Effect of Mo dopants on improving hydrogen production by redox of iron oxide: catalytic role of Mo cation and kinetic study

• Published in: RSC advances Vol. 3; no. 26; pp. 10341 - 10348
• Main Authors: Wang, Hui, Zhang, Jielan, Wen, Fei, Bai, Jinbo
• Format: Journal Article
• Language: English
• Published: Royal Society of Chemistry 01.01.2013
• Subjects: Activation energy; Catalysis; Catalysts; Cations; Decomposition; Engineering Sciences; Hydrogen production; Iron oxides; Micro and nanotechnologies; Microelectronics; Stores; Graphene nanosheet support; Lithium ion batteries; Electrochemical performance; Iron oxide; Carbon coated
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c3ra22135k

Iron oxide (Fe sub(2)O sub(3)) is a promising substitute for other hydrogen storage materials, which can store/produce hydrogen by a reversible redox process (Fe sub(3)O sub(4) + 4H sub(2) reversible reaction 3Fe + 4H sub(2)O). In order to evaluate the effectiveness of iron oxide for this purpose, a series of Mo-doped iron oxides (Fe sub(2)O-5%Mo, -8%Mo and -10%Mo) were prepared by a hydrothermal synthesis. The catalytic effect of Mo cations on hydrogen production was investigated. The results show that the addition of an Mo ion to Fe sub(2)O sub(3) could improve the hydrogen production in water decomposition at a relatively modest temperature (300-400 degree C) and the Fe sub(2)O sub(3)-8%Mo sample was the most effective one. A reasonable explanation for this result is that the repeated change (Mo super(4+) reversible reaction Mo super(3+) + Mo super(0)) of valence of the Mo ion during the redox process resulted in the change of composition and microstructure of the doped samples, which suppressed sintering. The apparent activation energy of Fe sub(2)O sub(3) and Fe sub(2)O sub(3)-8%Mo at the H sub(2) production step is about 55.5-65.3 and 36.2-45.2 kJ mol super(-1), respectively. The cooperative effect of Mo ions and active Fe on water decomposition is the main reason for lowering the activation energy, which was also the reason for enhancing hydrogen production.