K. Swider-Lyons
Plug Power,
United States
Summary:
Interest in Polymer electrolyte membrane water electrolysis (PEMWE) has grown tremendously in the last ten years due to the promise of generating “green hydrogen” when powered through renewable sources. Despite often being call the “new technology” compared to alkaline electrolysis PEM fuel cells and electrolyzers have been in use since the very first PEMs made for the Gemini and Apollo programs. Almost immediately oxidation of the membrane was identified as the limiting factor in the lifetime of these systems. Further investigations demonstrated that HOOH, hydrogen peroxide is a byproduct of fuel cell or electrolyzer operation and is in fact HOOH is generated any time H2, O2 and platinum are present. HOOH further breaks down to .OH and/.OOH radicals, greatly accelerated by the presence of iron, even at almost undetectable levels. The .OH radical has been shown to be the nefarious actor. This radical can readily attack C-H bonds, as well as aromatic and ether linkages, greatly limiting the chemistries available for PEMWE membranes. The invention of Nafion™ a perfluorinated sulfonic acid (PFSA) membrane with PTFE (Teflon) as a backbone in the late 1960s greatly extended the operating temperature (now >70°C) and lifetimes of PEM devices, taking lifetimes from 100s to greater than 10,000 hours. Unfortunately, the same thing that makes these materials so attractive, their chemical durability has made them a concern as perfluorinated and partially perfluorinated materials, broadly, PFAs, have been building up in the environment and are in measurable quantities in everybody’s blood stream. This has led to a renewed effort in a long history of failures to find a non-perfluorinated alternative. This talk will look at some of these approaches and what the likelihood of success. It will also look at the life cycle of PFSAs in current PEM devices, as well as efforts to recapture/recycle/reuse these materials at end of life.