Acid-Base Model for Thy--Mochemical Water Splitting. Results of Experimental Tests on Manganese-Based Thermochemical Cycles

摘要

An acid-base model for thermochemical water splitting cycles is described, together with the results of its application to cycles based upon reactions of manganese oxides. Experiments confirmed that at least 12 acids-HCl, H sub 2 SO sub 4 , H sub 3 PO sub 4 , MoO sub 3 , NaPO sub 3 , Na sub 4 P sub 2 O sub 7 , SiO sub 2 , Cr sub 2 O sub 3 , TiO sub 2 , Al sub 2 O sub 3 , SnO sub 2 , and Fe sub 2 Onumber-drive the thermal decomposition of NaMnO sub 2 at temperatures below 1400 exp 0 K. Only rather strong bases-NaOH, LiOH, BaO, Li sub 2 CO sub 3 , Na sub 2 CO sub 3 -can drive the steam oxidation of Mn(II) below 1300 exp 0 K. In accord with the model, the acids HCl, H sub 2 SO sub 4 , H sub 3 PO sub 4 , and MoO sub 3 are too strong to be used in Mn(III)/(II) cycles, because their Na, Li, and Ba salts are too stable. Cycles were demonstrated with the other 8 acids and either NaOH or Na sub 2 CO sub 3 . Because such cycles evolve O/sub 2(g)/ in the presence of air, solar furnaces are appropriate sources of thermal energy for them. (ERA citation 05:025449)