The cobalt-oxide/iron-oxide binary system for use as high temperature thermochemical energy storage material

The use of thermochemical reactions is a promising approach for heat storage applications. Redox-reactions involving multivalent cations are recently envisaged for high temperature applications. In temperature range of 900-1000 degrees C, however, where heat storage required for concentrated solar power (CSP) processes only few metal oxides with sufficient heat storage capabilities do exist. Binary systems, on the other hand, could provide a wider range of suitable materials. In the present experimental study the cobalt-oxide/iron-oxide binary system is investigated. For pure iron-oxide the transformation of Fe2O3/Fe3O4 occurs at 1392 degrees C with a reaction enthalpy of 599 J/g. The reaction temperature, however, is far too high for CSP applications. Cobalt-oxide, on the other hand, reacts from Co3O4/CoO at 915 degrees C with an enthalpy of 576 J/g. Iron-doped cobalt-oxides transform at similar temperature as pure cobalt-oxide but the reaction enthalpy gradually decreases with increasing iron content. Microstructural stability and related long-term reversibility of the chemical reaction, however, is higher with respect to pure cobaltoxide. Compositions of around 10% iron-oxide were identified having appropriate enthalpies and being beneficial in terms of microstructural stability. (C) 2013 Elsevier B.V. All rights reserved.