Evaluation of a Second-Generation Bulky Cation for Anion Exchange Membranes
Authors: Liu Ye , Zhang Bingzi , Yan Yushan , Liberatore Matthew W , Herring Andrew M 
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) as low temperature fuel cells have been fully studied and well developed due to their advantages of high conductivity and fast start-up time. However, their commercialization is hampered by the high manufacturing cost of using a noble metal catalyst (typically platinum) in electrodes. Nowadays, alkaline fuel cells (AFCs) receive more investigations as one of the most promising fuel cells that can outperform all known low temperature fuel cells.1 Anion exchange membranes (AEMs) are used as the solid electrolyte to prevent leakage and component corrosion. The insufficient chemical stability and conductivity of AEMs are main limitations of AFCs compared to PEMFCs.2,3

A series of bulky novel cations, including sulfonium,4 imidazolium,5 phosphonium,6 ruthenium,7 have been studied besides most frequently used quaternary ammonium in order to improve the chemical stability. Besides these bulky cations, the long alkyl chain configuration has been reported to dramatically prevent OH- attack onto the central cation.8,9 Further more, Kreuer10 recently found dimethyl piperidinium is a very promising candidate with 87.3 h half-life degradation time compared to trimethyl ammonium of 4.2 h by treating cations in 6M NaOH at 160 °C.

In this study, we developed a hexanol methyl piperidinium functionalized triblock anion exchange membrane (Figure 1), which expects to hold an excellent alkaline stability and conductivity. Degradation study was performed by treating the membrane in 1 M sodium hydroxide solution at 80 °C. The degradation of cationic groups were determined in terms of the IEC based on the titration of Cl- form membranes. Conductivities at different temperatures under 95% RH are performed by using electrochemical impedance spectroscopy (EIS). Morphologies are obtained from small angle X-ray scattering (SAXS). Insights on overall impact of block copolymer structure and long chain piperidinium cation on conductivity and durability performances are discussed.

Figure 1. Structure of hexanol methyl piperidinium functionalized triblock copolymers 

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Figure 1