Electrochemical characterization of the CMX cation exchange membrane in buffered solutions: Effect on concentration polarization and counterions transport properties

• The ohmic region resistance is constant whatever the acetic acid concentration.
• The plateau slopes (1/Rpol) increase linearly with the counter-ion concentration.
• The concentration polarization theory is insufficient to explain these results.

In the present work, the combination of both properties of buffer and weak electrolyte solutions and their effects on concentration polarization phenomena, particularly on the limiting current density and the ohmic region resistance (Rohm) is investigated. Acetic acid (pKa = 4.75) plays the role of weak electrolyte while at the same time buffers the pH of the system with acetate co-ions. In order to better understand the effect of the counterion nature and the pKa of the buffer acid/base pair, different electrolyte solutions are studied. The current–voltage curve characteristic values such as the limiting current density, the ohmic resistance (Rohm) and the polarization plateau resistance (Rpol) are determined and discussed according to the classical concentration polarization theory. However, it remains insufficient to explain the most important result obtained: The addition of acetic acid increases linearly the limiting current density while the ohmic resistance remains constant whatever the acetic acid concentration is.