PEM water electrolysis for large-scale energy storage may also serve as an actor for grid stability in energy grids with a high share of fluctuating, renewable energy sources. The major challenge the technology is facing is to reduce the system cost. In that context, acceptable lifetime under variable operation conditions has yet to be proven. Degradation studies are still scarce, but considered crucial for a further market implementation.

In this study, a small single cell set up is utilized to extract information about degradation mechanisms. The major parameters of interest are the operational conditions. Therefore, long term tests are performed with electrochemical characterization through polarization curves and EIS while changing the input signal.

Preliminary results of the study show a high reversible share of the voltage increase, which can be recovered through a short interruption of cell operation (see figure). That is particularly interesting for grid service applications, since the data suggests that dynamic operation may be beneficial.

However, the voltage profiles alone do not reveal enough information about what causes the degradation. Periodically performed EIS experiments on the operational cell support the analysis of which part of the cell causes performance loss. It was found that the purely ohmic contribution to cell impedance is mostly affected in the initial period and stabilizes afterwards. Other contributions on the other hand influence cell aging throughout the whole investigated timespan of 1000h so far.

Furthermore, a model-based analysis of the changes in polarization curves over time is carried out as in previous studies on cell performance. The extracted parameters are linked to activation processes and ohmic contributions that stem from the membrane and the contacts resistances.