What drives ions through polymer membranes?

Ion exchange membranes are needed in (photo)electrolyzers, fuel cells and batteries to separate ions and enable the desired processes. Polymeric membranes such as synthetically produced compounds like NAFION are particularly efficient, but they cannot be degraded. A ban on the use of these "eternal chemicals" is currently under discussion in the European Union, and the development of suitable alternatives will be a major challenge. So, it is crucial to understand why NAFION and other established polymeric membranes work so well.