Modulating Electronic Structure of NiMoO₄ by Ultralow-Content Iridium Single Atoms for Synergistically Boosting Urea Oxidation Dataset

1. Experimental section1.1 chemicalsNi(NO3)2⋅6H2O and (NH4)6Mo7O24⋅4H2O were purchased from Sinopharm Chemical Reagent Co. Ltd., China. Iridium (IV) oxide (IrO2 , 99.9%), Iridium(III) 2,4-pentanedionate (C15H21O6Ir, ≥97% ) and potassium hydroxide pellets (KOH, ≥85%) were purchased from Aladdin. Commercial Pt/C (20 wt%) was purchased from Zhengzhou Feynman Biotechnology Tech Co., LTD. Deionized (DI) water was obtained from a Millipore system. All reagents were utilized without further purification.1.2 Preparation of electrodesPretreatment of Nickel foamNickel foam (NF, thickness of 2.0 mm) was acquired from Kunshan guangshengjia New Material Co., Ltd. All the NF (1 cm × 4 cm) used as substrates were cleaned by ultrasonic treatment: firstly, they were washed in 3.0 M HCl for 15 minutes, and then successively washed in ethanol and DI water for 30 minutes, respectively.Preparation of NiMoO4/NF electrode. The NiMoO4/NF electrode was prepared via a hydrothermal method. Briefly, 0.04 mol of Ni (NO3)2⋅6H2O and 0.04 mol of (NH4)6Mo7O24⋅4H2O were dissolved into 75 mL of water in sequence with vigorously stirring for 1 h. After that, a pretreated NF (1 cm × 4 cm) and the above solution were transferred into a 100 mL Teflon-lined stainless-steel and kept at 150 ℃ for 6 h. The resulting electrodes were washed with ethanol/waterand for several times and dried in a vacuum at 60 ℃. Ir/NiMoO4/NF electrode. The Ir/NiMoO4/NF electrode were prepared by atomic layer deposition (ALD) using the as-prepared NiMoO4/NF as support. Typically, the NiMoO4/NF was transferred into a homemade hot-wall, closed-chamber ALD reactor. Ir deposition was carried out at a chamber temperature of 250b°C by sequentially exposing NiMoO4/NF to Ir (acac)3 (maintained at 180°C) and ozone generated by an ozone generator. The pulse, exposure, and purge times for Ir (acac)3 were 7, 25, and 35 s, respectively, while those for ozone were 2, 15, and 28 s, respectively. The as-synthesized electrodes were named as xIr-NiMoO4/NF, where x represents the number of Ir ALD cycles (x=2, 6, 8, 10, 12, and 15).1.3 CharacterizationsScanning electron microscopy (SEM) measurements were conducted on a Zeiss Gemini 300 microscope at an accelerating voltage of 20 kV. Transmission electron microscopy (TEM) characterization was performed using a Zeiss Sigma 300 instrument operating at 200 kV. Power X-ray diffraction (XRD) was operated at D8 ADVANCE with Cu Kα radiation (λ = 0.154 nm). Aberration-corrected high angle annular dark-field scanning transmission electron microscopy(HAADF-STEM) images and mapping were acquired utilizing a JEOL ARM 300F2 TEM/STEM, equipped with a spherical aberration corrector and energy-dispersive X-ray spectroscopy (EDS) and operated at 200 kV. X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha) spectra were obtained at 120 W. All XPS spectra were calibrated against the C 1s peak at a binding energy of 284.8 eV.X-ray absorption fine spectroscopy (XAFS)X-ray absorption spectroscopy (XAS) measurements at the Ni, Mo, and Ir edges were carried out at the ID26 beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The storage ring was operated at an electron energy of 6.0 GeV under top-up mode, ensuring a highly stable incident photon flux during data acquisition. The incident X-ray energy was selected using a Si (311) double-crystal monochromator, providing high energy resolution suitable for detailed XANES and EXAFS analyses. Higher-order harmonics were suppressed by detuning the monochromator. XAS spectra at the Ni and Mo K-edges were collected in transmission mode using ionization chambers placed before and after the sample. For the Ni K-edge, the energy was scanned from approximately 8.20 to 9.00 keV, while for the Mo K-edge, the energy range covered approximately 19.8 to 21.2 keV, ensuring adequate coverage of the pre-edge, XANES, and EXAFS regions. In contrast, XAS measurements at the Ir L₃-edge were performed in fluorescence detection mode using a multi-element silicon drift detector (SDD) positioned at 90° relative to the incident beam, which is appropriate for samples with low Ir content. The Ir L₃-edge spectra were collected over an energy range of approximately 11.10 to 12.30 keV. For Ni and Mo measurements, the samples were prepared by mixing the finely ground powders with cellulose and pressing them into self-supported pellets with appropriate thickness to achieve optimal absorption in transmission mode. For the Ir measurements, the samples were prepared by uniformly spreading the powders onto Kapton tape, and stacking multiple layers to optimize the fluorescence signal while minimizing self-absorption effects. All measurements were conducted at room temperature under ambient conditions. Energy calibration was performed by simultaneously measuring Ni, Mo, and Ir metal foils, with the first inflection points of the corresponding absorption edges used as internal energy references.Extended X-ray absorption fine structure (EXAFS) analysisThe spectra were normalized with respect to the edge height after subtracting the pre-edge and post-edge backgrounds using Athena software. To extract EXAFS oscillations, background was removed in k-space using a five-domain cubic spline. The corresponding k-space data, k2χ(k), was then Fourier transformed. EXAFS curve fitting was carried out with Artemis software using ab initio-calculated phases. The EXAFS fitting results of coordination number (CN), bond distance (R (Å)) and Debye-Waller factor (σ2) are given at Table S1