Electrical energy harvesting by a form stable phase change material composite

Abstract

In one aspect, the disclosure relates to methods for harvesting and storing solar and thermal energy and producing electricity using a form-stable phase change material (PCM) composite, wherein the PCM composite is placed in a first environment and connected electrically to a second environment having a difference in at least one property such as temperature, salinity, relative humidity, atmospheric CO2 concentration, ion identity in solution, conductive filler identity in PCM composites, or a combination thereof, such that the difference in property creates a gradient in that property from one PCM composite to the second environment. Also disclosed are methods of making the PCM composite, including methods of making shape-memory vitrimer (SMV) materials to contain the PCM composite.

Description

ELECTRICAL ENERGY HARVESTING BY A FORM STABLE PHASE CHANGE MATERIAL COMPOSITECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application Ser. No. 63 / 594,703, filed October 31 , 2023 and U.S. Provisional Application Ser. No. 63 / 550,188, filed February 6, 2024. Both applications are incorporated herein by reference in their entireties.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under grant numbers 1946231 and 1736136 awarded by the National Science Foundation. The government has certain rights in this invention.BACKGROUND

[0003] Owing to the crisis of climate change, developing renewable energy is one of the challenges facing human beings. The transition to a lower-carbon economy can benefit from clean energy, which reduces environmental pollution and energy depletion. Solar energy is one candidate to produce converted electrical and mechanical energy and mitigates the climate change without any negative environmental impact.

[0004] To meet the requirements for absorbing a large amount of external sunlight or thermal energy, phase change material (PCM) is an appropriate substance that has a high heat of fusion for undergoing thermal energy storage (TES) during the phase transition process. Because of their high thermal density, chemical stability, and non-toxicity, PCMs can be utilized as a working material with the ability to absorb and release thermal energy during the transition of solid and liquid states. It maintains the TES ability during cyclic phase transition process. Typically, solidliquid PCMs such as polyethylene glycol (PEG), paraffin, and fatty acid are widely utilized in various applications due to the appropriate phase change temperature and high latent heat (AH). Compared with other categories of PCMs, solid-liquid PCMs show a high TES capacity and a wide range of phase transition temperatures that can generally exhibit excellent reliability and durability, resulting in various applications under different external conditions. However, the problem of PCM leakage from thermal energy generation (TEG) and / or TES devices restricts further application of solid-liquid PCMs, since leakage can cause loss of the PCMs during the melting process.

[0005] Furthermore, it has been found that it is difficult for pure PCMs to absorb both sunlight and thermal energy for producing electrical energy. Therefore, it is necessary to fabricate a form stable PCM composite that can maintain the liquid state without any leakage. To do this, microencapsulation method to prevent PCM leakage has been reported and microsphere structures of PCM composite with high form stability have been demonstrated. Considering the volume expansion of solid-liquid PCM during the melting process, flexible supporting materials were required to fabricate the form stable PCM composite. In general, melamine resin, poly(methyl methacrylate) (PMMA), and polyaniline (PANI) have been selected as supporting materials to construct core-shell like PCM composites, which exhibit high flexibilities during the phase transition process. Although the microencapsulated PCM composites sustain their liquid state without any leakage, the weight fraction of the pure PCMs is reduced, which leads to TES loss for general applications. Furthermore, the microencapsulated PCM composite decreased the heat of fusion significantly during the phase transition process.

[0006] Despite advances in solar and thermal energy research, there is still a scarcity of systems and methods for producing and harvesting energy that are able to harness the energy storage and harvesting power of phase change materials without leakage of the PCMs and subsequent degradation of the systems when the PCMs are in a liquid state. An ideal system would have a high weight fraction of pure PCMs to avoid TES loss and increase duration of energy storage and must have a high heat of fusion during the phase transition process These needs and other needs are satisfied by the present disclosure.SUMMARY

[0007] In accordance with the purpose(s) of the present disclosure, as embodied and broadly described herein, the disclosure, in one aspect, relates to methods for harvesting and storing solar and thermal energy and producing electricity using a form-stable phase change material (PCM) composite, wherein the PCM composite is placed in a first environment and connected electrically to a second environment having a difference in at least one property such as temperature, salinity, relative humidity, atmospheric CO2 concentration, ion identity in solution, conductive filler identity in PCM composites, or a combination thereof, such that the difference in property creates a gradient in that property from one PCM composite to the second environment. Also disclosed are methods of making the PCM composite, including methods of making shapememory vitrimer (SMV) materials to contain the PCM composite.

[0008] Other systems, methods, features, and advantages of the present disclosure will be orbecome apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims. In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

[0010] FIG. 1 shows schematics of thermoelectric energy harvesting during the PCM phase transition process. The carbon dioxide (CO2) can dissolve into the water to generate the hydrogen, bicarbonate, and carbonate ions to promote the electrical conductivity. Definitely, the different CO2 concentration creates the conductivity gradient for converting solar energy to electrical energy during the light-on / -off process.

[0011] FIGs. 2A-2F show FTIR results of (FIG. 2A) TAI and (FIG. 2B) final shape memory vitrimer (SMV). (FIG. 2C) TGA peaks of SMVs and pure PCMs. (FIG. 2D) contact angle results of pre- vitrimer and final SMV. (FIG. 2E) Electrical resistivity curves of pre-vitrimer and final SMV under the increase in RH at the initial CO2 concentration. (FIG. 2F) Electrical resistivity peaks of SMVs at RH 70%, 80%, and 90%, which are flexible under the change of CO2 concentration.

[0012] FIGs. 3A-3D show electrical resistivity of (FIG. 3A) pre-vitrimer and final SMV, (FIG. 3B) initial RH with 700 ppm CO2 concentration, (FIG. 3C) initial RH with 1200 ppm CO2 concentration, and (FIG. 3D) CO2 dissolving ability under the temperature variation.

[0013] FIG. 4A shows UV-Vis peaks of pre-vitrimer and SMV with different thickness. FIG. 4B shows the result of SMV temperature sweep. FIG. 4C shows form stability photo images of pre- vitrimer and SMV after light-on / -off process. FIG. 4D shows recovery stress of SMV at 90 °C.

[0014] FIG. 5A shows an IR camera temperature gradient of SMV and SMV supported PCM composites during the light-on process. FIG. 5B shows temperature peaks during light-on process. FIG. 5C shows temperature peaks during light-off process. FIG. 5D shows IR camera temperature gradient of SMV and SMV supported PCM composites during the light-off process.

[0015] FIGs. 6A-6D show for the assembly made of RH 70% SMV supported 1-TD and RH 90% SMV supported PEG, (FIG. 6A) output voltage with different CO2 concentrations during the lighten process and (FIG. 6B) output current with different CO2 concentrations during the light-on process. (FIG. 6C) Output voltage with different CO2 concentrations during the light-off process and (FIG. 6D) output voltage with different CO2 concentrations during the light-off process.

[0016] FIG. 7A shows the basic equation of carbon dioxide (CO2) dissolving into the water and FIG. 7B shows the design of electrical energy harvesting.

[0017] FIG. 8 shows the procedure of synthesizing cross-linked shape memory vitrimer (SMV) by thermal curing.

[0018] FIG. 9 shows the procedure of synthesizing the final SMV through 3D printing by ultraviolet curing.

[0019] FIG. 10A shows the fabrication of SMV supported PCM composite. FIG. 10B shows optical images of different size of SMV containers.

[0020] FIGs. 11A-11F show FTIR results of (FIG. 11 A) diphenyl carbonate, (FIG. 11B) di(trimethylolpropane), (FIG. 11C) tris(2-aminoethylamine), (FIG. 11D) pre-vitrimer, (FIG. 11E) pre-mixture before 3D printing, and (FIG. 11 F) final SMV at different temperature.

[0021] FIGs. 12A-12D show XPS results of diphenyl carbonate at (FIG. 12A) C1s peaks and (FIG. 12B) O1s peaks. The di(trimethylolpropane) at (FIG. 12C) C1s peaks and (FIG. 12D) O1s peaks.

[0022] FIGs. 13A-13D show XPS results of pre-synthesized polymer without mixing with tris((2- (acryloyloxy)ethyl) isocyanurate (TAI) (FIG. 13A) C1s peaks and (FIG. 13B) O1s peaks, and (FIG. 13C) N1s peaks. (FIG. 13D) Atomic spectrum of three elements.

[0023] FIGs. 14A-14D show XPS results of final SMV (FIG. 14A) C1s peaks and (FIG. 14B) O1s peaks, and (FIG. 14C) N1s peaks. (FIG. 14D) Atomic spectrum of three elements.

[0024] FIGs. 15A-15D show Raman peaks of (FIG. 15A) diphenyl carbonate, (FIG. 15B) di(trimethylolpropane), (FIG. 15C) pre-vitrimer, (FIG. 15D) final SMV.

[0025] FIG. 16A shows stress-strain curves of pre-vitrimer and final SMV. SEM images of (FIG. 16B) final SMV, (FIG. 16C) pure 1-TD, and (FIG. 16D) pure PEG.

