluate the sample impedance. Membrane resistance is obtained from a differential impedance measurement of a solution without and with a membrane. Resistance of AMX and CMX membranes is determined.