Analysis of Different Factors Affecting the Product Selectivity of Electrochemical CO₂ Reduction Modeled in a Flow Cell

Abstract: Using renewable energy sources, the electrochemical CO₂ reduction (ECR) into industrially important feedstock is a promising technology to neutralize the carbon cycle and generate energy-dense fuels. Herein, the ECR modeling in a flow cell to produce formate using Sn electrode is presented. We show the effect of different factors such as pressure, velocity, cell potential on the faradaic efficiency and current density of several products and pH around the cathode. The results show that high pressure is required to achieve high current density to maintain a constant faradaic efficiency at a constant velocity. For 2.7 V cell potential, the formate faradaic efficiency increases by 18% when the velocity is increased by an order of magnitude and this variation is not explicit at high-pressure values. The great influence on the formate current density can be observed at a constant cell potential when the pressure is increased, provided that the reduction process limits the mass transfer. At atmospheric pressure and 3.1 V cell potential, enhancing the velocity improves the cathode usage to perform CO₂ reduction because decreased concentration boundary layers are observed at high velocity, which improves the CO₂ flux for the cathode and also provides the CO₂ across the cathode height. Moreover, different electrolytes; sodium bicarbonate (NaHCO₃), potassium sulfate (K₂SO₄), potassium chloride (KCl), sodium sulfate (Na₂SO₄), along with the electrolyte used in the present study, potassium bicarbonate (KHCO₃) have also been experimentally investigated to demonstrate and understand their effects on ECR in detail. The results of the present work can provide useful insights for future experimental research studies on flow cells to adopt optimized operating conditions, consequently improving the overall ECR efficiency.