Generation of H2 and CO by solar thermochemical splitting of H2O and CO2 by employing metal oxides

Generation of H-2 and CO by splitting H2O and CO2 respectively constitutes an important aspect of the present-day concerns with energy and environment. The solar thermochemical route making use of metal oxides is a viable means of accomplishing these reduction reactions. The method essentially involves reducing a metal oxide by heating and passing H2O or CO2 over the nonstoichiometric oxide to cause reverse oxidation by abstracting oxygen from H2O or CO2. While ceria, perovskites and other oxides have been investigated for this purpose, recent studies have demonstrated the superior performance of perovskites of the type Li(1-x)A(x)Mn(1-y)M(y)O(3) (Ln=rare earth, A=alkaline earth, M=various +2 and +3 metal ions), in the thermochemical generation of H-2 and CO. We present the important results obtained hitherto to point out how the alkaine earth and the Ln ions, specially the radius of the latter, determine the performance of the perovskites. The encouraging results obtained are exemplefied by Y0.5Sr0.5MnO3 which releases 483 mu mol/g of O-2 at 1673 K and produces 757 mu mol/g of CO from CO2 at 1173 K. The production of H-2 from H2O is also quite appreciable. Modification of the B site ion of the perovskite also affects the performance. In addition to perovskites, we present the generation of H2 based on the Mn3O4/NaMnO2 cycle briefly. (C) 2015 Elsevier Inc. All rights reserved.