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 Cl gas. Onsite Cl regeneration from HCl is highly desirable as it eliminates the need to buy new Cl and dispose HCl waste. A gaseous HCl electrolysis with Fe /Fe redox-mediated cathode is demonstrated for Cl regeneration. HCl is oxidized to generate Cl and protons in the anode while Fe is reduced to Fe in the cathode. Simultaneously Fe is regenerated by chemical oxidation of Fe 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 , leading to a low energy consumption of 483 kWh per ton of Cl (124 kJ molCl2 ) which is about 50-55 % of state-of-the-art HCl electrolysis processes.