Stack Degradation

In plain terms

As an electrolyzer runs, catalysts lose activity, membranes thin and contact resistances grow. To keep the same hydrogen output, each cell needs a little more voltage every month. That rise is stack degradation.

It is reported two ways. µV/h or mV/kh is the cell voltage increase per operating hour (1 mV/kh = 1 µV/h). %/1,000 h is the same rise as a share of the starting voltage. The US DOE declares a stack at end of life when voltage has risen 10 %, and derives stack lifetime from the degradation rate.

Typical range

Solid oxide rates are measured on different test bases by the two agencies. Variable operation, frequent starts and impurities in the feed water can push real-world rates above these values.

Why it moves LCOH

Degradation hits LCOH twice. First, rising voltage means rising specific energy consumption, so the plant buys more electricity per kilogram each year. Second, the stack must be replaced at end of life, a large mid-project CAPEX line. A PEM stack with a 40,000 h life running 5,000 h a year needs replacing about every eight years.

Common mistake