Preparation Of Form Stable Phase Change Composites And Study On Their Photothermal Energy Storage Properties

As the problem of global energy consumption has become increasingly prominent,the research and application of the use of renewable solar energy for energy conversion and storage have increasingly attracted the attention of the whole society.Phase change materials（PCMs）with excellent energy storage capacity and constant phase transition temperature can be used for thermal conversion and storage of solar energy.As one of the most widely used phase change materials,organic solid-liquid phase change materials have minor volume change,suitable phase transition temperature,and high latent heat during the phase transition process.It is appropriate to apply them to the field of photothermal energy storage.However,organic solid-liquid phase change materials have some problems that need to be solved urgently,such as low thermal conductivity,easy leakage,and single function.In response to these problems,this paper used organic solid-liquid phase change materials as the phase change medium,renewable biomass as raw materials to prepare functionalized porous materials as supporting materials by various methods.The prepared form stable phase change materials（FSPCMs）have good shape stability and can effectively prevent leakage.At the same time,FSPCMs possess excellent solar thermal energy storage capacity and other performance.（1）Renewable pectin and economic attapulgite（ATP）were used as raw materials to prepare hierarchically porous carbonized aerogels.The addition of cations(Ca²⁺)initiates supramolecular bonding of chains in the polymer and enhances the performance of the aerogel.Compared with the direct carbonized biomass materials reported in the literature,the ATPP（ATPP-Pectin）carbonized aerogels prepared this time have enhanced mechanical properties,with a compressive strength of up to 0.4 Mpa at 80%strain.The dodecylamine（DDA）was loaded into the carbonized aerogel by the melt dipping method to obtain a stable phase change material with excellent performance.Furthermore,the chemical structure,microstructure,thermal stability,mechanical properties,heat storage performance,and thermal conductivity of ATPPs and those of as-prepared DDA/ATPP composite PCMs were determined by various characterization techniques.The results demonstrate that ATPPs can effectively improve the shape stability and thermal conductivity of composite PCMs.At the same time,the composite ATPP-15 melts at 26.96℃,the melting enthalpy is 175.7 k J·kg^-1,and the light-to-heat conversion efficiency is 77.5%.The structure and thermal properties of those cost-effective carbon-based FSPCMs reveal their potential application in light and heat storage.（2）A kind of Ti₃C₂/pectin aerogels was prepared by self-assembly of pectin and MXene nanosheet（Ti₃C₂T_x）by solution blending method.Dodecylamine（DDA）was loaded into MXene-pectin aerogels to prepare shaped phase change materials by the melt impregnation method.The results show that the PCM composites with 3 wt.%Ti₃C₂ have a phase change temperature of 25.47℃（at which the human body feels comfortable）,latent heat of phase change of 218.8 k J·kg^-1,and thermal conductivity of 0.1817 W·m^-1·K^-1.The prepared FSPCMs have the characteristics of suitable phase change temperature,high latent heat,good melting/freezing cycle reliability,strong mechanical properties,significant photothermal energy conversion capacity（more than 92%）,and good thermal insulation performance.Therefore,the corresponding pectin-based composites with better light absorption and mechanical properties are expected to have broad application prospects in energy conversion and building energy conservation.（3）Phase change gypsum blocks are prepared by filling the phase change composite material into the calcined gypsum.Dodecanol was adsorbed by expanded graphite and microencapsulated with pectin and sodium alginate solution.The prepared phase-change composite material was combined with the calcined gypsum of construction to prepare a dodecanol/expanded graphite phase-change composite gypsum block.The dodecanol/expanded graphite phase change composite gypsum block has the highest phase change enthalpy value of36.11 k J·kg^-1 and the fracture load of 10800 N.At the same time,the dodecanol/expanded graphite phase change composite gypsum blocks have good thermal insulation ability,have passed the pilot scale-up test,and are reliable building energy-saving materials.