It is critical to control Fe impurity concentrations in oxygen-evolution-reaction electrocatalysis experiments so that unambiguous assignments of activity and mechanistic details can be made. An established method to prepare Fe-free KOH electrolyte is by using particulate Ni(OH)2 or Co(OH)2 as absorbents to remove the Fe from KOH or other neutral-to-alkaline electrolytes. However, this method yields residual Ni or Co species in the electrolyte which can be redeposited on the working electrode. Thus, current methods of Fe removal could convolute studies of OER. In this work, we compared two different methods, continuous electrolysis and nano-filtration, to remove the Ni and/or Co species from Fe-free alkaline electrolyte. We found the best approach is to pass the Fe-free electrolyte through a hydrophilic 0.1 μm polyethersulfone filter which decreases the Ni species concentration in 1 M KOH to single ppb levels. This result suggests the remaining Ni or Co species are primarily particulate in nature, consistent with their small solubility as ions. In comparison, extended pre-electrolysis of the electrolyte removed only a portion of the Ni/Co.

Anion-exchange-membrane water electrolyzers (AEMWEs) in principle operate without soluble electrolyte using earth-abundant catalysts and cell materials and thus lower the cost of green H₂ . Current systems lack competitive performance and the durability needed for commercialization. One critical issue is a poor understanding of catalyst-specific degradation processes in the electrolyzer. While non-platinum-group-metal (non-PGM) oxygen-evolution catalysts show excellent performance and durability in strongly alkaline electrolyte, this has not transferred directly to pure-water AEMWEs. Here, AEMWEs with five non-PGM anode catalysts are built and the catalysts' structural stability and interactions with the alkaline ionomer are characterized during electrolyzer operation and post-mortem. The results show catalyst electrical conductivity is one key to obtaining high-performing systems and that many non-PGM catalysts restructure during operation. Dynamic Fe sites correlate with enhanced degradation rates, as does the addition of soluble Fe impurities. In contrast, electronically conductive Co₃ O₄ nanoparticles (without Fe in the crystal structure) yield AEMWEs from simple, standard preparation methods, with performance and stability comparable to IrO₂ . These results reveal the fundamental dynamic catalytic processes resulting in AEMWE device failure under relevant conditions, demonstrate a viable non-PGM catalyst for AEMWE operation, and illustrate underlying design rules for engineering anode catalyst/ionomer layers with higher performance and durability.