Data for the testing of electrochemical performance and the characterisation of catalysts

Electrochemical experiments were performed in a flow-type electrolytic cell with gas diffusion electrodes and a Nafion 117 proton exchange membrane to isolate the cathode from the anode. A CHI 1140D work station was applied to record the electrochemical responses. The experiments were performed in CO2-saturated 0.5 M KHCO3 solution at ambient temperature and pressure, with a platinum (Pt) foil as the counter electrode and a silver (Ag)/silver chloride (AgCl) electrode filled with a saturated potassium chloride (KCl) solution as the reference electrode. The X-ray diffraction (XRD) spectra were obtained by using a Bruker D8 advance X-ray diffractometer (Karlsruhe, Germany) with a Cu target (λ = 1.54178 Å) selected as the anode target, the scan angle (2θ) set at 10-90°, the sweep speed at 2° min-1, and the voltage and current at 40 kV and 40 mA, respectively. X-ray photoelectron spectroscopy (XPS) spectra were recorded using a thermal ESCALAB 250 (ThermoFisher Scientific, Waltham, MA, USA) with an excitation source of Al Kα (hλ = 1486.6 eV). Binding energies were calculated by referencing the C (1s) binding energy of adventitious carbon contamination, which was estimated to be 284.8 eV. Scan electron microscopy (SEM) was executed on a ZEISS Merlin Compact Field Emission Scanning Electron Microscope with an acceleration voltage of 5 kV. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) characterizations were carried out using a Tecani-G2 T20 and F20 operating at an acceleration voltage of 200 kV. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) was employed to visualize Ni single atoms (Ni SACs). The HAADF-STEM images were obtained using a scanning/transmission electron microscope set to 300 kV and outfitted with a probe spherical aberration corrector.