Fig. 1.

Crystal structure and OER activity of SrCo_0.9Ir_0.1O_3−δ. Crystal structures of a PLD-SrIrO₃¹⁷, b pseudo-cubic SrCo_0.9Ir_0.1O_3−δ, and c m-SrIrO₃. d scanning electron microscopy (SEM) images of as-prepared m-SrIrO₃ (scale bar, 5 µm) and SrCo_0.9Ir_0.1O_3−δ (scale bar, 20 µm)_. e Rietveld refinement of X-ray diffraction (XRD) patterns of as-prepared m-SrIrO₃ and SrCo_0.9Ir_0.1O_3−δ; minor IrO₂ phase is found in the as-prepared m-SrIrO₃ and a single SrCo_0.9Ir_0.1O_3−δ phase is obtained; the reliability factors for m-SrIrO₃ are R_wp = 8.41%, R_p = 6.47%, x² = 3.398; the reliability factors for the SrCo_0.9Ir_0.1O_3−δ are R_wp = 2.52%, R_p = 1.95%, x² = 1.521. During the refinement, the structure parameters (space group: C 2/c) of SrIrO₃ reported by Qasim is used and only the lattice parameters of m-SrIrO₃ were refined¹⁹. The refined lattice parameters for m-SrIrO₃ are a = 5.5865(8), b = 9.648(1), c = 14.153(1), alpha = 90°, beta = 93.048(9)°, and gamma = 90°. The detailed structure parameters for SrCo_0.9Ir_0.1O_3−δ are presented in Supplementary Table 1. A refined occupancy ratio for Ir in SrCo_0.9Ir_0.1O_3−δ is 0.093, which confirms the Ir has been successfully doped in the Co site. f, g High-resolution transmission electron microscopy (HRTEM) images taken from m-SrIrO₃ and SrCo_0.9Ir_0.1O_3−δ (scale bar, 5 nm). The corresponding inverse fast Fourier transformed (FFT) images are taken from white square box regions (scale bar, 5 1/nm). The measured interplanar distances from inverse FFT images correspond well with the XRD refinement results, which are in brackets. The selected area electron diffraction (SAED) patterns from corresponding zone axes are presented and indexed based on the data from XRD refinement. h Specific OER activities of IrO₂, m-SrIrO₃, and SrCo_0.9Ir_0.1O_3−δ in 0.1 M HClO₄. The specific OER activities of PLD-SrIrO₃ in 0.5 M H₂SO₄ are from the literature¹³. For the activity of PLD-SrIrO₃ samples, the activity evolution within 0–10 min and 2–30 h are shown as bars. i Calculated range for turnover frequency (TOFs) of Ir from different samples at an overpotential of 270 mV. The TOFs are calculated by assuming Ir at outermost surfaces (upper limit), Ir from reconstructed surface regions (the intermediate value) and all Ir from the bulk (lower limit) are involved in catalyzing water oxidation. The error bars correspond to the s.d