Stainless-steel electrodes for anion-exchange membrane water electrolysis: modes of metal contamination and stable operation

Anion-exchange membrane (AEM) water electrolysis enables hydrogen production at lower cost, in particular by using earth-abundant catalytic materials. However, these systems still suffer from limited stability due to catalyst and system degradation. In this work, we tested porous transport layer (PTL) electrodes made of stainless steel as anodes delivering a high voltage efficiency of up to 3.5 A cm-2 at 2 V. Significant amounts of Fe were identified as solid precipitates in the membrane and on the cathode surface after test. The involved metal leaching and subsequent precipitation are strongly dependent on pH and thus KOH concentration. We further investigated operation modes in concentrated and diluted alkaline environment, as well as dry and wet cathode operation to identify different pathways introducing Fe to the system. Within the first 100 h of testing, a significant non-linear and non-reversible increase of cell voltage occurs. This voltage increase can mostly be attributed to anode deactivation, which is shown by edge-type reference electrode measurements. In 1 M KOH, the degradation rate eventually stabilizes to only 7 µV h-1 for the last 800 h of a 1000 h constant current hold at 1 A cm-2.