Preparation And Properties Of Paraffin/Cellulose-Derived Carbon Scaffolds Composites For Electro-Driven Thermal Energy Storage

Paraffin,an important type of organic solid-liquid phase-change materials(PCMs),has received considerable attention as latent heat storage material because of high latent heat storage,minimal or no supercooling,long-term chemical stability and non-corrosiveness.However,similar to other organic PCMs,paraffin has drawbacks such as inferior heat transfer,leakage during phase-change and inability of energy conversion,thereby limiting its application scope.To address these issues,the present study designs new composites of paraffin wax(PW)and cellulose-derived carbon scaffolds,which solve the problem of solid-liquid phase change flow and significantly improve the heat transfer performance as well as enable the electrothermal conversion and storage function to realize the application of composites as thermal management materials.Supporting materials such as porous carbon scaffolds obtained through carbonization of cellulosic materials are ideal for acquiring shape-stabilized PCMs with sufficient conductivity.Thus,raw cotton which has 90%-95%cellulose content was transformed into a conductive carbon scaffold through pyrolysis at 900? under an inert atmosphere.The porosity features were enhanced by treating cotton in aqueous sodium hydroxide solution and washing prior to the pyrolysis.The obtained fibrous network of carbon scaffold successfully encapsulated 85 wt%PW.The composite with leak-proof performance achieved latent heat storage density as high as 182.2 J g-1.Due to the long and interconnected conductive fibers of carbonized cotton,the PCM composite showed a remarkable electrothermal storage efficiency of 81.1%under low voltage(3 V).A carbonized cotton cloth was used as a flexible supporting material to overcome the intrinsic rigidity of shape-stabilized PCM composites,and expanded the application scope.A shape-stable and flexible PCM composite was prepared by infusing PW with optimum loading in the carbonized cloth and through subsequent coating of thermoplastic polyurethane(TPU).With the confinement effect of carbonized scaffold and TPU,the loading of PW reached as much as 50 wt%in the composite with leakage-resistant property.The PCM composite showed flexibility below and above the phase change temperature of PW.Under applied voltage(4 V),the composite achieved electrothermal storage efficiency of 67.4%.Moreover,the PCM composite showed electro-driven motion-sensing property,making it suitable for smart thermal management systems.Cellulose acetate is among the most commercially important cellulose derivatives.It is used to prepare cigarette filters which have become a major cause of solid waste pollution.Therefore,this study employed waste cigarette filters as a source of cellulose for carbonization and to prepare a carbon scaffold.The carbonization of plain cigarette filters results into carbon ash,by contrast the graphene oxide(GO)coated cellulose acetate fibers retained the 3D skeleton after carbonization.The composite was shape-stable with PW content of 80 wt%and achieved latent heat storage density of 157 J g-1.The hybrid carbonized scaffold containing reduced graphene enhanced the electrical conductivity of PCM composite up to 211.3 S m-1.The PCM composite showed outstanding electrothermal storage efficiency of 88.7%under voltage bias of 2 V.Moreover,the simple experimental device demonstrated the energyefficient thermal management function of PCM composite as electrothermal storage element for practical applications.