1 Introduction
Solar radiation energy, as the core driving force for Earth's life activities and human development, is crucial for sustainable development through its efficient utilization
[1-2]. Converting incident light energy into thermal energy is one of the important pathways to achieve solar energy utilization, with its efficiency core depending on the material's light harvesting capability and photothermal conversion efficiency
[3]. However, the significant spatiotemporal uneven distribution of solar resources poses severe challenges to stable energy supply
[4]. In this context, high-efficiency thermal energy storage technologies, particularly latent heat storage based on phase change materials (PCMs), have become key solutions for enhancing solar energy utilization rates and reliability due to their high energy storage density and near-constant temperature heat output characteristics
[5-6].
Among various thermal energy storage media, organic PCMs (such as paraffin, polyethylene glycol, fatty acids, etc.) have attracted significant attention in the field of thermal energy storage due to their advantages of high energy storage density, a wide range of selectable melting points, low risk of phase separation, and good cycling stability.
[7]However, the application of such PCMs in actual solar-thermal conversion and storage systems still faces significant challenges, mainly limited by the following inherent defects: first, low intrinsic thermal conductivity leads to insufficient heat transfer and release rates; second, narrow solar spectrum absorption bandwidth and limited spectral response capability severely constrain the improvement of solar-thermal conversion efficiency.
[8].
To overcome these limitations, researchers have combined three-dimensional porous carrier materials with strong light-harvesting and high thermal conductivity properties with PCMs to construct a three-dimensional composite PCM system featuring synergistically enhanced "photothermal conversion-heat transfer-phase change storage." Preferred three-dimensional porous carriers include aerogels, carbon foams, metal foams, expanded graphite, metal-organic frameworks (MOFs), and their derivatives. These materials not only provide stable encapsulation for PCMs thanks to their high specific surface area but also promote heat transfer by constructing efficient thermal conduction pathways, thereby comprehensively improving the photothermal conversion performance of the composite PCMs. Based on multiple physical mechanisms such as plasmonic local heating, non-radiative relaxation of electron-hole pairs, and molecular thermal vibrations, and combined with optimized design of materials and microstructures, three-dimensional composite PCMs ultimately achieve efficient conversion and storage from light energy to thermal energy, and then to latent heat of phase change.
This review focuses on the latest research progress in integrated photo-thermal-storage three-dimensional composite PCMs. It first analyzes the multi-scale synergistic mechanisms of light harvesting, photothermal conversion, and thermal energy storage. Building on this, it deeply explores the design strategies, structure-property relationships, and optimization pathways of photothermal PCMs based on various three-dimensional porous carriers (aerogels, carbon foams, metal foams, expanded graphite, MOFs, and their derivatives). Furthermore, combined with typical application cases, it comprehensively outlines key breakthroughs of such materials in frontier fields including smart wearables, biomedicine, building energy efficiency, seawater desalination, and extreme environment protection (
Figure 1); finally, this paper summarizes the current key scientific and technical challenges facing integrated photo-thermal-storage three-dimensional composite PCMs and, from an interdisciplinary integration perspective, proposes a forward-looking outlook on future development directions.
2 Mechanism of Photothermal Conversion and Storage in Phase Change Materials
Photothermal conversion is the core link in achieving solar-driven thermal energy storage; its essence is the process by which photothermal fillers absorb photon energy and effectively convert it into thermal energy. After photons of specific wavelengths are absorbed by the photothermal fillers, they trigger the excitation of internal electrons; subsequently, these excited electrons return to the ground state through methods such as non-radiative relaxation, releasing the absorbed photon energy in the form of heat during this process.
[9-11]. The photothermal conversion efficiencies of different photothermal fillers vary significantly, which is primarily determined by the response characteristics of their electronic band structures (such as bandgap size, band edge positions, and defect state density) to incident light radiation; these factors directly affect the material's light absorption efficiency and energy relaxation pathways.
[12-13].
Thermal energy storage mainly includes two methods: sensible heat storage and latent heat storage. Sensible heat storage achieves heat storage through changes in the heat capacity of the storage medium (manifested as temperature rise or fall), without undergoing a phase change during the process; common media include solids, liquids, and gases.
[14]. In contrast, latent heat storage utilizes the absorption or release of large amounts of latent heat when PCMs undergo a phase transition. Latent heat storage offers significant advantages due to its high energy density characteristic, while the inherent near-isothermal nature of the phase change process can effectively optimize heat transfer. This feature not only facilitates precise temperature control but also significantly reduces the risk of local overheating, thereby enhancing the thermal management performance of the system.
[15-17]. In composite PCMs, the photothermal conversion process provides the necessary thermal energy input for latent heat storage through three microscopic physical mechanisms: plasmonic local heating effects, non-radiative relaxation of excited electron-hole pairs, and molecular thermal vibrations.
[18].
2.1 Localized surface plasmon resonance effect of metals
The localized surface plasmon resonance (LSPR) effect is a unique physical phenomenon triggered by the collective coherent oscillation of conduction band electrons in sub-wavelength metal nanostructures, which confines incident light to the nanoscale and significantly enhances light-matter interactions.
[19-20]. When the energy of incident photons resonates with the LSPR mode, free electrons in the metal are excited to oscillate in phase with the electromagnetic field, forming plasmons; this process is accompanied by intense electromagnetic field enhancement and a high optical absorption cross-section.
[21-22]. Subsequently, the plasmons decay rapidly, transferring energy to individual electron-hole pairs via Landau damping.
[23-25]. This process completes rapidly without photon energy loss, and the resulting high-energy electrons are termed "hot carriers".
[23,26-27]. Next, the hot carriers undergo electron-electron collision relaxation, transferring energy to low-energy electrons and achieving thermalization within the electron system. Subsequently, energy is transferred to the metal lattice via electron-phonon scattering, causing the lattice temperature to rise.
[28]. Finally, the thermal energy accumulated within the metal structure is released into the surrounding environment through phonon-phonon collisions, completing the conversion and transfer of light energy to thermal energy.
[12].
2.2 Interband/intraband transitions and non-radiative relaxation in semiconductors
In addition to metal plasma effects, non-plasma semiconductor materials can also generate photothermal effects through direct interband/intraband electron transitions. When the energy of incident photons is greater than or equal to the semiconductor bandgap, electron-hole pairs are excited. The energy of the excited state can be released via radiative recombination (luminescence) or non-radiative relaxation
[29-30]. During the non-radiative relaxation process, energy is released in the form of phonons (quanta of lattice vibration) through carrier recombination, leading to an increase in the material's lattice temperature. The resulting heat distribution depends on the optical absorption characteristics of the semiconductor and the surface/bulk recombination rates. The main non-radiative recombination mechanisms include: Shockley-Read-Hall recombination, which occurs via defect states (traps) within the bandgap
[31]; Auger recombination, where under high carrier concentrations, when an electron and a hole recombine, they transfer their energy to another carrier (electron or hole), which subsequently relaxes by emitting phonons
[32]. These non-radiative recombination processes ultimately convert absorbed light energy into thermal energy.
