Stabilization of salt hydrates using flexible polymeric networks
Joey Aarts, Bas G. P. van Ravensteijn, Hartmut Fischer, O.C.G. Adan, Henk Huinink
Abstract
The use of salt hydrates for thermochemical energy storage is associated with mechanical instabilities during cyclic hydration/dehydration. On the other hand, some salt hydrates do not suffer from these drawbacks, but manufacturing of mm-sized particles is still a challenge. In this work a one pot synthesis method is presented which results in composites using poly (dimethyl siloxane) (PDMS) as binder. Energy densities of 1.14 GJ/m3 and 0.67 GJ/m3 are achieved for a K2CO3 and CaC2O4 composite, respectively. Swelling upon hydration decreases compared to non-stabilized particles. The best K2CO3 composite shows mechanical stability for at least 35 cycles, and the average power output at 50 % conversion increases with cycling to 50–55 kW/m3 at 20 °C and 33 % relative humidity. Also, a stable CaC2O4 composite is made suitable for heat storage. The particle volume and hydration kinetics remain constant for at least 20 cycles. An average power output at 50 % conversion of 5 kW/m3 at 20 °C and 33 % relative humidity is generated. The results from this work show how a one-pot fabrication method can be used to obtain mm-sized particles with enhanced mechanical stability during cycling. Stabilization can be achieved independent of the salt hydrate solubility or material properties.