Study On The Construction And Thermal Storage Performance Of ZIF-67 Derivative-based Photo-thermal Phase Change Energy Storage Integrated Material

As a clean renewable energy source,solar energy is susceptible to weather,time and space,and has intermittent,transient and periodic problems,resulting in a mismatch between energy supply and demand in space and time and a low effective utilization rate.As a kind of solar energy storage technology,organic phase change heat storage technology has the characteristics of high heat storage density and long storage period.However,organic phase change materials have the problems of low thermal conductivity and easy leakage of phase change,and weak absorption of sunlight,and often do not have the ability of photo-thermal conversion.ZIF-67derivatives are metal/carbon composites obtained by high-temperature carbonization of ZIF-67under inert atmosphere.Since ZIF-67 is a zeolite-like molecular sieve topological material formed by tetra-ligand self-assembly of metallic cobalt and imidazole,ZIF-67 derivatives have well-developed pore structure,good thermal conductivity and photo-thermal conversion ability as the support body.Therefore,this thesis proposes a research idea of constructing integrated photothermal phase change energy storage materials by vacuum melting method with ZIF-67derivatives as the support body.The thermal storage properties of the shaped phase change material were evaluated by differential scanning calorimetry（DSC）and thermal constant analyzer,and the interaction between the support and the phase change core material was elucidated by combining N₂ adsorption-desorption,Fourier infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）and Raman spectroscopy（Raman）characterization.To reveal the influencing mechanism of the thermal storage performance and deformation ability of the photo-thermal phase change energy storage integrated materials constructed based on ZIF-67 derivatives.（1）The effects of Co700 on the thermal storage properties and deformability of fatty acids with different carbon chain lengths（myristic acid（MA,C14）,stearic acid（SA,C18）and sorbic acid（BA,C22））were investigated using ZIF-67 derivatives（Co700）as supports.The results showed that the average pore size of Co700 expanded from 1.63 nm to 2.63 nm after carbonization of ZIF-67 at 700℃,and the leakage rates of MA/Co700,SA/Co700 and BA/Co700 were 1.32%,2.89%and 5.21%at a loading rate of 50 wt.%,respectively.Compared with MA（0.171 W/（m·K））,SA（0.180 W/（m·K））,BA（0.177 W/（m·K））,its thermal conductivity is 0.442 W/（m·K）,0.464 W/（m·K）and 0.458 W/（m·K）,which is an improvement of 158.5%,157.8%and 158.7%,respectively.（2）The tannic acid etching of ZIF-67 was used to directionally modulate the pore structure of ZIF-67 derivatives to further enhance the deformation ability of the phase change core material,and the effect of modulating the tannic acid etching time on the pore structure of the support was investigated.The results showed that when the tannic acid inscription was applied to the cores,the cores were not able to be used in the process.The results showed that the pore volume of HX-C increased from 0.240 cm³/g to 0.498 cm³/g and the average pore diameter increased from 2.63 nm to 9.69 nm when the tannic acid etching time was increased from 0 min to 10 min.The thermal conductivity（0.469 W/（m·K））is 156.11%higher than that of SA（0.180W/（m·K））,and the photo-thermal conversion efficiency is up to 76.29%,and there is no morphological change or leakage during the phase change process,and the good thermal storage capacity is still available after 100 repeated storage/exhaust cycles.（3）Zn-doped ZIF-67 derivatives were used to regulate the pore structure to further enhance the thermal conductivity and shaping ability of the phase change core material,and the effect of the regulated Zn doping amount and carbonization temperature on the pore structure of the support was investigated.The results show that modulating the Zn doping amount and carbonization temperature can effectively regulate the Co_xT pore structure,and the Co_xT pore volume expands to 0.551 cm³/g～0.939 cm³/g and the average pore diameter is 7.05 nm～15.90nm compared with that of Co700（0.260 cm³/g）and the average pore diameter（2.63 nm）.Among them,SA/Co₂900 has 78.69%thermal storage efficiency,73.82%photo-thermal conversion efficiency and 201.67%higher thermal conductivity（0.543 W/（m·K））compared to SA（0.180 W/（m·K））.SA/Co₂900 has no morphological changes and leakage during the phase change process,and still has good thermal storage capacity.