(Figure 2.7c),[107] heat‐to‐electricity (Figure 2.7d),[108] and photo‐to‐heat‐to‐electricity (Figure 2.7e)[105] routes, providing a strong support for the popularization of advanced energy‐related devices and systems associated with functional PCMs. Also, both solid–liquid and solid–solid polymeric phase change composites can realize these energy conversion routes.
2.4.1 Electro‐to‐Heat Conversion
Electric thermal storage technique based on PCMs is expected to improve the utilization efficiency of power generation equipment and exhibits broad prospects in the field of off‐peak electricity. Unfortunately, the electrical conductivity of PCMs is inherently low, which makes it impossible to directly employ them for electro‐to‐heat conversion. It is usually necessary to incorporate functional fillers to improve the electrical conductivity of phase change composites, and carbon materials, including biomass carbon,[110] carbon nanofiber (CNF),[111] CNT,[109] and graphene[112], are preferentially considered. Of critical importance is the electro‐to‐heat conversion and storage efficiency (ηe), which can be defined by the ratio of stored heat energy to applied electric energy during phase change process and determined by the electro‐thermal calculation Eq. (2.2).
Table 2.4 Thermal conductivity of polymeric phase change composites.
| Material systems | Processing methods | Thermally conductive filler loading | Melting enthalpy (Jg−1) | Thermal conductivity (W m−1 K−1) | Thermal conductivity enhancement (%) |
|---|---|---|---|---|---|
| PEG/diatomite/silver nanoparticle[84] | Vacuum impregnation | 7.2 wt% | 111.3 | 0.82 | 127 |
| PEG/EVM/silver nanowire[51] | Physical blending and impregnation | 19.3 wt% | 99.1 | 0.68 | 172 |
| PEG/SiO2/cupper[85] | Sol–gel and in‐situ doping method | 2.1 wt% | 110.2 | 0.414 | 15 |
| PW/silver‐PVP nanowire aerogel[87] | Vacuum impregnation | 5.43 wt% | ∼163 | 0.49 | ∼133 |
| PEG‐co‐N,N′‐dihydroxyethyl aniline/single‐walled CNT[88] | Vacuum evaporation | — | 100.5 | 0.334 | 25 |
| PEG/single‐walled CNT[90] | Solution blending | 10 wt% | 165.4 | 3.43 | 1329 |
| PEG/SiO2/CF[91] | Sol–gel and in‐ situ doping method | 3 wt% | 142.6 | 0.45 | 73 |
| PEG/EG[54] | Melt blending | 10 wt% | 161.2 | 1.324 | 344 |
| PEG/GO/GNP[92] | Solution blending | 6 wt% | 167.4 | 1.72 | 493 |
| PEG/unsaturated polyester resin/GNP[93] | Free radical copolymerization and solution blending | 2 wt% | 140.8 | 0.67 | 131 |
| PEG/single‐walled CNT[89] | Vacuum impregnation | 8 wt% | 162.1 | 2.73 | 950 |
| PEG/GNP[89] | Vacuum impregnation | 4 wt% | 169.3 | 3.11 | 1096 |
| Poly(hexadecyl acrylate)/cellulose/graphene[94] | Atom transfer radical polymerization (ATRP) and injection molding | 9 wt% | 78 | 1.32 | 560 |
| PEG/biological porous carbon[16] | Vacuum impregnation | 14.6 wt% | 158.8 | 4.489 | 953 |
| PEG/cellulose‐graphene aerogel[68] | Vacuum impregnation | 5.3 wt% | 156.1 | 1.35 | 463 |
| PEG/microcrystalline cellulose‐GNP aerogel[95] | Vacuum impregnation | 1.51 wt% | 182.6 | 1.03 | 232 |
| PEG/GO‐GNP aerogel[55] | Vacuum impregnation | 2.23 wt% | 181.5 | 1.43 | 361 |
| PEG/cellulose nanofiber‐GNP hybrid‐coated melamine foam[96] | Vacuum impregnation | 0.65 wt% | 178.9 | 0.26 | 189 |
| PEG/Si3N4 nanowires[97] | Solution blending | 10 wt% | 152.3 | 0.362 | 89 |
| PEG/SiO2/Al2O3[99] | Ultrasound‐assisted sol–gel and in‐situ doping method |
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