Enhanced Thermal-to-Flexible Phase Change Materials Based on Cellulose/Modified Graphene Composites for Thermal Management of Solar Energy

Recent advances and perspectives in solar photothermal conversion and storage systems: A review

Developing high-efficiency solar photothermal conversion and storage (SPCS) technology is significant in solving the imbalance between the supply and demand of solar energy utilization in time and space. Aiming at the current research status in the field of SPCS, this review thoroughly examines the phase change materials and substrates in SPCS systems. It elucidates the design principles and methods of SPCS integrated composites. Comparatively, it analyzes the parameters of various types of SPCS composites in terms of photothermal conversion, thermal conductivity, energy density, and cycling stability. Additionally, the review discusses the trade-offs between each parameter to achieve the most optimal effect of SPCS. By sorting out the current status of the application of SPCS technology in solar thermal/photovoltaic, aerospace, buildings, textile, and other industries, this analysis clarifies the requirements for various latent heat, phase change temperature, and other properties under different environmental conditions. Through a comprehensive discussion of SPCS technology, this paper accurately captures the development trend of efficiently and comprehensively utilizing solar energy by analyzing existing scientific problems. It identifies bottlenecks in SPCS technology and suggests future development directions that need focused attention. The insights gained from this analysis may provide a theoretical basis for designing strategies, enhancing performance, and promoting the application of SPCS.

Eco-friendly synthesis of chemically cross-linked chitosan/cellulose nanocrystal/CMK-3 aerogel based shape-stable phase change material with enhanced energy conversion and storage

Phase change materials (PCMs) have attracted numerous attention owing to their high energy storage density, cost-effective and operationally simple, however, the "solid-liquid" leakage and limited solar absorbance seriously hinder their widespread applications. Herein, an innovative chitosan/cellulose nanocrystal/CMK-3 (CS/CNC/CMK-3) aerogel based shape-stable PCM (SSPCM) was successfully synthesized, in which chemically cross-linked CS and CNC acted as three-dimensional supporting skeleton, CMK-3 endowed solar-to-thermal energy conversion ability and the impregnating polyethylene glycol (PEG) acted as the latent heat storage unit. The as-synthesized CS/CNC/CMK-3 aerogel/PEG (CCCA/PEG) showed ultrahigh melting/crystallization enthalpy of 178.5/171.1 J g-1 and excellent shape stability. The PEG was effectively embedded into the hierarchical porous architecture and the composite PCM could preserve its original shape without any leakage even compressed above the melting point of PEG. Meanwhile, the CCCA/PEG exhibited robust thermal reliability with an ultralow enthalpy fading rate of 0.030 ± 0.012 % per cycle over 100 thermal cycles. Intriguingly, the introduction of CMK-3 also significantly improved the solar-to-thermal energy conversion performance of CCCA/PEG, and a high solar-to-thermal conversion efficiency of 93.1 % could be realized. This work provided a potential strategy to design and synthesize high-performance sustainable SSPCM, which showed tremendous potential in the practical solar energy harvesting, conversion and storage applications.

Advances in Biocarbon and Soft Material Assembly for Enthalpy Storage: Fundamentals, Mechanisms, and Multimodal Applications

High-value-added biomass materials like biocarbon are being actively pursued integrating them with soft materials in a broad range of advanced renewable energy technologies owing to their advantages, such as lightweight, relatively low-cost, diverse structural engineering applications, and high energy storage potential. Consequently, the hybrid integration of soft and biomass-derived materials shall store energy to mitigate intermittency issues, primarily through enthalpy storage during phase change. This paper introduces the recent advances in the development of natural biomaterial-derived carbon materials in soft material assembly and its applications in multidirectional renewable energy storage. Various emerging biocarbon materials (biochar, carbon fiber, graphene, nanoporous carbon nanosheets (2D), and carbon aerogel) with intrinsic structures and engineered designs for enhanced enthalpy storage and multimodal applications are discussed. The fundamental design approaches, working mechanisms, and feature applications, such as including thermal management and electromagnetic interference shielding, sensors, flexible electronics and transparent nanopaper, and environmental applications of biocarbon-based soft material composites are highlighted. Furthermore, the challenges and potential opportunities of biocarbon-based composites are identified, and prospects in biomaterial-based soft materials composites are presented.

