Understanding the influence of iridium oxide catalyst state on the performance in oxygen evolution reaction

Figure 1a: X-ray diffractograms for as-prepared, and post-calcined (at 400 °C, 500 °C, 600 °C, and 700°C) Ir-oxide nanoparticles (2theta vs. intensity /a.u.).

Figure 1b: X-ray diffractograms for the reference spectrum for the tetragonal rutile IrO2 (JPCD card no. 15-0870), and Ir fcc (COD, 1512514), (2theta vs. intensity /a.u.).

Figure 2a: TEM image for the Ir-oxide nanoparticles calcined at 400 °C.

Figure 2b: TEM image for the Ir-oxide nanoparticles calcined at 500 °C.

Figure 2c: TEM image for the Ir-oxide nanoparticles calcined at 600 °C.

Figure 2d: TEM image for the Ir-oxide nanoparticles calcined at 700 °C.

Figure 3a: Comparison of the high-resolution Ir 4f spectra obtained from the XPS measurements on Ir-oxide nanoparticles (as-prepared, calcined at 400°C and calcined at 700°C), (binding energy / eV vs. intensity /a.u.).

Figure 3b: Comparison of the high-resolution O 1s spectra obtained from the XPS measurements on Ir-oxide nanoparticles (as-prepared, calcined at 400°C and calcined at 700°C), (binding energy / eV vs. intensity /a.u.).

Figure 3c: The hydroxide-to-oxide ratio for the post-calcined Ir-oxide nanoparticles.

Figure 4: Cyclic voltammograms of the post-calcined Ir-oxide nanoparticles (potential, E vs current density, j).

Figure 5a: Measured current densities at E = 1.53 V at 25 mV·s-1, j@1.53V, for all post-calcined Ir-oxide samples (potential, E vs current density, j).

Figure 5b: Change in the calculated total surface area of the particles present in the bulk vs. change in j@1.53V when calcination temperature increased (change / % vs calcination change interval).

Figure 6: Experimental and simulated CV data (at 200 mV·s-1) for the Ir-oxide nanoparticles calcined at 400 °C, 500 °C, 600 °C, and 700 °C (potential, E vs current density, j).

Figure 7a: Experimental and simulated CV curves recorded at the scan rates of 200, 100, 50, and 25 mV·s-1 for the Ir-oxide nanoparticles calcined at 400 °C.

Figure 7b: Experimental and simulated CV curves recorded at the scan rates of 200, 100, 50, and 25 mV·s-1 for the Ir-oxide nanoparticles calcined at 500 °C.

Figure 7c: Experimental and simulated CV curves recorded at the scan rates of 200, 100, 50, and 25 mV·s-1 for the Ir-oxide nanoparticles calcined at 600 °C.

Figure 7d: Experimental and simulated CV curves recorded at the scan rates of 200, 100, 50, and 25 mV·s-1 for the Ir-oxide nanoparticles calcined at 700 °C.

Figure 8a: Current density simulated at E=1.53V, j@1.53V-sim, double layer capacitance, Cdl, density of active CUS sites, ρCUS, versus calcination temperatures; values extracted from the simulations for post-calcined Ir-oxide particles.

Figure 8b: Current density simulated at E=1.53V, j@1.53V-sim, double layer capacitance, Cdl, versus density of active CUS sites, ρCUS; values extracted from the simulations for the post-calcined Ir-oxide particles.

Figure 9a: Comparison of the free reaction energies of all the elementary steps (Step 1−7) of OER on CUS on the post-calcined Ir-oxide nanoparticles (reaction coordinate vs free reaction energy / eV).

Figure 9b: Comparison of the activation energies of all the elementary steps (Step 1−7) of OER on CUS on the post-calcined Ir-oxide nanoparticles (reaction coordinate vs activation energy / eV).

Figure 9c: Comparison of the interaction energies of all the elementary steps (Step 1−7) of OER on CUS on the post-calcined Ir-oxide nanoparticles (reaction coordinate vs interaction energy / eV).

Figure 9d: Comparison of the free reaction energies for the one-electron redox transition on BRI for the post-calcined Ir-oxide nanoparticles (reaction coordinate vs free reaction energy / eV).

Figure 9e: Comparison of the activation energies for the one-electron redox transition on BRI for the post-calcined Ir-oxide nanoparticles (reaction coordinate vs activation / eV).

Figure 9f: Comparison of the interaction energies for the one-electron redox transition on BRI for the post-calcined Ir-oxide nanoparticles (reaction coordinate vs interaction energy / eV).

Figure 9g: Comparison of the bridge site fraction for the post-calcined Ir-oxide nanoparticles.

