Pore morphology evolution and atom distribution of doped Fe2O3 foams developed by freeze-casting after redox cycling

Abstract

Chemical looping water splitting systems operate at relatively high temperatures (450–800 °C) to produce, purify, or store hydrogen by the cyclic reduction and oxidation (redox) of a solid oxygen carrier. Therefore, to improve long-term operation, it is necessary to develop highly stable oxygen carriers with large specific surface areas. In this work, highly interconnected doped Fe2O3 foams are fabricated through the freeze-casting technique of a submicrometric camphene-based suspension to prevent Fe sintering and pore clogging during redox operation. The influence of the dopant elements (Al and Ce) over the pore morphology evolution, and redox performances are examined. The use of an Fe2O3 porous structure with initial pore size above 100 microns shows a significant reduction of the sample densification, and the addition of Al2O3 by the citrate method prevent the rapid formation of an Fe3O4 layer at the foams struts that diminish the reoxidation rate step in the redox processing.