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

Corresponding Author

* Mu Yang, yangmu@ustb.edu.cn

* Ge Wang, gewang@mater.ustb.edu.cn

Keywords: carbon quantum dots, divinyl benzene, 3D network carbon, phase change materials,

thermal energy storage

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Figure S1. Color evolution of the reaction system at different time stage: (1) 0 h, (2) 0.5 h, (3) 1 h, (4) 2

h, (5) 3 h, (6) 4 h.

Notably, facts have proved that CQDs obtained from the aldol reaction of acetone assisted

by NaOH and DVB is productive. Overall, Figure S1 clearly presents the color changes of the

reaction process, which was gradually evolved from pink to dark brown. Simultaneously, the

state of the reaction system was transformed from liquid, tremellose to solid.

Figure S2. (a) FTIR spectrum, (b) XRD pattern of CQDs with 0% DVB.

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Figure S3. TEM images of the products at different calcining stages with 0% DVB, (a) room

temperature, (b) 700 °C, (c) 800 °C, (d) 900 °C.

Figure S4. SEM images of porous carbon obtained at different contents of DVB at 800 °C,

(a) 0%, (b) 1%, (c) 2%, (d) 3%.

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Figure S5 compares the XRD patterns of porous carbon samples obtained from diverse

calcination conditions. As can be seen, two broad peaks at about 25° and 44° are detected in

XRD data, corresponding to the characteristic diffraction peaks (002) and (101) of graphitic

carbon, respectively. No other diffraction peaks were observed, confirming that 3D porous

carbon maintains high purity. The diffraction peaks of the carbon samples are gradually

enhanced as increasing calcination temperature, indicating that the temperature, to some extent,

favors the crystallization behavior of carbon material. The diffraction peaks of the samples

prepared with DVB are evidently stronger than that of the corresponding samples without DVB,

indicating that the introduced DVB can promote the crystallization and graphitization of porous

carbon.

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Figure S5. XRD patterns of CQDs-derived porous carbon.

The functional groups of porous carbon samples obtained from different calcination

temperatures and DVB content were studied by FTIR (Figure S6). The typical stretching

vibrations of -OH at 3435 cm-1, -CH3 at 2960 cm-1, -CH2- at 2870 and 1080 cm−1, C=O at 1710

cm−1, and C=C at 1660 cm−1 are observed. Similar occurrence of FTIR spectra with and without

DVB is reasonable since the contained functional groups in DVB such as C-H and C=C are all

detected in the aldol reaction process. Therefore, adding DVB does not affect the species of

functional groups of 3D porous carbon.

Figure S6. FTIR spectra of CQDs-derived porous carbon, (a) before cross-linking, (b) after cross-linking.

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XRD patterns presented in Figure S7 clarify that there is an excellent chemical

compatibility between 3D porous carbon and pure PEG8000. The typical diffraction peaks at

19°and 23° are assigned to pure PEG8000 crystals. Compared with pure PEG8000, all the sharp

and intense diffraction peaks corresponding to PEG8000 are straightforward observed in the

fabricated composite PCM, revealing that the crystallization behavior of PEG 8000 is still

maintained after it is impregnated in the porous carbon prepared with or without the introduction

of DVB. This observation indicates that the integration between PEG8000 and porous carbon is a

simple physical hybrid without influencing the crystallinity of PEG8000. Thus, the synthesized

porous carbon is particularly acceptable as an advantageous carrier for thermal energy storage

due to the superior chemical compatibility.

Figure S7. XRD patterns of PEG8000 @ CQDs-derived porous carbon composite PCMs.

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FTIR spectra of the composite PCMs was performed to explore the interaction of the

functional groups between pure PEG8000 and supporting material. The FTIR of pure PEG8000

shown in Figure S8 is in good consistency with the literature, which exhibits the representative

stretching vibrations of C-H at 965 and 2890 cm-1, corresponding to -CH2 of pure PEG8000. At

the same time, the stretching vibrations of C–O and –OH of PEG8000 are also examined at 1110

and 3445 cm-1, respectively. More significantly, all the characteristic peaks of pure PEG8000 are

also detected in the FTIR spectrum of the composite PCMs, including C-H, C-O and –OH

stretching vibrations. Meanwhile, the functional groups of primary porous carbon obtained with

or without DVB, such as C-OH, C-H, C=O and C=C stretching vibrations, are also observed in

the FTIR spectrum of the composite PCMs. Additionally, no crucial new peaks are found,

indicating that the obtained PEG8000@porous carbon composite PCMs is just a simple physical

combination without any chemical interaction between PEG8000 and porous carbon. On the

basis of XRD and FTIR data, it is concluded that PEG8000 was successfully impregnated into

the 3D porous carbon without destroying the crystalline of pure PEG8000.

