Sol-Gel Synthesis of Nanocrystalline Ni-Ferrite and Co-Ferrite Redox Materials for Thermochemical Production of Solar Fu
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Sol-Gel Synthesis of Nanocrystalline Ni-Ferrite and Co-Ferrite Redox Materials for Thermochemical Production of Solar Fuels Rahul R. Bhosale1 , Ivo Alxneit2 , Leo L. P. van den Broeke1 , Anand Kumar1 , Mehak Jilani1 , Shahd Samir Gharbia1 , Jamila Folady1 , Dareen Zuhir Dardor1 1 Department of Chemical Engineering, Qatar University, Doha, Qatar. 2 Solar Technology Laboratory, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland. ABSTRACT In this contribution, we report the synthesis and characterization of Nix Fe3-x O4 and Cox Fe3-x O4 redox nanomaterials using sol-gel method. These materials will be used to produce solar fuels such as H2 or syngas from H2 O and/or CO 2 via solar thermochemical cycles (STCs). For the sol-gel synthesis of ferrites, the Ni, Co, Fe precursor salts were dissolved in ethanol and propylene oxide (PO) was added dropwise to the well mixed solution as a gelation agent to achieve gel formation. Freshly synthesized gels were aged, dried, and calcined by heating them to 600o C in air. The calcined powders were characterized by powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy. Their suitability to be used in STCs for the production of solar fuels was assessed by performing several reduction/re-oxidation cycles using a thermogravimetric analyzer (TGA). INTRODUCTION The world's current energy economy is still based to a large extent on the abundance of fossil fuels. This has led to a rapid depletion of the easily accessible oil reserves resulting in continuously rising oil prices. Furthermore severe environmental problems caused by the CO 2 induced greenhouse effect have begun to become apparent [1-4]. Thus, there is a pressing need to develop technologies to produce carbon free renewable fuels such as H2 or renewable precursors for fuels such as syngas (a mixture of H2 and CO). The latter can be processed to liquid fuels (gasoline, jet fuel) via the Fischer-Tropsch process [5]. Solar radiation is an essentially inexhaustible energy source that delivers about 100,000 TW to the earth. To harvest the solar radiation and to convert it effectively into renewable fuels from H2 O and captured CO 2 provides a promising path for a future sustainable energy economy. One of the potential routes to produce solar fuels is metal oxide based solar thermochemical cycles (STCs) [6]. In these cycles, the first step consists of the endothermic thermal reduction of a metal oxide at elevated temperatures releasing O 2 . This step is achieved by using concentrated solar radiation as an energy source. The second step consists of the slightly exothermic re-oxidation of the reduced metal oxide at lower temperatures by H2 O, CO 2 , or a mixture of the two producing H2 , CO or syngas. Among the many metal oxides investigated so far for solar fuel production, in recent years, research has been focused towards non-volatile mixed metal oxides such as ferrites [7-11]. Ferrites are particularly attractive because their reduced form is a solid and hen
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