26 Million current cycles in the sub-second scale for fast dynamic electrolysis operation with a 30 layer electrolyte-supported cell stack

Fast dynamic operation in the sub-second scale is demonstrated for high-temperature steam electrolyzers. The current was switched between thermoneutral voltage and OCV (i.e., two operation points without the need for thermal management) using pulse width modulation with a 200 ms ON and 200 ms OFF profile. Under these conditions, the ON period is shorter than the steam-conversion relaxation time (around 1 s from impedance spectroscopic measurements), which allows calculated steam-conversion rates in the ON phase to go well above 100%. Long-term operation (8000 h) in electrolysis mode is presented with two dynamic phases (3000 h) alternated with steady-state phases (5000 h). A total of 26 million ON/OFF cycles of 400 ms time were performed during two sequences of the dynamic/steady-state phases with temperature corrected degradation rates of 15 and 22 mV kh −1 at a current density of −0.43 A cm −2 and –0.40 A cm −2 , respectively. Notably, the degradation rate remained constant when transitioning between dynamic and steady-state conditions, highlighting that the long-term dynamic switching – over millions of cycles – does not add degradation. Further, the Faradaic efficiency of the stack was analyzed throughout the test. The shown operation strategy paves the way to the integration of this type of electrolyzers for electricity grid balancing.