2.3 Intrinsic photothermal effect of molecular vibrations
Carbon-based materials (such as graphene and carbon black) and certain organic polymers also exhibit excellent photothermal conversion performance, with heat generation primarily originating from molecular vibrational relaxation. Although σ-σ* transitions of high-energy σ bonds (such as C—C, C—O, C—H) require high-energy photons, under lower-energy irradiation (such as visible light or near-infrared), delocalized π electrons in the material can be excited, undergoing π-π* transitions
[13,33-34]. The specific process is as follows: photons meeting the energy conditions excite π electrons from the ground state (Highest Occupied Molecular Orbital, HOMO) to an excited state (Lowest Unoccupied Molecular Orbital, LUMO); the excited electrons rapidly relax back to the ground state (HOMO) through vibronic coupling, releasing the excess energy not as photons but as molecular vibrational energy (heat)
[13,35]; furthermore, conjugation or hyperconjugation effects of π orbitals can significantly reduce the HOMO-LUMO energy gap, making them more easily excited by low-energy photons, thereby enhancing photothermal conversion efficiency in specific wavelength bands
[35-36].
In summary, the photothermal conversion and storage process involves two key steps: first, photothermal materials convert absorbed light energy into thermal energy through microscopic mechanisms; subsequently, this thermal energy is effectively transferred to PCMs via heat conduction, inducing their phase change, thereby achieving stable storage of thermal energy in the form of latent heat.
3 Light-heat-storage integrated three-dimensional composite phase change material
The core of constructing integrated light-heat-storage composite PCMs lies in the organic integration of the phase change matrix and photothermal fillers, with their overall performance primarily depending on light harvesting capability, photothermal conversion efficiency, and phase change heat storage density.
[1,12]. To break through the performance bottlenecks of single components, current research focuses mainly on the fine regulation of the micro-nano structure of photothermal units and the composite functional design of carrier materials. Compared with traditional zero-dimensional particles, one-dimensional fibers, or two-dimensional sheet dispersion systems, three-dimensional porous skeletons exhibit unique topological network structural advantages: First, their ultra-high porosity and large specific surface area provide ample encapsulation space for the phase change matrix, effectively ensuring high loading rates and high energy density of the composites; second, the continuous interpenetrating skeleton network constructs rapid phonon transmission channels, significantly overcoming the inherent poor thermal conductivity of organic PCMs; finally, the abundant active sites on the skeleton surface provide a platform for multifunctional modification, facilitating the introduction of heterogeneous photothermal components to significantly enhance the material's light response capability through multi-mechanism synergistic effects.
[37]. Based on this, this chapter will systematically elaborate on the structural reinforcement design and latest application progress of five typical types of three-dimensional porous carriers—aerogels, carbon foams, expanded graphite, metal foams, and MOFs—in integrated light-heat-storage composite PCMs. The key thermophysical properties and photothermal conversion performances of various three-dimensional composite PCMs are summarized in
Table 1.
3.1 Aerogel-based integrated photo-thermal-storage composite phase change material
Due to their continuous 3D porous network structure, ultra-high porosity, large specific surface area, and tunable mechanical properties, aerogels are considered the preferred carriers for encapsulating PCMs.
[38]However, since most aerogel skeletons inherently possess weak photothermal conversion capabilities, early research primarily focused on introducing high light-absorbing components through physical doping or chemical grafting to enhance the photothermal response performance of the composites. In recent years, researchers have significantly improved the photothermal conversion efficiency of aerogel-based composite PCMs through material compounding and structural innovation strategies, while also achieving multifunctional development of composite PCMs, providing important solutions for a new generation of high-performance solar thermal management systems.
Integrating high-performance photothermal aerogel fillers into PCMs is an effective approach to enhance the photothermal conversion performance of aerogel-based composite PCMs. To address this issue, conventional research primarily focuses on improving performance by introducing components with high light absorption. For example, Zhang et al.
[39]synthesized silanized bacterial cellulose (BC)/hydroxylated carbon nanotubes (CNTs)/polyethylene glycol (PEG) composite aerogels via a one-step in-situ method. They utilized trimethylsiloxane as a crosslinker to chemically bond with the active hydroxyl groups on the BC surface, achieving uniform dispersion of the components and significantly enhancing the photothermal conversion capability of the composite material. A similar strategy was also applied to graphene systems, where Xi et al.
[40]encapsulated sodium acetate trihydrate (SAT) within reduced graphene oxide (rGO) aerogels to construct composite PCMs. Leveraging the broad-spectrum absorption characteristics of rGO itself, the composite material achieved a photothermal conversion efficiency of 86.3% while maintaining a high phase change enthalpy of 252.8 J/g. To further broaden the spectral response range, Du et al.
[41]constructed a 3D interconnected porous aerogel by ultrasonically exfoliating black phosphorus nanosheets and combining them with cellulose nanofibers (CNFs), followed by impregnation with n-octadecane. When the black phosphorus content was increased to 24%, the photothermal conversion efficiency of the composite PCMs reached as high as 87.6%. Similarly, in the study by Wang et al.
[42]on MXene/cellulose aerogel composite PCMs, MXene served as an efficient photon captor and molecular heater, capable of converting light energy into thermal energy with high efficiency (91.6%).
However, simple component compositing often fails to address the disordered heat conduction pathways within aerogels; therefore, regulating the geometric orientation of the skeleton has become a new direction for performance enhancement. Ren et al.
[43]designed graphene aerogel composite PCMs with CNFs as the supporting skeleton. Based on directional freezing technology, this study used CNFs as natural biomass spacers to effectively inhibit the stacking of graphene sheets. Leveraging the synergistic effect between the graphene skeleton and the formed gully-like structure, the composite material under 100 mW/cm
2 solar irradiation reached a temperature of 76 ℃ within 600 s, with a photothermal conversion efficiency as high as 91.0% (
Figure 2a). Compared with disordered structures, the directional ordered arrangement of photothermal fillers can more effectively improve photothermal conversion and thermal management efficiency. Based on the same ordered design concept, Li et al.
[44]used attapulgite-loaded phase change materials as the core, coated the surface with polydopamine (PDA), and then assembled them with chitosan, graphene oxide (GO), and bacterial cellulose into a 3D ordered aerogel via chemical crosslinking and unidirectional freezing. This 3D ordered structure not only promotes uniform heat transfer and effectively reduces heat loss but also synergizes with GO and PDA to achieve efficient light absorption. Under outdoor natural sunlight, the surface temperature of this aerogel can rapidly rise to 60 ℃. When applied to wearable devices, this aerogel can efficiently utilize solar energy for active temperature regulation, dynamically maintaining a comfortable body sensation temperature for humans in scenarios with changing environments (
Figure 2b).
With the deepening of research, the synergistic optimization of multi-level structural design and novel photothermal conversion mechanisms has begun to attract attention. Zhu et al.
[45]constructed anisotropic MXene aerogels with longitudinally interconnected pore structures using directional freezing-laser modification technology and encapsulated myristic acid (MA). The nano-TiO
2/amorphous carbon composite light-absorbing layer on the surface of the composite material, combined with the accelerating effect of longitudinally interconnected channels on heat transfer, enabled it to achieve a photothermal conversion efficiency of 93.5% while maintaining a high energy storage density of 192.4 J/g and a thermal conductivity of 0.45 W/(m·K), allowing for rapid energy conversion and transfer under illumination (
Figure 3a). Xu et al.
