Solar-assisted production of hydrogen and chlorine from hydrochloric acid using hexachloroiridate (III) and (IV)

Abstract

Abstract The production of H 2 and Cl 2 from HCl solution is important in relation to commercial H 2 production, utility load leveling and solar energy storage. The production of H 2 from electrolysis and Cl 2 from photolysis of a 6M HCl solution containing IrCl 6 3 − /IrCl 6 2 − was investigated for this purpose. Using a 1 m 2 solar concentrator, the photolysis of IrCl 6 2 − was carried out, forming IrCl 6 3 − and converting aqueous Cl − ions to gaseous Cl 2 . The amount of IrCl 6 2 − destroyed under photolysis was established using light absorption at 425 nm; corresponding yields for formation of Cl 2 were inferred by stoichiometry. Electrolysis of the solution was carried out at a constant current density. During electrolysis the H 3 O + is reduced at the cathode to form H 2 , while IrCl 6 3 − formed during photolysis is oxidized back to IrCl 6 2 − at the anode. Electrolysis in the presence of the iridium complex proceeds at a lower voltage than the electrolysis of HCl solution itself. Formation of H 2 was inferred from Faraday's laws, as well as from a stoichiometric relationship with the amount of IrCl 6 2 − formed under electrolysis, which was again measured by light absorption at 425 nm. Overall, aqueous HCl/IrCl 6 3 − solutions form IrCl 6 2 − plus H 2 during electrolysis, whereas aqueous HCl/IrCl 6 2 − solutions form IrCl 6 3 − plus Cl 2 during photolysis.