(Invited) Development of Alkaline- and Bipolar-Membranes for Hybrid Fuel Cell Applications
Authors: Grew Kyle N. , McClure Joshua P. , Chu Deryn 
Published: February 2020

The development of technologies which offer efficient and scalable energy conversion and storage is a challenge of considerable importance. Potential applications range from the integration of renewable energy supplies into the domestic power grid to reducing the logistic burden of supplying energy to our military and defense forces. Electrochemical processes are a natural fit for addressing many of these problems; however, system limitations and technical issues confound development efforts. Cost, reliability, scalability, and ease of integration are often among the leading challenges for established domestic technologies, whereas size, weight, storage/transportability, and environmental considerations are of utmost importance for defense applications.
Research and development efforts for electrochemical energy conversion and storage technologies are driven by materials requirements. Materials in these electrochemical systems typically have demanding functional requirements (e.g., conductivity, catalyst activity, selectivity, mechanical strength, etc.), which must be met under aggressive operating conditions (e.g., acidic or basic electrolytes, the presence of strong solvents and/or contaminants, highly oxidizing and reducing electrode processes, high temperatures, etc.). All of these functional requirements must be met with expectations for little-to-no degradation during operation and cycling (e.g., loss in active catalyst area, poisoning or chemical degradation, corrosion, fatigue, crack formation, etc.). In many cases the individual constituent materials cannot meet the complex and intertwined functional, environmental, and stability requirements alone, which has driven research and development efforts towards the use of heterogeneous materials.
Our own research and development efforts focus on hybrid acidic- and alkaline-membranes for portable fuel cell applications [1-2]. Proton exchange membrane (PEM) electrolytes are relatively well established. Alkaline anion exchange membrane (AEM) electrolytes have more recently come to prevalence. AEMs have been ushered into the fuel cell community based on the prospect of developing cheaper and more compact systems via reductions in noble-metal catalyst content, membrane and packaging materials costs, and water and fuel management requirements [3]. However, development efforts have been hindered by challenges with materials performance and stability [3-5], penalties for anodic processes including hydrogen oxidation [6], and thermodynamic and resistive losses associated with the presence of carbon dioxide [7-8], among others. These challenges have led us to explore the development of hybrid-membrane approaches, such as the bipolar membrane which was shown by Unlu et al [9]. We believe that this type of approach can mitigate some of the catalyst and water/fuel management challenges. However, a suitable AEM and acid-alkaline membrane interface are needed for such an approach. This has led us to study the modification of the underlying AEM materials as well as the introduction of heterogeneity through processing (e.g., via electrospinning processes popularized for fuel cells in the PEM community [10]).
In this modeling and theory focused talk, we address the introduction of heterogeneity into membrane electrolyte materials, its influence on key material properties, and the corresponding impact of its integration to bipolar membrane fuel cells.

Acknowledgement:

The authors gratefully acknowledge the support of the U.S. Department of the Army, Army Materiel Command, and U.S. Army Research Development and Engineering Command.

References:

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[2] J.P McClure, K.N. Grew, D. Chu, ECS Trans., 69#A01-0053, Accepted (2015).
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