(673k) Lignin based Ion Conducting Polymers with Controlled Ion Exchange Capacities (IECs) for Energy Conversion and Storage Devices

Ion conducting polymers (Ionomers) play a critical role on the performance of energy conversion and storage devices such as fuel cells, batteries, electrolyzers and so on. The current state-of-the-art ionomer Nafion conducts protons efficiently. However, Nafion is very expensive and not environment friendly. Here we demonstrate lignin based ionomers as a cheap and potential alternate to Nafion. Being naturally abundant polymer, lignin is very cheap. If ion conducting functionalities are imparted to lignin, it can act like ionomers. But the key is to limit the water solubility, an issue with commercial lignin sulfonate. In this work, we demonstrated systematic approach to design a range of Kraft lignin based ionomers with controlled ion exchange capacity (IEC). We explored the role of IEC on water solubility and self-assembly of the ionomers in solution and solid state. Also the ion conductivity and mechanical properties of these ionomers in thin film and membrane format were explored. The results proved the great potential of lignin based ionomers as catalyst binder and bulk membrane for energy conversion and storage devices.