Ar carrier

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.

Photocatalytic methane halogenation experiments were performed in CH₄ atmosphere at room temperature using sodium chloride as halogenation agent. Typically, 100 mg sample and specific amounts of NaCl (e.g., 10 mg, 20 mg) were dispersed in 5 mL water in a home-made quartz reactor with a diameter of 6 cm. The sample was sonicated for 5 min to form a uniform suspension and transferred in an oven at 80 °C for 5 h. After drying, 100 µL water was dropped into the notch on the reactor. The reactor was purged with CH₄ (99.999%) for 30 min and sealed with rubber seals. Then the reactor was irradiated by a 300 W xenon lamp (PLS-SXE300, Perfect light) with a lighting area of 28.26 cm². After irradiation for 4 h, the reacted gas was detected by gas chromatography (GC, 7890B, Ar carrier, Agilent) equipped with a methanation reactor (i.e., a nickel catalyst tube), a flame ionization detector (FID) and a thermal conductivity detector (TCD) for the determination of methane halides, hydrocarbons, H₂, CO and CO₂.