TCMs for versatile thermal energy storage - from salt hydrates to oxides

Abstract

Thermal energy storage can play a crucial role in supporting the European Union Green Deal via reducing the need of fossil fuels for industrial process heat as well as domestic heating and warm water supply. In contrast to some applications based on sensible heat or latent heat using phase change materials (PCMs) already on the market the principle of thermochemical energy storage based on reversible chemical solid-gas reactions is still at a rather low technology readiness level [1]. However, several classes of compounds have been identified via a systematic algorithmic database search as promising candidates [2]. Among these the salt hydrates represent a peculiar class of compounds we investigated in the last decade. Presenting a few examples of our research the challenges and chances with respect to cycle stability [3] as well as thermal property tuning [4] are discussed. Furthermore, there is another class of compounds using water for a reversible thermochemical energy storage material, i.e. the metal oxides being hydrated to metal hydroxides. For example, for medium temperature applications the system MgO + H2O ⇌ Mg(OH)2 is presented with respect to the performance enhancement we could achieve via Ca-doping [5].