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 Fe3+/Fe2+ redox-mediated cathode is demonstrated for Cl-2 regeneration. HCl is oxidized to generate Cl-2 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 Vis 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(Cl2)(-1)) which is about 50-55% of state-of-the-art HCl electrolysis processes.