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Figure S8. FTIR spectra of PEG8000 @ CQDs-derived porous carbon composite PCMs.

Figure S9. SEM images of PEG8000 @ CQDs-derived porous carbon composite PCMs, (a) 55 wt% loading

at 700 °C, (b) 60 wt% loading at 800 °C, (c) 65 wt% loading at 900 °C, (d) 70 wt% loading at 700 °C, (e) 75

wt% loading at 800 °C, (f) 85 wt% loading at 900 °C, (a-c) before cross-linking, (d-f) after cross-linking.

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Figure S10. DSC thermogram of PEG8000 @ CQDs-derived porous carbon composite PCMs.

Table S1. Thermal characteristics of PEG8000 @ CQDs-derived porous carbon composite PCMs

PCMs Loading (wt%) Tm/Tf (°C) △Hm/△Hf (J/g) Theoretical △Hm/△Hf

(J/g)

700-0%DVB@PEG8000 55% 60.36/39.44 69.4/61.4 106.0/96.7

800-0%DVB@PEG8000 60% 62.41/40.96 89.6/80.3 115.6/105.5

900-0%DVB@PEG8000 65% 63.19/41.13 109.5/98.2 125.3/114.3

700-3%DVB@PEG8000 70% 60.06/37.15 122.5/110.8 134.9/123.1

800-3%DVB@PEG8000 75% 63.42/40.42 136.4/123.5 144.5/131.9

900-3%DVB@PEG8000 85% 63.73/39.23 160.3/145.8 163.8/149.5

Pure PEG8000 100% 63.89/35.60 192.7/175.9 192.7/175.9

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Figure S11. (a, b) Pore diameter distribution and (c) pore structure of CQDs-derived porous carbon before

and after loading PEG8000, (d, e) thermal characteristics of PEG8000 @ CQDs-derived porous carbon

composite PCMs.

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Figure S12. (a, b, c) TGA curve of CQDs-derived porous carbon before and after loading PEG8000, and (d, e,

f) corresponding DTG thermogram.

Figure S13. Thermal conductivities of corresponding maximum loading content of various CQDs-derived

porous carbon materials.

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Thermal cycling properties is also essential to the practical feasibility of the composite

PCMs. Thus, the fabricated composite PCMs should be still thermally stable via undergoing

numerous melting and freezing cycles. Figure S14 illustrates little change in the latent heat after

long-term service cycles, indicating no seepage of liquid PEG8000 during the heating-cooling

cycling test. Meanwhile, it is noted that there is no evident difference at the melting and freezing

temperature of the composite PCMs before and after the thermal cycling. This observation

indicates that our developed PEG8000@porous carbon PCMs is indeed thermally cycling stable.

Figure S14. DSC thermogram of PEG8000 @ CQDs-derived porous carbon composite PCMs after 50

times thermal cycling.

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Figure S15. Digital photographs of shape-stabilized ability of composite PCMs with

maximum loading content.

Figure S16. Leakage test of different composite PCMs, (a, e) pure PEG8000,

(b) 700-0%DVB@55%PEG8000, (c) 800-0%DVB@60%PEG8000,

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(d) 900-0%DVB@65%PEG8000, (f) 700-3%DVB@70%PEG8000,

(g) 800-3%DVB@75%PEG8000, (h) 900-3%DVB@85%PEG8000.

Figure S17. The quality change of composite PCMs was measured at different thermal

treatment time over the phase transition temperature. (a) 700-0%DVB@55%PEG8000,

(b) 800-0%DVB@60%PEG8000, (c) 900-0%DVB@65%PEG8000, (d) 700-

3%DVB@70%PEG8000, (e) 800-3%DVB@75%PEG8000, (f) 900-3%DVB@85%PEG8000.

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Figure S18. Time-temperature curves of the CPU before and after infiltrating PCMs (inset shows digital photo

of the CPU and corresponding schematic diagram after infiltrating PCMs).

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