Electrolysis of the CuCl/HCl Aqueous System for the Production of Nuclear Hydrogen

The copper-chlorine (Cu-Cl) thermochemical cycle uses both heat and electricity to carry out a series of chemical and electrochemical reactions with the net reaction being the splitting of water into hydrogen and oxygen. The process forms a closed loop with all intermediate chemicals being recycled. All of the chemical and electrochemical reactions can be carried out at temperatures that do not exceed about 530°C. Thus, the heat requirement of this process can be satisfied by intermediate temperature nuclear reactors such as the Super Critical Water Reactor (SCWR) developed in Canada by Atomic Energy of Canada Limited (AECL). AECL is particularly interested in developing the electrochemical reactions that comprise the Cu-Cl cycle. There are two variations on the Cu-Cl cycle. In the original cycle copper metal is produced electrochemically by the disproportionation of cuprous chloride (CuCl), which is dissolved in hydrochloric acid (HCl) electrolyte. It is expected that this reaction will be carried out at a temperature that is below 100°C. Hydrogen gas is then produced by a chemical reaction that takes place between the copper metal and gaseous HCl at a temperature of 430–475°C. It was recognized by AECL that these two reaction steps could be replaced by a single electrochemical reaction that generates hydrogen directly. It is expected that this step will also be carried out at a temperature below 100°C. In this process, referred to as the CuCl/HCl electrolysis step, hydrogen gas is produced at the cathode of an electrochemical cell by the reduction of protons that are supplied by aqueous 6 M HCl while cupric chloride (CuCl₂) is produced at the anode by the oxidation of CuCl, which is dissolved in 6 M HCl. The CuCl₂ that is formed is recycled and is used in a reaction with steam at 400°C to produce a copper oxychloride. This reaction is common to both versions of the Cu-Cl cycle. It is the purpose of this paper to present electrochemical results from both half-cell and single-cell studies carried out to verify and understand the CuCl/HCl electrolysis step. Half-cell electrochemical data is presented that demonstrates the practicality of the electrode reactions. Electrochemical data is presented to show that the CuCl/HCl electrolysis step can be carried out in a single-cell. In both the half-cell and single-cell experiments platinum electrocatalysts are used to carry out the desired reactions.