Abstract
One of the most important factors defining the complex of operational characteristics of heterogeneous ion-exchange membranes that represent a composite material is their structure. Composite material electroconductivity depends on the nature of phases setting the system and on their relative position. Impedance spectroscopy is one of the effective methods of structure definition and electrochemical characteristics not only of the composite material generaly but also the phases which it consists of. In this paper by the method of impedance spectroscopy the electrochemical characteristics of the heterogeneous ion-exchange membranes МС-40 (H+, Na+, К+, NH4+ - forms) and МА-41 (Cl- and NO3- - forms) in the range of the alternating current frequencies 100 KHz – 20 MHz are researched. The comparison of the contact and contact-differential ways of measuring membrane impedance is done. It is shown that in the case of impedance contact measuring of the sample the borders “electrode/membrane” influence the electrochemical impedance system spectrum greatly. In connection with this the contact-differential variant of the experimental procedure in the impedance measuring of the membrane system is more preferable. The interpretation of the received electrochemical impedance spectra in terms of the composite material conductivity is given. Basing on the method of equivalent circuits it is suggested representing the impedance of the heterogeneous ion-exchange membrane as a sum of pure resistance (resistance of ion-exchanger particles), sequentially connected with the impedance of the dielectric layers (resistance and capacity of polyethylene and dissolvent). The analysis of the spectra of electrochemical impedance of ion-exchange membranes in different ion forms showed that the quantity of the semicircle locus impedance radius is inversely proportional to the coefficient of counter-ion diffusion and directly proportional to the part of the membrane intergel phase.
Highlights
most important factors defining the complex of operational characteristics of heterogeneous ion-exchange membranes that represent a composite material is their structure
Composite material electroconductivity depends on the nature of phases setting the system
In this paper by the method of impedance spectroscopy the electrochemical characteristics of the heterogeneous ion-exchange membranes
Summary
Для исследования процессов в биполярных мембранах метод частотного спектра импеданса впервые применен в работе [3], где дано подробное описание системы "мембрана-раствор". Метод теоретического описания спектров импеданса монополярных мембран предложен в работе [4]. Целью работы являлось исследование импеданса гетерогенных ионообменных мембран при высокой частоте переменного тока. Для оценки импеданса индивидуальной мембраны проводили векторное вычитание импедансов двух и одной мембран. Годографом импеданса для схемы, представляющей собой параллельный RC-контур, является полуокружность диаметром R с центром на оси Z', проходящая через начало координат (рисунок 4а) [2].
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