Multiple Thermochemical Water-Splitting Cycles for H2 Generation Using Sol-Gel Derived Ferrites In A Packed Bed Reactor

Multiple Thermochemical Water-Splitting Cycles for H₂ Generation Using Sol-Gel Derived Ferrites In A Packed Bed Reactor.

Rahul R. Bhosale, Rajesh V. Shende, Jan A. Puszynski

Department of Chemical & Biological Engineering,

South Dakota School of Mines & Technology, Rapid City, SD 57701

Two-step thermochemical water-splitting process which utilizes mixed valence metal oxide i.e. ferrite based redox reactions is one of the green ways of producing H₂. In this process, the first step belongs to endothermic reduction of ferrite at elevated temperatures by releasing O₂. Whereas, the second step corresponds to the oxidation of the reduced ferrite by taking O₂ from water and producing H₂ via water-splitting reaction at lower temperatures. As the current research trends in H₂ generation via thermochemical water-splitting process are focused towards higher levels of H₂ production at lower operating temperatures, it is believed that ferrite nanoparticles synthesized by using sol-gel technique will significantly improve the H₂ yield¹. Sol-gel derived ferrite nanoparticles with higher specific surface area are believed to be potential candidates to overcome the hydrodynamic limitations associated with this process and might provide higher number of active sites for water-splitting reactions resulting into higher yields of H₂. In this investigation, phase pure ferrites that include Ni-/Zn-/Sn-/Mn-/Co-ferrite and doped ferrites such as Ni-Zn-/Ni-Mn-/Ni-Co-/Co-Zn-/Co-Mn-ferrite were synthesized using sol-gel technique. As-synthesized gels were aged for 24 h and heated rapidly in a muffle furnace at 600^oC in air environment and quenched. The calcined powder thus obtained was characterized using powder X-ray diffraction, BET surface area analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ferrite powder was placed in a packed bed reactor and water-splitting reaction was performed at different temperatures. After water-splitting reaction, the material was regenerated in the temperature range of 900^oC – 1100^oC and reused for multiple thermochemical cycles. An attempt was made to perform tens of thermochemical cycles at lower water-splitting and regeneration temperatures of 800 – 1100^oC. Synthesis and characterization of ferrites and transient H₂ profiles obtained using online H₂ sensor during multiple thermochemical cycles at various experimental conditions will be presented. Furthermore, efforts are underway to investigate the water-splitting reaction kinetics and transport modeling of the thermochemical water-splitting in a packed bed reactor.

1.      Rahul R. Bhosale, Rajesh V. Shende, Jan A. Puszynski, Thermochemical water-splitting for H₂ generation using sol-gel derived Mn-ferrite in a packed bed reactor, International Journal of Hydrogen Energy, 2011 (In press).