Research Papers

Solar Hydrogen Productivity of Ceria–Scandia Solid Solution Using Two-Step Water-Splitting Cycle

[+] Author and Article Information
Chong-il Lee

e-mail: lee.c.ab@m.titech.ac.jp

Qing-Long Meng

e-mail: meng.q.ab@m.titech.ac.jp

Hiroshi Kaneko

e-mail: kaneko.h.ac@m.titech.ac.jp

Yutaka Tamaura

e-mail: tamaura.y.aa@m.titech.ac.jp

Department of Chemistry,
Tokyo Institute of Technology,
Ookayama 2–12-1, Meguro-ku, Tokyo
152–8552, Japan

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received October 12, 2011; final manuscript received May 6, 2012; published online June 22, 2012. Assoc. Editor: Wojciech Lipinski.

J. Sol. Energy Eng 135(1), 011002 (Jun 22, 2012) (7 pages) Paper No: SOL-11-1221; doi: 10.1115/1.4006876 History: Received October 12, 2011; Revised May 06, 2012

The reactivity of CeO2–Sc2O3 solid solution for solar hydrogen production via two-step water-splitting reaction has been studied in this work. The CeO2–Sc2O3 solid solution was synthesized by polymerized complex method (PCM) with various Sc content between 0 and 20 mol. %. Analysis results from online direct gas mass spectrometry (DGMS) suggest that Ce3 + formed by CeO2–Sc2O3 solid solution in the O2-releasing step could be completely oxidized by H2O to generate hydrogen and return to Ce4 + in the H2-generation step. A Ce0.97Sc0.03O1.985 generates the largest amount of O2 and H2 among present samples, and the reduction and oxidation ratios are about 9.9% (Ce) and 10% (Ce), respectively. An estimated H2-generation reaction rate is about 4 ml g−1min−1 for Ce0.97Sc0.03O1.985. This value is about seven times greater than that of Ce0.89Zr0.11O2. The high reaction rate of Ce0.97Sc0.03O1.985 makes all formed Ce3 + completely oxidized by H2O in 5 min in the H2-generation step. The reasons for high performance are discussed from the views of lattice distortion and the amount of oxygen vacancies formed in the lattice.

Copyright © 2012 by ASME
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Fig. 1

The phase diagram between Ce and O in the temperature range of (a) 200–1200 °C and (b) 1150–1350 °C. These diagrams are reported in previous study [11,12-11,12].

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Fig. 2

Two-step water splitting experimental set-up

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Fig. 3

Temperature and environmental gas conditions for the two-step water splitting

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Fig. 4

XRD patterns: (A) overall view and (B) enlarged view of each sample. (a) CeO2, (b) Ce0.99Sc0.01O1.995, (c) Ce0.97Sc0.03O1.985, (d) Ce0.93Sc0.07O1.965, (e) Ce0.9Sc0.1O1.95, and (f) Ce0.8Sc0.2O1.9.

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Fig. 5

Lattice constant versus Sc content in CeO2–Sc2O3 solid solution

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Fig. 6

DGMS profiles of (a) Ce0.97Sc0.03O1.985 and (b) Ce0.9Zr0.1O2 (as an example) for two-step water splitting cycle and calibration

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Fig. 7

SEM images of Ce0.97Sc0.03O1.985; (a) after synthesis and (b) after two-step water splitting cycles

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Fig. 8

Reduction and oxidation ratio in each cycle of (a) CeO2 reduction, (b) CeO2oxidation, (c) Ce0.99Sc0.01O1.995 reduction, (d) Ce0.99Sc0.01O1.995 oxidation, (e) Ce0.97Sc0.03O1.985 reduction, (f) Ce0.97Sc0.03O1.985 oxidation, and (g) Ce0.93Sc0.07O1.965




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