Three-Dimensional Hollow Reduced Graphene Oxide Tube Assembly for Highly Thermally Conductive Phase Change Composites and Efficient Solar-Thermal Energy Conversion

Due to their extraordinary mechanical strength and electrical and thermal conductivities, graphene fibers and their derivatives have been widely utilized in various functional applications. In this work, we report the synthesis of a three-dimensional (3D) hollow reduced graphene oxide tube assembly (HrGOTA) using the same wet spinning method as graphene fibers. The HrGOTA has high thermal conductivity and displays the unique capability of encapsulating phase change materials for effective solar-thermal energy conversion. The HrGOTA comprises layers of moisture-fused hollow reduced graphene oxide tubes (HrGOTs), whose individual thermal conductivity is up to 578 W m^-1 K^-1. By impregnating 1-octadecanol into HrGOTs, a 1-octadecanol-filled HrGOT phase change composite (PCC) with a latent heat of 262.5 J g^-1 is obtained. This high latent heat results from the interfacial interaction between 1-octadecanol and the reduced graphene oxide tube, as evidenced by the shifts in XRD patterns of 1-octadecanol-filled and 1-octadecanol/multiwalled carbon nanotube-filled HrGOTA samples. In addition, 1 wt % multiwalled carbon nanotubes are added to the PCC to enhance visible light absorption. Because of their high thermal conductivity and visible light absorption rates, these new PCCs display high solar-thermal energy conversion and storage efficiencies of up to 81.7%, commensurate with state-of-the-art carbon-based PCCs but with significantly lower carbon weight percentages.

Flexible, Highly Thermally Conductive and Electrically Insulating Phase Change Materials for Advanced Thermal Management of 5G Base Stations and Thermoelectric Generators

Thermal management has become a crucial problem for high-power-density equipment and devices. Phase change materials (PCMs) have great prospects in thermal management applications because of their large capacity of heat storage and isothermal behavior during phase transition. However, low intrinsic thermal conductivity, ease of leakage, and lack of flexibility severely limit their applications. Solving one of these problems often comes at the expense of other performance of the PCMs. In this work, we report core-sheath structured phase change nanocomposites (PCNs) with an aligned and interconnected boron nitride nanosheet network by combining coaxial electrospinning, electrostatic spraying, and hot-pressing. The advanced PCN films exhibit an ultrahigh thermal conductivity of 28.3 W m-1 K-1 at a low BNNS loading (i.e., 32 wt%), which thereby endows the PCNs with high enthalpy (> 101 J g-1), outstanding ductility (> 40%) and improved fire retardancy. Therefore, our core-sheath strategies successfully balance the trade-off between thermal conductivity, flexibility, and phase change enthalpy of PCMs. Further, the PCNs provide powerful cooling solutions on 5G base station chips and thermoelectric generators, displaying promising thermal management applications on high-power-density equipment and thermoelectric conversion devices.

Synthesis and characterization of biopolyurethane crosslinked with castor oil-based hyperbranched polyols as polymeric solid-solid phase change materials

Novel crosslinking bio polyurethane based polymeric solid-solid phase change materials (SSPCM) were synthesized using castor oil (CO) based hyperbranched polyols as crosslinkers. CO-based hyperbranched polyols were synthesized by grafting 1-mercaptoethanol or α-thioglycerol via a thiol-ene click reaction method (coded as COM and COT, respectively). Subsequently, the three SSPCMs were synthesized by a two-step prepolymer method. Polyethylene glycol was used as the phase change material in the SSPCMs, while the CO-based hyperbranched polyols and two types of diisocyanate (hexamethylene diisocyanate (HDI) and 4,4'-diphenylmethane diisocyanate) served as the molecular frameworks. Fourier transform infrared spectroscopy indicated the successful synthesis of the SSPCMs. The solid-solid transition of the prepared SSPCMs was confirmed by X-ray diffraction analysis and polarized optical microscopy. The thermal transition properties of the SSPCMs were analyzed by differential scanning microscopy. The isocyanate and crosslinker types had a significant influence on the phase transition properties. The SSPCM samples prepared using HDI and COT exhibited the highest phase transition enthalpy of 126.5 J/g. The thermal cycling test and thermogravimetric analysis revealed that SSPCMs exhibit outstanding thermal durability. Thus, the novel SSPCMs based on hyperbranched polyols have great potential for application as thermal energy storage materials.

