Radiation-Grafted Anion-Exchange Polymer Electrolytes for Clean Energy Applications

Abstract

Anion-exchange polymer electrolyte materials are being developed and studied for an increasing diversity of clean energy technologies, such as alkaline polymer electrolyte fuel cells, redox flow batteries, biological fuel cells, and reverse electrodialysis cells. These technologies include the application of the anion-exchange polymer electrolytes in conditions that span the pH range from highly acidic, through more neutral environments, and finally to highly alkaline. This presentation will highlight the versatility of the radiation-grafting methodology in that it allows the production of polymer electrolytes containing numerous different morphologies and chemistries, including both cation-exchange and anion-exchange types. Once initial (small scale) experiments have been conducted and synthesis protocols have been developed, this methodology has the advantage that reasonably large (for lab-scale) quantities of materials can be synthesised, e.g. 10 – 100s of grams and several m2 sized batches, with excellent repeatabilities; this also allows for a large number of tests and experiments to be conducted on the same batch of material. This synthesis platform therefore facilitates research into such materials including research that compares ion-exchange materials where a single variable has varied: e.g. anion-exchange polymer electrolyte materials with the same ion-exchange capacities and polymer backbones but where the chemistries of the cationic head-groups is varied, anion-exchange polymer electrolyte materials with the same ion-exchange capacities and cationic head-groups but where the polymer backbones are varied, or anion-exchange polymer electrolyte materials with the same polymer backbone and head-group chemistries but where the ion-exchange capacity is varied.The materials to be discussed include radiation-grafted anion-exchange membranes (with similar ion-exchange capacities) that possess an array of cationic head-group chemistries, including the benchmark benzyltrimethylammonium, benzyltriethylammonium, benzylimidazoliums, benzylpyridiniums, benzylpiperidiniums, and benzylmorpholinium. Some of these anion-exchange polymer electrolytes have reasonable stabilities at alkaline pHs (e.g. for use in alkaline polymer electrolytes fuel cells), whilst others can only be applied to systems where the pHs, that the materials are exposed to, are more neutral (e.g. materials for use in reverse electrodialysis cells). The ionic conductivities of these materials appear to be high enough for use in the above mentioned technologies. As a small aside, it will also be demonstrated that cation-exchange membranes with different chemistries can also be synthesised and this is of interest to applications such as the more well-known proton-exchange membrane fuel cells as well as reverese electrodialysis. Figure 1