Experimental assessment of the cyclability of the Mn2O3/MnO thermochemical cycle for solar hydrogen production

The cyclability of Mn₂O₃/MnO thermochemical cycle for solar hydrogen production has been experimentally evaluated. The results of three consecutive cycles show a stable hydrogen production per mass of initial solid that is in agreement with the maximum expected amount according to the stoichiometry of the process. The characterization of the material recovered after each cycle shows a mixture of different manganese oxide phases that are completely converted into MnO in the subsequent thermal reduction, maintaining the productivity of the cycles. Based on that, a modification of the thermochemical cycle scheme is proposed taking into account the differences observed between the first cycle and the following ones. MnO₂/MnO thermochemical cycle appears as a promising alternative, working in the same temperature range but with a theoretical hydrogen production per unit mass of solid manganese oxide almost twice than that obtained with the conventional Mn₂O₃/MnO cycle. Finally, the results of exergy efficiency of the complete cycle give new insights into the commercial possibilities of the cycle for hydrogen production, demonstrating the sustainable cyclability of the process regarding the manganese containing materials at lower temperatures than those theoretically reported in literature and consequently with higher exergy efficiencies that the common values associated to this cycle.