Activating the passivated Ir sites in 3R-IrO₂ by intercalating Pt atoms for enhanced oxygen reduction reaction activity

Iridium oxide (IrO2) has traditionally been considered to exhibit limited oxygen-reducing capacity. An effective approach to improve the oxygen reduction reaction (ORR) activity in parent catalytic materials is through atomic intercalation. However, the challenge lies in achieving a delicate balance between high ORR activity, structural stability, and minimizing the use of precious metals. Herein, we fabricate 3R-phase iridium oxide (3R-IrO2) with superior ORR activity by intercalating a tiny amount of Pt (3.6 wt% Pt) into the interlayers of 3R-IrO2 (3.6 wt% Pt-3R-IrO2). When employed as an acidic ORR electrocatalyst, 3.6 wt% Pt-3R-IrO2 shows a high half-wave potential (E-1/2) of 0.92 V (vs. RHE) in O-2-saturated 0.1 M HClO4 electrolyte, much better than those of Pt/C (0.850 V), 3R-IrO2 (0.616 V), and Pt nanoparticles on 3R-IrO2 surface (3.6 wt% Pt@3R-IrO2) (0.618 V) electrocatalysts. It achieves high mass activity of 0.170 A mg(Ir)(-1) at the potential of 0.9 V, which is 5.5 and 11.3 times than that of Pt/C (0.031 A mg(Ir)(-1)) and 3.6 wt% Pt@3R-IrO2 (0.015 A mg(Ir)(-1)), respectively. Density functional theory (DFT) calculations and experiment results co-jointly demonstrate that the active center of Pt-3R-IrO2 is anchored to the activated Ir atoms of the 3R-IrO2 rather than Pt atoms. The d-band center of Ir 5d orbitals of Pt-3R-IrO2 is simultaneously regulated, which optimizes the energy barrier of adsorption/desorption toward the ORR process. Intriguingly, the intercalation of Pt atoms into trigonal rhodium oxide (Tri-RhO2) also activates the ORR activity of Rh, suggesting the universality of this strategy. This discovery may provide a new and general way for activation of ORR activity of other precious metal-intercalated nonprecious metal oxide electrocatalysts.