[0026] FIGs. 17A-17B show form stable test optical images of (FIG. 17A) pure 1-TD and 1-TD composites, and (FIG. 17B) pure PEG and PEG composites.

[0027] FIGs. 18A-18D show volume expansion ratios of (FIG. 18A) SMV supported 1-TD composite and (FIG. 18B) SMV supported PEG composite. (FIG. 18C) thermal conductivity results of pure PCM and PCM composites. (FIG. 18D) XRD peaks of SMV, pure PCM, and PCM composites.

[0028] FIGs. 19A-19D show DSC cycling results of (FIG. 19A) SMV, (FIG. 19B) pure -1TD, and (FIG. 19C) pure PEG. (FIG. 19D) XRD peaks after 100 cycles.

[0029] FIG. 20A shows the final temperature with different RH at 15 mW / cm2solar light intensity. Electrical resistivity peaks of (FIG. 20B) RH 70% with initial 400 ppm CO2 concentration, (FIG. 20C) RH 80% with initial 400 ppm CO2 concentration, and (FIG. 20D) RH 90% with initial 400 ppm CO2 concentration.

[0030] FIGs. 21A-21 F show electrical resistivity peaks of (FIG. 21 A) RH 70% with 700 ppm CO2 concentration, (FIG. 21 B) RH 80% with initial 700 ppm CO2 concentration, (FIG. 21 C) RH 90% with initial 700 ppm CO2 concentration, (FIG. 21 D) RH 70% with initial 1200 ppm CO2 concentration, (FIG. 21 E) RH 80% with initial 1200 ppm CO2 concentration, and (FIG. 21 F) RH 90% with initial 1200 ppm CO2 concentration.

[0031] FIGs. 22A-22F show the electrical resistivity at RH 70%, the different thickness of SMV supported 1-TD composite under (FIG. 22A) 400 ppm CO2 concentration, (FIG. 22B) 700 ppm CO2 concentration, (FIG. 22C) 1200 ppm CO2 concentration. For the different thickness of SMV supported PEG composites under (FIG. 22D) 400 ppm CO2 concentration, (FIG. 22E) 700 ppm CO2 concentration, and (FIG. 22F) 1200 ppm CO2 concentration.

[0032] FIGs. 23A-23F show the electrical resistivity at RH 80%, the different thickness of SMV supported 1-TD composite under (FIG. 23A) 400 ppm CO2 concentration, (FIG. 23B) 700 ppm CO2concentration, (FIG. 23C) 1200 ppm CO2 concentration. For the different thickness of SMV supported PEG composites under (FIG. 23D) 400 ppm CO2concentration, (FIG. 23E) 700 ppm CO2 concentration, and (FIG. 23F) 1200 ppm CO2 concentration.

[0033] FIGs. 24A-24F show the electrical resistivity at RH 90%, the different thickness of SMV supported 1-TD composite under (FIG. 24A) 400 ppm CO2 concentration, (FIG. 24B) 700 ppmC02concentration, (FIG. 24C) 1200 ppm CO2concentration. For the different thickness of SMV supported PEG composites under (FIG. 24D) 400 ppm CO2concentration, (FIG. 24E) 700 ppm CO2 concentration, and (FIG. 24F) 1200 ppm CO2 concentration.

[0034] FIGs. 25A-25F show the temperature peaks of different thickness of SMV supported 1- TD composites, the light-on process at (FIG. 25A) RH 40% with 400 ppm CO2 concentration, (FIG. 25B) RH 40% with 700 ppm CO2concentration, (FIG. 25C) RH 40% with 1200 ppm CO2concentration. For light-off process, (FIG. 25D) RH 40% with 400 ppm CO2concentration, (FIG. 25E) RH 40% with 700 ppm CO2concentration, (FIG. 25F) RH 40% with 1200 ppm CO2concentration.

[0035] FIGs. 26A-26F show the temperature peaks of different thickness of SMV supported PEG composites, the light-on process at (FIG. 26A) RH 40% with 400 ppm CO2concentration, (FIG. 26B) RH 40% with 700 ppm CO2concentration, (FIG. 26C) RH 40% with 1200 ppm CO2concentration. For light-off process, (FIG. 26D) RH 40% with 400 ppm CO2concentration, (FIG. 26E) RH 40% with 700 ppm CO2concentration, (FIG. 26F) RH 40% with 1200 ppm CO2concentration.

[0036] FIGs. 27A-27H show the temperature peaks of 3.5 mm height SMV supported 1-TD composite, the light-on process at (FIG. 27A) RH 40% with different CO2concentration, (FIG. 27B) RH 70% with different CO2concentration, (FIG. 27C) RH 80% with different CO2concentration, and (FIG. 27D) RH 90% with different CO2concentration. For light-off process, (FIG. 27E) RH 40% with different CO2concentration, (FIG. 27F) RH 70% with different CO2concentration, (FIG. 27G) RH 80% with different CO2concentration, and (FIG. 27H) RH 90% with different CO2concentration.

[0037] FIGs. 28A-28H show the temperature peaks of 3.5 mm height SMV supported PEG composite, the light-on process at (FIG. 28A) RH 40% with different CO2concentration, (FIG. 28B) RH 70% with different CO2concentration, (FIG. 28C) RH 80% with different CO2concentration, and (FIG. 28D) RH 90% with different CO2concentration. For light-off process, (FIG. 28E) RH 40% with different CO2concentration, (FIG. 28F) RH 70% with different CO2concentration, (FIG. 28G) RH 80% with different CO2concentration, and (FIG. 28H) RH 90% with different CO2concentration.

[0038] FIG. 29 shows schematics of thermoelectric energy harvesting. The single walled carbon nanotube (SWCNT) embedded PDMS foam supported PCM composite can absorb and release a lot of thermal energy during the phase transition process. Obviously, the PDMS foams withdifferent weight fractions of SWCNTs show different electrical conductivities and the final PCM composites connected power generator harvests electrical energy during the phase transition process.

[0039] FIG. 30A shows optical images of PDMS / CNTs and final PCM composites. (FIG. 30B) Weight fraction of pure PCMs in the PCM composites. PDMS / CNT1 : (FIG. 30C) SEM image and (FIG. 30D) pore size distribution. PDMS / CNT2: (FIG. 30E) SEM image and (FIG. 30F) pore size distribution. SEM images of (FIG. 30G) 1-TD / PDMS and (FIG. 30H) PEG / PDMS.

[0040] FIG. 31 A shows form stable optical images of pure PCM and PCM composites. (FIG. 31 B) Electrical resistivity of PCM composites. DSC results of (FIG. 31C) pure 1-TD and 1-TD / PDMS composite, (FIG. 31 D) pure PEG and PEG / PDMS composite.

[0041] FIG. 32 shows fabrication method of form stable PCM / PDMS composite.

[0042] FIG. 33 shows elastic springback test of PDMS / CNT foams.

[0043] FIGs. 34A-34D show TEM images of (FIG. 34A) PDMS / CNT1 and (FIG. 34B) PDMS / CNT2. SEM images of (FIG. 34C) pure 1-TD and (FIG. 34D) pure PEG.

[0044] FIG. 35A shows XRD results of PDMS foams, pure PCM, and PCM composites. (FIG. 35B) Thermal conductivity of the PCM composites. TGA peaks of (FIG. 35C) PDMS / CNT1 , pure 1-TD, and 1-TD / PDMS composite; (FIG. 35D) PDMS / CNT2, pure PEG, and PEG / PDMS composite.

[0045] FIG. 36A shows DSC cycling result of 1-TD / PDMS and (FIG. 36B) FTIR peaks after 100 cycles. (FIG. 36C) DSC cycling result of PEG / PDMS and (FIG. 36D) FTIR peaks after 100 cycles.

[0046] FIG. 37 shows a schematic of one phase change material (PCM) is used for converting sunlight to electricity. (Left): seawater within an indoor air-conditioned “cold house”; (Right) seawater within an outdoor “hot house”.

[0047] FIG. 38 shows the voltage and current peaks during the light-on / -off process.

[0048] FIG. 39 shows images of an LED bulb is lit up during the light-on / -off process.

[0049] FIG. 40 shows a schematic of seawater temperature difference for absorbing the sunlight to generate the electrical energy harvesting. By the Seebeck Effect, a temperature gradient exists with seawater depth (i.e., the ocean floor is at a lower temperature than the surface). Along with the temperature gradient, an ion concentration gradient is observed. The ion concentrationgradient leads to a potential difference, and this combination of factors results in the ability to harvest energy.

[0050] FIG. 41 shows the voltage and current peaks and LED bulb photo image.

[0051] Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.DETAILED DESCRIPTION

[0052] In one aspect, thermal energy storage (TES) capacity is proportional to the pure phase change material (PCM) mass ratio and it is indispensable to keep a high weight fraction of the pure PCM in any composite material used for energy storage and / or harvesting. In another aspect, a 3D porous material can be used as an advanced supporting material due to its high porosity and large surface area, which can maintain high TES of form stable PCM composites. In another aspect, the 3D porous material can infiltrate a plenty of pure PCM into the pores and sustain a high form stability during the phase transition process.

