Agilent 600 mhz

The morphology was studied via field emission transmission electron microscope (FETEM, FEI Tecnai G2 F20 S-TWIN TMP) operating at 200 kV. Surface elemental analysis was performed on X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra Dld). The structure of the catalysts was characterized by X-ray powder diffraction (XRD, D8 Advance, Bruker), nuclear magnetic resonance measurements (NMR, Agilent 600 MHz) and Fourier-transform infrared spectra (FTIR, Tensor 27, Bruker).

¹⁵N₂ (Wuhan Newradar Special Gas Co. Ltd 99 atom% ¹⁵N) was used as the feeding gas in the labeling experiment. A low-velocity gas flow system was adopted due to the limited supply and expense of ¹⁵N₂. After electrolysis at 0 V vs. RHE for 10 h, 10 ml of the electrolyte was taken out, and its pH was adjusted to 3 by adding 0.5 M H₂SO₄. Then, the solution was concentrated to 2 ml and 0.9 ml of the resulting liquid was taken out, followed by adding 0.1 ml of D₂O as an internal standard. The produced ammonia was quantified using ¹H nuclear magnetic resonance measurements (¹H NMR; Agilent 600 MHz).

For the colorimetric method, the concentration of ammonia in the LiCl solution was determined using the same method as that in distilled water, except that the standing time was changed to 10 min. The concentration of ammonia in the HCl solution was determined using the same method as that in distilled water. For the NMR measurements, the standard curve was constructed by measuring a series of areas of the NMR peak for the reference solutions at different ammonium sulfate concentrations. The weighted linear regression model was used for calibration. The electrolytes in the cathode and acid trap were mixed and concentrated to 30 ml after electrolysis. Then, 0.5 ml of the resulting liquid was taken out, followed by adding 0.1 ml of DMSO-d6. Maleic acid was used as the internal standard. The produced ammonia was quantified by using ¹H NMR spectroscopy (Agilent 600 MHz).