Integration of Multifunctionality in a Colloidal Self-Repairing Catalyst for Alkaline Water Electrolysis to Achieve High Activity and Durability

Self-repairing catalysts are useful for achieving alkaline water electrolyzers with long lifetimes under intermittent operation. However, rational methodologies for designing self-repairing catalysts have not yet been established. Herein, hybrid cobalt hydroxide nanosheets (Co-ns), with a high deposition (repairing) rate, and β-FeOOH nanorods (Fe-nr), with high oxygen evolution reaction (OER) ability, are electrostatically self-assembled into composite catalysts. This strategy is developed to integrate multifunctionality in self-repairing catalysts. Positively charged Co-ns and negatively charged Fe-nr form uniform composites when dispersed in an electrolyte. These composites are electrochemically deposited on a nickel electrode by electrolysis at 800 mA cm⁻². Co-ns form a conductive mesoporous assembly of CoOOH nanosheets as a support. Fe-nr are then distributed on the CoOOH nanosheets as active sites for the OER. Because of the high deposition rate of Co-ns, the amount of Fe-nr deposited increases 22 times compared to when Fe-nr is deposited alone, and the OER current density increases 14 times compared to that of Co-ns alone. The composite self-repair catalyst shows the highest activity and durability under an accelerated durability test (ADT), and its degradation rate decreases from 84 μV cycle⁻¹ (Fe-nr only) to 60 μV cycle⁻¹ (composite catalyst) under ADT conditions without repair.