[0053] In one aspect, 3D porous graphene aerogels have been utilized to fabricate form stable PCM composites and prevent leakage successfully. In a further aspect, except for the porous structure, carbon based material is easy to absorb sunlight and facilitate the pure PCM to store thermal energy. In still another aspect, the carbon-based material can contribute to the solar photo-thermal conversion and storage using carbon-based material to fabricate the PCM composite. In some aspects, a porous graphene aerogel supported PCM composite contains a large weight fraction of pure PCM and has been connected to the thermal energy generation (TEG) for producing electrical energy.

[0054] In some aspects, electrical energy was obtained by connecting a single PCM composite to the hot side of the TEG device and fixing the temperature of the cold side. Further in this aspect, the PCM composite absorbed enough thermal energy before removing the heat source and the TEG can induce current due to the temperature difference between the two sides of the TEG device.

[0055] In an aspect, by connecting two types of PCM composites with different transition temperatures to the two sides of a TEG, electrical energy has been obtained during the heating and cooling process. In another aspect, the carbon aerogel supported PCM composites showed a highly efficient thermal and sunlight-driven energy storage for harvesting electrical energy. Although this concept is very interesting, it still needs to connect two PCM composites with the two sides of a TEG device. This energy harvesting method faces low-efficiency and high-cost problem. Furthermore, even if the temperature difference exists in the PCM composites, it cannot produce electrical voltage and current without a TEG device. Generating electrical energy merely using two different PCM composites without a TEG device is an unprecedented research.

[0056] In one aspect, and without wishing to be bound by theory, it was hypothesized that based on the well-known Seebeck effect, by directly connecting two types of phase change materials with different conductivities and different phase transition temperatures, stable electrical energy output would be feasible without a TEG. To validate this new concept, in one aspect, disclosed herein is the use of polydimethylsiloxane (PDMS) is to fabricate a 3D porous foam structure, and single-walled carbon nanotube (SWCNT) is dispersed into the PDMS porous skeletons to increase electrical conductivity of the system. Compared with the previously-known aerogel structure, PDMS foam exhibits much higher flexibility and better mechanical properties to construct excellent internal skeletons as electrical carriers.

[0057] In one aspect, polyethylene glycol (PEG) and 1 -tetradecanol (1-TD) are selected as two types of PCMs for fabricating PDMS / SWCNT supported form stable PCM composites. The concentration of SWCNT is different in each PDMS foam in order to observe the thermoelectric energy harvesting under the heating and cooling processes. In a further aspect, the SWCNT embedded PDMS foam can convert sunlight to thermal energy and then to electricity effectively.

[0058] Herein, it is proposed to eliminate the energy harvesting devices by directly connecting two types of PCM composites with different electrical conductivities and different phase change temperatures. In an aspect, it works under the Seebeck effect. In one aspect, it is proposed to produce the different electrical conductivities by changing the surface humidity of the PCM composites with different concentrations of dissolved carbon dioxide (CO2).

[0059] In an aspect, herein it is proposed to use 3D printed hydrophilic shape memory vitrimer (SMV) or vitrimer for short as the supporting material to prepare form-stable PCM composites. In one aspect, a reason for using SMV to manufacture the supporting container is that under cyclic thermal loading, fatigue failure may occur in the container of the form-stable PCM composites. Ina further aspect, the cracks, if not healed, will lead to leaking of the PCM and the energy harvesting assembly will stop working. In a further aspect, at the end of the service life, one may want to recycle the container and the PCM to make the system sustainable. In an aspect, SMVs, as chemically cross-linked thermoset polymers, have outstanding mechanical properties, shape memory effect, self-healing capability, and recyclability. In an aspect, a combination of shape memory effect and intrinsic self-healing capability can help heal wider opened cracks per the biomimetic close-then-heal (CTH) strategy. In some aspects, although most SMVs exhibit low electrical conductivity, it can be increased rapidly under the moisture environment with high concentrations of carbon dioxide (CO2), if the SMVs are hydrophilic. Further in this aspect,, by simply changing the humidity and the concentration of carbon dioxide on the surface of the hydrophilic SMV supporting material, different electrical conductivities can be obtained. In one aspect, coupled with the different phase transition temperatures by infiltrating different PCMs, the form-stable PCM composites satisfy the requirement for different electrical conductivities and different phase transition temperatures. As a result, electricity can be generated by directly connecting the two PCM composites based on the Seebeck effect.

[0060] In one aspect, the Seebeck effect can be further explained as follows. In one aspect, it is known that ions in aqueous solution can move from the hot side to the cold side in a medium under the existence of temperature gradient. In a further aspect, the ion diffusion ability at the hot side is higher than that at the cold side. In yet another aspect, the ion movements cause an ion concentration gradient, which produces a potential difference. Therefore, the idea of obtaining electrical energy by merely using SMV supported two types of PCM composites is disclosed herein. Although the dissolving ability of CO2is decreased at higher temperatures, both ionization of carbonic acid and ion diffusivity are increased rapidly to speed up the ion movements from the hot side to the cold side. In another aspect, and without wishing to be bound by theory, he increase in ion concentration at the cold side promotes the generation of carbonic acid and recombine into CO2. In a word, the CO2 enters the hot side, decomposes into ions, moves to the cold side, and recombines into CO2. The working principle is further illustrated in FIGs. 7A-7B.

[0061] In another aspect, to produce continuous electricity output, light-on and light-off cycles can be used to maintain a constant temperature gradient between the two SMV-supported PCM composites. In a further aspect, during the light-on process, the PCMs change from solid to liquid, absorbing a large amount of heat, but almost keeping the temperature at their corresponding phase transition temperature, thus maintaining a constant thermal gradient, which is one critical requirement for the Seebeck effect. In another aspect, to keep continuous electricity output, alight-off process must follow. In one aspect, during light-off, the two PCMs change from liquid to solid, which releases heat, but almost maintains a constant thermal gradient, again, satisfying the requirement for Seebeck effect. In another aspect, this light-on / -off process completes one cycle.

[0062] In still another aspect, the subsequent cycles will repeat the first cycle, i.e., a light-on branch, followed by a light-off branch. In one aspect, as a result, continuous and constant temperature gradient will be maintained, leading to continuous electricity production.

[0063] In one aspect, herein polyethylene glycol (PEG) and 1 -tetradecanol (1-TD) are used as two types of pure PCMs. In a further aspect, the shape memory vitrimer (SMV) container, which is a rectangular hollow box, is obtained by 3D printing using digital light processing (DLP) type of 3D printer. In some aspects, the two types of PCM composites are then connected with each other and water is sprayed on their surfaces. In a further aspect, with different concentrations of carbon dioxide dissolved in the water, which is provided from a CO2storage tank, different electrical conductivities between the two sides of the PCM composites can be created, as shown in FIG. 1. In the Examples, the preparation and test results of the new energy harvesting device are reported.Phase Change Materials (PCMs) and Composites Thereof

[0064] In one aspect, in the disclosed systems and methods, the phase change material can be a liquid-solid phase change material. In another aspect, the PCM can be or include 1-TD, PEG, or a combination thereof. In another aspect, the PEG can have an average molecular weight of from about 4000 Da to about 8000 Da, or of about 4000 Da, about 6000 Da, about 8000 Da, or any combination thereof. Other phase change materials are also contemplated and should be considered disclosed. In one aspect, the phase change material can be an inorganic phase change material, such as, for example, KF-4H2O, Mn(NO3)2-6H2O, CaCI2-6H2O, LiNO3-3H2O; an inorganic eutectic such as, for example, 66.6% CaCI2-6H2O + 33.3% MgCI2-6H2O, 45% Ca(NO3)2-6H2O + 55% Zn(NO3)2-6H2O; an organic eutectic such as, for example, 67.1% naphthalene + 32.9% benzoic acid; or an organic phase change material such as, for example, dimethyl sulfoxide, C16-C18 paraffin, or C13-C24 paraffin. Mixtures and combinations of these phase change materials can also be used in the form-stable PCM composites.

[0065] Also disclosed herein is a form-stable PCM composite including a shape memory vitrimer (SMV) structure, where the SMV structure is filled with a PCM. In another aspect, no chemical reactions occur between the PCM and the SMV structure. In still another aspect, the form stable PCM composite is stable through at least about 100 thermal cycles.

[0066] In an alternative aspect, the form-stable PCM composite can include a PDMS foam and a phase change material. In some aspects, the PDMS foam can include single walled carbon nanotubes (SWCNTs). In a further aspect, the SWCNTs are present in the PDMS foam in a weight fraction of from about 0.33% to about 1%, or of about 0.33, 0.5, 0.75, or about 1%. In a further aspect, the form-stable PCM composite can recover at least 99% of its original volume following compression. In one aspect, the PDMS foam has an average pore diameter of from about 150 pm to about 160 pm.Method for Producing Electricity

[0067] In one aspect, disclosed herein is a method for producing electricity by harvesting solar and / or thermal energy, the method including at least the steps of:(a) placing a form-stable PCM composite as disclosed herein in a first environment;(b) providing an electrical connection between the first form-stable PCM composite and a second environment; wherein the first environment and the second environment differ in at least one property, creating a gradient in the at least one property between the form-stable PCM and the second environment; and wherein electric current flows along the electrical connection between the first form-stable PCM composite and the second environment due to the gradient.