[46]introduced PDA into chitosan/CNFs carbon aerogels to enhance photothermal conversion performance. The composite PCMs effectively absorb light energy through the conjugated and hyperconjugated structures in PDA molecules and efficiently convert it into thermal energy via electron transitions, increasing the photothermal conversion efficiency to 94.9%. Furthermore, Li et al.
[47]inspired by neural network structures, grew ZIF-67 in situ on BC and calcined it at high temperatures to construct a composite aerogel composed of "soma" (Co/C polyhedra), "axons" (porous CNFs), and thermal storage units (paraffin wax, PW). This design cleverly utilizes the strong LSPR effect of Co/C polyhedra and the enhanced photon transmission pathways constructed by porous CNFs, enabling the composite PCMs to achieve a photothermal conversion efficiency as high as 95.3%.
With breakthroughs in the photothermal conversion and storage performance of aerogel-based composite PCMs, research focus has gradually expanded toward multi-scenario applications. Shi et al.
[48]developed a "five-in-one" multifunctional composite PCM based on carbonized polyimide (PI)/Kevlar nanofiber/GO@ZIF-67 bidirectional composite aerogel, integrating photothermal, electrothermal, magnetic thermal, thermoelectric conversion, and electromagnetic shielding functions (
Figure 3b), demonstrating potential in fields such as solar energy utilization, thermoelectric power generation, outdoor de-icing, and human thermal therapy. Addressing water resource issues, Zheng et al.
[49]prepared MXene/PI/PEG hybrid aerogels, innovatively applying photothermal conversion to drive seawater desalination. Leveraging MXene's excellent conductivity and strong light-harvesting capability, the system achieved efficient photothermal conversion to directly drive the desalination process, while storing excess heat as latent heat in PEG to sustain continuous water production under non-illuminated conditions. Furthermore, Luo et al.
[50]inspired by atmospheric temperature regulation mechanisms, designed a bilayer composite PCM based on gradient rGO aerogel to achieve bidirectional thermal regulation. The bottom layer, composed of strongly reduced rGO aerogel with strong light absorption, is responsible for photothermal conversion and thermal insulation; the top layer, consisting of weakly reduced rGO aerogel partially impregnated with octadecane, handles heat storage and temperature control (
Figure 3c). In a cold environment of -5 °C, the composite material stabilized the simulated skin interface temperature at 27 °C through photothermal heat generation, aerogel insulation, and PCM heat release; in a hot environment of 40 °C, the endothermic buffering effect of the PCMs combined with the insulating properties of the aerogel effectively prevented overheating.
3.2 Carbon foam-based integrated photo-thermal-storage composite phase change material
Carbon foam, by virtue of its continuous 3D network structure, tunable porosity, and excellent phonon transport properties, constructs an efficient photothermal carrier platform for PCMs. This three-dimensional structure not only provides good encapsulation space for PCMs, but its interconnected carbon skeleton also forms an efficient heat conduction pathway. Furthermore, the large specific surface area of carbon foam offers numerous sites for modifying photothermal nano-additives, providing a solid structural foundation for building efficient photon capture networks and thermal energy transport systems.
To address the limited light absorption capacity of pristine carbon foam, surface modification is the most direct strategy for improvement. By constructing photothermal active nanostructures on the carbon foam surface, the material's light harvesting capability and photothermal conversion efficiency can be significantly enhanced. Li et al.
[51]employed a PDA-assisted aqueous copper plating method to grow Cu nanoparticles in situ on the surface of carbon foam (CF), followed by vacuum impregnation encapsulation with octadecanol (ODA), constructing a CF/Cu/ODA composite photothermal system. The synergistic effect between the 3D porous skeleton of CF and the Cu nanoparticles significantly enhanced full-spectrum absorption capacity, increasing the photothermal conversion efficiency to 81.6% and achieving a thermal conductivity of 3.17 W/(m·K). Similarly, Zhou et al.
[52]prepared graphitic carbon foam with surface-modified 3D hierarchical porous carbon through surface microstructure design, serving as a carrier skeleton for stearic acid (SA). The fluffy porous carbon layer on the surface of the graphitic carbon foam creates a "light trap" effect at the microscopic level, effectively extending the optical path and suppressing reflection; combined with the continuous thermal conduction network of the graphitic ligaments, under 200 mW/cm
2irradiation, the photothermal conversion efficiency of the composite PCMs reached as high as 90.14%. To endow the materials with superior mechanical adaptability, Yang et al.
[53]used CF as a flexible substrate, introduced hydroxylated boron nitride nanosheets (HO-BNNS) as thermally conductive fillers, and copper oxide (CuO) as a photothermal converter, achieving a photothermal conversion efficiency of 91.8% for the composite PCMs. Notably, these composite PCMs possess both flexibility and thermally driven shape memory properties, providing an innovative solution for efficient solar energy utilization.
Considering the high cost of traditional synthetic carbon foams, pyrolytic carbonization based on biomass precursors has become a green and economical alternative pathway. This method not only features a simple process and low cost but also utilizes renewable raw materials, fully embodying the material design concept of sustainable development. He et al.
[54]Inspired by "fruit growth," using loofah sponge as the "core" and phenolic resin as the "flesh," Fe
3O
4nanoparticles were introduced to regulate the pore structure. After high-temperature carbonization, a hierarchically porous carbon foam was obtained, which was then vacuum-impregnated with PW to form composite PCMs (
Figure 4a). Benefiting from the graphitized structure rich in π-electrons formed by the high-temperature carbonization of the porous carbon foam (sp
2hybridized carbon), this biomass carbon skeleton can efficiently absorb solar energy. Under 100 mW/cm
2irradiation, the photothermal conversion efficiency of the composite PCMs reached 84.0%, and heat conduction was accelerated through the interconnected network. On this basis, Hu et al.
[55]prepared king oyster mushroom-derived porous carbon using a NaCl-assisted carbonization process and impregnated it with PEG to form composite PCMs. This highly graphitized derived porous carbon achieved an absorption rate of up to 95.1% across the full spectral band, realizing rapid conversion and storage of photothermal energy.
With the diversification of application demands, carbon foam-based composite PCMs are evolving towards multifunctional integration. Li et al.
[56]developed Co/N co-doped carbon foam-based multifunctional composite PCMs. By leveraging the synergy between the LSPR effect of Co nanoparticles and the full-spectrum absorption capability of the carbon foam skeleton, combined with rapid light/phonon transport characteristics, they enhanced the photothermal conversion efficiency to 95.2% (
Fig. 4band
c). To reduce interfacial thermal resistance, Chen et al.
[57]constructed a multi-dimensional heterogeneous carbon-metal interconnected network by integrating three-dimensional CF, one-dimensional CNTs, and zero-dimensional Co nanoparticles. The synergy between the LSPR effect of Co nanoparticles and photosensitive CF/CNTs carbon hybrids achieved efficient broad-spectrum light absorption. Meanwhile, this carbon-metal network effectively reduced phonon scattering, increasing the photothermal conversion efficiency of the composite PCMs to 97.1% and achieving a photothermoelectric conversion output voltage of 246.9 mV (100 mW/cm
2,
Fig. 4d). Building on this, Wu et al.