Synthesis and Properties of Shape-Stabilized Phase Change Materials Based on Poly(triallyl isocyanurate-silicone)/n-Octadecane Composites

Triallyl isocyanurate (TAIC) was modified by hydrogen silicone oil (SO) via hydrosilylation reaction, generating the original TAIC-SO (TS) intermediate. After the cross-linking polymerization of TS (PTS), the shape-stabilized phase change materials (PCMs) consisting of n-octadecane and silicone-modified supporting matrix were first synthesized by an in situ reaction. Remarkably, the novel three-dimensional PTS network effectively prevents the leakage of n-octadecane during its phase transition, solving the prominent problem of solid-liquid PCMs in practical applications. Moreover, n-octadecane is uniformly dispersed in the continuous and high-strength cross-linked network, contributing to excellent thermal reliability and structural stability of PTS/n-octadecane (TSO) composites. Differential scanning calorimetry analysis of the optimal TSO composite indicates that melting and freezing temperatures are 29.05 and 22.89 °C, and latent heats of melting and freezing are 130.35 and 129.81 J/g, respectively. After comprehensive characterizations, the shape-stabilized TSO composites turn out to be promising in thermal energy storage applications. Meanwhile, the strategy is practical and economical due to its advantages of easy operation, mild conditions, short reaction time, and low energy consumption.

Dopamine-Decorated Ti3C2Tx MXene/Cellulose Nanofiber Aerogels Supported Form-Stable Phase Change Composites with Superior Solar-Thermal Conversion Efficiency and Extremely High Thermal Storage Density

The exploitation of from-stable phase change materials (PCMs) with superior energy storage capacity and excellent solar-thermal conversion performance is crucial for the efficient exploitation of solar energy. Herein, 2D-layered polymerized dopamine-decorated Ti₃C₂T_x MXene nanosheets (P-MXene) with superior photothermal effects and excellent oxidation stability were synthesized from Ti₃AlC₂ particles by the selective etching and self-polymerization of dopamine. Then, novel biomass-derived PCM composites, eMPCMs, were fabricated by impregnating erythritol into P-MXene/cellulose nanofiber (CNF) hybrid aerogels. The porous and interconnected 3D aerogels adequately support erythritol and resist liquid leakage during thermal storage. Differential scanning calorimetry (DSC) results showed that the eMPCMs based on P-MXene/CNF aerogels exhibited an extremely high thermal storage density (325.4-330.6 J/g) and excellent PCM loading capacity (up to 1929%). The introduction of P-MXene nanosheets into eMPCMs significantly increased the solar-thermal conversion and storage efficiency, solar-thermal-electricity conversion capacity, and thermal conductivity of the synthesized PCM composites. Moreover, the P-MXene/CNF hybrid aerogel-based PCM composites possessed excellent long-term thermal reliability and thermostability. Hence, the synthesized eMPCMs reveal tremendous potential for efficient solar-thermal storage fields.

Multifunctional Phase Change Composites Based on Elastic MXene/Silver Nanowire Sponges for Excellent Thermal/Solar/Electric Energy Storage, Shape Memory, and Adjustable Electromagnetic Interference Shielding Functions

Multifunctional phase change materials (PCMs) are highly desirable for the thermal management of miniaturized and integrated electronic devices. However, the development of flexible PCMs possessing heat energy storage, shape memory, and adjustable electromagnetic interference (EMI) shielding properties under complex conditions remains a challenge. Herein, the multifunctional PCM composites were prepared by encapsulating poly(ethylene glycol) (PEG) into porous MXene/silver nanowire (AgNW) hybrid sponges by vacuum impregnation. Melamine foams (MFs) were chosen as a template to coat with MXene/AgNW (MA) to construct a continuous electrical/thermal conductive network. The MF@MA/PEG composites showed a high latent heat (141.3 J/g), high dimension retention ratio (96.8%), good electrical conductivity (75.3 S/m), and largely enhanced thermal conductivity (2.6 times of MF/PEG). Moreover, by triggering the phase change of the PEG, the sponges displayed a significant photoinduced shape memory function with a high shape fixation ratio (∼100%) and recovery ratio (∼100%). Interestingly, the EMI shielding effectiveness (SE) can be adjusted from 12.4 to 30.5 dB by a facile compression-recovery process based on shape memory properties. Furthermore, a finite element simulation was conducted to emphasize the advantage of the MF@MA/PEG composites in the thermal management of chips. Such flexible PCM composites with high latent heat storage, light-actuated shape memory, and adjustable EMI shielding functions exhibit great potential as smart thermal management materials in military and aerospace applications.