[0068] In another aspect, the at least one property can be salinity, relative humidity, atmospheric CO2 concentration, ambient temperature, or any combination thereof. In one aspect, the ambient temperature of the first environment is higher than the ambient temperature of the second environment. In another aspect, the first environment can be outdoors and the second environment can be indoors, such as, for example, in an air-conditioned building. In an alternative aspect, the ambient temperature of the second environment can be higher than the ambient temperature of the first environment. Further in this aspect, the first environment is outdoors and the second environment is indoors, such as, for example, inside a power plant or inside a factory.

[0069] In another aspect, the first environment and the second environment include saline solutions, such as, for example, seawater. In still another aspect, the saline solution in the first environment and the saline solution in the second environment have different concentrations. In an alternative aspect, the form-stable PCM composite can hold a volume of a second saline solution. In some aspects, the first environment can be an ocean surface and the secondenvironment can be the ocean floor. In any of these aspects, the electrical connection can be provided by a conducting wire.Method for Storing Electricity

[0070] In one aspect, disclosed herein is a method for storing thermal energy, the method including at least the steps of:(a) performing the method as disclosed herein to harvest solar and / or thermal energy; and(b) increasing the temperature of the first environment, causing the phase change material of the form-stable PCM composite to undergo a phase change from solid to liquid; wherein thermal energy is stored in the liquid phase of the form-stable PCM composite.

[0071] In another aspect, increasing the temperature of the first environment occurs when the ambient temperature of the first environment increases, such as an increase in temperature of an outdoor environment due to weather conditions. In another aspect, the first environment is indoors and the ambient temperature increases due to heat given off by an industrial process. In any of these aspects, stored energy in the form-stable PCM composite is released when the phase change material of the PCM composite undergoes a phase change from liquid to solid as the temperature of the first environment decreases.Shape-Memory Vitrimer (SMV) Structure

[0072] In an aspect, disclosed herein is a method for synthesizing a SMV, the method including at least the steps of:(a) admixing a first monomer and a second monomer to form a monomer composition;(b) admixing a polymerization agent with the monomer composition, wherein the polymerization agent initiates polymerization, forming a pre-polymer;(c) admixing the pre-polymer with a pre-vitrimer and a photoinitiator to form the SMV.

[0073] In a further aspect, the first monomer can be diphenyl carbonate. In another aspect, the second monomer can be di(trimethylolpropane). In still another aspect, the polymerization agent can be tris(2-aminoethylamine). In yet another aspect, the pre-vitrimer can be tris((2- (acryloyloxy)ethyl) isocyanurate (TAI). In an aspect, the photoinitiator can be diphenyl(2,4,6- trimethylbenzoly)phosphine oxide (TPO). Although one SMV is described, other SMVs arecontemplated for use herein and should be considered disclosed. Also disclosed are SMVs produced by the disclosed method.

[0074] In one aspect, the SMV absorbs atmospheric water, carbon dioxide, or both. In another aspect, the SMV experiences changes in electrical resistivity resulting from changes in relative humidity such as, for example, a decrease in electrical resistivity with an increase in relative humidity. In another aspect, absorption of carbon dioxide changes with a change in external temperature, such as a decrease in absorption of carbon dioxide with an increase in external temperature.

[0075] In one aspect, the SMV remains solid and substantially retains its original shape between at least 25 °C and 80 °C. In an aspect, the SMV has a tensile strength of from about 0.05 MPa to about 10.0 MPa, or of about 0.05, 0.1, 0.5, 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8,5, 9, 9.5, or about 10 MPa, and, in some aspects, the SMV is optically transparent. Without wishing to be bound by theory, an optically transparent SMV allows sunlight to contact the PCM held within the SMV.

[0076] In another aspect, disclosed herein is a structure containing the disclosed SMV. In some aspects, the structure can be a hollow box. In one aspect, the structure has a wall thickness of from about 1 mm to about 4 mm. In another aspect, the structure is 3D printed.

[0077] Many modifications and other embodiments disclosed herein will come to mind to one skilled in the art to which the disclosed compositions and methods pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the disclosures are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. The skilled artisan will recognize many variants and adaptations of the aspects described herein. These variants and adaptations are intended to be included in the teachings of this disclosure and to be encompassed by the claims herein.

[0078] Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0079] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure.

[0080] Any recited method can be carried out in the order of events recited or in any other order that is logically possible. That is, unless otherwise expressly stated, it is in no way intended that any method or aspect set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not specifically state in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including matters of logic with respect to arrangement of steps or operational flow, plain meaning derived from grammatical organization or punctuation, or the number or type of aspects described in the specification.

[0081] All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

[0082] While aspects of the present disclosure can be described and claimed in a particular statutory class, such as the system statutory class, this is for convenience only and one of skill in the art will understand that each aspect of the present disclosure can be described and claimed in any statutory class.

[0083] It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed compositions and methods belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and should not be interpreted in an idealized or overly formal sense unless expressly defined herein.

[0084] Prior to describing the various aspects of the present disclosure, the following definitions are provided and should be used unless otherwise indicated. Additional terms may be defined elsewhere in the present disclosure.Definitions

[0085] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of,” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.” Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.

[0086] As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a shape memory vitrimer,” “a phase change material,” or “an ion concentration gradient,” include, but are not limited to, mixtures, series, or combinations of two or more such shape memory vitrimers, phase change materials, or ion concentration gradients, and the like.

[0087] It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disclosed, then “10” is also disclosed.

[0088] When a range is expressed, a further aspect includes from the one particular value and / or to the other particular value. For example, where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure, e.g. the phrase “x to y” includes the range from ‘x’ to ‘y’ as well as the range greater than ‘x’ and less than ‘y’. The range can also be expressed as an upper limit, e.g. 'about x, y, z, or less’ and should be interpreted to include the specific ranges of ‘about x’, 'about y’, and ‘about z’ as well as the ranges of ‘less than x’, less than y’, and ‘less than z’. Likewise, the phrase ‘about x, y, z, or greater’ should be interpreted to include the specific ranges of ‘about x’, ‘about y’, and ‘about z’as well as the ranges of ‘greater than x’, greater than y’, and ‘greater than z’. In addition, the phrase “about ‘x’ to ‘y’”, where ‘x’ and ‘y’ are numerical values, includes “about ‘x’ to about ‘y’”.

[0089] It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or subranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a numerical range of “about 0.1 % to 5%” should be interpreted to include not only the explicitly recited values of about 0.1% to about 5%, but also include individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.

[0090] As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as recited in the claims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some circumstances, the value that provides equivalent results or effects cannot be reasonably determined. In such cases, it is generally understood, as used herein, that “about” and “at or about” mean the nominal value indicated ±10% variation unless otherwise indicated or inferred. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about,” “approximate,” or “at or about” whether or not expressly stated to be such. It is understood that where “about,” “approximate,” or “at or about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0091] As used herein, the term “effective amount” refers to an amount that is sufficient to achieve the desired modification of a physical property of the composition or material. For example, an “effective amount” of a salt (or salts) in a solution such as, for example, seawater, refers to an amount that is sufficient to achieve the desired concentration gradient for achieving electricity generation. The specific level in terms of wt% of salts in a seawater solution or salt solution required as an effective amount will depend upon a variety of factors including the amount and type of salt or salts, volume of water, transition temperature of the phase change material, andambient temperature of the seawater or salt solution.

[0092] As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

[0093] Unless otherwise specified, temperatures referred to herein are based on atmospheric pressure (i.e. one atmosphere).

[0094] Now having described the aspects of the present disclosure, in general, the following Examples describe some additional aspects of the present disclosure. While aspects of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit aspects of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of the present disclosure.EXAMPLES

[0095] The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and / or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the disclosure and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric.Example 1 : Morphologies of the synthesized shape memory vitrimer