[58]developed an efficient phase change system integrating photothermoelectric conversion with seawater desalination, driven by a photothermal conversion layer composed of polypyrrole (PPy)/PEG-doped CF. This layer not only efficiently captures solar energy to generate heat but also directionally transfers thermal energy to the hot end of a thermoelectric generator (TEG) for power generation. Simultaneously, waste heat from the cold end of the TEG is captured by a CF cooling layer modified with single-sided hydrophobicity, directly driving seawater evaporation. PEG can store heat, ensuring continuous power supply under intermittent illumination. This strategy achieves efficient cascaded energy utilization, enhancing the comprehensive efficiency of solar energy use.
3.3 Expanded graphite-based integrated photo-thermal-storage composite phase change material
Expanded graphite (EG) is a worm-like porous material formed by intercalation and expansion of natural graphite. Through high-temperature expansion, its specific surface area and adsorption capacity are significantly improved, while retaining the original corrosion resistance and self-lubricating properties of natural graphite.
[59]. In view of the above characteristics, EG is often used as a carrier material for constructing photothermal PCMs.
[60-61].
When used as a single carrier, the porous structure and carbon matrix characteristics of EG have been confirmed to exhibit excellent performance. For example, Yang et al.
[62]prepared lauric acid (LA)/EG composite PCMs, which showed that the absorption capacity for ultraviolet-visible light continuously increased with the EG content. When the EG content was 15% (by mass), the material achieved a photothermal conversion efficiency of up to 95.0%, combining a high thermal conductivity of 10.55 W/(m·K) with a phase change enthalpy of 148.0 J/g. To meet higher phase change enthalpy requirements, Yan et al.
[63]employed the melt impregnation method to load erythritol into EG, achieving a loading capacity of up to 95% (by mass). The thermal conductivity of the composite PCMs was enhanced to 5.97 W/(m·K), while possessing an ultra-high melting enthalpy of 290.5 J/g and significantly suppressing supercooling. Under 100 mW/cm
2irradiation, the heating rate of the material increased by 21.2% compared to pure erythritol, confirming its superior photothermal conversion properties. To further improve photothermal conversion efficiency, Lei et al.
[64]constructed an organic-inorganic hybrid porous shape-stabilized composite PCM using EG as the carrier, n-eicosane as the stabilizer, and SAT as the core for phase change energy storage. In this system, EG serves as the carrier to provide shape stability and thermal conductivity channels, while n-eicosane acts as a stabilizer to coat SAT, forming a eutectic structure that reduces the degree of supercooling, ultimately achieving synergistic effects among all components. The results indicate that the composite PCMs containing 3.3% (by mass) EG exhibited optimal performance, with a phase change enthalpy of 266.5 J/g, a supercooling degree of only 2.2 ℃, and a photothermal conversion efficiency of 91.1%.
Although EG exhibits good thermal conductivity, single EG carriers still have room for improvement in broad-spectrum absorption. Therefore, researchers have attempted to composite them with other functional materials to achieve synergistic performance. For example, Liu et al.
[65]designed a PPy-coated EG-based composite PCM (PEG@EG/PPy). Utilizing the conjugated structure of PPy to enhance full-spectrum absorption, it synergizes with EG to form an efficient dual-photon capture system, significantly improving photothermal conversion capability (
Figure 5a). In addition to organic polymers, MOFs have also been used to modify EG. Ren et al.
[66]composited Cu-Zn MOF with EG and prepared an EG/Cu-ZnMC support material via high-temperature carbonization (
Figure 5b). During this process, the porous structure formed by Zn volatilization enhanced PEG adsorption capacity, while Cu nanoparticles uniformly dispersed on the EG surface enhanced light absorption through the LSPR effect. When the Cu-Zn ratio was appropriate, the composite PCMs possessed both a high thermal conductivity of 6.10 W/(m·K) and a high phase change enthalpy of 174.6 J/g. Under 150 mW/cm
2irradiation, the photothermal conversion efficiency was 88.7%. Dai et al.
[67]combined EG-encapsulated SA with highly oriented graphene films (GF) via hot-press co-assembly. Herein, EG provides a porous encapsulation structure and basic thermal conduction paths, while GF forms oriented thermal conduction channels through parallel stacking. Benefiting from the synergy between the two, the material achieved a thermal conductivity as high as 27.10 W/(m·K) when the thermal filler content was 12.6% (by mass). Further device testing showed that this structure rapidly transfers surface heat through oriented thermal conduction, reducing heat dissipation losses, while significantly improving photothermal conversion efficiency. Ultimately, under 100 mW/cm
2irradiation, the system achieved a high surface temperature of 87.2 °C, with the internal temperature gradient approaching zero (
Figure 5c, d).
3.4 Metal foam-based integrated photo-thermal-storage composite phase change material
Metal foams (such as copper and aluminum foams), combining the high thermal/electrical conductivity of metals with the low density and high specific surface area of porous materials, have become important skeleton materials for constructing high-thermal-conductivity photothermal PCMs.
[68-69]. Among them, copper foam has become the mainstream choice due to its excellent thermal conductivity approaching 400 W/(m·K); however, the high reflectivity of metal surfaces limits their intrinsic photothermal conversion efficiency. Therefore, surface modification of metal foam skeletons to enhance light harvesting capability has become a key research direction in this field.
Introducing photothermal active nanostructures is a direct means to improve the light absorption performance of metal foams. For example, Yu et al.
[70]optimized the photothermal conversion performance of the copper metal foam/PW phase change system by doping Fe
3O
4nanoparticles. They systematically investigated the effects of nanoparticle mass fraction and metal foam pore density (PPI). The results showed that when the nanoparticle mass fraction was 1.0% and the PPI was 15, the heating rate of the system was the fastest, with the temperature difference growth rate increasing by 24.82%. To construct microscopic light-trapping structures, Guo et al.
[71]grew Cu nanowires in situ on the surface of copper foam and embedded flake graphite. The modified copper foam surface formed nanoscale rough structures and secondary thermal conductivity networks; the LSPR effect of Cu nanowires synergized with the high light absorption of graphite, enhancing multiple reflections and absorption of light within the pores, thereby improving solar energy capture capability. The results showed that under 100 mW/cm
2irradiation, the composite PCMs reached a stable temperature of 72.2 °C and a thermal conductivity of 4.10 W/(m·K), far superior to pure PW and unmodified PW/copper foam. Building on this, the team further modified the copper foam using a MOF-derived multi-walled carbon nanotube (MWCNT) network
[72]. The synergy between the MWCNT network and the copper foam significantly improved the material's light absorption capacity; under an irradiance of 100 mW/cm
2, the surface temperature of the composite PCMs could rapidly rise to 88.5 °C, demonstrating excellent photothermal conversion performance. Meanwhile, the high thermal conductivity of up to 7.30 W/(m·K) facilitates the rapid transfer of heat generated by photothermal conversion.
In addition to surface chemical modification, hierarchical network structure design provides a new approach for optimizing the performance of composite PCMs. For example, Guo et al.
[73]developed a copper foam-expanded graphite (Cu/EG) bicontinuous network structure (
Figure 5e). In this structure, the copper foam constitutes the primary heat conduction network, while EG forms a secondary continuous network within its pores. The dual-network structure exposed at the top acts as an efficient light absorber, enhancing solar energy capture through multiple reflections and absorptions; meanwhile, the bottom ensures rapid and uniform heat transfer to the PCMs. This composite PCM achieves an absorption rate of up to 94% across the full spectrum, and combined with its high thermal conductivity of 5.30 W/(m·K), it realizes effective conversion and storage of photothermal energy. A similar structural synergy strategy was also adopted by Duan et al.
