Segmented and Blocky Proton Conducting Membranes for Solar Fuels Generator Applications

The Department of Energy’s Office of Basic Energy Sciences has identified a need for new proton conducting membranes for solar fuel generator applications. Specifically, development of block copolymers with good proton conductivity at ambient temperatures and low gas diffusion and ionic transports are needed. There are currently 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 program is to design, develop and manufacture segmented and blocky copolymers with controlled molecular weights and tailorable morphology specifically for solar fuel generator applications.The morphology of the block copolymers will allow tunable proton conductivity and gas transport behavior. The phase-separated block copolymers shall have good mechanical durability. In Phase I, end-functionalized, hydrophilic, sulfonated segments and rigid, hydrophobic segments shall be synthesized and utilized as building blocks for new durable 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. Additionally, a new synthetic technique for blocky PEEK membranes will also be investigated during this project. 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 4. TRL 6 shall be reached via membrane incorporation into electrolyzer cells, impedance testing, and gas diffusion properties by our Phase I partners at Virginia Tech, and at an independent National Laboratory and/or potential Phase II partners. Durable proton conducting membranes for electrochemical devices shall be commercialized primarily for solar fuel generators with several energy companies. These proton conducting membranes may be transitioned for use in stationary power storage applications, general water electrolyzers, and as part of the developing hydrogen infrastructure.