Understanding Degradation Effects of Elevated Temperature Operating Conditions in Polymer Electrolyte Water Electrolyzers

The cost of polymer electrolyte water electrolysis (PEWE) is dominated by the price of electricity used to power the water splitting reaction. We present a liquid water fed polymer electrolyte water electrolyzer cell operated at a cell temperature of 100 degrees C in comparison to a cell operated at state-of-the-art operation temperature of 60 degrees C over a 300 h constant current period. The hydrogen conversion efficiency increases by up to 5% at elevated temperature and makes green hydrogen cheaper. However, temperature is a stress factor that accelerates degradation causes in the cell. The PEWE cell operated at a cell temperature of 100 degrees C shows a 5 times increased cell voltage loss rate compared to the PEWE cell at 60 degrees C. The initial performance gain was found to be consumed after a projected operation time of 3,500 h. Elevated temperature operation is only viable if a voltage loss rate of less than 5.8 mu V h(-1) can be attained. The major degradation phenomena that impact performance loss at 100 degrees C are ohmic (49%) and anode kinetic losses (45%). Damage to components was identified by post-test electron-microscopic analysis of the catalyst coated membrane and measurement of cation content in the drag water. The chemical decomposition of the ionomer increases by a factor of 10 at 100 degrees C vs 60 degrees C. Failure by short circuit formation was estimated to be a failure mode after a projected lifetime 3,700 h. At elevated temperature and differential pressure operation hydrogen gas cross-over is limiting since a content of 4% hydrogen in oxygen represents the lower explosion limit.