Avance av 3 400

The isotopic labeling experiment used K¹⁵NO₃ with ¹⁵N enrichment of 99% as the feeding N-source to clarify the source of ammonia. 1 M KOH was used as the electrolyte and K¹⁵NO₃ with a concentration of 1 M was added into the cathode compartment as the reactant. After the electrolysis, 0.1 mL of DMSO-d₆ and 0.1 mL of 6 mM DSS solution were added into 0.4 mL of the electrolyte, followed by adding 0.05 mL of HCl (0.1 M) to adjust the pH of the solutions. Then the obtained ¹⁵NH₄⁺ was identified on a Varian 400 MHz NMR spectrometer (Bruker AVANCE AV III 400).

After each electrolysis, the gaseous products in the headspace of the cathode side or the gas bag were analyzed by the gas chromatography (GC, 7890A and 7890B, Ar carrier, Agilent). The sampled gas was separated by three packed columns. H₂ was detected by thermal conductivity detector (TCD). CO was converted to CH₄ by a methanizer and then analyzed by flame ionization detector (FID). CH₄ and C₂H₄ were analyzed by another FID. The gas product quantification was determined using a serious of standard curves of H₂, CO, CH_4, and C₂H₄. For liquid products analysis, ¹H NMR (Bruker AVANCE AVIII 400) was used. Five hundred milliliters of catholyte after electrolysis was mixed with 100 µL of D₂O and 0.02 µL of dimethyl sulfoxide (DMSO). DMSO was added as an internal standard. The 1D ¹H spectrum was measured with water suppression. The faradaic efficiency of each product was calculated using the following equation:
$$\mathrm{FE}\left(\%\right)=(n_{\mathrm{e}}\times n\times F)/Q\times 100\%$$ where F is the Faraday constant (96 485 C mol⁻¹); n is the mole amount of the product; n_e is the number of electrons that are needed to produce one molecule of product (n_e = 2, 2, 2, 6, 8, 12, 12, and 18 for H₂, CO, HCOOH, CH₃OH, CH₄, C₂H₄, C₂H₅OH, and n‐C₃H₇OH, respectively); Q is the total amount of charge (in units of coulombs) passed through the working electrode.

The ¹⁴N and ¹⁵N isotopic labeling experiments were conducted using ¹⁴N₂ and ¹⁵N₂ as the feeding gases (99% enrichment of ¹⁵N in ¹⁵N₂ feeding gas, Supplied by Hefei Ninte Gas Management Co., LTD). Prior to use, ¹⁴N₂ and ¹⁵N₂ feeding gases were pre-purged by the Cu-Fe-Al catalyst, CrO₃ column, 1.0 mM H₂SO₄ solution (20 mL) and distilled water (20 mL) to eliminate the potential NO_x and NH₃ contaminants based on the reported protocols^{45 (link),46 (link)}. After the electrochemical reaction at −0.25 V (vs. RHE) for 1 h, the reaction solution of both cathodic and anodic chambers (100 mL) was concentrated to 2.0 mL at 80 °C. Then, 1.0 mL of above solution mixed with 0.2 mL of D₂O was used for ¹H NMR spectroscopy measurement (Bruker AVANCE AV III 400). The ¹H NMR analysis and calibration curve construction were carried out in accordance with the reported method.

TEM images and high-resolution TEM image were performed by using a JEOL-2010 TEM with an acceleration voltage of 200 kV. The Sn K-edge XAFS was measured at the Shanghai Synchrotron Radiation Factory and the National Synchrotron Radiation Laboratory, China. Thermal gravimetric analysis (TGA) of the as-synthesized samples were carried out on a Shimadzu TA-50 thermal analyser at a heating rate of 10 °C min⁻¹ from room temperature to 700 °C in air. The liquid products were quantified by nuclear magnetic resonance (Bruker AVANCE AV III 400) spectroscopy. CO₂ adsorption isotherms measurements for all the synthetic samples were carried out by using an automatic microporous physical and chemical gas adsorption analyser (ASAP 2020M+C).

XRD patterns were recorded by using a Philips X’Pert Pro Super diffractometer with Cu-Kα radiation (λ = 1.54178 Å). XPS measurements were performed on a VG ESCALAB MK II X-ray photoelectron spectrometer with an exciting source of Al Kα = 1486.6 eV. The liquid products were examined on a Varian 400 MHz NMR spectrometer (Bruker AVANCE AV III 400). SEM images were taken using a Hitachi SU8220 scanning electron microscope. TEM images were taken using a Hitachi H-7650 transmission electron microscope at an acceleration voltage of 100 kV. SAED were carried out on a JEOL ARM-200F field-emission transmission electron microscope operating at an accelerating voltage of 200 kV using Cu-based TEM grids. Inductively coupled plasma atomic emission spectroscopy (Atomscan Advantage, Thermo Jarrell Ash, USA) was conducted to determine the concentration of Ag species. X-Ray Fluorescence Spectrometer (XRF-1800, SHIMADZU) was used to qualify the molar ratio of Ag to P for the GDE of Ag₃PO₄ cubes. The in situ ATR-FTIRS measurements were carried out on a Nicolet iS50 with a wavenumber resolution of 4 cm⁻¹ at room temperature.