Increasing the Ion Conductivity By Modification of Anion Exchange Membranes for Alkaline Fuel Cells
Authors: Leppin Janine , Clark Cassius , Behnken Julian , Harms Corinna , Dyck Alexander 
Published: February 2020

Fuel Cells have received a lot of attention in the area of clean renewable power sources because of their high efficiency, low emission, and the wide range of potential applications such as automobiles, portable devices etc. The state-of-the-art commercial proton exchange membrane fuel cell (PEMFC) systems are based on Nafion® as an electrolyte. Recently, Anion Exchange Membrane (AEM) based fuel cells have received much attention from researchers not only due to possibility to use non-precious catalyst [1] but also because of other advantages in comparison to the PEMFC systems such as the fast kinetic of the oxygen reduction reaction and lower cost by using non-precious metals as electrocatalysts [2, 3]. However there are still many challenges to develop commercial AEMFC systems including lower power density, higher degradation rate and more complicated water management in comparison to the PEMFC [4-6]. There are different possibilities to improve the system like using highly active catalysts, optimization of the operating parameters, and development of different AEM materials [4]. One of the main challenges is to produce an AEM which possess high ionic conductivity as well as chemical, thermal, and mechanical stability. The increased number of active groups in the membrane structure usually leads to a decrease of the mechanical properties. Most of the developed and reported AEMs show poor dimensional stability with their presence of functional groups which lead to strong swelling and brittleness of the membrane after drying [7, 8]. The chemical degradation is also a known effect in the alkaline membranes and limits its long term stability [5, 8-10]. To avoid these disadvantages of AEMs, there are several promising methods reported in the literature. Some promising methods for the modifications are pore-filling technique [11], chemical crosslinking [12], reinforcement [13] and the synthesis of porous membranes [14, 15].

The goal of this research work is to develop AEMs with high ionic conductivity without sacrificing their physical and chemical properties. It has been considered that the formation of pores leads to the improvement of the water content and thus the transport and mobility of the anion during operation. With the use of a commercial anion exchange polymer and different types of additive porous AEMs are developed. The modified porous AEM relevant properties were studied and also compared with a commercially available AEM. Ionic conductivity was measured with four-probe electrodes as a function of temperature and relative humidity by using electrochemical impedance spectroscopy. The thermal behaviour and the released substances in the steps of degradation for the modified membranes were studied with a thermogravimetric system coupled to a GC/MS system. In addition, other properties such as mechanical properties, water uptake and swelling behaviour were also studied and reported. For future research, the modified membranes will be used for the production of alkaline electrolyte membrane fuel cells.

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