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

Gaseous HCl as a by‐product is often produced from chlorination processes using Cl₂ gas. Onsite Cl₂ regeneration from HCl is highly desirable as it eliminates the need to buy new Cl₂ and dispose HCl waste. A gaseous HCl electrolysis with Fe³⁺/Fe²⁺ redox‐mediated cathode is demonstrated for Cl₂ regeneration. HCl is oxidized to generate Cl₂ and protons in the anode while Fe³⁺ is reduced to Fe²⁺ in the cathode. Simultaneously Fe³⁺ is regenerated by chemical oxidation of Fe²⁺ 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 Cl₂ (124 kJ mol ^?1) which is about 50–55 % of state‐of‐the‐art HCl electrolysis processes.