Towards stable performance of salt hydrates in thermochemical energy storage: A review

A review is provided on how to achieve stable performance of salt hydrates in thermochemical energy storage. For packed bed application mm-sized particles are required. Stability is divided into different levels: the (sub)crystal and powder level, individual particle (composite) level of which the packed bed is composed, and reactor level. The most prevalent stability issues at each level are discussed as well as the solutions to tackle them using encapsulation, salt in porous matrix, and shaping synthesis techniques. Various advantages and problems connected to these solutions are discussed, as well as the lessons learned from them. It is concluded that most materials lack extensive cyclic testing and powder density measurements. The most promising route identified for stabilization of salt hydrates is through the salt in porous matrix technique, using a well-defined mm-sized porous material with high interconnected porosity.