Solar hydrogen production using Ce{sub 1-x}Li{sub x}O{sub 2-{delta}} solid solutions via a thermochemical, two-step water-splitting cycle
- Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-Ku, Tokyo 1528850 (Japan)
- Solutions Research Laboratory, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-Ku, Tokyo 1528850 (Japan)
The reactivity of Ce{sub 1-x}Li{sub x}O{sub 2-{delta}} (x=0.025, 0.05, 0.075 and 0.1) solid solutions during the redox and two-step water-splitting cycles has been investigated in this work. Thermogravimetric analysis (TGA), X-ray diffraction (XRD) patterns and field-emission scanning electron microscopy (FE-SEM) indicate that there are two reaction mechanisms in the O{sub 2}-releasing step and the shift in the reaction mechanisms occurs in the O{sub 2}-releasing step because of sintering at high temperatures, and a decrease in the concentration of lattice oxygen occurs as the O{sub 2}-releasing step proceeds. The reaction in the O{sub 2}-releasing step follows a second-order mechanism over a temperature range of 1000-1170 Degree-Sign C and a contracting-area model over a temperature range of 1170-1500 Degree-Sign C. According to direct gas mass spectroscopy (DGMS), ceria doped at 5 mol% Li exhibits the highest reactivity in the O{sub 2}-releasing step during both redox cycles in air and two-step water-splitting cycles, whereas ceria doped at 2.5 mol% Li yields the highest amount of hydrogen (4.79 ml/g) in the H{sub 2}-generation step during the two-step water-splitting cycles, which is higher than ceria doped with other metals. DGMS and electrochemical impedance spectroscopy (EIS) suggest that the average reaction rate in the H{sub 2}-generation step is influenced by the concentration of extrinsic oxygen vacancies, and thus, the reactivity in the H{sub 2}-generation step, to some degree, could be tuned by varying the concentration of extrinsic oxygen vacancies (Li content). - Graphical abstract: Average reduction fraction of Ce{sub 1-x}Li{sub x}O{sub 2-{delta}} (x=0.025, 0.05, 0.075 and 0.10) solid solutions versus Li content in the O{sub 2}-releasing step during the redox cycles in air and the two-step water-splitting cycles. Highlights: Black-Right-Pointing-Pointer We have investigated Li-doped ceria for hydrogen production using two-step water-splitting cycles. Black-Right-Pointing-Pointer The sintering effect on the reaction mechanisms was first clarified. Black-Right-Pointing-Pointer The shift of reaction mechanisms occurs during the O{sub 2}-releasing step. Black-Right-Pointing-Pointer The reaction-mechanism shift occurs because of sintering at high temperatures. Black-Right-Pointing-Pointer Doping at 2.5 mol% Li results in the highest H{sub 2} yield and cyclability for hydrogen production.
- OSTI ID:
- 22149869
- Journal Information:
- Journal of Solid State Chemistry, Vol. 194; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
- Country of Publication:
- United States
- Language:
- English
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