[0096] FIGs. 11A-11 B show the FTIR peaks of diphenyl carbonate and di(trimethylolpropane) which were utilized as monomers to synthesize the SMV. The C=O peak of the diphenyl appears at 1750 cm-1, and the aromatic structure is close to 3000 cm-1. The C-0 peak of di(trimethylolpropane) is detected at 1000 - 1150 cm-1, which indicates the intrinsic structure before the synthesizing process. The tris(2-aminoethylamine) (TREN) result is shown in FIG. 11C and the initial Tris[2-(acryloyloxy)ethyl] isocyanurate (TAI) chemical structure is shown in FIG. 2A. There are representative peaks of functional groups such as amide, C=O, and C=C that would be crosslinked to a network structure. The TAI only 3D printed pre-vitrimer result is shown in FIG. 11D. The two monomers synthesized TAI pre-polymer exhibited different absorption peakintensities, as shown in FIG. 11 E. After 3D printing, the peak of the final SMV is presented in FIG. 2B. The -CH peak intensity is increased during the curing process. It indicates that the diphenyl carbonate and di(trimethylolpropane) synthesized TAI pre-polymer is polymerized into a crosslinked SMV structure. To verify the chemical stability at different temperatures, FIG. 11F shows the FTIR result and there is no chemical reaction from 25 °C to 80 °C. To further demonstrate the synthesis of the SMV by the two monomers, the XPS measurement result is provided. FIGs. 12A-12B show the results of diphenyl carbonate while FIGs. 12C-12D are the results of di(trimethylolpropane). After crosslinking these two monomers, the structure is changed, as shown in FIGs. 13A-13D. The N 1 s peak in FIG. 13C indicates that the diphenyl carbonate and di(trimethylolpropane) are crosslinked by TREN effectively. The results of the final 3D printed SMV are presented in FIGs. 14A-14D. All generated functional groups appear in C1s and N1s peaks. In addition, the atomic spectrum of the final SMV is shown in FIG. 14D and nitrogen is increased significantly compared with the pre-polymer as shown in FIG. 13D. The fabricated SMV exhibits an amorphous structure which is confirmed by the results of Raman peaks as shown in FIGs. 15A-15D. To compare with TAI only 3D printed pre-polymer and the synthesized SMV, FIG. 2C shows the TGA results and the characteristics are listed in Table 1. It is observed that the synthesized final SMV exhibits better thermal stability than the pre-vitrimer. The stress-strain behaviors are shown in FIG. 16A. The tensile strength of the SMV is close to 10.0 MPa while the pre-vitrimer merely stops at 4.8 MPa. Both the TGA and stress-strain results demonstrate that the synthesized SMV has excellent thermal and mechanical properties and is suitable for being utilized as a supporting material to fabricate the form-stable PCM composite.

[0097] FIG. 2D shows the contact angle measurement. The synthesized SMV is hydrophilic due to the incorporation of hydrogen functional groups. It can be concluded that the final SMV can easily absorb moisture and dissolve CO2 from the environment. The surface structure of the SMVwas obtained by SEM images, as shown in FIG. 16B. The SMV shows a flat surface structure while the 1-TD and PEG contain a lot of wrinkles as presented in FIGs. 16C-16D.

[0098] The result of electrical resistivity under the increase in external relative humidity (RH) is shown in FIG. 2E. It is seen that the electrical resistance of the SMV decreases rapidly at RH 70% (the initial RH in the air is 40%). Furthermore, the electrical resistivity of the SMV can be decreased further with the increase in CO2 concentration (the initial CO2 concentration in the air is 400 ppm), as shown in FIG. 2F. The electrical resistivity of the SMV is decreased from 4.16 kQ at 40% RH to 1.27 kQ at RH 70%. At RH 80%, the electrical resistivity is changed from 3.32 kQ to 1.06 kQ, while it is changed from 2.57 kQ to 0.92 kQ under the RH 90% condition. It is easy to confirm that the electrical resistivity is difficult to decrease with the increase in temperature or CO2concentration at the initial RH of 40%, as shown in FIGs. 3A-3C. One of the key points is that the CO2 dissolving ability decreases with the increase in external temperature as indicated in FIG. 3D. In this work, the RH 70%, 80%, and 90% were utilized and the 400 ppm, 700 ppm, and 1200 ppm CO2 concentrations were provided to obtain the electrical energy harvesting using the formstable 1-TD and PEG composites during the light-on / -off process.Example 2: Thermal and form stabilities of PCM composites

[0099] FIG. 4A shows the UV-Vis peaks of pre-vitrimer and SMV with different thicknesses. It is obvious that all SMVs can transmit sunlight. As a result, the sunlight can pass through the SMV container and cause the phase transition process in the PCMs inside. The thermal stability is important for the supporting material to maintain an initial solid state without damage. The temperature sweep result is reported in FIG. 4B. Both storage modulus and loss modulus decreased rapidly when the temperature was over 65 °C and the maximum Tan Delta appeared at 70 °C. It indicated that the glass transition temperature (Tg) was close to 70 °C and the SMV became flexible above 70 °C. Therefore, the thermal reliability tests for the two kinds of supporting materials were conducted under the change of external temperature from 25 °C to 80 °C. After several thermal cycles, the SMV supporting material kept the initial shape successfully while the pre-vitrimer fractured on the surface as shown in FIG. 4C. It was illustrated that the SMV supporting material exhibited a great flexibility and thermal stability to prevent the damage subjected to thermal cycles. To demonstrate the shape memory effect of the SMV sample, the rectangular-shaped specimen was put into the MTS chamber to undergo a hot programming process. The temperature of the MTS chamber was increased to 150 °C and was maintained to achieve a thermal equilibrium state. Then the specimen was compressed at a loading rate of 0.20mm / min until 13% strain. The cooling and unloading process were followed to complete the whole compression programming process. Eqns. (1) and (2) are used to calculate the shape fixity ratio Rf and shape recovery ratio Rr, respectively:is the fixed strain after removing the load and is the strain before load removal. The et( / V) and st(N - 1) are the final strains of the samples with shape memory effect above the glass transition temperature (Tg). For total recovery, et(N - 1) is eliminated when the IV - 1 (et(0) equals to 0).

[0100] The results of shape fixity ratio R and shape recovery ratio Rrwere listed in Table 2. The SMV showed excellent shape recovery property and it can contribute to keep the high thermal stability without damage. Based on the close-then-heal (CTH) strategy, recovery stress plays an important role in bringing fracture surfaces in touch. Therefore, a recovery stress test was conducted. The compression programmed SMV sample was placed back into the MTS chamber and started the recovery test. FIG. 4D shows the SMV recovery stress at 90 °C as a function with time. It was found that the maximum stress was 1.84 MPa, which is sufficient to close micro-scale fatigue cracks. Therefore, the SMV can heal the potential fatigue cracks under cyclic thermal loading.

[0101] To confirm the form stability of the SMV supported PCM composites, optical images of the pure PCM and PCM composites were taken, which demonstrated the form stabilities, as shown in FIGs. 17A-17B. It indicates that both the pure 1-TD and PEG were fully melted into the liquid state at 80 °C. The different sizes of the SMV supported PCM composites maintained the initial solid state without any leakage during the melting process. The volume expansion results of the PCM composites are shown in FIGs. 18A-18B. The different sizes of the SMV containers merely exhibit a slight volume expansion especially for the 3.5 mm and 4.0 mm thick specimens. The thermal conductivity measurement was conducted and both the SMV supported 1-TD and PEGcomposites was close to 0.33 W / mK as indicated in FIG. 18C. Definitely, the thermal conductivity of the PCM composites were mainly correlated to the SMV container. FIG. 18D shows the XRD peaks of the SMV, pure PCMs, and PCM composites. Only intrinsic crystal peaks appear, which confirms that no chemical reaction occurred between the SMV and pure PCMs. To verify the temperature gradients during the light-on / -off process, the IR camera images were taken as shown in FIGs. 5A-5D. The temperature of the SMV container was changed rapidly while the SMV supported 1-TD and PEG composites underwent almost isothermal phase transition. From FIGs. 5B-5C, it is seen that the SMV supported PEG and 1-TD composites had nearly an isothermal process within a certain period of time (a section of the temperature-time curve is almost a horizonal line), which is the phase transition period of each PCM. It is also seen that the period of time corresponding to the isothermal process for these two composites is different, suggesting that a certain temperature gradient can be maintained to trigger the Seebeck effect. The DSC results of the SMV and pure PCMs demonstrated the phase change temperature and latent heat (AT) property, as shown in FIGs. 19A-19D. The PEG had higher melting and cooling points (Tmp, Tcp) than those of 1-TD, as shown in FIGs. 19B-19C. From FIG. 19A, it is seen that the SMV is also stable after 100 thermal cycles. The stability under thermal cycles of the SMV, 1- TD, and PEG can be further validated by FIG. 19D. Furthermore, the DSC cycling results are listed in Table 3. It is seen that there is only a slight difference after completing the 100 heating / cooling cycles, suggesting that the composite assembly is stable.

