Journal
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY
Volume 37, Issue 8, Pages 7017-7025Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijhydene.2011.10.124
Keywords
Thermochemical water splitting; Hydrogen production; Manganese oxide
Categories
Funding
- Comunidad de Madrid [S2009/ENE-1617]
- European Social Fund [S2009/ENE-1617]
- Ministerio de Ciencia e Innovacion of Spain (Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica) [2008-20]
- Fondo Europeo de Desarrollo Regional (FEDER) [PSE-120000-2009-3]
- Universidad Rey Juan Carlos
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In this work, a complete thermodynamic study of the first step of the Mn2O3/MnO thermochemical cycle for solar hydrogen production has been performed. The thermal reduction of Mn2O3 takes place through a sequential mechanism of two reaction steps. The first step (reduction of Mn2O3 to Mn3O4) takes place at teomperatures above 700 degrees C, whereas the second reaction step (reduction of Mn3O4 to MnO) requires temperatures above 1350 degrees C to achieve satisfactory reaction rates and conversions. Equilibrium can be displaced to lower temperatures by increasing the inert gas/Mn2O3 ratio or decreasing the pressure. The thermodynamic calculations have been validated by thermogravimetric experiments carried out in a high temperature tubular furnace. Experimental results corroborate the theoretical predictions although a dramatically influence of chemical kinetics and diffusion process has been also demonstrated, displacing the reactions to higher temperatures than those predicted by thermodynamics. Finally, this work demonstrates that the first step of the manganese oxide thermochemical cycle for hydrogen production can be carried out with total conversion at temperatures compatible with solar energy concentration devices. The range of required temperatures is lower than those commonly reported in literature for the manganese oxide cycle obtained from theoretical and thermodynamic studies. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
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