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Ru, M. Hu, L. Din and T. Xu, Polym. Chem., 2015, DOI: 10.1039/C4PY01671H.
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Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x www.rsc.org/
Anion exchange membranes (AEMs) based on
Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and its derivatives
Jin Ran, a
Liang Wu, a
Yanfei Ru, a
Min Hu, a
Liang Din, a and Tongwen Xu* a ,
Polymeric anion exchange membranes (AEMs) attract increasing attention, because they have prominent roles in various energy and environment-related fields. The most important prerequisite toward high performance AEMs is to search for an appropriate base polymeric material, which should be chemically stable and easily handled for fabricating AEMs.
Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is considered to be a promising candidate since it enables versatile routes to obtain high performance AEMs. Furthermore, the properties of these AEMs can be feasibly adjusted and controlled to meet various application requirements.
In this review, recent progresses in PPO based AEMs are comprehensively presented. Herein, we highlight the strategies used for designing PPO based AEMs and hope to provide promising principles, concepts, and routes into the synthesis of other polymers based AEMs. 1. Introduction 1
Ion exchange membranes (IEMs) play significant roles in 2 numerous fields. Current research focuses on the development 3 of IEMs for separation processes and energy conversion 4 devices,1-4 which can be applied to electrodialysis and diffusion 5 dialysis for industrial wastes treatment.5 More recently, there 6 are increasing interests in various electrochemical energy 7 generation and storage systems, including polymer electrolyte 8 membrane fuel cells,6-11 redox flow batteries (RFBs),12,13 9 reverse electrodialysis cells (REDs),14,15 microbial fuel cells 10 (MFCs),16 and hydrogen production (water electrolysis and 11 artificial photosynthesis based membrane).17,18 These 12 technologies rely upon IEMs that separate and transport ions 13 between the anode and cathode.19 These IEMs should meet 14 several requirements: reasonable ionic conductivity, good 15 chemical and dimensional stability, long-term durability in the 16 actual operating environment, mechanical toughness, and 17 sufficient heat tolerance.20,21 18
IEMs for practical applications are broadly divided into cation 19 exchange membranes (CEMs) and anion exchange membranes 20 (AEMs). AEMs provide an environment for electrochemical 21 reactions at high pH that may reduce the need for platinum 22 catalysts in electrochemical devices such as fuel cells.22-25 23
However, the investigations about AEMs based systems are 24 still in their infancy, which is mainly due to the development 25 lag of AEMs. To date, there are no readily available AEMs that 26 serve as the standard-bearer, while commercially available 27
Nafion (Dupont) membranes as state-of-the-art CEMs have 28 driven the progresses of CEMs related process.26 29
There have been significant advances in preparing AEMs from 30 a variety of polymer main chains ranging from poly(olefin)s, 31 poly(styrene)s, poly(phenylene)s, poly(ether sulfone)s, 32 poly(ether imide)s, and poly(arylene ether)s to organic–33 inorganic hybrid composites. 27-31 The AEMs can be obtained 34 by chloromethylation of these polymers and followed by 35 reaction with trimethylamine (TMA) to form 36 benzyltrimethylammonium groups. Although it contributes to 37 the progresses of AEMs, this route is especially environmental 38 unfriendly and relatively complicated. In the chloromethylation, 39 the commonly used chloromethyl methyl ether (CME) and bis-40 chloromethylether (BCME), are considered to be carcinogens. 41
Their usage have been restricted since the 1970s and thus large-42 scale production is limited.32-34 43
To overcome this hurdle, poly(2,6-dimethyl phenylene oxide) 44 (PPO) as a potential candidate has been extensively studied to 45 produce AEMs by both our group and other researchers. Apart 46 from its excellent physicochemical properties, the most 47 attractive advantage lies on the easy and controlled preparation 48 procedures to obtain AEMs. The original route is as follows: 49
PPO is brominated to access benzylhalide groups for 50 subsequent quaternization as an alternative to 51 chloromethylation.35 Consequently, studies about PPO and its 52 derivative AEMs are moving forward all the time. 53
In this review, key developments in PPO-based AEMs are 54 discussed: (1) AEMs prepared from bromination of PPO 55 (BPPO), (2) AEMs prepared from PPO through Friedel-Crafts 56 acylation, (3) AEMs prepared from PPO derivatives through in-57 situ polymerization, (4) inorganic-organic AEMs prepared from 58