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 molCl2 ^-1 ) which is about 50-55 % of state-of-the-art HCl electrolysis processes.