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Interplay of material thermodynamics and surface reaction rate on the kinetics of thermochemical hydrogen production

Davenport, Timothy C. and Kemei, Moureen and Ignatowich, Michael J. and Haile, Sossina M. (2017) Interplay of material thermodynamics and surface reaction rate on the kinetics of thermochemical hydrogen production. International Journal of Hydrogen Energy, 42 (27). pp. 16932-16945. ISSN 0360-3199.

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Production of chemical fuels using solar energy has been a field of intense research recently, and two-step thermochemical cycling of reactive oxides has emerged as a promising route. In this process, the oxide of interest is cyclically exposed to an inert gas, which induces (partial) reduction of the oxide at a high temperature, and to an oxidizing gas of either H_2O or CO_2 at the same or lower temperature, which reoxidizes the oxide, releasing H_2 or CO. Thermochemical cycling of porous ceria was performed here under realistic conditions to identify the limiting factor for hydrogen production rates. The material, with 88% porosity and moderate specific surface area, was reduced at 1500 °C under inert gas with 10 ppm residual O_2, then reoxidized with H_2O under flow of 600 sccm g^(−1) of 20% H_2O in Ar to produce H_2. The fuel production process transitions from one controlled by surface reaction kinetics at temperatures below ∼1000 °C to one controlled by the rate at which the reactant gas is supplied at temperatures above ∼1100 °C. The reduction of ceria, when heated from 800 to 1500 °C, is observed to be gas limited at a temperature ramp rate of 50 °C min^(−1) at a flow of 1000 sccm g^(−1) of 10 ppm O_2 in Ar. Consistent with these observations, application of Rh catalyst particles improves the oxidation rate at low temperatures, but provides no benefit at high temperatures for either oxidation or reduction. The implications of these results for solar thermochemical reactors are discussed.

Item Type:Article
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Haile, Sossina M.0000-0002-5293-6252
Additional Information:© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. Received 13 March 2017, Revised 23 May 2017, Accepted 25 May 2017, Available online 22 June 2017. This work was supported by the Advanced Research Projects Agency – Energy (award no. DE-AR0000182) of the U.S. Department of Energy. Support for T.C.D. was provided by an EERE Postdoctoral Research Award. SEM micrographs were obtained at the Caltech GPS Division Analytical Facility supported in part by NSF MRSEC under DMR-0080065. We thank Dr. Yong Hao for valuable discussions and for sharing details of earlier studies.
Funding AgencyGrant Number
Advanced Research Projects Agency-Energy (ARPA-E)DE-AR0000182
Subject Keywords:Solar fuels; Thermochemical cycle; Kinetics; Ceria
Issue or Number:27
Record Number:CaltechAUTHORS:20170627-082354890
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Official Citation:Timothy C. Davenport, Moureen Kemei, Michael J. Ignatowich, Sossina M. Haile, Interplay of material thermodynamics and surface reaction rate on the kinetics of thermochemical hydrogen production, International Journal of Hydrogen Energy, Volume 42, Issue 27, 2017, Pages 16932-16945, ISSN 0360-3199, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78593
Deposited By: Tony Diaz
Deposited On:27 Jun 2017 20:15
Last Modified:03 Oct 2019 18:10

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