[0102] The SMV supported PCM composites maintain excellent thermal and chemical stabilities during the cycling test, which is also validated by the XRD peaks as shown in FIG. 19D. Therefore, the SMV container can support the pure 1-TD and PEG to fabricate form-stable PCM composites, which can be further utilized in smart and controllable energy harvesting.Example 3: Electrical energy production under different conditions

[0103] The sunlight intensity on the surface of the PCM composites was defined as 15 mW / cm2which exhibited an appropriate electrical energy production during the light-on / -off process. The final temperatures of the SMV with different RHs are shown in FIG. 20A. It is clear that the SMV can reach 81 °C within the range of RH from 40% to 90%. At the initial air condition with 400 ppm CO2, the electrical resistivity of the SMV was gradually increased during the light-on heating process. The decrease in CO2 dissolving ability caused the low ion concentration in the moisture at different RHs as shown in FIGs. 20B-20D. However, after increasing the CO2 concentration to 700 ppm, the electrical resistivity became lower than the initial state as shown in FIGs. 22A-21C. At the highest CO2concentration up to 1200 ppm, the electrical resistivity was a little lower than that at the 700 ppm concentration level due to the dissolving of additional CO2as shown in FIGs. 21D-21F. Thus, the 700 ppm and 1200 ppm CO2 concentrations can provide a good external environment to make a conductible SMV structure. FIGs. 22A-22D shows the electrical resistivity of the SMV supported 1-TD and PEG composites with different SMV container sizes at RH 70% condition. Both the SMV supported 1-TD and PEG composites merely exhibited a slight difference within the range of CO2 concentration from initial 400 ppm to 1200 ppm. The electrical resistivity at the RH 80% and 90% is similar as shown in FIGs. 23A-24F, respectively. However, the PCM has an optimum volume size in order to effectively transfer the stored thermal energy to electrical energy during the phase transition process. To find out the optimum size of the SMV supported PCM composites, the temperature variation test was conducted and FIGs. 25A-25F shows the result of different sizes of the 1-TD composite under different CO2 concentrations. It is clear that the 2.5 mm and 3.0 mm thick SMV container supported 1-TD composites exhibit a lower phase transition field. The 3.5 mm and 4.0 mm thick SMV supported 1-TD composites had a similar result under the 400 ppm, 700 ppm, and 1200 ppm CO2 concentrations. On the other hand, the 3.5 mm thick SMV supported PEG composite exhibited the most appropriate temperature peaks as shown in FIGs. 26A-26F. Based on the results of temperature peaks, the 3.5 mm thick SM supported 1-TD and PEG composites were selected to generate electrical energy under different RH and CO2concentrations.

[0104] FIGs. 27A-27H show the temperature peaks of the 1-TD composite under the three different CO2concentrations during the light-on / -off process. The CO2 concentration changes from the initial 400 ppm to 1200 ppm, the heating rate was increased under the light-on heating process while the cooling rate was decreased due to the CO2 greenhouse effect. The PEG composite saw the same effect as the 1-TD composite at the same range of RH and CO2 concentrations, as shown in FIGs. 28A-28H.Example 4: Materials

[0105] Diphenyl carbonate, Di(trimethylolpropane), Tris(2-aminoethylamine), Dichloromethane, Tris((2-(acryloyloxy)ethyl) isocyanurate (TAI), Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), 1 -tetradecanol (1-TD), and Polyethylene glycol (PEG, Mn= 6000) were purchased from the Sigma-Aldrich.Preparation of shape memory vitrimer supporting material

[0106] The first step to fabricate a shape memory vitrimer (SMV) supporting material was to mix 90.0 g diphenyl carbonate with 21 .0 g di(trimethylolpropane) in a 140 °C oil bath for 2 hours. After that, 0.6 g tris(2-aminoethylamine) was dissolved in 6.50 mL dichloromethane (CH2CI2), and was poured into the melted mixture which acted as a cross-linking agent to cause polymerization reaction as shown in FIG. 8. The pre-polymer was added to tris((2-(acryloyloxy)ethyl) isocyanurate (TAI) at a 120 : 90 mass ratio and stirred for 5 minutes. 9.0 g photo-initiator diphenyl(2,4,6-trimethylbenzoly)phosphine oxide (TPO) was then added to the polymer mixture. After that, the mixture was put into an oven at 120 °C for 30 minutes. The melted solution was then taken out and stirred for 1 hour with a stirring bar (500 rpm) and cooled down to room temperature in 30 minutes. As shown in FIG. 9, the pre-polymer was put into the 3D printer. The SMV hollow box with a dimension of 20 mm x 20 mm x 2.5 mm was printed by the 3D printer. To compare the mechanical and hydrophilic properties of the synthesized SMV, hollow box container was also printed by using TAI only, which was labeled as pre-vitrimer. To confirm the optimum thickness of SMV containers, four different container thicknesses were fabricated and labeled as 2.5 mm, 3.0 mm, 3.5 mm, and 4.0 mm.Preparation of SMV supported form-stable PCM composites

[0107] FIG. 10A shows the fabrication route of form-stable PCM composite. The 3D printed SMV container has a 1 mm edge thickness which can prevent the pure PCM from leaking. The pure 1- TD and PEG were melted to a liquid state and poured into two SMV containers until full. The prepolymer (pre-SMV) was painted onto two surfaces of the SMV containers and push them in contact. The assembly was then put into an ultraviolet (UV) chamber. After 80 seconds of UV curing treatment, a form-stable SMV supported PCM composite device was fabricated successfully. To determine an appropriate size of PCM composite device, the SMV containers with four different sizes, as shown in FIG. 10B, were utilized to fabricate the SMV supported 1- TD and PEG composites. The weight of SMV container and PCM composites are listed in Table 4. To verify the electrical resistivity under the change of external relative humidity (RH) and carbondioxide (CO2) concentrations, the initial state of RH 40% with 400 ppm CO2 was changed gradually by increasing both the RH and CO2 concentration.Characterization

[0108] Fourier transform infrared spectroscopy (FTIR, Spectrum Two, PerkinElmer, MA, USA) was utilized to observe the chemical functional groups of the monomers and final SMV. The surface structures of the SMV and phase change materials (PCMs) were obtained by Field emission scanning electron microscope (FE-SEM, Quanta 3d FEG Dual Beam, FEI, Hillsboro, USA) after platinum coating. The transmittance of SMVs with various thickness were measured using UV-vis-NIR spectrophotometer under the 190 ~ 1000 nm wavelength (UV-3600, Shimadzu, Kyoto, Japan). The typical crystal structures of the PCM composites were measured by X-ray diffraction (XRD, Panalytical Empyrean, Malvern, UK) at the range of 10 - 60° with a scan rate of 3° min-1. The stress-strain and shape recovery behaviors of the SMV were determined by using the 2610 Universal Testing Machine (UTM, Norwood, MA, USA). The sample dimension for recovery stress was 10.34 mm x 9.24 mm x 4.70 mm. A thermal gravimetric analyzer (TGA550, TA Instruments, DE, USA) was utilized to measure the thermal stabilities of SMV and pure PCMs. For the SMV supported form-stable PCM composites, a rheometer (HR30, TA Instruments, DE, USA) was used to observe the volume expansion under the temperature variation from 25 °C to the final 80 °C. To demonstrate the SMV structures which were synthesized by monomers, X-ray photoelectron spectroscopy (XPS, Scienta omicron, Uppsala, Sweden) and Raman spectroscopy (Renishaw Invia Raman Microscope, TX, USA) were used to confirm the intrinsic functional peaks. A contact angle analyzer (FTA1000, First Ten Angstroms, VA, USA) was utilized to obtain the hydrophilic ability of the SMV material. The thermal conductivities of the pure PCM and PCM composites were confirmed by the thermal conductivity analyzer (C-Therm TCi, C-Therm Technologies Ltd, NB, Canada). The phase transition temperature and latent heat (AT) wereobtained using a differential scanning calorimetry (DSC4000, PerkinElmer, MA, USA) with the range of 0 °C to 90 °C at a scanning rate of 10 °C / min. The temperature gradients of the SMV supported PCM composites during the light-on / -off process were observed by an IR high- resolution thermal camera (B20, HIKMICRO, Hangzhou, China). The temperature change of the SMV supported PCM composites was measured by a functional multi-meter (UT61 , Guangdong, China), and the electrical energy output was recorded by a source meter (SourceMeter2400, KEITHLEY, OR, USA).Example 5: Materials for carbon nanotube (CNT) formulations

[0109] Polydimethylsiloxane (PDMS), hardener (Sylgard® 184), n-Hexane, polyethylene glycol (PEG Mn=6000, density 1.20 g / cm3), and 1 -tetradecanol (1-TD, density 0.82 g / cm3) were purchased from Sigma-Aldrich. Single-walled carbon nanotubes (SWCNTs) (>85 %; Average diameter: 3 nm; Average length: 5 pm) were purchased from TCI.Preparation of polydimethylsiloxane / carbon nanotube open-cell foam structures

[0110] The ratio of polydimethylsiloxane (PDMS) and hardener was kept at 2:1. Two grams (2g) PDMS and 1g hardener were poured into a paper cup for mixing as shown in FIG. 32. N-hexane was added into the mixture for diluting the PDMS due to their similar solubility. To generate the Seebeck effect with two different PDMS foams, SWCNT content was a key factor. Two different SWCNT concentrations were used in preparing the PDMS foams. The first group included 10 mg of SWCNT in the PDMS solution while the other was increased up to 30 mg, which led to SWCNT weight fraction of 0.33% and 1%, respectively. The SWCNT embedded PDMS solutions were well-dispersed after 30 min ultrasonication. A homogeneous structure was obtained after 30 min additional vigorous stirring (9000 rpm). Thereafter, the PDMS solution was placed into an oven and vacuumed for 60 min to evaporate the n-hexane. Finally, the SWCNT / PDMS blends were subsequently cured at 150 °C for 2 h to obtain the porous SWCNT / PDMS foams.Preparation of form stable phase change material composites

[0111] The 10 mg and 30 mg SWCNT embedded PDMS foams were selected to infiltrate pure 1-TD and PEG, respectively. These two PDMS foams were labeled as PDMS / CNT1 and PDMS / CNT2 in this work. The liquid impregnation method was utilized in the fabrication of the PCM composites. The pure 1-TD and PEG were melted into liquid state at 80 °C. The two types of PDMS foam supporting materials were placed into the liquid PCMs to induce the infiltrationprocess. After several hours, the heat source was removed and SWCNT / PDMS supported 1-TD and PEG composites were fabricated after cooling to room temperature.Characterization

