Mixed-Matrix Anion Exchange Membranes for Solar Fuels Generators

Solar fuels generators like solar-to-hydrogen devices that use sunlight to drive the conversion of water to hydrogen, a storable chemical fuel, could contribute in the decarbonization of the energy infrastructure. A dearth of suitable anion exchange membranes, however, has inhibited broad commercialization of solar generators utilizing highly alkaline environments. Currently available membranes fail to demonstrate the high permselectivity, mechanical strength, and long-term stability required for device-level use. This proposal will develop a composite polymer membrane designed to: (1) support low device current densities with high permselectivity for OH–, (2) retain adequate mechanical and transport properties for use in devices, and (3) operate stably under highly alkaline conditions. The engineering of composite membranes will enable its properties, including ionic conductivity and permeability, to be independently optimized. In Phase I, a stable, cationic covalent organic framework (COF) will be designed and synthesized to target low gas permeability without a concomitant loss of ionic conductivity. A stable polymer support will be designed concurrently to provide appropriate chemical and mechanical stability. Several COF-polymer membrane fabrication strategies, including thin-film composite and mixed matrix morphologies, will be developed and rigorously tested, both in situ and ex situ, to identify the best-performing membrane structure and composition. In the near term, assuming small-scale production of COF-polymer membranes in Phase II, national laboratories would benefit from membranes that lead to higher device efficiencies and enable more sustainable, inexpensive catalysts. Future phases of commercialization will entail the scale-up to a membrane production level sufficient for a partnership with an electrolyzer manufacturer in order to target market entry in the electrolyzer industry. The membranes would benefit the public by helping create a resilient, decarbonized, and decentralized grid.