[74], who designed a hierarchical micro-nano structure based on a PVA-graphene coated Cu(OH)
2@Cu foam as a supporting skeleton for modified PW. By leveraging the synergistic effect between Cu(OH)
2 nanowires and PVA-reduced graphene oxide films, multiple light reflections and absorptions were effectively enhanced. Under irradiation of 120 mW/cm
2, its photothermal conversion efficiency reached 90.3%.
In addition, the special structures of organisms in nature also provide references for material design. For example, Huang et al.
[75]Inspired by the structure of pine needles, they constructed a pine needle-like hierarchical porous scaffold on the surface of copper foam. They grew Cu-MOF nano-arrays on the copper foam and then encapsulated PEG to form composite PCMs. This bionic hierarchical structure can enhance multiple scattering and trapping of light within the material, achieving a full-spectrum absorptance exceeding 97% and demonstrating good adaptability to different incident light angles (
Figure 5f). Meanwhile, the copper foam skeleton and the pine needle-like hierarchical structure synergistically constructed an efficient heat conduction network with a thermal conductivity of 2.35 W/(m·K), ensuring that the heat generated by photothermal conversion is rapidly transferred, ultimately yielding a measured photothermal conversion efficiency of 96.9%.
3.5 Metal-Organic Framework-Based Integrated Photo-Thermal-Energy Storage Composite Phase Change Materials
Metal-organic frameworks (MOFs), with their highly tunable pore structures, ultra-high specific surface areas, and organic-inorganic hybrid characteristics, have become novel porous carriers for encapsulating PCMs.
[76]. Since the photon capture cross-sections of most pristine MOF materials in the visible-near infrared region are small, their direct photothermal conversion efficiency often fails to meet practical application requirements. To address this intrinsic defect, current research strategies primarily focus on two directions: constructing composite photothermal systems and developing high-temperature derived functional materials.
Introducing high-light-absorbing components for surface modification or pore filling is a direct approach to improving the photothermal conversion performance of MOF-based PCMs. For example, Liu et al.
[77]synthesized Cr-MIL-101-NH
2 via a hydrothermal method to encapsulate ODA, and coated a PPy layer on the MOF surface through in situ polymerization (
Figure 6a). This design utilizes the nanoconfinement effect of MOF pores to prevent PCM leakage, while leveraging the conjugated molecular structure of PPy to achieve broadband light absorption. Experimental results indicate that PPy not only achieves broadband light absorption across the full spectral region due to its conjugated molecular structure but also constructs a phonon transport network. Under irradiation of 150 mW/cm
2, the photothermal conversion efficiency of the composite PCMs increases with higher PPy content, reaching 88.3% at 6% PPy. Furthermore, to further enhance the photothermal conversion characteristics of MOF-based composite PCMs, in contrast, Xiao et al.
[78]focused on exploring the intrinsic photothermal potential of MOF metal nodes. They grew ZIF-67 in situ on EG to construct a hierarchical layered composite structure. Benefiting from high specific surface area and pore volume, the 3D macroporous layered MOF/EG composite significantly improved PW loading capacity and shape stability. The study found that tetrahedral Co
2+ ions in ZIF-67 directly absorb light energy through d-d transitions and generate heat via non-radiative relaxation of electron-hole pairs. This strategy, which leverages the intrinsic properties of metal nodes, avoids the introduction of additional photothermal agents, enabling the composite PCMs to achieve a photothermal conversion efficiency of 95.6% while maintaining a high phase change enthalpy of 159.2 J/g.
In addition to direct compositing, utilizing high-temperature pyrolysis to reconstruct the topological structure of MOFs and prepare carbon-based derivatives is another important pathway for obtaining photothermal carriers with high stability and high thermal conductivity. The high-temperature carbonization process can convert organic ligands into highly conductive carbon skeletons while simultaneously reducing metal nodes in situ into nanoparticles with plasmonic effects. For example, Chang et al.
[79]carbonized HKUST-1 at high temperatures to prepare a hierarchical porous carbon skeleton loaded with CuO nanoparticles, which was used as a photothermal carrier for palmitic acid (PA) (
Figure 6b). Benefiting from the synergistic effect between the LSPR effect of CuO nanoparticles and the conjugated electron system of the carbon skeleton, this composite material exhibited significantly enhanced full-spectrum absorption, achieving a photothermal conversion efficiency of 81.8% under 300 mW/cm
2 irradiation. Building on this, to endow the material with richer field-responsive characteristics, Tang et al.
[80]used ZIF-67@ZIF-8 as a precursor to prepare Co/N co-doped magnetic carbon nanocages, constructing a photothermal conversion system capable of rapid charging and discharging (
Figure 6c). This structure not only achieved a photothermal conversion efficiency of 90.7% through synergistic light absorption by Co nanoparticles and the carbon matrix but also introduced a magnetic field-assisted enhancement mechanism—under the action of a magnetic field, the magnetic nanocages could accelerate heat transfer to the internal PEG, increasing the apparent photothermal conversion efficiency to 115.8%. Notably, after integrating this system with a thermoelectric module, it could simultaneously output a voltage of 290 mV and a current of 92.6 mA, realizing cascaded light-heat-electricity energy conversion and providing a new solution for efficient solar energy utilization. Furthermore, by regulating precursor growth, the team constructed ZnCo-MOFs on CNTs and calcined them to obtain a 1D/3D tightly heterogeneous carbon network decorated with Co nanoparticles
[81]. This heterogeneous structure effectively reduced interfacial thermal resistance and optimized photon capture pathways, enhancing the photothermal conversion efficiency of the composite PCMs to 98.1%.
Current research on MOF-based composite PCMs is gradually evolving from single photothermal conversion toward multi-physics field synergistic response. For example, Li et al.
[82]utilized spatial confinement growth technology to construct a 3D interconnected forest-like array carbon network anchored with Co nanoparticles on a melamine-carbonized foam skeleton. After encapsulating PEG, this composite system integrated three stimulus-response modes: light, electricity, and magnetism. Under 100 mW/cm
2irradiation, the photothermal conversion efficiency reached 93.1%; under 2.5 V voltage, the electrothermal conversion efficiency was 92.9%; and it exhibited good magnetothermal response, confirming its application potential in multimodal human hyperthermia. To expand response capabilities across the electromagnetic spectrum, the team further prepared magnetic NiCo-modified open carbon microcages via pyrolysis of NiCo-MOF, achieving multi-field response to light/magnetism/microwaves (
Figure 6d)
[83]. The introduction of NiCo nanoparticles not only enhanced light absorption through the LSPR effect but also achieved efficient magnetothermal conversion via Néel and Brownian relaxation effects. More importantly, thanks to optimized impedance matching characteristics, this composite material exhibited excellent microwave absorption performance (minimum reflection loss of -38.1 dB), demonstrating its potential for achieving intelligent thermal management and stealth compatibility in complex electromagnetic environments.
4 Advanced Applications of Integrated Light-Heat-Storage 3D Composite Phase Change Materials
Photothermal PCMs can efficiently absorb solar energy and convert it into thermal energy, driving reversible phase change processes in materials, thereby achieving thermal energy storage and on-demand release. In recent years, integrated photo-thermal-storage 3D composite PCMs have demonstrated promising application potential in cutting-edge fields such as smart wearables, biomedicine, building energy efficiency, seawater desalination, and extreme environment protection, promoting interdisciplinary technology integration and functional upgrades.
