Photo-electro-chemical chlorination of cuprous chloride with hydrochloric acid for hydrogen production

In this paper, a new photochemical cell is developed and analyzed for copper disproportionation within the Cu–Cl water splitting cycle. In the disproportionation step, cuprous chloride reacts with hydrochloric acid to generate cupric chloride and hydrogen gas. In past literature, it has been demonstrated that this reaction can be conducted electrochemically at 24 bars and 100 °C. This reaction is attractive because it generates compressed hydrogen. Consequently, the work required to compress hydrogen from standard pressure – to 350 bars for example – reduces approximately by 95%. To conduct this reaction electrochemically, the process requires electricity input. Rather than using an external supply, the method proposed in this paper drives the reaction 2CuCl(aq) + 2HCl(aq) → 2CuCl2(aq) + H2(g) with photonic energy derived from solar radiation. The photochemical cell comprises one photochemical and one electrochemical reactor separated by a proton conducting membrane. The electrochemical reactor is a half electrolysis cell where CuCl liquid is disproportionated with hydrochloric acid by releasing protons, according to 2CuCl(aq) + 2HCl(g) → 2CuCl2(aq) + 2H+ + 2e−. The electrons are transferred to the second reactor by an electron-conducting media, consisting of electrodes and an external circuit. In the photochemical reactor, there are supramolecular complexes dissolved in dimethylformamide that generate multi-electrons at active sites under the influence of solar radiation and catalyze water reduction according to 2H2O + 2e− → H2(g) + 2OH−. Gaseous hydrogen is collected from above the second reactor, while hydroxyl ions combine with the protons that cross the PEM to supply water according to 2OH− + 2H+ → 2H2O. The overall process is assisted electrically by a dye sensitized solar cell. An optical system including solar concentration, spectral splitting and an optical fibre is developed for enhanced solar energy absorption to supply thermally and electrically the Cu–Cl cycle with energy input. This paper examines the feasibility and expected efficiency of the photochemical disproportionation cell and describes the potential benefits of the thermo-photochemical water splitting process, in contrast to conventional thermochemical water splitting.

► A new photochemical cell is developed for copper disproportionation and H2 generation.
► The proton conducting membrane separates a photochemical and an electrochemical reactor.
► Supramolecular complexes in DMF generate multi-electrons at active sites.
► Benefits of the thermo-photochemical vs thermochemical Cu–Cl water splitting processes are reported.