Figure 3. OER performance of heterostructured Au−Ir catalysts. (A) OER polarization curves of different catalysts in 0.1 M HClO4 solution. Scan rate = 5 mV/s. (B) Ir-mass-based OER activities of Ir and Au−Ir catalysts. (C) Corresponding Tafel plots of Ir and Au−Ir catalysts. (D) Chronopotentiometric measurements of Ir and Au−Ir catalysts at a current density of 10 mA/cm2 . (E) CV curves of Ir and Au−Ir catalysts in 0.1 M HClO4 solution showing the Ir(III)/Ir(IV) redox peak. (F) Specific OER activities of Ir and Au−Ir catalysts at an overpotential of 300 mV that are normalized to the surface-accessible Ir sites.