4.1 Smart Wearables
Smart wearable devices integrated with PCMs can automatically regulate the human microclimate temperature based on ambient environmental conditions, not only enhancing the wearer's thermal comfort experience but also opening new avenues for achieving precise and personalized temperature management. In this context, smart wearable devices with photo-responsive characteristics are rapidly becoming a research hotspot for the new generation of intelligent wearable systems due to their unique photothermal conversion capabilities and environmental adaptability. For example, Bai et al.
[111]designed a directionally structured chitosan/carbon fiber powder aerogel as a support carrier for PWs for solar-driven thermal management. Owing to the directional pore structure design, the composite PCMs exhibit excellent thermal conductivity and solar-to-thermal conversion capabilities. A human body hot pack developed based on this material, after being solar-charged to 50 °C and applied to the human arm, maintains a comfortable temperature of around 40 °C on the skin-contact side; even after light exposure ceases, it sustains the therapeutic temperature for 1795 s, meeting the daily duration requirements for human body hot compress therapy.
To overcome the functional singularity and mechanical performance limitations of traditional phase change materials in wearable applications, Zhang et al.
[112]developed a weavable phase change fiber prepared via a gravity-assisted dual-gel method. Using BC as the matrix, this study constructed flexible silanized BC/hydroxylated CNT aerogel fibers. After loading with n-eicosane, the aerogel fibers exhibited excellent comprehensive performance: a phase change enthalpy reaching 105.0 J/g, while maintaining a tensile strength of 23.9 MPa and a toughness of 8.7 MJ/m
3, combining good weavability and hydrophobic characteristics. Furthermore, this textile can maintain human skin temperature at a comfortable 38.9 ℃ through photothermal conversion, achieving long-term warmth retention in outdoor environments without external energy sources (
Figure 7a). Building on this, Wang et al.
[113]prepared a highly flexible phase change film using a salt-template-assisted and dip-coating method. Using n-eicosane as the phase change matrix, the film achieves a phase change enthalpy of 109.5~117.8 J/g and a phase change temperature of approximately 36 ℃, closely matching the human thermal comfort zone. The 3D interconnected polysiloxane network formed by vinyl dimethyl siloxane and hydrogen silicone oil endows the film with outstanding flexibility, stretchability, and shape adaptability, allowing it to fit tightly to various complex parts of the human body. By introducing MWCNTs, an efficient photothermal conversion network was constructed, achieving a photothermal conversion efficiency of 92.3% and realizing solar-driven thermal management functionality. More innovatively, this phase change film also integrates strain sensing capabilities, with a gauge factor reaching 46.3, enabling real-time monitoring of joint bending in fingers, wrists, elbows, and knees, as well as subtle movements such as facial expressions and vocal cord vibrations, with rapid and stable response. This design, integrating "thermal management" and "motion monitoring" functions, provides new insights for the development of next-generation smart wearable devices.
4.2 Biomedical
Phase change materials, with their unique phase change heat storage/release characteristics, show broad application prospects in the biomedical field. In particular, integrated photo-thermal-storage composite PCMs can not only maintain stable ambient temperatures through the phase change process but also achieve controllable thermal management via light stimulation, providing innovative solutions for precision medicine.
In terms of hyperthermia applications, researchers have developed various functionalized PCMs. For example, Li et al.
[82]designed 3D forest-like carbon heterostructure composite PCMs, achieving photothermal/electrical/magnetic multi-mode conversion. When applied as phase-change films for human hyperthermia, they can meet moderate hyperthermia requirements of 40–50 °C. To break through the limitations of single-function hyperthermia, Li et al.
[114]developed a multifunctional inorganic-organic phase-change hydrogel with excellent photothermal conversion and strain sensing capabilities. Leveraging the high light absorption and thermal conductivity of EG and graphene, the phase-change hydrogel can absorb and store light energy, slowly releasing heat through phase change to stabilize joint temperature at around 50 °C for up to 700 s, effectively preventing burns caused by direct irradiation from physiotherapy lamps. Meanwhile, its excellent strain sensing function enables real-time monitoring of joint activity, achieving integration of hyperthermia and rehabilitation monitoring, providing an innovative solution for personalized medicine.
In the field of controlled drug release, PCMs also demonstrate unique advantages. For example, Liu et al.
[115]developed an intelligent nanofiber dressing with a Janus structure. This dressing employs a unique core-shell design, using a hydrophilic PCL@PDA-ε-PL nanofiber membrane as the substrate, onto which coaxial nanofibers containing lauric acid (LA) and ibuprofen are deposited. This structure innovatively achieves a dual controlled-release mechanism: on one hand, regulating the drug release rate through the phase change process of LA, and on the other, enabling on-demand drug release via the near-infrared photothermal effect of PDA. Experiments show that under near-infrared irradiation, the photothermal effect generated by PDA can precisely trigger the phase change of LA, thereby intelligently regulating the release kinetics of ibuprofen. Furthermore, Chen et al.
[116]organically combined the phase change material LA with the antitumor drug doxorubicin hydrochloride (DOX) and the thermosensitizer apotosol (Az) to design a combination therapy system based on a polyacrylonitrile/ZIF-8 derived hollow carbon fiber scaffold (
Figure 7b). Under near-infrared laser regulation, the reversible phase change of LA not only precisely controls the therapeutic temperature within a safe range but also synchronously regulates drug release: DOX acts directly on tumor cells to exert chemotherapeutic effects, while Az significantly enhances the sensitivity of tumor cells to mild hyperthermia by inhibiting the expression of heat shock protein 70. This photothermal-chemotherapy synergistic strategy demonstrates excellent antitumor efficacy in animal experiments while minimizing damage to normal tissues, providing innovative insights for combination cancer therapy.
4.3 Building Energy Efficiency
With the continuous growth of global building energy consumption, improving building energy efficiency has become an important topic for sustainable development. PCMs, due to their excellent thermal energy storage capacity and temperature regulation characteristics, provide innovative solutions for building energy saving
[117-118]. Integrating PCMs into building envelopes (such as walls and roofs) can significantly enhance their thermal inertia: absorbing and storing excess heat during the day and releasing stored thermal energy at night, thereby narrowing the range of indoor temperature fluctuations and significantly reducing HVAC system energy consumption. Integrated photo-thermal-storage composite PCMs achieve smarter building thermal management by integrating photothermal conversion and phase change heat storage functions.
In practical applications, researchers focus on enhancing the thermal buffering performance and environmental adaptability of composite materials. For example, Chen et al.
[119]encapsulated PW within a chitosan-carboxymethyl cellulose composite wall material and embedded it into a gypsum matrix; the resulting composite exhibited thermal buffering performance far superior to that of traditional gypsum-based materials. Furthermore, Zhang et al.
[120]designed layered cellulose/PEG/Fe
3O
4composite PCMs significantly improved thermal conductivity and photothermal conversion efficiency. After surface modification with hydrophobic fluorocarbon resin, the material demonstrated excellent hydrophobicity (contact angle 137.1°) along with self-cleaning properties. In model house tests, this composite material, through a synergistic mechanism of photothermal conversion, heat storage, and heat release, successfully controlled the indoor temperature fluctuation range within the comfortable interval of 32–38 °C. Addressing the specific needs of agricultural greenhouses, Hao et al.