Scalable Flexible Phase Change Materials with a Swollen Polymer Network Structure for Thermal Energy Storage

3D porous structural materials are proved to be enticing candidates for the fabrication of high-performance organic phase change materials (PCMs), but the stringent fabrication process and poor processability greatly hampered their commercialization. Herein, flexible leakage-proof composite PCMs with pronounced comprehensive performance are fabricated by a scalable polymer swelling strategy without using any solvent, in which the paraffin wax (PW) segment is confined in a robust flexible 3D polymer network, giving rise to the composite PCMs with excellent form stability even at 160 °C, a high latent heat energy storage density of 133.6 J/g, and an outstanding thermal conductivity of up to ∼5.11 W/mK. More importantly, the mass production of the flexible composite phase change fiber, film, and bulk products can be achieved by adopting mature processing technologies. These resultant composite PCMs exhibit promising thermal management ability to solve the overheating problem of electronics and high-efficiency solar-thermal energy conversion capacity.

Cellulose nanofibril/carbon nanotube composite foam-stabilized paraffin phase change material for thermal energy storage and conversion

The leakage and low thermal conductivity of paraffin phase change material (PCM) must be addressed to achieve a more efficient energy storage process. In this study, cellulose nanofibril (CNF) foams were prepared as the porous support of paraffin to prevent its leakage, and multiwalled carbon nanotubes (CNTs) were incorporated in the foams to improve heat transfer performance. Treatment of CNF with methyltrimethoxysilane improved compatibility between the foams and paraffin. The prepared highly porous (porosity >96%) foams had paraffin absorption capacities exceeding 90%. The form-stable PCM composites displayed negligible paraffin leakage and had a compact structure. The prepared PCM composites had enhanced heat transfer performance, reasonable phase change properties and thermal stabilities. The enthalpy of the SCNF/CNT₅₀-Pw PCM composite decreased by 6% after 100 melting/freezing cycles. Compared with pristine paraffin, the PCM composites exhibited superior form-stabilities and improved thermal properties, which suggested application in a solar-thermal-electricity energy harvesting and conversion system.

Recent Advances in Polymer-Containing Multifunctional Phase-Change Materials

Phase-change materials (PCMs) play a key role in thermal energy storage owing to their high-energy storage density and small temperature fluctuation during the phase-transition stage. Polymers, either as a supporting material to prevent liquid leakage during the phase-change process or used with specific target, have been widely recognized in the fabrication of PCM composites. In the meantime, due to the continued demand for variety of PCMs, a single thermal energy storage function seems to be insufficient to meet these needs. Thanks to the good compatibility with PCMs and the structural adjustable properties of polymers, they have been broadly used as the second component in the multifunctional PCMs composite. In this Review, strategies for multifunctional PCMs supported by polymers and their potential energy applications, such as thermal energy harvesting and storage, shape memory, wearable devices, self-cleaning, and other forms of applications, are summarized comprehensively. The future research directions and challenges of multifunctional PCMs with polymers are also discussed.

Ultrafast Fabrication of Graphene-Reinforced Nanocomposites via Synergy of Steam Explosion and Alternating Convergent-Divergent Flow

