Microencapsulation of molten salt in stable silica shell via a water-limited sol-gel process for high temperature thermal energy storage

[Display omitted] •Microencapsulated potassium nitrate is synthesized via a novel water-limit sol-gel process.•Microcapsules have excellent thermal stability at high temperature up to 400 °C.•The microencapsulation process can provide a high encapsulation ratio of 95.2%.•The microencapsulation process is demonstrated to be precisely controllable. Microencapsulated phase change material as high temperature latent heat storage (LHS) has great potential for renewable energy applications. However, high temperature compatible microencapsulation techniques have rarely been reported so far. Successful microencapsulation of molten salt with high melting point and high latent heat is demonstrated in this work. The microcapsules are demonstrated to be thermally stable at a relatively high melting point of the salt (334 °C) with a high encapsulation ratio (95.2%) which can be well controlled through a Tetraethyl orthosilicate (TEOS) hydrolysis/condensation process. The demonstrated stability and excellent controllability of this process makes the synthesized KNO3@silica microcapsule the first real demonstration of a controllable micro/nanoencapsulation technique that can be used for high temperature applications without much limitation on PCM selection, especially for molten salts.