LAUSR

Summary Iron-nickel oxy/hydroxide (FeNiO x ) films are widely known to mediate the oxygen evolution reaction efficiently at modest current densities (10 mA/cm 2 ). We report here the electrochemical stability and metal composition of these electrocatalyst films when subjected to sustained electrolysis in strong base at 200 mA/cm 2 , conditions that are better aligned with practical commercial-scale electrolysis. We found that most of the iron in the film was liberated during the first 24 hr of electrolysis and deposited on the cathode. We confirmed these observations by interrogating the relative metal content of the electrodes before and after electrolysis by using X-ray fluorescence, energy-dispersive X-ray, and X-ray photoelectron spectroscopies. The rate at which iron was leached from FeNiO x anodes was reduced at 10 mA/cm 2 but was still significant. These results highlight that one must account for the instability of this mixed-metal composition when drawing structure-property relationships and when considering the scale-up of electrocatalysts.