[0112] A field emission scanning electron microscope (Quanta 3d FEG Dual Beam, FEI, Hillsboro, USA) analysis was utilized to measure the surface structures of samples after coating by platinum. To observe the SWCNT embedded PDMS foam structure, a cryogenic transmission electron microscope (Cryo-TEM, JEQL-1400, Tokyo, Japan) was employed. Fourier transform infrared spectroscopy (FTIR, Spectrum Two, PerkinElmer, MA, USA) was used to observe the chemical structures of both the PDMS foams and PCM composites. The intrinsic crystal structures of the composite samples were obtained by an X-ray diffraction (XRD, Panalytical Empyrean, Malvern, UK) at the range of 10 - 600at a rate of 3 ° min-1. A thermal gravimetric analyzer (TGA550, TA Instruments, DE, USA) was selected to measure the thermal stabilities of PDMS supporting material, pure PCMs, and PCM composites. The phase transition properties were confirmed by a differential scanning calorimetry (DSC4000, PerkinElmer, MA, USA) and the temperatures were applied from 15 °C to 90 °C at a rate of 10 °C min-1. The solar light (Ultra- vitalux 300W, Germany) was utilized as a light source and the output electrical voltage was collected by a functional multi-meter (UT61 , Guangdong, China) under the change of external conditions.Example 6: Morphologies of polydimethylsiloxane foams and phase change material composites

[0113] The SWCNT embedded porous PDMS foams were utilized as supporting materials to fabricate form stable PCM composites. According to the difference in SWCNT weight fraction between the two PDMS foams, there was an electron movement within the connected PCM composites by the change of external temperature as shown in FIG. 29. The PEG and 1-TD have different phase transition zones, which cause the temperature difference and, as a result, the electrons move towards the hot side of the PCM composite to generate electrical current in the closed circuit. FIG. 33 shows the two types of PDMS foams with approximately 3.62 cm diameter and 0.50 cm thickness as listed in Table 5. Both of these PDMS foams showed excellent elastic properties after the compression test, with recovery ratios 99.60 % and 99.41 %, respectively. The pure 1-TD and PEG infiltrated PCM composites were shown in FIG. 30A with the pure PCMs filled in the internal voids. FIG. 30B shows the weight fraction of the pure PEG was 72.59 % while the 1-TD was 60.79 % due to the different densities. The porosity and pore volume were listed inTable 6 and both PDMS foams can infiltrate plenty of pure PCMs to fabricate the PCM composites. The SEM image of PDMS / CNT1 is shown in FIG. 30C, which demonstrated that the PDMS foam had a porous internal structure. The pore size distribution of PDMS / CNT1 was obtained and the average diameter was close to 154.83 pm as shown in FIG. 30D. The results of PDMS / CNT2 porous structure are shown in FIGs. 30E-30F where the average diameter was 151.56 pm to hold the pure PEG. To observe the SWCNT in the PDMS foams, FIGs. 34A-34B show the TEM results of PDMS foams. From the TEM measurement, the long SWCNTs with high aspect ratios were captured and it indicated that the SWCNTs were fully dispersed in the PDMS foams. The pure 1-TD and PEG are shown in FIGs. 34C-34D while the PCM composites were presented in FIGs. 30G-30H. The pure 1-TD and PEG were fully infiltrated into the PDMS foams that can be utilized in thermoelectric energy harvesting.Example 7: Form stability and thermal properties of phase change material composite

[0114] The optical image of the form stable test is shown in FIG. 31 A. Both the pure 1-TD and PEG were melted into the liquid state when the temperature was increased from 25 °C to 80 °C. After infiltrating into the PDMS foams, the 1-TD and PEG composites exhibited high form stability with the increase in external temperature without any leakage. To confirm the final crystal structures of the PCM composites, the PDMS foams, pure PCMs, and PCM composites were measured by the XRD test and the results are shown in FIG. 35A. Definitely, there were similar peaks between the pure PCM and PCM composites and no chemical reactions occurred during the infiltration process. To obtain the electrical properties of the PCM composites, FIG. 31 B shows the results of electrical resistivity within the range of temperature from 25 °C to 80 °C. The 10 mg SWCNT embedded 1-TD / PDMS composite exhibited higher electrical resistivity than the 30 mgSWCNT embedded PEG / PDMS. The initial electrical resistivity of 1-TD / PDMS was 7.68 kQ, while it was a little bit decreased during the phase transition process and reached about 7.00 kQ at the final temperature of 80 °C. On the contrary, the PEG / PDMS showed 3.83 kO at 25 °C. The electrical resistivity was decreased to 3.27 kQ at 80 °C which was lower than the 1-TD / PDMS. The thermal conductivities of 1-TD and PEG composites are shown in FIG. 35B and both 1-TD and PEG composites had increased the thermal conductivities during the phase transition process.

[0115] To evaluate the thermal stabilities of the PCM composites, TGA measurement was conducted, and the results are shown in FIGs. 35C-35D. After infiltrating the pure PCMs into the PDMS foams, both 1-TD and PEG composites were still maintaining excellent thermal stability from 25 °C to 80 °C as listed in Table 7. It indicated that the PDMS foam supported 1-TD and PEG composites can be utilized for generating electrical energy under the change of external temperature. The thermal properties of the PCM composites were confirmed by the DSC measurement as shown in FIGs. 31C-31D. The pure 1-TD started the solid-liquid phase transition at 31.91 °C and the melting point was 41.87 °C, while the results of the 1-TD / PDMS composite were shifted slightly as given in Table 8. The melting and cooling latent heat (AH) of the pure 1- TD are 213.39 J / g and 210.75 J / g, respectively. The 1-TD / PDMS composite had 128.48 J / g and 126.67 J / g upon melting and cooling processes due to the replacement of a portion of the pure 1- TD by the supporting material. The pure PEG had a higher phase transition temperature than the 1-TD and the results of latent heat (AH) were 181.68 J / g and 162.76 J / g, respectively. Although the supporting material decreased the value of latent heat (AH), the PEG / PDMS composite stored thermal energy up to 130.76 J / g during the phase transition process. To confirm the thermal stabilities of the PCM composites, the DSC cycling tests were conducted and the results are shown in FIGs. 36A-36D. After 100 cycles, both the 1-TD and PEG composites merely had a little shift without large variations. In addition, there was still similar latent heat (AH) during the melting and cooling processes as listed in Table 9. The FTIR was measured after 100 cycles of the DSC test and there was no chemical reaction of the PCM composites under the cycling process. According to the thermal stability test result, the PDMS supported PCM composites showed excellent form stability and thermal reliability. Because only reversible physical changes are involved in producing electricity, it is estimated that the lifetime would be controlled by physical aging of the materials. For PDMS and PCMs, the lifetime would be well over 10 years._ _Example 8: Harvesting solar energy based on the air-conditioned indoor and ambient outdoor environment

[0116] This example considers converting solar energy to electricity when indoor and outdoor have a temperature difference, such as inside an air-conditioned building and outside the building, or inside an air-conditioned residential house and outside. In summer, this usually suggests cold inside and hot outside; and in winter, this usually suggests hot inside and cold outside. The idea is that seawater can be used as the conductor and use the temperature difference between the indoor and outdoor to create thermal gradient. To create the conductivity gradient, different seawater outdoors and indoors can be used, for example, diluted seawater can be used indoors but conventional seawater outdoors; the conductivity gradient can be further enhanced by diluting indoor seawater but condensing seawater outdoor by water evaporation. To maintain the thermal gradient, the indoor water will be maintained at the same temperature as the temperature inside the room because it is air-conditioned. The outdoor seawater can be put in a container, forexample, a “hot house”, by jacketing the house or container with phase change materials (PCMs) so that the PCM will absorb the solar energy in daytime, and release heat during the night. As a result, the outdoor seawater will maintain the high temperature day and night. In such a way, consistent thermal gradient and conductivity gradient will be maintained day and night, thereby producing consistent electricity. It is noted that this idea is also applicable to another scenario, where the outdoor is cold and the indoor is hot, for example, the indoor is a power plant or other manufacturing facility that produce a lot of heat. In such a way, a phase change material can still be used to maintain consistent outdoor temperature for the seawater so that stable electricity output can be obtained. Herein is shown an example where outdoor is the hot side while indoor is the cold side such as in the summer. FIG. 37 shows a schematic of only one PCM is used to converting solar energy to electricity.

