Ion Exchange Membranes Used in Fuel Cells
In the realm of energy conversion systems, fuel cells have garnered significant attention due to their potential to offer clean and efficient power generation. Among the critical components of fuel cells are ion exchange membranes (IEMs), which play a pivotal role in separating reactants, facilitating ion transport, and ensuring overall system stability. In the context of fuel cells, IEMs act as electrolytes, enabling the selective transport of ions while maintaining separation between reactants. Various types of ion exchange membranes have been proven for use in fuel cells, including cation exchange membranes, anion exchange membranes, bipolar ion exchange membranes, and perfluorosulfonic acid membranes.
Ion Exchange Membrane Selection Guide for Fuel Cells
The material properties of ion exchange membranes play a pivotal role in determining their suitability and performance. Key considerations include ion exchange capacity (IEC), ionic conductivity, permselectivity, as well as dimensional, chemical, mechanical, and thermal stabilities, etc.
Cation Exchange Membrane for Fuel Cells
Cation exchange membranes (CEMs) selectively facilitate the passage of positively charged ions (cations) while impeding the transport of negatively charged ions (anions). On the specialized front, proton exchange membranes (PEMs) are a noteworthy subset of CEMs, specifically designed to transport protons (H+ ions). Proton exchange membrane fuel cells (PEMFC) have attracted attention due to their high-power density and fast start-stop capabilities.
Schematic design of the PEM fuel cell. [1]
Anion Exchange Membrane for Fuel Cells
In contrast to CEMs, anion exchange membranes (AEMs) selectively permit the passage of negatively charged ions (anions) while obstructing the transport of positively charged ions (cations). Notably, AEMs have shown promising potential in revolutionizing fuel cell technology, including low hydrogen crossover, high volumetric efficiency, and rapid cycling capabilities.
In an anion exchange membrane fuel cell (AEMFC), the membrane electrode assembly (MEA) consists of the AEM, anode and cathode catalyst layers, and a cathode gas diffusion layer (GDL).
Schematic diagram of AEMFC. [2]
Bipolar Ion Exchange Membrane for Fuel Cells
Bipolar ion exchange membranes (BIEMs) integrate both cation and anion exchange functionalities within the same membrane, enabling the separation of both cations and anions in different compartments. Bipolar membranes for fuel cell applications (BPMFC) were first discovered by Unlu in 2009 and consist of a BPM electrode assembly, which consists of a cathode, anode and BPM. This innovative approach holds promise for advancing fuel cell technology by addressing various challenges associated with ion transport and system stability.
Schematic diagram of BPMFC. [3]
Perfluorosulfonic Acid Membrane for Fuel Cells
Perfluorosulfonic acid (PFSA) membranes stand out as a prominent category of ion exchange membranes widely utilized in fuel cell applications. PFSA-based polymers are considered low-temperature PEMs for fuel cell applications. These membranes exhibit high chemical, hydrolytic, and thermal stability, making them well-suited for demanding operational conditions.
Schematic diagram of PFSA membrane. [4]
References
- S.J. Peighambardoust, et al. International Journal of Hydrogen Energy, 2010, 35(17), 9349-9384.
- MaΕ‘a Hren, et al. Sustainable Energy Fuels, 2021, 5, 604-637.
- S S Daud, et al. IOP Conf. Ser.: Mater. Sci. Eng. 2020, 736 032003.
- Tushar Kanti Maiti, et al. Chemical Engineering Journal Advances, 2022, 12(15), 100372.
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