[121]developed a shape-stabilized composite PCM specifically designed for smart greenhouses. By constructing a 3D porous network structure via calcium-crosslinked sodium alginate and introducing EG, the composite achieved favorable photothermal conversion performance; under an irradiance of 120 mW/cm
2, it realized a photothermal conversion efficiency of 73.8%. Practical greenhouse applications indicated that the composite PCMs could extend by 100% the duration maintaining the optimal crop growth temperature range (25–35 °C), providing an efficient and energy-saving temperature regulation solution for modern facility agriculture.
In recent years, significant breakthroughs have been achieved in intelligent temperature-controlled photothermal phase change systems featuring system integration and multimodal temperature regulation. For example, He et al.
[122]developed a passive temperature-controlled house adopting a dual-module design: the roof integrates high-efficiency photothermal conversion phase change plates with indoor low-supercooling hydrated salt phase change radiators. By intelligently adjusting the light-receiving area of the phase change plates and the arrangement of radiators, this system maintains a comfortable temperature above 18 °C throughout the day during autumn and winter, extending nighttime heat retention by nearly 2 hours. Even under extreme low-temperature conditions of -16.3 °C, the effective indoor heat retention duration is far superior to conventional systems. Addressing the year-round heating and cooling demands of buildings, Wang et al.
[123]developed a dual-functional phase change composite film that, by integrating a radiative cooling coating with a photothermal conversion layer loaded with PCMs, achieves the collection, storage, and utilization of cold energy throughout the day (
Figure 7c). The upper layer of this composite film consists of a cost-effective radiative cooling coating (PMMA/BaSO
4, solar reflectance ≈ 0.94, atmospheric transparent window emissivity ≈ 0.96), while the lower layer comprises high-thermal-conductivity composite PCMs capable of storing excess cold energy generated by the nighttime radiative cooling layer to compensate for insufficient daytime cooling. By simply flipping the top and bottom surfaces of the composite film, solar photothermal storage can also be utilized, thereby enabling energy regulation for winter space heating.
4.4 Desalination
Facing the dual challenges of freshwater scarcity and energy transition, solar-driven desalination technology has become a research focus due to its clean and sustainable characteristics
[124]. However, traditional photothermal evaporation technology faces key challenges such as the intermittency of solar radiation and low thermal energy utilization efficiency. Integrated photo-thermal-storage composite PCMs significantly enhance the stability of the evaporation process by constructing a closed-loop system of "photothermal conversion-latent heat storage-continuous energy supply," promoting the development of this technology towards high-efficiency, continuous operation, and multi-energy cogeneration.
Innovative applications of phase change materials have opened new pathways for sustainable seawater desalination technology. For example, Zheng et al.
[49]developed PI/MXene hybrid aerogel/PEG composite PCMs. By combining the excellent full-spectrum absorption properties of MXene with the porous structure of PI aerogel, these composites demonstrate significant advantages in solar-driven evaporation systems. Experiments show that the composite PCMs achieve a seawater evaporation efficiency of 50.6% under 100 mW/cm
2irradiation. Crucially, under non-illuminated conditions, the latent heat released by the PEG phase change component within the material can still sustain the evaporation process, enhancing continuous water production capacity. After long-term cycling tests, the material maintains stable evaporation performance, and the produced water quality meets the drinking water standards specified by the WHO.
In recent years, multifunctional integrated photothermal PCMs have demonstrated significant research value in the field of seawater desalination combined with thermoelectric power generation. Tang et al.
[125]biomimetically prepared amino-functionalized attapulgite/graphene hybrid aerogels and encapsulated LA within them. Based on their excellent photothermal conversion and heat storage properties, they designed an interfacial evaporator composed of composite PCMs and water-absorbing cotton, applied simultaneously to solar-driven desalination and thermoelectric power generation. Under an irradiation of 100 mW/cm
2, the seawater evaporation rate reached 2.13 kg/(m
2·h); in darkness, due to latent heat release from the PCMs, an evaporation rate of 1.21 kg/(m
2·h) was maintained, while the concentration of metal ions in the desalinated water was significantly reduced, meeting WHO standards. Regarding thermoelectric power generation, the solar thermoelectric generator integrated with composite PCMs achieved a power density of 1.57 W/m
2 under
2conditions, and could delay the temperature drop at the hot end in darkness by releasing latent heat, thereby driving the operation of small electronic devices (
Figure 8a).
To pursue a high-output, integrated hydroelectric co-production system, Li et al.
[126]developed a hierarchically structured 3D solar evaporator. This evaporator combines PW with a circular concave 3D scaffold covered by carbon black nanoparticle-modified PET fabric, alleviating performance limitations under intermittent illumination. Among them, the 3D-printed scaffold captures sunlight to enhance absorption efficiency, while the hydrophilic and hydrophobic modified PET fabric fully absorbs sunlight for simultaneous power generation and water evaporation, achieving a high output voltage of 3.51 V and 4.00 kg/(m
2·h) high evaporation rate. Compared with similar devices without PCMs, the capacitor charging time of this evaporator was significantly shortened by 57.9%, while the fresh water production increased by 29.9% (
Figure 8b). This innovative design demonstrates excellent dual-function integration capability, providing an important solution for achieving simultaneous power generation and fresh water supply.
4.5 Extreme Environment Protection
Ice and snow accumulation under extreme weather conditions poses serious safety risks to equipment such as power grids, ships, aircraft, and communication towers. Traditional de-icing technologies, such as manual removal, chemical de-icers, and electric heating, suffer from issues like environmental pollution and high energy consumption, making it difficult to meet the sustainable development needs of scenarios like polar regions and aviation.
[127]. Integrated photo-thermal-storage composite PCMs can convert solar energy into controllable thermal energy and achieve continuous protection through phase change energy storage, providing a new approach for improving de-icing efficiency and sustainability. For example, Sheng et al.
[128], inspired by the thermal energy storage mechanism of alpine plants, developed an EG/PW/polydimethylsiloxane composite material, achieving continuous photothermal de-icing. Under conditions of -40 °C and 100 mW/cm
2 irradiation, this composite PCM delayed droplet freezing for over 2 h, far longer than surfaces without PCMs. In actual environments, its de-icing rate reached up to 2.21 kg/(m
2·h), enabling continuous anti-icing/de-icing performance in low-temperature environments across different cities. To achieve further breakthroughs, Zhu et al.
[129] synthesized a novel 3D porous graphene scaffold and encapsulated MA. Among them, GO was reduced to rGO via laser action, serving as a thermal bridge connecting adjacent laser-induced graphene to form a gully-like surface and a 3D overlapping network structure. Its gully-like surface not only enhances light absorption to delay the freezing of the interfacial water layer but also reduces ice adhesion. Therefore, this composite PCM exhibits a high photothermal conversion efficiency of 94.1% and hydrophobicity with a contact angle of 135°; under 100 mW/cm
2 irradiation, a covered 0.5 mL ice block could melt within 5 min, providing a feasible solution for solar-driven high-efficiency anti-icing technology (
Figure 8c).
