Chemical-looping water splitting over ceria-modified iron oxide: Performance evolution and element migration during redox cycling

Abstract

Ceria-modified iron oxide exhibits high redox performance superior to that of pure iron oxide, which can inhibit the deactivation caused by sintering of materials. In the present work, the ceria-modified iron oxide is investigated as an oxygen carrier for hydrogen production via chemical-looping water splitting process (CLWS). To identify the role of CeO2, the performance evolution and element migration of the mixed oxides during redox cycling were discussed in detail. Comparing the obvious deactivation of pure iron oxide sample, ceria-modified iron oxide shows relative constant production of hydrogen during the successive recycling water splitting. FeCe20 sample with a CeO2 mole percent of 20% shows the highest average yield of hydrogen (8651 μmol/g) with a Fe average oxygen recovery rate of 67.7% among Fe-Ce mixed oxides with different Ce molar percentage (x = 0, 10, 20 and 40%). In spite of materials sintering, the oxygen releasing/acquiring capacity and reactivity of Fe-Ce mixed oxides are three times higher than that of pure iron oxide after redox treatment. This can be ascribed to the preferable dispersion of Ce-based sub-micro particles (CeO2 and CeFeO3) and enhanced Fe-Ce interactions generated from active sites at the contact interface between iron oxides (mainly Fe3O4 particles) and Ce-based sub-micro particles (CeO2 and CeFeO3) after cycling.