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

• Perovskite oxides based on Mn are ideal for the two-step thermochemical splitting of CO2 and H2O.
• In Ln1−xAxMnO3 perovskite (Ln=rare earth, A=alkaline earth) both Ln and A ions play major roles in the thermochemical process.
• H2O splitting is also achieved by the use of the Mn3O4-sodium carbonate system.
• Thermochemical splitting of CO2 and H2O using perovskite oxides is explained.
• Mn based perovskites.

Generation of H2 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 Ln1−xAxMn1−yMyO3 (Ln=rare earth, A=alkaline earth, M=various +2 and +3 metal ions), in the thermochemical generation of H2 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 µmol/g of O2 at 1673 K and produces 757 µmol/g of CO from CO2 at 1173 K. The production of H2 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.

Ln0.5A0.5Mn1−xMxO3 (Ln=lanthanide; A=Ca, Sr; M=Al, Ga, Sc, Mg, Cr, Fe, Co) perovskites are employed for the two step thermochemical splitting of CO2 and H2O for the generation of CO and H2.Figure optionsDownload as PowerPoint slide