The Electrolytic Oxygen Generator (EOG) used aboard U.S. nuclear submarines to produce breathing oxygen for the crew uses an asbestos diaphragm to separate the electrochemically generated hydrogen and oxygen gas. Due to environmental, safety and economic concerns, a program to develop a substitute diaphragm material was implemented under a Naval Research Laboratory contract.Polyphenylene sulfide (PPS) was shown to be a suitable replacement material for asbestos. Initial tests using PPS cloth revealed an inadequate separation of the hydrogen and oxygen gas. A new, advanced PPS spun cast sleeve was developed, analyzed (including electron microscopy and XREF), surface-modified and then a full-scale prototype was tested. With successful full-scale testing, a complete set of sixteen EOG cells was assembled and installed in an EOG. These cells have recently completed a two thousand-hour endurance test with performance results similar to those of standard asbestos diaphragm cells.