"The Department of Energys Office of Basic Energy Sciences has identified a need for new ion conducting membranes for solar fuel generator applications. Specifically, development of phase separated membranes with good proton conductivity at ambient temperatures, very low gas (fuel) diffusion/permeability, and selective ionic transport is required. Currently there are no commercially available proton conducting membranes which possess these qualities. While there are similarities, membranes developed for fuel cells have not displayed good performance in solar fuel generators. The objective of this STTR program is to design, develop and manufacture phase separated membranes based on segmented and blocky polymers. The polymer structure and architecture will be manipulated via adjustments to segment lengths which will afford tailorable morphology specifically for solar fuel generator applications. The morphology of the ionomeric polymers will allow tunable ionic conductivity and gas and molecular transport behaviors. The phase-separated block copolymers shall have good mechanical durability and dimensional stability in the hydrated state and low CO2 plasticization. In Phase I, end-functionalized sulfonated (hydrophilic) segments and rigid hydrophobic segments shall be synthesized and utilized as building blocks for new polysulfone copolymers with tailored properties specifically for solar fuel generator applications. The influence of block length (i.e., segment molecular weight) on membrane properties, including proton conductivity, gas diffusion, ionic transport, and mechanical and chemical stability shall be evaluated. The rigid hydrophobic segments will serve to block undesirable permeability and diffusion of gas(es) and other species through the bulk structure of the membrane. Concurrently, a new synthetic technique for blocky sulfonated and quaternized PEEK membranes will also be investigated during this project with university partners. The blocky PEEK is synthesized through a gel-state functionalization process which allows retention of a high degree of crystallinity. A detailed property-structure relationship study shall be conducted to help design better membranes for solar fuel generator applications, which will afford validation of a Technology Readiness Level 3. TRL 5 shall be reached via membrane incorporation into electrolyzer cells, impedance testing, and gas diffusion properties by our Phase I university partners, and subsequently at an independent National Laboratory and/or potential Phase II industrial partners. Robust proton conducting membranes for electrochemical devices shall be commercialized primarily for solar fuel generators through several US energy integrators and manufacturers. These ion conducting membranes may be transitioned for use in stationary power storage applications, including redox flow batteries, electrolyzers, and as part of the developing hydrogen infrastructure."
