Nanocrystalline Nickel-based alloys were investigated as catalysts for the oxygen evolution reaction(OER) at industrial operation conditions for alkaline water electrolysis. Different alloys were prepared by rapid solidification and subsequent high-energy milling. Regarding OER activity, the best efficiency was obtained for a nanocrystalline Ni-Fe alloy in 29.9 wt.% KOH at 298 K. However, at elevated temperature (333 K), comparable activities were determined in short-term experiments for nanocrystalline Ni-Fe and Ni alloys as well as for polycrystalline Ni. This initially incomprehensible outcome can be explained by the incorporation of Fe, which is present as impurity in the reagent grade KOH solution, into the NiOOH anode surface layer. However, after a long-term operation, the nanocrystalline Ni-Fe alloy shows a significantly better activity, in particular, at altering current density of up to 1 A cm(-2). As a result, the nanocrystalline Ni-Fe alloy exhibits a very high efficiency and excellent long-term activity (375 mV overpotential at 0.3 A cm(-2)) after 95 h of operation at different loads. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.