Sol-Gel Derived NiFe 2 O 4 Modified with ZrO 2 for Hydrogen Generation from Solar Thermochemical Water-Splitting Reactio
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Sol-Gel Derived NiFe2O4 Modified with ZrO2 for Hydrogen Generation from Solar Thermochemical Water-Splitting Reaction Rahul R. Bhosale, Rajesh V. Shende and Jan A. Puszynski Department of Chemical and Biological Engineering, South Dakota School of Mines & Technology, Rapid City, SD 57701-3901, USA. ABSTRACT This investigation reports the synthesis of Ni-ferrite and ZrO2 added Ni-ferrite powdered materials for H2 generation from thermochemical water-splitting reaction. NiFe2O4 was synthesized using sol-gel technique in which salts of Ni and Fe were sonicated in ethanol until a visually clear solution was obtained. To this solution, propylene oxide was added to achieve the gel formation. As-prepared gel was dried at 100oC for 1 h and calcined upto 600oC at a ramp rate of 40oC/min. The calcined sample from the furnace was removed at 600oC and cooled down at room temperature in air. To synthesize NiFe2O4/ZrO2 powdered mixture, ZrO2 nanoparticles were mixed with the calcined ferrite powder using vortex mixer. These powdered materials were analyzed using powder x-ray diffractometer (XRD), BET surface area analyzer and scanning (SEM) and transmission electron microscopy (TEM). As-prepared NiFe2O4 and ZrO2 added NiFe2O4 powdered materials were loaded in an Inconel tubular reactor to investigate H2 generation from four consecutive thermochemical cycles where water-splitting and regeneration was performed at 900o and 1100oC, respectively. INTRODUCTION The harnessing of the huge energy potential of solar radiation and its effective conversion to chemical energy carriers such as H2 is a subject of primary technological interest [1]. Among H2 production technologies [2-4], thermochemical water-splitting coupled to a solar energy source constitute one of the promising options for the H2 production [5]. Solar concentrating systems are able to provide the necessary temperatures to drive the two-step thermochemical water-splitting process [6], which utilizes redox reactions of metal oxides (MO) [1]. In the first step, the reduced MO is oxidized by taking O2 from water producing H2 via water-splitting reaction. Whereas in the second step, the oxidized MO is converted back to its reduced form by releasing O2 during thermal reduction step [7]. Current research efforts are focused on the synthesis of different ferrite materials for water-splitting applications, which include Ni-ferrite, Zn-ferrite, Mn-ferrite, Co-ferrite, Ni-Mnferrite, Ni-Sn-ferrite and Ni-Zn-ferrite. Among the ferrites investigated so far, Ni-ferrite was reported to be the most promising material for H2 production. For instance, Fresno et al.[6] investigated the H2 generation ability of commercially available Ni-ferrite from Sigma Aldrich and reported that this material is capable of producing an average of 7.6 mL/g·cycle of H2 in three consecutive thermochemical cycles where water-splitting and regeneration steps were carried out at 1000oC and 1300oC, respectively. Contrasting to this, Bhosale et al. [7] reported 31.63 mL H2/g·cycle using sol-gel derived Ni-ferrite in
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