J. Phys. IV France 09 (1999) Pr3-331-Pr3-335
Solar hydrogen from a manganese oxide based thermochemical cycleM. Sturzenegger1, J. Ganz2, P . Nüesch1 and Th. Schelling1
1 High-Temperature Solar Technology, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland
2 Amstein & Walthert AG, 8050 Zurich, Switzerland.
The three chemical reactions of a new Mn-oxide based thermochemical cycle for sustainable H2 production have been investigated. The reactivity of MnO with NaOH has been studied under a inert gas flow and under dynarnic vacuum. H2 and α-NaMnO2 were obtained above 750 K as the only products with yields > 92 % under both conditions. The equilibrium pressure of the reaction was determined to be 9±2 mbar H2. Recovery of the Mn-oxide and the NaOH was investigated by hydrolyzing α-NaMnO2 in clean H2O and in NaOH-H2O solutions (5 ≥ c(NaOH) ≥ 0.01 M). The solid product of the hydrolyses has a chemical composition with a molar ratio Na/Mn ≈ 0.1 which is due to the presence of a birnessite-like ternary Na-Mn-oxide and a binary Mn-oxide (Mn3O4). Solar thermal reductions of Mn-oxides were effected in a direct absorbing gas/particle reactor open to air. Under mean flux densities of 2000 kW m-2 the preparation of MnO besides Mn3O4 was achieved in air for the first time with such a reactor.
© EDP Sciences 1999