Thin Film Metal Ferrite Spinels for Solar-thermochemical Redox Cycles to Split Water

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0966201WeimerThere is a need to develop cost-effective, renewable energy processes for the production of clean fuels such as hydrogen gas (H2). If H2 can be obtained cost effectively by the splitting of water using concentrated sunlight, then it is possible to operate a fuel cell using renewable H2 to generate electricity or to synthesize other fuels based on renewable H2. Intellectual Merit The overall objective of the proposed research is to develop a fundamental understanding of the ability of metal ferrite spinels to split water into hydrogen gas via a solar-thermal reduction/oxidation (REDOX) cycle. The focus of the research is nickel ferrite (NixFe3-xO4) produced through atomic layer deposition (ALD) on zirconia and alumina substrates. The ALD process allows for precise control of the atomic ratio of Ni/Fe in this material, and also has the potential to provide tight control over the mass loadings of the active ferrite on high surface area substrates.The performance of various ferrite materials and alternative water splitting cycles will be evaluated for their potential to produce H2. Variables to be investigated include ferrite stoichiometry, substrate composition, substrate surface area, REDOX temperatures, rate of reduction heating, and water concentration for oxidation. Specific measurements include REDOX reaction rates and thermochemical cycling using thermogravimetric analysis (TGA) for both thermal reduction at up to 1500 C and steam oxidation at up to 1200 C; depth profiling via X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) to evaluate chemical and structural changes during REDOX cycling; and finally, atomic force microscopy (AFM) to evaluate the robustness of ferrite materials and to assess the possibility of "islanding" resulting from sintering. Experiments are planned to carry out the REDOX cycles under simulated solar-thermal conditions using a High Flux Solar Furnace equipped with a TGA for real-time measurement of heating and cooling rates. By all of these approaches, the importance of diffusion vs. kinetic rate limitations on the splitting of water to H2 by metal ferrite spinels can be assessed.The proposed research is potentially transformative because metal ferrite materials produced through the ALD process have unique a potential to provide high hydrogen gas production rates at the efficiencies needed to make solar-thermal hydrogen production technology viable. Broader ImpactThe education activities will make use of existing NSF (REU) and Department of Education programs (GAANN) to recruit and train undergraduate and graduate students in the proposed research, including students from under-represented groups. Outreach to K12 will also be organized through these programs using students involved in the proposed research.