Journal
JOURNAL OF MEMBRANE SCIENCE
Volume 596, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.memsci.2019.117720
Keywords
Anion exchange membranes; Fuel cells; Polyhydroxyalkylation
Categories
Funding
- National Science Foundation of China [51661145024, 21774123]
- Development of Scientific and Technological Project of the Jilin Province [20160519017JH]
- Pakistan Science Foundation [PSF/NSFC-Eng/KP-COMSATS-ABT-04]
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To study the effect of cation groups on the alkaline stability and other properties of anion exchange membranes (AEMs), common quaternary ammonium (QA), N-alicyclic quaternary ammonium and imidazolium cations with bulky substituents were grafted onto an aryl ether-free polyaromatic backbone synthesized via acid-catalyzed polyhydroxyalkylation. The size of cation groups is calculated by Gaussian. The size of bulky imidazolium (MIm) is much larger than QA and N-alicyclic quaternary ammonium (Py and Pi). Because of the large size of the cation groups, the chain entanglement density of AEM with bulky imidazolium (PFBA-MIm-0.4) is lower than other three membranes, resulting PFBA-MIm-0.4 displays the highest water uptake of 225.1% at 80 degrees C, whereas the IEC of PFBA-MIm-0.4 is the lowest (1.49 mmol g(-1)). Meanwhile, the toughness of the membranes decreases when the size of the cation group increases. AEM with common quaternary ammonium (PFBA-QA-0.4) exhibits the highest hydroxide conductivity of 142 mS cm(-1) at 80 degrees C because it exhibits the highest ion exchange capacity (IEC). More interestingly, PFBA-QA-0.4 shows long term alkaline stability that is as good as that of the AEMs with alicyclic quaternary ammonium or bulky imidazolium, even in 5 mol L-1 aqueous NaOH at 80 degrees C; however, the small size of the substituents of common quaternary ammonium does not have steric hindrance that is as large as that of the substituents of alicyclic quaternary ammonium and bulky imidazolium. Therefore, we selected PFBAQA-0.4 to prepare a membrane electrode assembly for the further study of alkaline H-2/O-2 fuel cell performance. The single H-2/O-2 fuel cell exhibits a peak power density as high as 559 mW cm(-2) at 80 degrees C under 100% RH with 0.1 MPa backpressure. These results of the comparison of AEMs with different size cation groups give some insights for future directions in the development of advanced AEMs.
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