Figure 4.

(a) Tafel plots for SC (100th cycle), SCF02 (100th cycle), and SC + Fe³⁺ (2nd cycle in Fe-spiked KOH) normalized to the oxide surface area. The benchmark catalysts, IrO₂⁴¹ and BSCF,¹² are included for comparison. Error bars represent the standard deviation from three independent measurements. The inset shows the EIS of SC, SCF02, and SC + Fe³⁺ recorded at 1.6 V vs RHE. (b) Schematic illustration of the structure–activity relationship between SC, SC + Fe³⁺, and SCF02. The specific activity at 1.6 V vs RHE is used as the metric for activity comparison. Sr, Co, and Fe atoms are shown as green, blue, and gold balls, respectively. For simplicity, the residual Sr in the surface layers and oxygen atoms in the surface as well as the bulk are omitted.