Carbon dioxide hydrates for cold thermal energy storage: A review

Cold thermal energy storage provides suitable solutions for electric air conditioning systems to reduce peak electricity use and for solar cooling systems to alleviate energy supply intermittency. Due to the high latent heat (501–507 kJ kg⁻¹), CO₂ hydrates have been widely reported as promising cold storage media that suit a wide range of air conditioning systems i.e. low-temperature, conventional, and high-temperature systems. This paper reviews the research progress on CO₂ hydrate thermodynamics (i.e. phase equilibrium, supercooling, thermal hysteresis, and hydrate reformation), kinetics (i.e. induction time, stochastic nucleation, and memory effect), and effects of transport phenomena on CO₂ hydrate formation (i.e. heat and mass transfer) pertinent to cold thermal energy storage. Limitations of CO₂ hydrate-based cold storage applications are discussed including side effects of additives, the storage of released CO₂ gas, and the use of CO₂ hydrate slurry as a cooling carrier. Successful CO₂ hydrate characterisation methods, thermodynamic and kinetic models, CO₂ hydrate-based cold storage laboratory demonstrations and system simulations are summarised.