Electrochemical CO2R was studied at room temperature (20–25°C) under ambient pressure using a three-electrode setup in a flow-cell reactor with an Autolab PGSTAT302N potentiostat. The prepared catalyst was used as work electrode, the work electrode reaction area was 1–4.5 cm2. Ag/AgCl (3.0 M KCl, Pine Instruments) was used as the reference electrode, Pt plate (Tianjin Aida Hengsheng Technology Development Co., Ltd.) and Ni foam (Shenzhen Teensky Technology Co., Ltd.) were used as the counter electrodes in pH 1, 4, 7 and 13.5 solution, respectively. The long-term stability test was carried out in a two-electrode flow cell without using an Ag/AgCl reference electrode and without iR correction. We used a cation exchange membrane (CEM, NafionTM 117, Fuel Cell Store) for electrochemical CO2 reduction in electrolytes at pH 1, 4, 7, and an anion exchange membrane (AEM, Fumasep FAB-PK-130, Fuel Cell Store) at pH 13.5. The catholyte of pH 1 were 0.05 M sulfuric acid (H2SO4) and 3 M potassium chloride (KCl) solution, and pH was adjusted to around 1 by a few drops of 5 M potassium hydroxide (KOH). The catholyte of pH 4 were 3 M KCl solution, and pH was adjusted to around 4 by a few drops of H2SO4. The catholyte of pH 7 were 3 M KCl solution, and pH was adjusted to around 7 by a few drops of 1 M KOH. The catholyte of pH 13.5 were 0.75 M KOH solution. The anolyte of pH 1 and 4 were 0.5 M H2SO4, the anolyte of pH 7 were 1 M KHCO3, and the anolyte of pH 13.5 were 0.75 M KOH. Electrochemical impedance spectroscopy (EIS) was measured to estimate the electrolyte resistance for iR compensation. The electrolyte resistance was measured at open circuit potential in a frequency range from 10 MHz to 0.1 Hz with an amplitude of 10 mV. All potentials versus the reference electrodes were converted to potentials versus the reversible hydrogen electrode (VRHE) using the following equations:
CO2 was passed through the cathodic compartment at a constant flow rate of 20 mL min−1. The gaseous CO2 reduction products were quantified using gas chromatography (Perkin Elmer Clarus 680). The liquid products were quantified using NMR spectroscopy (Bruker AVIII 600 MHz) and dimethyl sulfoxide (≥99.9%, Alfa Aesar) was added as an internal standard. The 1H NMR spectrum was measured by water suppression using the pre-saturation method. All experimental results were repeated at least three times while keeping all conditions consistent.
CO2 was passed through the cathodic compartment at a constant flow rate of 20 mL min−1. The gaseous CO2 reduction products were quantified using gas chromatography (Perkin Elmer Clarus 680). The liquid products were quantified using NMR spectroscopy (Bruker AVIII 600 MHz) and dimethyl sulfoxide (≥99.9%, Alfa Aesar) was added as an internal standard. The 1H NMR spectrum was measured by water suppression using the pre-saturation method. All experimental results were repeated at least three times while keeping all conditions consistent.
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