Thermochemical energy storage using silica gel: Thermal storage performance and nonisothermal kinetic analysis

The benefits of thermochemical heat storage include high-energy storage density, long storage time, and negligible heat loss during storage. Silica gel has recently been widely studied as a heat storage material. However, most of the research has focused on its heat storage performance in the reactor; the form of water inside silica gel and the specific heat storage mechanism remain to be clarified. We employed nuclear magnetic resonance to investigate changes in the internal water binding form and content of silica gel before and after water adsorption and determined the equation for the thermochemical reaction. We further investigated the effects of temperature and humidity on the adsorbability of silica gel. The theoretical heat-storage density of silica gel was 1029.63 kJ/kg. Kinetic analyses of desorption gave an activation energy of 66.75 kJ/mol, suggesting that the most probable mechanism function is a 3D diffusion model. The diffusion of water vapor in micropores is the limiting step for the reaction. Silica gel is highly competitive with other thermochemical heatstorage materials, considering the heat-storage density, reaction difficulty, and cycling performance.