Low-Voltage Gaseous HCl Electrolysis with an Iron Redox-Mediated Cathode for Chlorine Regeneration

Abstract Gaseous HCl as a by‐product is often produced from chlorination processes using Cl 2 gas. Onsite Cl 2 regeneration from HCl is highly desirable as it eliminates the need to buy new Cl 2 and dispose HCl waste. A gaseous HCl electrolysis with Fe 3+ /Fe 2+ redox‐mediated cathode is demonstrated for Cl 2 regeneration. HCl is oxidized to generate Cl 2 and protons in the anode while Fe 3+ is reduced to Fe 2+ in the cathode. Simultaneously Fe 3+ is regenerated by chemical oxidation of Fe 2+ by oxygen (air) that also produces water. A low operational voltage and high coulombic efficiency are achieved by using a novel composite porous membrane and hydrophobic anode. Specifically, a cell voltage of only 0.64 V is needed at the typical current density of 4 kA m −2 , leading to a low energy consumption of 483 kWh per ton of Cl 2 (124 kJ mol −1 ) which is about 50–55 % of state‐of‐the‐art HCl electrolysis processes.