With the increasing demands placed on extravehicular activities (EVA) for International Space Station (ISS) maintenance, there is a critical need for oxygen delivery for EVA's from on-station sources. Since mechanical compressors have significant lifetime issues, NASA is evaluating high pressure PEM electrolyzer technology to generate and compress oxygen on the ISS. State-of-the-art electrolyzers use Nafion® and similar perfluorosulfonic acid membranes which have significant hydrogen (H2) permeation issues. To achieve the efficiencies desired, NASA requires a 50% or more reduction in H2 permeation with less than 10% reduction in ionic conductivity. Lynntech proposes to manufacture nanocomposite membranes with significantly reduced H2 permeation while maintaining high ionic conductivity. Preliminary results showed an unprecedented reduction in H2 permeation with minimal reduction in ionic conductivity (which have not been demonstrated before), no acid generation, and increased water transfer capability. In Phase I, Lynntech will further optimize the membrane microstructure to achieve a target 60 to 70% reduction in H2 permeation with less than 10% reduction in ionic conductivity. The anticipated Technology Readiness Level at the beginning and ending of Phase II will be 3 and 4, respectively.