Materials science: Cracks help membranes to stay hydrated

by Kamcev J, Freeman BD

Nature, 2016 Apr 28;532(7600):445-6. doi: 10.1038/532445a.

The synthetic polymer membranes used in fuel cells, water purifiers and systems for harvesting electricity from the sea must be hydrated — desiccation diminishes their performance. This is a problem, because some of these applications (including fuel cells) operate at high temperatures in low-humidity environments. On page 480 of this issue, Park et al.1 describe membranes that limit their own dehydration, substantially improving the membranes’ performance in low-humidity environments.

The membranes in question are called ion-exchange membranes (IEMs), and they are made from polymers in which acidic or basic chemical groups are covalently bound to a polymer backbone2. IEMs swell when in contact with water, causing the attached groups to dissociate into fixed and mobile ions, and so making the membranes highly charged. The membranes therefore selectively and efficiently transport counter-ions (ions that have an opposite charge to that of the polymer’s charged groups), so that rates of ion transport through the membranes are high. This high ionic conductivity is crucial for many membrane-based technologies because it reduces energy losses and therefore lowers costs…

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