Spectra 300

Before imaging, the as-prepared catalysts were added into anhydrous ethanol by using an ultrasonator to form a very dilute colloid suspension, then 20 μl suspension was dripped onto 230 mesh Cu grids coated with ultrathin carbon. The high-resolution HAADF-STEM image was acquired using a Thermo Fisher Spectra 300 microscope equipped with an aberration corrector for the probe-forming lens, operated at 300 kV. The beam current was lower than 40 pA and the STEM convergence semi-angle was ~25 mrad, which provided a probe size of ~0.6 Å at 300 kV. The HADDF-STEM images with a 30° tilt of the sample were taken by tilting double tilt holder −30°(α), which can be moved in α (±35°) and β (±30°) directions. The HADDF-STEM image simulations were carried out using Dr. Probe software^{34 (link)}, the parameters were set as same as the experimental condition. The accuracy of simulation results was 0.008 nm/pix.

XRD analysis was carried out by a powder diffractometer (Bruker D8 Advance) with a Cu-Kα (λ = 1.5405 Å) radiation. The morphology and size of the products were characterized by a field-emission transmission electron microscopy (TEM, FEI Tecnai G2 F20) equipped with an energy dispersive X-ray spectroscopy (EDS, Aztec X-Max 80 T). Scanning transmission electron microscope (STEM) imaging was performed on a spherical aberration-corrected STEM instrument, ThermoFisher Spectra 300, equipped with a 5th order aberration corrector. The beam current of the electron probe is set to be ≈50 pA and a typical dose level of ≈0.4–1 × 10⁸ e nm⁻² as used for high-resolution imaging. Afterglow spectra were recorded on an OmniFluo-Xray-JL system (PMT-CR131-TE detector, 185-900 nm) with a mini MAGPRO X-ray excitation source. X-ray photoelectron spectroscopy analyses were performed using Thermo Fisher Scientific K-Alpha with tube voltage 15 kV and tube current 15 mA. To measure the TL glow curves, the NPs were exposed to the X-ray source for 60 s at room temperature. Afterwards signals were recorded by using the LTTL-3DS multifunctional defect fluorescence spectrometer with tube voltage of 50 kV and tube current of 80 μA, while the temperature range was set between 30 and 500 °C at a heating rate of 2 °C s⁻¹. EPR was carried out using a Bruker model A300 spectrometer recorded at 9.852 GHz.

XRD patterns were collected using a Bruker D8 Advance (operating tube voltage of 40 kV, tube current at 30 mA, Cu Kα λ = 1.5406 Å, Germany). The element valances were determined by XPS spectroscopy (Thermo Fisher Scientific K-Alpha, USA). ICP-OES (Agilent ICPOES730, USA) was used to determine element contents. FTIR spectra were recorded using a Nexus 670 FTIR spectrometer over the range of 500–4000 cm^–1. The morphologies and microstructure were characterized by field-emission SEM (Zeiss, S-3500N, Japan) and cold-field-emission spherical aberration corrected TEM (Thermo Fisher Scientific, Spectra 300, USA). EELS was used to analyze the surface elemental valence states and concentration distributions.

Atomic resolution STEM-HAADF images were obtained on a double aberration-corrected S/TEM Thermofisher Spectra 300 at 300 kV with a field emission gun. The probe convergence angle was 24.5 mrad, and the angular range of the HAADF detector was from 79.5 mrad to 200 mrad. iDPC data were also collected on the same microscope with a 24.5 mrad convergence angle using 8 segments annular detector, which exhibits a higher contrast on oxygen anions.
4D-STEM data in Supplementary Fig. 7 were collected on a double aberration-corrected S/TEM Thermofisher Titan G2 at 300 kV with a 22.5 mrad convergence angle. The diffraction patterns of the 4D-STEM datasets were recorded with a 128 × 128 pixel array detector (EMPAD) at an acquisition rate of 1000 frames per second. The scanning area of 2.6 × 2.6 nm was acquired with a scanning step size of 0.2 Å. Maximum collection semi-angle of the EMPAD detector was 67 mrad.
A center of mass (COM) signal image can be obtained directly as the center of mass motion is calculated from each diffraction pattern in the 4D-STEM dataset. A differentiated COM (dCOM) signal image is generated by calculating the divergence of the COM image^{39 (link)}.

The chemical composition of the spent and regenerated powders was determined by ICP-OES (Agilent ICPOES730, USA). The valence state of the surface elements was determined by X-ray photoelectron spectroscopy (XPS; Thermo Scientific K-Alpha, USA). The phase composition was determined by X-ray diffraction (XRD; Bruker D8 Advance, Germany) with Cu Kα radiation in the 2θ range 10–80°. The morphology and microstructure were observed by field-emission scanning electron microscopy (FESEM; Zeiss, S-3500N, Japan) and HRTEM (FEI Talos F200x, USA). A Thermogravimetric analyzer (TG; Mettler-Toledo TG2, Switzerland) coupled with a Fourier Transform Infrared spectrometer (Thermo Scientific IS50, USA) was used to analyze the decomposition of Li₂DHBN. Temperature-dependent XRD was performed from 30 °C to 800 °C at a heating rate of 5 °C min⁻¹ and then kept at 800 °C for 1 h. Electron energy loss spectroscopy (EELS; ThermoFischer Spectra 300, USA) was used to analyze the element valence states.

The transmission electron microscope (TEM) was applied to obtain the cross-sectional view patterns of the Ir/IrO_x film on ITO substrate. The samples for the cross-sectional TEM were prepared by the focused ion beam (FIB). The special aberration-corrected transmission electron microscope (AC-TEM) was performed on the 300 kV Thermo Fisher Spectra 300. For the AC-TEM characterization, the colloidal solution of Ir/IrO_x nanoparticles was diluted to 1% of the initial concentration with methanol. Then, the solution was dripped onto the copper mesh using a pipette gun.