Stabilization of salt hydrates using flexible polymeric networks

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.