Solar hydrogen from a manganese oxide based thermochemical cycle

The three chemical reactions of a new Mn-oxide based thermochemical cycle f or sustainable H-2 production have been investigated. The reactivity of MnO with NaOH has been studied under a inert gas flow and under dynamic vacuum . H-2 and alpha-NaMnO2 were obtained above 750 K as the only products with yields > 92% under both conditions. The equilibrium pressure of the reactio n was determined to be 95+/-2 mbar H-2. Recovery of the Mn-oxide and the Na OH was investigated by hydrolyzing alpha-NaMnO2 in clean H2O and in NaOH-H2 O solutions (5 greater than or equal to c(NaOH) greater than or equal to 0. 01 M). The solid product of the hydrolyses has a chemical composition with a molar ratio Na/Mn approximate to 0.1 which is due to the presence of a bi rnessite-like ternary Na-Mn-oxide and a binary Mn-oxide (Mn3O4). Solar ther mal reductions of Mn-oxides were effected in a direct absorbing gas/particl e reactor open to air. Under mean flux densities of 2000 kW m(-2) the prepa ration of MnO besides Mn3O4 was achieved in air for the first time with suc h a reactor.