Figure 10a_left: Effective reaction rates of the elementary steps of the OER mechanism on CUS for Ir-oxide nanoparticles calcined at 400 °C (potential, E vs reaction rate, r).

Figure 10a_right: Surface coverage of the adsorbed species on CUS for Ir-oxide nanoparticles calcined 400 °C (potential, E vs surface coverage).

Figure 10b_left: Effective reaction rates of the elementary steps of the OER mechanism on CUS for Ir-oxide nanoparticles calcined at 700 °C (potential, E vs reaction rate, r).

Figure 10b_right: Surface coverage of the adsorbed species on CUS for Ir-oxide nanoparticles calcined 700 °C (potential, E vs surface coverage).

Figure_S1a: XRD diffractograms of as-prepared Ir oxide nanoparticles (2theta vs. intensity /a.u.).

Figure_S1b: XRD diffractograms of Ir-oxide nanoparticles calcined at 400 °C (2theta vs. intensity /a.u.).

Figure_S1c: XRD diffractograms of Ir-oxide nanoparticles calcined at 500 °C (2theta vs. intensity /a.u.).

Figure_S1d: XRD diffractograms of Ir-oxide nanoparticles calcined at 600 °C (2theta vs. intensity /a.u.).

Figure_S1e: XRD diffractograms of Ir-oxide nanoparticles calcined at 700 °C (2theta vs. intensity /a.u.).

Figure_S1f: XRD diffractograms of tabulated reference for tetragonal rutile IrO2 and fcc Ir metal (2theta vs. intensity /a.u.).

Figure S2a-d: Electron diffraction results of Ir-oxide samples calcined at a) 400 °C, b) 500 °C, c) 600 °C, and d) 700 °C.

Figure S3a: SEM images of Ir-oxide samples calcined 400 °C.

Figure S3b: SEM images of Ir-oxide samples calcined 500 °C.

Figure S3c: SEM images of Ir-oxide samples calcined 600 °C.

Figure S3d: SEM images of Ir-oxide samples calcined 700 °C.

Figure S4: a) High-resolution O 1s spectrum of the Ir oxide nanoparticles calcined at 500 °C and 600 °C; b) High resolution C 1s spectrum of the Ir oxide nanoparticles as-prepared and calcined at 400 °C, 500 °C, 600 °C and 700 °C.

Figure S5: XPS survey scan of the Ir oxide nanoparticles calcined at a) 700 °C, b) 600 °C, c) 500 °C, d) 400 °C and e) as-prepared.

Figure S6a: Experimental CV curves recorded at the scan rates of 200, 100, 50, 25, and 200 mV/s on the iridium oxide nanoparticles calcined 400 °C (potential, E vs current density, j).

Figure S6b: ExperimentalCV curves recorded at the scan rates of 200, 100, 50, 25, and 200 mV/s on the iridium oxide nanoparticles calcined 500 °C (potential, E vs current density, j).

Figure S6c: ExperimentalCV curves recorded at the scan rates of 200, 100, 50, 25, and 200 mV/s on the iridium oxide nanoparticles calcined 600 °C (potential, E vs current density, j).

Figure S6d: ExperimentalCV curves recorded at the scan rates of 200, 100, 50, 25, and 200 mV/s on the iridium oxide nanoparticles calcined 700 °C (potential, E vs current density, j).

Figure S7a: Scan rate–normalized CVs for the Ir-oxide samples calcined at 400 °C.

Figure S7b: Scan rate–normalized CVs for the Ir-oxide samples calcined at 500 °C.

Figure S7c: Scan rate–normalized CVs for the Ir-oxide samples calcined at 600 °C.

Figure S7d: Scan rate–normalized CVs for the Ir-oxide samples calcined at 700 °C.

Figure S8: Comparison of average current density j versus scan rate for all post-calcined Ir-oxide samples.

Figure S9: Surface area–normalized cyclic voltammograms recorded at 200mV/s for the Ir-oxide catalysts calcined at 400 °C, 500 °C, 600 °C, and 700 °C.

Figure S10a: Comparison of the experimental and simulated CV curves at the scan rate of 200 mV/s, for the Ir-oxide nanoparticles calcined at 400 °C (potential, E vs current density, j).

Figure S10b: Comparison of the experimental and simulated CV curves across all scan rates for the Ir-oxide nanoparticles calcined at 400 °C (potential, E vs current density, j).

Figure S10c: Free reaction energy diagram for all elementary steps of the oxygen evolution reaction (OER) at E=0V, E=1.23V, and E=1.6V for the Ir-oxide nanoparticles calcined at 400 °C (reaction coordinate vs free reaction energy / eV).