With the development of multi-spectral detection technology, the synergistic monitoring of visible light and infrared poses severe challenges to traditional camouflage materials. Integrated optical-thermal-storage composite PCMs can dynamically regulate target surface temperature through the photothermal effect, achieving environment-adaptive camouflage. For example, Tang et al.
[130]designed a double-layer 3D hybrid scaffold with reversible light-absorbing characteristics: the upper layer is a black BC layer containing thermochromic particles, and the lower layer is a white BC layer containing boron nitride (BN), with the whole structure impregnated with PEG. Leveraging the reversible color-changing properties of the thermochromic particles, the material appears black at low temperatures to efficiently absorb sunlight and convert it into thermal energy; when the temperature rises to the PEG phase change point, it turns white to reduce light absorption and prevent continuous temperature rise, thereby stabilizing the temperature near the phase change point. Li et al.
[131]designed a three-layer MXene/rGO hybrid aerogel composite material that achieves dual camouflage in both visible light and infrared by integrating n-octadecane and a thermochromic coating. Utilizing the synergistic effect of the aerogel's thermal insulation and the PCMs' heat storage, the temperature difference between the target and the environment can be reduced to 0.9°C, allowing humans or equipment to fully blend into the infrared background and effectively interfere with target detection. Furthermore, the top thermochromic coating changes from green to yellow under sunlight, matching environmental colors from jungle to desert, while the bottom PCMs prevent target overheating, achieving efficient visible light camouflage. This composite material can simultaneously achieve dual camouflage in complex scenarios such as day/night cycles, jungles, and deserts, effectively countering multi-band monitoring.
5 Conclusion and Outlook
This review systematically summarizes the latest research progress on integrated photo-thermal-storage three-dimensional composite PCMs. The core strategy lies in utilizing three-dimensional porous carriers (including aerogels, carbon foams, metal foams, expanded graphite, MOFs, and their derivatives) to address the defects of traditional organic PCMs, such as weak light absorption, poor thermal conductivity, and leakage, significantly enhancing the photothermal conversion efficiency, thermal energy storage density, and thermal management performance of composite PCMs. Studies show that the three-dimensional skeleton not only constructs an efficient thermal conductivity network and reduces interfacial thermal resistance, but its unique micro-nano structure also significantly enhances light absorption capability. By synergizing multiple photothermal conversion mechanisms (such as plasmonic resonance, non-radiative relaxation, and molecular thermal vibration), it has repeatedly achieved record-high photothermal conversion efficiencies for composite PCMs. These materials demonstrate broad application prospects in various fields, including smart wearables, biomedicine, building energy efficiency, seawater desalination, and extreme environment protection.
Comprehensive comparison of various carriers reveals distinct differentiated characteristics in their performance advantages and limitations. Aerogels, by virtue of their ultra-high porosity and specific surface area, provide excellent phase change material loading space and leakage prevention capabilities, with extremely low density, making them suitable for weight-sensitive wearable devices. However, their intrinsically low thermal conductivity limits rapid heat charging and discharging, often requiring the introduction of high-thermal-conductivity fillers to construct thermal pathways. Metal foams exhibit superior mechanical strength and thermal conductivity, significantly enhancing the system's thermal response speed. Yet, their higher density, susceptibility to corrosion, and weak intrinsic light absorption capability often necessitate surface modification with photothermal coatings. Carbon-based materials (expanded graphite, carbon foams) achieve a favorable balance among thermal conductivity, chemical stability, and cost. Expanded graphite, in particular, holds great potential for large-scale industrial applications due to its low cost and excellent corrosion resistance. MOFs and their derivatives stand out in precise temperature control and multifunctional integration owing to their atomically tunable pore structures and abundant functional sites. Although current preparation costs are high, MOF-derived carbon skeletons produced via high-temperature carbonization, combining the porosity of MOFs with the high thermal conductivity of carbon materials, are considered strong contenders for next-generation high-performance photothermal carriers.
Although the photothermal conversion efficiency of integrated light-heat-storage three-dimensional composite PCMs has currently generally exceeded 90%, to achieve the leap from "laboratory samples" to "engineered products," future research focus should shift from merely pursuing efficiency to the following specific key technological breakthroughs.
(1) The R&D efficiency of the traditional trial-and-error method is relatively low, necessitating the introduction of AI technology to build a new R&D system: existing data on the composition, structure, and properties of materials can be integrated to establish a standardized database; adapted machine learning models can be leveraged to predict key material characteristics and design novel structures; based on model results, experimental verification should be prioritized to develop new photothermal materials that combine performance advantages with low cost, low toxicity, environmental friendliness, long cycle life, and recyclability, thereby driving innovation in material systems.
(2) Existing research mostly focuses on the macroscopic performance characterization of integrated photo-thermal-storage composite PCMs, while the investigation into the microscopic mechanisms of the full chain within the system—"light absorption-energy conversion-heat transfer-phase change storage"—is not yet deep enough. Subsequent efforts need to strengthen the construction of multi-scale theoretical models to clarify the coupling laws of heat transfer dynamics, solid-liquid phase change behavior, and photothermal conversion mechanisms in composite systems, especially the influence mechanism of interfacial effects on energy conversion efficiency; meanwhile, advanced characterization techniques should be combined to provide experimental basis for the verification and optimization of theoretical models.
(3) A single function is no longer sufficient to meet complex practical demands. In the future, composite PCMs can be developed as core components for multifunctional devices: for instance, integrating thermoelectric generators in seawater desalination to achieve simultaneous water and power production; or realizing dual-mode dynamic temperature regulation that combines radiative cooling and photothermal energy storage in the building sector. Precise design principles linking "performance-structure-composition" should be established based on the specific requirements of different application scenarios. Examples include meeting flexibility and lightweight criteria for wearable devices, balancing low cost with fire resistance ratings for building materials, and ensuring salt corrosion resistance and environmental safety for seawater desalination systems.
(4) It is necessary to break the limitations of laboratory material research, promote the transformation of integrated light-thermal-storage 3D composite PCMs towards functional devices and system integration, and develop integrated application systems adapted to actual needs; meanwhile, establish unified key performance testing standards to provide normative basis for material performance evaluation and industrial application, facilitating the transition of technology from the R&D stage to engineering applications.
(5) The long-term reliability and environmental adaptability of materials are essential prerequisites for their large-scale application. It is necessary to establish a full life cycle assessment system covering raw material acquisition, preparation and processing, usage and maintenance, and recycling and regeneration. Focus on resource utilization efficiency, energy consumption control, and environmental impact at each stage to enhance the long-term reliability and environmental adaptability of materials under complex operating conditions (such as intermittent sunlight, extreme temperature and humidity, and mechanical stress). Simultaneously, explore feasible pathways for recycling and regeneration to ensure the sustainability of material applications.
Looking ahead, through interdisciplinary innovation and collaborative efforts among industry, academia, and research, continuous breakthroughs in material design theory, preparation processes, and application technologies are expected to enable integrated photo-thermal-storage 3D composite PCMs to play a pivotal role in building a new energy system under the "dual carbon" goals, promoting efficient conversion and intelligent utilization of solar energy. It is recommended to prioritize frontier directions such as materials genome engineering, intelligent preparation technologies, and digital twin optimization to accelerate the transition from fundamental research to industrial applications, providing crucial material support and technical guarantees for global energy transformation.
Beijing Natural Science Foundation(2264105)
National Natural Science Foundation of China(52502356)
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