Phase Separated Proton Conducting Membranes for Solar Fuels Generators, Topic 18b

"The Department of Energy’s 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."