Nickel anode evolution and mass loss during intermittent alkaline water electrolysis

Nickel-based anodes are widely used in industrial alkaline electrolyzers, yet their long-term stability under dynamic operation remains poorly understood. Shutdowns in bipolar electrolyzers lead to reverse currents and discharging of the electrodes, triggering electrochemically driven phase transformations. In this study, we investigate the deterioration of bulk nickel 201 anodes subjected to repeated shutdown cycling, mimicking off-grid operation scenarios. While nickel is recognized for its excellent stability in alkaline environments, our results reveal strong correlations between anode mass loss and both the number and duration of shutdown cycles, with deterioration driven not by the reduction event itself but by the time spent in a reduced state. Elevated operation temperatures further accelerate this effect. Interestingly, moderate concentrations of iron in the electrolyte significantly suppress deterioration, likely by stabilizing nickel hydroxide phases and mitigating structural transformations. The data suggest that phase transitions between nickel hydroxide and oxyhydroxide allotropes introduce mechanical stress, leading to material detachment. These findings demonstrate how reverse currents have significant implications for the industrial design of electrodes, underscoring the importance of thick nickel coatings and robust catalyst–support interactions in electrolyzers operating under intermittent conditions.