Short summary: Thermochemical cycles for hydrogen production involve a series of reactions, with water decomposition as the net reaction. One of the reactions frequently encountered in these cycles is the reverse Deacon reaction, where chlorine reacts with water vapour to form hydrogen chloride at temperatures exceeding 500 °C.

In this work, an alternative, room-temperature approach is explored in which chlorine is dissolved in liquid water, and the resulting hypochlorous acid is decomposed to HCl and O₂. In the first stage, screening of the potential catalyst was performed, which included synthesis, characterization, and evaluation of catalytic activity towards hypochlorite decomposition. The most active catalyst, RuO₂, was further studied in a proof-of-concept study where the chlorine was successfully converted to a pure HCl solution. Finally, a new, Bi₃Ru₃O₁₁-based catalyst was developed, which showed a significant increase in activity compared to RuO₂.