Self-Supported Hierarchical IrO₂@NiO Nanoflake Arrays as an Efficient and Durable Catalyst for Electrochemical Oxygen Evolution

Although traditional IrO 2 nanoparticles loaded on a carbon support (IrO 2 @C) have been taken as a benchmark catalyst for the oxygen evolution reaction (OER), their catalytic efficiency, operation stability, and IrO 2 utilization are far from satisfactory due to the inferior powdery structure and inevitable corrosion of both IrO 2 and C under the oxidizing potentials. Here, a rational design of a self-supported hierarchical nanocomposite, composed of IrO 2 @NiO nanoparticle-built porous nanoflake arrays vertically growing on nickel foam, is proposed, which is demonstrated as a versatile strategy to achieve improved OER activity, remarkable long-term stability, and significantly reduced loading of IrO 2 (0.62 atom %). Impressively, the resultant catalyst drives a steady OER current density of 10 mA cm –2, requiring 278 mV overpotential in 1.0 M KOH electrolyte for 25 h and outmaneuvring commercial IrO 2 @C with much higher mass loading. Further electrochemical investigation and mechanism analysis disclose that the greatly improved electrocatalytic activity stems from the advantageous hierarchical structure and the synergistic effect between IrO 2 and underlying potential-induced NiOOH, whereas the outstanding durability is attributed to the unique role of NiO in preventing IrO 2 dissolution.