Most electrochemical conversion and storage devices, such as certain types of fuel cells, alkaline ion and redox-flow batteries, rely on the amazing properties of ion conducting membranes. These devices can function only if the corresponding membranes effectively separate the electrochemically active masses (electrodes) and mediate the electrochemical reactions taking place at the anode and cathode though conducting specific ions, which may be protons or hydroxide ions in the case of PEM-fuel cells, Li+ in lithium ion batteries or specific anions or cations in the case of redox-flow batteries. Apart from these key properties, many other especially stability requirements render the development of such membranes a formidable one! This lecture provides surprising new insights into membrane structure and dynamics on different length scales including the nature of the relevant interactions, which not only extend the understanding of well established membrane materials such as Nafion®, but also consolidate the basis for the development of alternative membranes for specific applications. If done efficiently, the latter must be a multi-disciplinary process comprising ab initio calculations, complex organic synthesis and comprehensive physico-chemical characterization. The great beauty of the approach is exemplified by retracing the development of proton conducting multi-block co-polymers for PEM fuel cell applications and Li+ conducting polyelectrolytes for application in Li-ion batteries (especially lithium/air).
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