Improved Round Trip Efficiency for Regenerative Fuel Cell Systems

The goal of this Office of Naval Research sponsored project is to develop high energy density energy storage systems for unmanned underwater vehicles UUVs. ONR is interested in regenerative fuel cells for UUV applications due to the capability for high energy storage density vs. batteries. Improved fuel cell and electrolyzer efficiency are desired for higher energy density and faster refueling times. ONR funded the first phase of this effort as a collaborative project between Proton Energy Systems dba Proton OnSite and W.L. Gore to make advancements in membrane technology, increasing the electrolyzer efficiency. Focus was on incorporation of reinforced membranes to enable lower ionic resistance through membrane thickness reduction. Current commercial electrolysis stacks utilize 7-10 mil 225-250 mum membranes, which can contribute up to 300 mV of overpotential at operating current densities. Past studies at Proton have indicated that 5-mil Nafion represents a practical limit for standard membrane thickness in electrolyzers, with failures seen under accelerated stress testing conditions, particularly at elevated temperatures. Past collaboration with Gore had shown robustness with full Gore MEAs even at 60-90 microns 2-4 mil but poor electrochemical performance. During the work reported here, a press technique was successfully developed to attach Proton electrodes to membranes from W.L. Gore without significant damage to the membrane.