Contents lists available at ScienceDirect Nano Energy journal homepage: www.elsevier.com/locate/nanoen Full paper Highly graphitized 3D network carbon for shape-stabilized composite PCMs with superior thermal energy harvesting Xiao Chen, Hongyi Gao, Mu Yang ⁎ , Wenjun Dong, Xiubing Huang, Ang Li, Cheng Dong, Ge Wang ⁎ Beijing Key Laboratory of Function Materials for Molecule & Structure Construction, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, PR China ARTICLE INFO Keywords: Carbon quantum dots Divinyl benzene 3D network carbon Phase change materials Thermal energy storage ABSTRACT One major barrier obstructing their scale engineered adoption of phase change materials (PCMs), currently, is their low thermal conductivity, which drastically constrains the power capacity. Our target is to enhance the PCMs thermal conductivity without evidently altering other thermal property criteria. Herein, we propose a facile, low-cost and controllable strategy to construct compactly interconnected 3D celosia-like highly graphi- tized thermally conductive network carbon via carbon quantum dots (CQDs) deriving from acetone and divinyl benzene (DVB). Novel function of CQDs is firstly developed for superior thermal energy harvesting, thus ex- panding their conventional fluorescence and catalysis field to novel thermal energy storage. Importantly, our constructed 3D graphitized network carbon better infiltrates macromolecule polyethylene glycol (PEG) and fully releases crystallization via controllable crosslinking reaction. This strategy simultaneously integrates sufficient power capacity and incremental thermal conductivity (enhanced by 236%) of the PCMs, and thermal enthalpy is considerably approaching the theoretical value. Alternatively, the composite PCMs are thermally and durably stable. These results indicate that resulting shape-stabilized PCMs are a very promising candidate for renewable thermal energy storage in virtue of the superior comprehensive properties. 1. Introduction Emerging thermal energy storage of PCMs stimulates a smart, fea- sible and attention-inspired approach for more energy storage and utilization in virtue of their inherent high volumetric energy density and small temperature variation during latent heat release and retrieval [1–6]. Currently, PCMs are predominantly utilized in thermal energy management system due to their smaller volume evolution and less energy loss [7–10]. Nevertheless, leakage issue and low thermal con- ductivity of pure PCMs tremendously constrain the energy storage ef- ficiency and charging-discharging ability, thus hindering their broad- scale practical utilization. Conventionally, porous supports are employed to prepare shape-stabilized composite PCMs, which guar- antee large thermal energy storage capacity, and simultaneously ad- dress the leakage of pure PCMs. Preliminary reports have certified that average pore size of the supports is exceedingly essential for thermal properties of shape-stabilized composite PCMs [11,12]. Briefly, if the mean pore size is too small, the PCMs molecular motion might be ob- structed; conversely, if it is too large, capillary force is not sufficient to package the liquid PCMs [13]. For instance, Wang and Li have reported that macromolecules PEG are not appropriately infiltrated into some microporous and mesoporous supports with very low enthalpy or even zero due to relatively strong confinement effect on molecule motion [12,14]. Hence, promising supports are anxiously further exploited for infiltrating PEG with large thermal storage capacity and superior charging-discharging ability. Except for the leakage issue, another major barrier of pure PCMs is their inherent low thermal conductivity, which initiates the hysteresis of thermal response. Adding high-thermal conductive additives is a simple and straightforward method to enhance thermal conductivity, including metal [15], carbon nanotube [16], carbon nanofiber [13] and graphene [17]. However, inadequate additives only obtain limited en- hancement of thermal conductivity due to large thermal resistances in the interfacial regions. Ample quantity of additives significantly pro- motes thermal conductivity with the consequence of obviously under- mining energy storage density [18–21]. Moreover, some dispersed ad- ditives might be unstable due to interface effect during phase transition [17]. Additionally, surface functionalization of the additive is devoted to reducing the interfacial thermal resistance and promoting the com- patibility between the support and the additive. Nevertheless, en- hancement effect is still insufficient due to inadequate functionalization [22]. Three-dimensional graphitized network carbon is a promising https://doi.org/10.1016/j.nanoen.2018.03.075 Received 10 February 2018; Received in revised form 27 March 2018; Accepted 30 March 2018 ⁎ Corresponding authors. E-mail addresses: yangmu@ustb.edu.cn (M. Yang), gewang@mater.ustb.edu.cn (G. Wang). Nano Energy 49 (2018) 86–94 Available online 31 March 2018 2211-2855/ © 2018 Published by Elsevier Ltd. T