Figure S10d: Identified free reaction energy parameters for steps 1−6 at the electrochemical standard conditions in comparison to DFT-calculated values for the Ir-oxide nanoparticles calcined at 400 °C (reaction step vs free reaction energy / eV).

Figure S11a: Comparison of the experimental and simulated CV curves at the scan rate of 200 mV/s, for the Ir-oxide nanoparticles calcined at 500 °C (potential, E vs current density, j).

Figure S11b: Comparison of the experimental and simulated CV curves across all scan rates for the Ir-oxide nanoparticles calcined at 500 °C (potential, E vs current density, j).

Figure S11c: Free reaction energy diagram for all elementary steps of the oxygen evolution reaction (OER) at E=0V, E=1.23V, and E=1.64V for the Ir-oxide nanoparticles calcined at 500 °C (reaction coordinate vs free reaction energy / eV).

Figure S11d: Identified free reaction energy parameters for steps 1−6 at the electrochemical standard conditions in comparison to DFT-calculated values for the Ir-oxide nanoparticles calcined at 500 °C (reaction step vs free reaction energy / eV).

Figure S12a: Comparison of the experimental and simulated CV curves at the scan rate of 200 mV/s, for the Ir-oxide nanoparticles calcined at 600 °C (potential, E vs current density, j).

Figure S12b: Comparison of the experimental and simulated CV curves across all scan rates for the Ir-oxide nanoparticles calcined at 600 °C (potential, E vs current density, j).

Figure S12c: Free reaction energy diagram for all elementary steps of the oxygen evolution reaction (OER) at E=0V, E=1.23V, and E=1.66V for the Ir-oxide nanoparticles calcined at 600 °C (reaction coordinate vs free reaction energy / eV).

Figure S12d: Identified free reaction energy parameters for steps 1−6 at the electrochemical standard conditions in comparison to DFT-calculated values for the Ir-oxide nanoparticles calcined at 600 °C (reaction step vs free reaction energy / eV).

Figure S13a: Comparison of the experimental and simulated CV curves at the scan rate of 200 mV/s, for the Ir-oxide nanoparticles calcined at 700 °C (potential, E vs current density, j).

Figure S13b: Comparison of the experimental and simulated CV curves across all scan rates for the Ir-oxide nanoparticles calcined at 700 °C (potential, E vs current density, j).

Figure S13c: Free reaction energy diagram for all elementary steps of the oxygen evolution reaction (OER) at E=0V, E=1.23V, and E=1.68V for the Ir-oxide nanoparticles calcined at 700 °C (reaction coordinate vs free reaction energy / eV).

Figure S13d: Identified free reaction energy parameters for steps 1−6 at the electrochemical standard conditions in comparison to DFT-calculated values for the Ir-oxide nanoparticles calcined at 700 °C (reaction step vs free reaction energy / eV).

Figure S14a_left: Effective reaction rates of the elementary steps of the OER mechanism for Ir-oxide nanoparticles calcined at 400 °C (potential, E vs reaction rate, r).

Figure S14a_right: Surface coverage of the adsorbed species for Ir-oxide nanoparticles calcined 400 °C (potential, E vs surface coverage).

Figure S14b_left: Effective reaction rates of the elementary steps of the OER mechanism for Ir-oxide nanoparticles calcined at 500 °C (potential, E vs reaction rate, r).

Figure S14b_right: Surface coverage of the adsorbed species for Ir-oxide nanoparticles calcined 500 °C (potential, E vs surface coverage).

Figure S14c_left: Effective reaction rates of the elementary steps of the OER mechanism for Ir-oxide nanoparticles calcined at 600 °C (potential, E vs reaction rate, r).

Figure S14c_right: Surface coverage of the adsorbed species for Ir-oxide nanoparticles calcined 600 °C (potential, E vs surface coverage).

Figure S14d_left: Effective reaction rates of the elementary steps of the OER mechanism for Ir-oxide nanoparticles calcined at 700 °C (potential, E vs reaction rate, r).

Figure S14d_right: Surface coverage of the adsorbed species for Ir-oxide nanoparticles calcined 700 °C (potential, E vs surface coverage).

Figure S15a: Surface coverage of the bridging hydroxyl (BRI-OH), θ_BRI-OH, for Ir-oxide nanoparticles calcined at 400 °C.

Figure S15b: Surface coverage of the bridging hydroxyl (BRI-OH), θ_BRI-OH, for Ir-oxide nanoparticles calcined at 500 °C.

Figure S15c: Surface coverage of the bridging hydroxyl (BRI-OH), θ_BRI-OH, for Ir-oxide nanoparticles calcined at 600 °C.

Figure S15d: Surface coverage of the bridging hydroxyl (BRI-OH), θ_BRI-OH, for Ir-oxide nanoparticles calcined at 700 °C.