AC:DC operation of 70-cell SOE stack-enabling dynamic operation and years of lifetime

AC:DC operation has delivered the current world durability record for solid oxide steam electrolysis (SOE) full stack testing, to the best of our knowledge. A 70-cell SolydEra stack was operated for 25000 h at a net -0.5 A/cm2 current density using the pulsed polarization-reversing AC:DC operation. Besides improving SOE stack operation durability, AC:DC operation decouples the hydrogen production rate from the thermal gradients developed within the stack. Principally, this enables a temperature increase from gas inlet to outlet regardless of the electrolysis load, therefore enabling dynamic SOE operation without imposing thermomechanical stress to the stack.
Below, details about the SolydEra G8-80 stack operated for 25000 hours are presented. Furthermore, we present test results from another G8-80 stack running under varying loads using AC:DC to highlight the impact of dynamic SOE operation. The stack performances are characterized in operando with electrochemical impedance spectroscopy (EIS) on cell-cluster level, and by rigorous analysis of a vast data-set. For the 25000h long-term test, results from post-mortem analysis using SEM are also presented, supporting the findings of EIS and the benefits of AC:DC operation.