Study of electric mass transfer peculiarities in electromembrane systems by the rotating membrane disk method

• A rotating membrane disk (RMD) with horizontally positioned membrane is described.
• The method for simultaneous recording of CVC and transport numbers of ions is developed.
• The coupled phenomena of concentration polarization were analyzed.
• Electrochemical characteristics of monopolar and bipolar asymmetric membranes were studied.

This study examines one of the current issues of membrane electrochemistry: the study of ion transport patterns through membranes under high and ultra-high current densities. It focuses on the new mechanisms for their delivery to membrane/solution interface, the role of concentration polarization coupled phenomena and its impact on intensification of mass transfer in electromembrane systems (EMS). Furthermore, an experimental device consisting of a rotating membrane disk (RMD) with horizontally positioned ion-exchange membrane is described. The device's design makes it possible to simultaneously obtain current–voltage characteristics (CVCs) and dependences of effective transport numbers for ions of electrolyte and water dissociation products on the current density. Partial CVCs are calculated and limiting current densities and diffusion layer thickness are determined at various disk rotation rates. It was established that the coupled phenomena of the concentration polarization are the reason for the distortion of the classic CVC form with a horizontal plateau. Such behavior observes even under conditions when the diffusion-layer thickness is stabilized by the RMD method. It was described that in the studied asymmetric bipolar membranes (aBPM) the ratio of chemical reaction part (water splitting at bipolar border) and electrodiffusive part of overall masstransfer shifts towards chemical reaction at high rotation speed.