Shape Stabilized Phase Change Materials Based on Polyethylene Glycol/Carbon Black/Multi-Walled Carbon Nanotubes for Latent Heat Thermal Energy Storage Systems

An impending shortage of fossil fuels, combined with the deterioration of the ecological environment, has sparked widespread interest in environmentally friendly renewable energy sources. Utilization of renewable energy and the development of high-performance energy storage solutions are now essential for scientific and technical progress. Thankfully, thermal energy storage (TES) technologies provide a unified answer to the supply continuity issues of sustainable energy storage systems. TES technologies are often classified as latent heat storage, sensible heat storage, or thermochemical energy storage. In general, latent heat storage is larger than sensible heat storage; as a result, less mass and volume of the material is necessary to achieve a high level of energy efficiency. Furthermore, the phase change occurs at a constant temperature, therefore avoiding corrosion by temperature and other handling issues. The PCM's latent heat property is employed to store energy during phase change. The phase shift includes liquid-vapour transition (latent heat of vaporization) and solid-liquid transition (latent heat of fusion), with the latter being used more often. PCMs are being researched in a wide range of industries, including the construction industry, automotive industry, asphalt industry, food industry, textile industry, and battery thermal management systems[1].<br/>Organic PCMs, such as paraffins, fatty acids, esters, alcohols, polyethylene glycol (PEG), etc., are widely used as TES materials since for their chemical stability, low cost, high phase transition enthalpy, adequate phase change temperature range, and little supercooling. Despite the improvement of latent heat storage technology, liquid phase leaks, poor thermal and electrical conductivity, low photoabsorption capacity, and intrinsic rigidity of pristine PCMs have often hindered the efficient collection and release of energy as needed. Liquid phase leakage and low thermal conductivity of pristine PCMs may cause possibly dangerous conditions and slow thermal charging/discharging rates, respectively. Concerning liquid phase leaks, the most common option is to put nanoporous supporting materials into PCMs to produce shape-stabilized composite PCMs through capillary force and hydrogen bonding interactions. Adding carbonaceous materials, two-dimensional boron nitride nanosheets and MXenes owing to their high electrical conduction, outstanding solar absorption, and high thermal conductivity is a thoughtful approach to achieving highly effective electric to thermal conversion and solar to thermal conversion in materials with poor thermal/electrical conductivity and low photoabsorption capacity[2].<br/>Here, PEG is used as a PCM, and carbon black and CNT are used to construct a supporting material and conductive pathway simultaneously. As a representative linear polymer, PEG is a typical and excellent solid to liquid PCM with the superior properties of nontoxicity, relatively high latent heat storage capacity, broad selectivity of molecular weight, low vapor pressure when melted, and excellent thermal and chemical stability. As a result of the shape-stabilized PCM process, PEG is well attached to the porous structure of carbon, and PEG leakage is prevented above PEG's melting points. Based on the interaction of the synergistic conductive network of CB/MWCNT, the thermal conductivity of composite is improved.<br/><br/><b>References</b><br/>[1] K.A.R. Ismail, F.A.M. Lino, P.L.O. Machado, M. Teggar, M. Arlcl, T.A. Alves, M.P.R. Teles, New potential applications of phase change materials: a review, J. Energy Storage, 53 (2022), Article 105202.<br/>[2] X. Chen, H. Yu, Y. Gao, L. Wang, G. Wang, The marriage of two-dimensional materials and phase change materials for energy storage, conversion and applications, EnergyChem, 4 (2022), Article 100071.