Producing high-quality graphene and polymer/graphene nanocomposite is facing the problems of complex procedure, low efficiency, and serious resource waste. To explore a new fabrication approach with high efficiency and low cost is crucial for solving these technical issues, which becomes a current research hotspot and also a great challenge. Herein, a one-step melt mixing strategy based on the synergy of steam explosion and alternating convergent-divergent flow, is innovatively developed to fabricate high-density polyethylene (HDPE)/graphene nanocomposites using industrial-grade expanded graphite (EG) without chemical agents and complex procedures. The co-action of the external force derived from elongational melts and the internal force generated by steam explosion make EG ultrafastly exfoliate into few-layer graphene nanosheets (GNS) and simultaneously disperse in melts within 4 min. The as-produced GNS have a lateral size of over 5 µm and a minimum thickness of 1.4 nm, can introduce super heterogeneous nucleation to HDPE macromolecules and greatly increases nanocomposite crystallinity up to 86.5%. Moreover, plentiful HDPE crystallites and well-dispersed GNS jointly form an improved thermally-conductive network, making nanocomposites with a rapid-respond ability in solar-to-thermal conversion and heat dissipation. This facile strategy will facilitate the development of scalable production and wide application of high-performance graphene and highly-filled nanocomposites.

Bio-nanocomposites of graphene with biopolymers; fabrication, properties, and applications

The unique properties of graphene and graphene oxide (GO) nanocomposites make them suitable for a wide range of medical, industrial, and agricultural applications. The addition of graphene or GO to a polymeric matrix can ameliorate its thermo-mechanical, electrical, and barrier characteristics. The present paper reviews the literature on graphene/GO-based bio-nanocomposites and examines the various fabrication methods, such as chemical vapor deposition, chemical synthesis, microwave synthesis, the solvothermal method, molecular beam epitaxy, and colloidal suspension. Each procedure potentially has its disadvantages, especially for mass production. Therefore, introducing an effective method for fabricating graphene on a large scale with high quality is essential. Recent studies have shown that graphene-based bio-nanocomposites are promising materials given their excellent performance in the development of biosensors, drug delivery systems, antimicrobials, modified electrodes, and energy storage systems among other applications. In this review, we evaluate the various procedures used for developing graphene/GO-based bio-nanocomposites and examine the features and applications of the related products. Furthermore, the toxicity of these compounds and attempts to uncover the optimal combinations of biopolymers and carbon nanomaterials for industrial applications will be discussed.

Waterproof Phase Change Material with a Facilely Incorporated Cellulose Nanocrystal/Poly(N-isopropylacrylamide) Network for All-Weather Outdoor Thermal Energy Storage

The incorporation of porous supporting materials to prepare shape-stable phase change materials (PCMs) is of great interest in recent years. However, extensive reported composite PCMs are shape-stable in the air atmosphere but neglected in the water environment. To develop shape-stable and waterproof PCMs is important for their outdoor applications but challenging. Herein, we report a novel cellulose nanocrystal/poly(N-isopropylacrylamide) (CNC/PNIPAM) gel-supported hexadecanol (H-anol) PCM with good thermal storage properties and excellent shape stability in both air and water environments. The CNC/PNIPAM hydrogel is prepared through an ultraviolet-induced C═C cross-linking reaction, and its physical structure and mechanical properties are well characterized. H-anol is then directly immerged into the CNC/PNIPAM alcogel by a facile and low-cost solvent-exchange strategy. The mechanism of the solvent-exchange strategy has been established. Because of the temperature-sensitive hydrophilic/hydrophobic transform behavior of the CNC/PNIPAM network, the CNC/PNIPAM/H-anol PCM displays excellent shape stability in a water environment by forming a dense hydrophobic surface, providing it with great potential in all-weather thermal energy storage applications.

Leakage-proof microencapsulation of phase change materials by emulsification with acetylated cellulose nanofibrils

We use acetylated cellulose nanofibrils (AcCNF) to stabilize transient emulsions with paraffin that becomes shape-stable and encapsulated phase change material (PCM) upon cooling. Rheology measurements confirm the gel behavior and colloidal stability of the solid suspensions. We study the effect of nanofiber content on PCM leakage upon melting and compare the results to those from unmodified CNF. The nanostructured cellulose promotes paraffin phase transition, which improves the efficiency of thermal energy exchange. The leakage-proof microcapsules display high energy absorption capacity (ΔH_m = 173 J/g) at high PCM loading (up to 80 wt%), while effectively controlling the extent of supercooling. An excellent thermal stability is observed during at least 100 heating/cooling cycles. Degradation takes place at 291 °C, indicating good thermal stability. The high energy density and the effective shape and thermal stabilization of the AcCNF-encapsulated paraffin points to a sustainable solution for thermal energy storage and conversion.