Diatomite-based magnesium sulfate composites for thermochemical energy storage: Preparation and performance investigation

Abstract

Thermochemical storage (TCS) offers a number of advantages over sensible and latent heat based thermal energy storage (TES) technologies, including low heat loss, small volume change and high energy density. However, two of key technological challenges are low cycle stability and slow charging and discharging kinetics. We report here a novel composite TCS material made from MgSO4 and diatomite using an impregnation method. The structures, sorption kinetics, thermal properties and cycle stability of the composite were investigated by using several analytical techniques including scanning electron microscope, surface area measurements, Raman microscope, thermal gravitational analyzer, dynamic vapor sorption analyzer and differential scanning calorimeter. The results show that the porous structure of the diatomite provides water vapor transport channels and contact area between water vapor and MgSO4, leading to an increased hydration rate of MgSO4, hydration state and cycle stability compared with pure MgSO4, and an improved sorption capacity and thermal performance. When MgSO4 in the composites reaches ∼60% by mass, the diatomite tends to be saturated with more MgSO4 in a high hydrated state, resulting in a superior heat storage performance with an energy storage density of 772.9 kJ/kg and a water adsorption capacity of 0.37 g/g in a low to medium temperature range of 80–150 °C.