Durability of NiFe-based oxygen evolution electrocatalysts in AEM water electrolyzer under fluctuating power supply

• Degradation mechanism of NiFe-based OER catalysts at fluctuating power is studied. • OER catalyst durability is positively correlated with fluctuating voltage interval. • Performance degradation includes both reversible and irreversible losses. • Irreversible loss is caused by catalyst collapse, dissolution and agglomeration. • Reversible loss is due to gas stagnation in the porous structure of catalyst. NiFe-based materials are widely utilized as anode electrocatalysts for the oxygen evolution reaction (OER) in anion exchange membrane water electrolyzers (AEMWE). However, their performance under actual fluctuating power supply remains poorly understood. In this study, the OER performance and degradation mechanisms of various NiFe-based OER catalysts are investigated in AEMWE under both constant and fluctuating voltage conditions. Among the tested materials, Ni x Fe 1−x S exhibits the best durability under both constant and fluctuating voltages, outperforming Ni x Fe 1−x P and NiFe LDH. Notably, its stability is found to be positively correlated with the interval of voltage fluctuation. The degradation of Ni x Fe 1−x S can be attributed to a combination of irreversible and reversible losses. Accelerated durability testing reveals that irreversible loss is primarily caused by the severe collapse, dissolution and agglomeration of catalyst particles on the electrode surface under fluctuating power supply. On the other hand, the reversible loss is linked to hindered contact between the electrolyte and the electrode surface, caused by gas retention within the catalyst’s porous structure. This reversible loss can be mitigated by introducing a rest period, which allows for the recovery of catalyst’s performance. This work provides valuable insights into the degradation mechanisms of NiFe-based OER catalysts under fluctuating power supply in AEMWE.