Invited for this month′s front cover is the group of Wolfgang Binder, collaborating with Michael D. Guiver of the National Research Council of Canada. The image demonstrates how an anion-exchange membrane based on clicked 1,2,3-triazoles can facilitate the transport of hydroxide ions. Read the full text of the article on page 1376
Why do we need anion exchange membranes in fuel cells?
1234Fuel cells are of central importance for energy storage, and thereby can help to enable a greener future for our planet. Alkaline fuel cells (AFCs), in contrast to acidic fuel cells, show advantages with respect to electrode reaction kinetics together with strongly reduced corrosion. In addition to their use in alkaline fuel cells, anion-exchange materials are highly relevant in other electrochemical energy conversion/storage devices such as redox flow batteries, electrodialysis stacks, and metal–air batteries. The anion-exchange polymer electrolyte investigated in our paper tackles the problem of leakage of liquid electrolytes, a severe issue affecting many AFCs. Thus, careful design is critical to enable these devices to achieve high efficiencies in energy storage and conversion.
What is limiting transport in alkaline fuel cells?
One can imagine that the transport of hydroxide ions in particular is limited by their low intrinsic mobility. One idea to enhance this mobility, and thus facilitate transport, is to use hydroxide transport facilitators.
Why did you choose hydroxide transport facilitators to promote transport in your membrane?
The basic idea was to design a polymer able to form nanometer-scale channels that serve to improve transport of ions. However, it is critical that such polymers maintain sufficient stability, together with a technically acceptable water uptake. To achieve this we designed relatively simple clicked triazoles as hydroxide-transport facilitators, which could either lose a proton, acting as a weak Brønsted acid, or accept a proton, acting as a weak Brønsted base.
How do the triazole moieties in the membrane promote anion transport?
One possible reason is that introducing the 1,2,3-triazole facilitators results hydrogen-bonding between water and hydroxides; the resulting continuous pathway facilitates ionic conduction and ion movement in a particular direction. The obtained membranes show a significantly higher conductivity (up to ten times) compared to anion exchange membranes without triazole groups.