Preparation And Properties Of Starch-based Porous Carbon/PEG Composite Phase Change Energy Storage Materials

The energy crisis and environmental pollution caused by the massive use of fossil energy have made the development of clean energy and efficient use of energy an important research direction in countries around the world.Phase change energy storage materials can effectively solve the problems of instability and low energy utilization efficiency in energy utilization such as solar energy and wind energy.In this paper,for solving the problems of easy leakage and low thermal conductivity of organic phase change materials,the thermal stability and storage/exothermic properties of different molecular weight PEGs(4000,6000,10000,and 20000)were explored,the effect of viscosity changes on the heat storage/release performance and supercooling of PEG were studied.Then,the porous carbon support material was prepared by hydrothermal carbonization method and KOH activation method using starch as the precursor,the phase change energy storage materials,such as porous carbon/PEG,porous carbon-expanded graphite/PEG and porous carbon-diatomite/PEG composites were prepared by the physical blending method,and their thermal properties were systematically studied.(1)Different molecular weight PEG(4000,6000,10000,20000)were characterized by TG,the viscosity and storage/exotherm curves after adding sodium carboxymethyl cellulose(CMC)and porous carbon were tested.The results show that PEG4000 has the best thermal stability and PEG20000 has the worst thermal stability.The addition of sodium carboxymethylcellulose(CMC)increased the viscosity of PEG,reduced the supercooling degree of PEG,increased the melting and freezing point,and increased the heat conduction rate,but the endothermic rate with the molecular weight of 20,000 decreased.The addition of porous carbon increased the thermal conductivity of PEG,reduced the degree of supercooling,and increased the melting and freezing point.(2)Porous carbon/PEG4000 composite phase change energy storage material was prepared by the physical blending method.The morphological stability of thecomposite phase-change energy storage materials was tested and characterized by using FT-IR,XRD,SEM,BET,DSC and TG,etc.The results show that the porous carbon had a loose and porous network structure with a specific surface area of600.11 m2/g,and PEG was adsorbed on the porous carbon uniformly.Composite phase change materials had good chemical compatibility.The weight loss rate of PEG at 600? was 60.4%,and it had good thermal stability when the temperature was lower than 275?.The melting temperature of PEG was 60.80?,the melting enthalpy was 110.8 J/g,the solidification temperature was 41.71?,and the solidification enthalpy was 100.9 J/g,PEG had relatively high latent heat of phase change.(3)Starch and expanded graphite were used as raw materials to prepare porous carbon-expanded graphite composite support material the by hydrothermal carbonization and KOH activation,and the porous carbon-expanded graphite/PEG4000 phase change storage composites were prepared by the physical blending method.The morphological stability of the phase-change energy storage composite materials were characterized and tested using FT-IR,XRD,SEM,BET,DSC and TG etc.The results show that the specific surface area of porous carbon-expanded graphite reached 613.08 m2/g,which was 12.97 m2/g higher than that of porous carbon.The weight loss rate of composite phase change PEG at600? was 65.67%,and its initial decomposition temperature was 295?.The melting and solidification temperature were 60.52? and 40.48 ?,respectively,and the melting and solidification enthalpy were 119.1 J/g and 112.6 J/g,respectively.Compared with porous carbon/PEG composite phase change energy storage materials,the adsorption capacity of PEG increased by 5.27%,the enthalpy of fusion and enthalpy of solidification increased by 8.3 J/g and 11.7 J/g,respectively,and the thermal stability was also improved.The thermal conductivity of PEG is 0.12 W/mK,the thermal conductivity of porous carbon/PEG composite phase change material was 0.36 W/mK,which was 200% higher than that of PEG.The thermal conductivity of porous carbon-expanded graphite/PEG composite phase change material was 0.63 W/mK,which was 75% higher than the porous carbon/PEG composite phase change material.(4)Porous carbon and diatomaceous earth was used as supporting materials to prepare the porous carbon-diatomite/PEG4000 composite phase change energy storage material by the physical blending method.The morphological stability of the composite phase-change energy storage materials was characterized and testedusing FT-IR,XRD,SEM,BET,DSC,and TG,etc.The results show that the diatomite had a disc-like sieve structure after the treatment,a porous structure with dense and even distribution of micropores was observed.The weight loss rate of PEG at 600? reached 67.42%,the initial decomposition temperature of the composite phase change material was 295?,the melting point was 60.86?,the melting enthalpy was 141 J/g,the freezing point was 42.16?,and the solidification enthalpy was 132.2 J/g.Compared with the porous carbon/PEG composite phase change material,the adsorption capacity of PEG increased by7.02%,the thermal stability was improved,the addition of diatomaceous earth can increase the phase change latent heat of the composite phase change material,and the enthalpy of fusion increased by 30.2 J/ g,the enthalpy of solidification increased by 31.3 J/g.