Solar water splitting for hydrogen production with monolithic reactors C. Agrafiotis a , M. Roeb b , A.G. Konstandopoulos a, * , L. Nalbandian a , V.T. Zaspalis a , C. Sattler b , P. Stobbe c , A.M. Steele d a Chemical Process Engineering Research Institute, Center for Research and Technology—Hellas (CERTH/CPERI), P.O. Box 361, 57001 Thermi-Thessaloniki, Greece b Deutsches Zentrum fu ¨ r Luft- und Raumfahrt e.V. (DLR), Institut fu ¨ r Technische Thermodynamik, Solarforschung, D-51170 Ko ¨ ln, Germany c Stobbe Tech Ceramics (STC), Vejlemosevej 60, DK-2840, Holte, Denmark d Johnson Matthey Fuel Cells Centre, Sonning Common, RG4 9NH Reading, UK Received 21 July 2004; received in revised form 12 November 2004; accepted 23 February 2005 Available online 4 June 2005 Communicated by: Associate Editor Sixto Malato-Rodrı ´guez Abstract The present work proposes the exploitation of solar energy for the dissociation of water and production of hydrogen via an integrated thermo-chemical reactor/receiver system. The basic idea is the use of multi-channelled honeycomb ceramic supports coated with active redox reagent powders, in a configuration similar to that encountered in automo- bile exhaust catalytic aftertreatment. Iron-oxide-based redox materials were synthesized, capable to operate under a complete redox cycle: they could take oxygen from water producing pure hydrogen at reasonably low temperatures (800 °C) and could be regenerated at tem- peratures below 1300 °C. Ceramic honeycombs capable of achieving temperatures in that range when heated by con- centrated solar radiation were manufactured and incorporated in a dedicated solar receiver/reactor. The operating conditions of the solar reactor were optimised to achieve adjustable, uniform temperatures up to 1300 °C throughout the honeycomb, making thus feasible the operation of the complete cycle by a single solar energy converter. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Water-splitting; Solar; Redox materials; Iron oxide; Honeycomb reactors; Hydrogen 1. Introduction The harnessing of the huge energy potential of solar radiation and its effective conversion to chemical energy carriers such as hydrogen is a subject of primary techno- logical interest. One of the reactions with tremendous economical impact because of the low value of its reactants is the dissociation of water (water splitting) to 0038-092X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.solener.2005.02.026 * Corresponding author. Tel.: +30 2310 498192; fax: +30 2310 498190. E-mail address: agk@cperi.certh.gr (A.G. Konstandopou- los). Solar Energy 79 (2005) 409–421 www.elsevier.com/locate/solener