[0117] The results of utilizing phase change material (PCM) and seawater to generate electrical energy harvesting were fully observed, which showed that the seawater is an advanced conductor for achieving solar-to-electrical energy harvesting. To investigate the idea, the seawater was placed into a glass tank with a dimension of 14 cm x 10 cm x 11 cm, and also fabricated formstable PCM composites by infiltration method. Two types of PCMs, 1 -Tetradecanol (1-TD) and polyethylene glycol (PEG), were selected and a porous black plastic open-cell foam was utilized as a supporting material. The dimension of black plastic foam was 14 cm x 10 cm x 3 cm. To produce the form-stable PCM, the foam is inserted into pure 1-TD and PEG liquids at 80 °C for 12 h under vacuum condition. To avoid leakage during the solid to liquid phase transition, the surface of the fabricated PCM composites were covered by a mixture of tris(2- (acryloyloxy)ethyl)isocyanaurate (TAI), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and carbon black, which was cured by UV light. The form-stable 1-TD and PEG composites showed high PCM weight percentages which were 97.84 % and 98.60 % for 1-TD and PEG, respectively. To connect the seawater in the two tanks, silicone wires were immersed into the seawater and 6 pairs of alligator clips wires were also utilized to observe the output electrical voltage and current.

[0118] In this example, two seawater tanks were prepared, and one was kept at room temperature as the “cold side” while the other was jacketed by a PCM composite and exposed to sunlight as the “hot side”. The seawater in the tank on the cold side was diluted by tap water. The PCM composite used was PEG composite. FIG. 38 shows the result of electrical energy under the light-on / -off process. It indicates that the temperature difference between the two tanks could trigger an electrical energy harvesting due to the Seebeck effect. The PEG composite absorbedthe sunlight to store as thermal energy and increased the seawater temperature successfully when the light is turned on. After removing the light source (light off), the stored thermal energy within the PEG composite started to release and still sustained a long time of temperature difference to generate electricity. The maximum voltage and current were 5 V and 17.25 mA, respectively. The output electrical energy can fully turn on a LED bulb during the light-on / -off process as shown in FIG. 39.Example 9: Harvesting solar energy directly from the ocean

[0119] 70% of the earth’s surface is covered by seawater. Therefore, the ocean can be farmed for energy directly. To achieve this, the temperature and conductivity difference along the depth of the ocean will be used. On the surface, the water is hot, and the seawater conductivity is high; with the increase in depth, the temperature gradually becomes cold, and the electrical conductivity of the seawater reduces. Therefore, there is a natural temperature gradient and electrical conductivity gradient in the ocean, which satisfies the requirements for the Seebeck effect. Therefore, electricity can be created by directly inserting a conducting wire along the depth of the ocean. The key is how to maintain the wire under the motion of the seawater. One end of the wire can be anchored on the seabed by concrete blocks, the other end of the wire can be tied to waste tires. When thousands or millions of waste tires are tied together, a floating dock in the ocean is obtained, similar to the offshore oil platforms used today. A non-fishing area, or the so-called dead-zone, can be chosen to construct the energy harvesting farm. Additional concrete blocks may be needed to anchor the waste tires to the ocean floor. FIG. 40 shows a schematic of the idea.

[0120] To observe the output voltage and current, two seawater tanks were used. Ice packs were placed into one tank of diluted seawater to simulate the seawater in the depth of the ocean. The other seawater tank was kept at room temperature to trigger the Seebeck effect. As a result, the electrical energy was collected as shown in FIG. 41 . The maximum output voltage was 5 V, and the output current was close to 13.67 mA. Again, an LED light bulb was lit up.

[0121] To summarize, by using PCM composites to create and maintain temperature gradients, and seawater as conductor, it was demonstrated that the seawater was an excellent resource to generate electricity. It is also low cost and has unlimited resources. If the seawater container would be much bigger, or directly trigger the solar-to-electrical energy harvesting in ocean, usable and clean electricity could be generated.

[0122] It should be emphasized that the above-described embodiments of the present disclosureare merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the abovedescribed embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.REFERENCES1. Abas, N, et al, Journal of CO2 Utilization, 2014, 8, 39-48.2. Ai, H, et al. An eco-friendly and facile montmorillonite nanosheets aerogel based phase change materials for efficient solar-to-thermal energy conversion. Energy Conversion and Management. 253 (2022) 115172.3. Bao, J, et al. A medium-temperature, metal-based, microencapsulated phase change material with a void for thermal expansion. Chemical Engineering Journal. 415 (2021) 128965.4. 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Claims

CLAIMSWhat is claimed is:

1. A method for producing electricity by harvesting solar energy, thermal energy, or both, the method comprising:(a) placing a form-stable phase change material (PCM) composite in a first environment;(b) providing an electrical connection between the first form-stable PCM composite and a second environment; wherein the first environment and the second environment differ in at least one property, creating a gradient in the at least one property between the form-stable PCM and the second environment; and wherein electric current flows along the electrical connection between the first form-stable PCM composite and the second environment due to the gradient.

2. The method of claim 1 , wherein the at least one property comprises salinity, relative humidity, atmospheric CO2 concentration, ambient temperature, dissolved ion identity, conductive filler identity, or any combination thereof.

3. The method of claim 1 , wherein an ambient temperature of the first environment is higher than an ambient temperature of the second environment.

4. The method of claim 3, wherein the first environment is outdoors and the second environment is indoors.

5. The method of claim 4, wherein the second environment comprises an air-conditioned building.

6. The method of claim 1 , wherein an ambient temperature of the second environment is higher than an ambient temperature of the first environment.

7. The method of claim 5, wherein the first environment is outdoors and the second environment is indoors.

8. The method of claim 7, wherein the second environment is inside a power plant or inside a factory.

9. The method of claim 1, wherein the first environment and the second environment comprise saline solutions.

10. The method of claim 9, wherein the saline solutions comprise seawater.

11. The method of claim 9, wherein a first saline solution in the first environment has a different concentration from a second saline solution in the second environment.

12. The method of claim 1 , wherein the form-stable PCM composite holds a volume of a first saline solution.

13. The method of claim 12, wherein the second environment comprises a second saline solution.

14. The method of claim 12 or 13, wherein the saline solution comprises seawater.

15. The method of claim 12 or 13, wherein the first saline solution and the second saline solution comprise different salt concentrations.

16. The method of claim 12, wherein the first environment is an ocean surface and the second environment is an ocean floor.

17. The method of claim 1 , wherein the electrical connection is provided by a conducting wire.

18. A method for storing thermal energy, the method comprising(a) performing the method of claim 1 to produce electricity; and(b) increasing the temperature of the first environment, causing the phase change material of the form-stable PCM composite to undergo a phase change from solid to liquid; wherein thermal energy is stored in the liquid phase of the PCM of the form-stable PCM composite.

19. The method of claim 18, wherein increasing the temperature of the first environment comprises an ambient temperature increase in the first environment.

20. The method of claim 18, wherein the first environment is outdoors and the ambient temperature increase occurs due to weather conditions.

21. The method of claim 18, wherein the first environment is indoors and the ambient temperature increase occurs due to heat given off by an industrial process.

22. The method of claim 18, wherein stored energy in the form-stable PCM composite is released when the phase change material of the PCM composite undergoes a phase change from liquid to solid as the temperature of the first environment decreases.

23. The method of claim 18, wherein the phase change material comprises a liquid-solid phase change material.

24. The method of claim 18, wherein the phase change material comprises 1 -tetradecanol (1-TD), polyethylene glycol (PEG), or any combination thereof.

25. The method of claim 19, wherein the PEG has a number average molecular weight of from about 4000 Da to about 8000 Da.

26. A system for producing electricity, the system comprising:(a) a form-stable phase change material (PCM) composite in a first environment;(b) an electrical connection between the first form-stable PCM composite and a second environment; wherein the first environment and the second environment differ in at least one property, creating a gradient in the at least one property between the form-stable PCM and the second environment; and wherein electric current flows along the electrical connection between the first form-stable PCM composite and the second environment due to the gradient.

27. A system for storing thermal energy, the system comprising the system for harvesting energy of claim 26; wherein when the phase change material of the form-stable PCM composite undergoes a phase change from solid to liquid, thermal energy is stored in the liquid phase of the formstable PCM composite.

28. A form-stable phase change material (PCM) composite comprising a shape memory vitrimer (SMV) structure, wherein the SMV structure is filled with a PCM.

29. The form-stable PCM composite of claim 28, wherein no chemical reactions occur between the PCM and the SMV structure.

30. The form-stable PCM composite of claim 28, wherein the form-stable PCM composite is stable through at least about 100 thermal cycles.

31. A form-stable phase change material (PCM) composite comprising a PDMS foam and a PCM.

32. The form-stable PCM composite of claim 31 , wherein the PDMS foam further comprises single walled carbon nanotubes (SWCNTs).

33. The form-stable PCM composite of claim 32, wherein the SWCNTs are present in the PDMS foam in a weight fraction of from about 0.33% to about 1%.

34. The form-stable PCM composite of claim 31 , wherein the phase change material comprises 1 -tetradecanol (1-TD), polyethylene glycol (PEG), or any combination thereof.

35. The form-stable PCM composite of claim 34, wherein the PEG has a number average molecular weight of from about 4000 Da to about 8000 Da.

36. The form-stable PCM composite of claim 31 , wherein the form-stable PCM composite recovers at least 99% of volume following compression.

37. The form-stable PCM composite of claim 31 , wherein the PDMS foam has an average pore diameter of from about 150 to about 160 pm.

38. A method for synthesizing a shape-memory vitrimer (SMV), the method comprising:(a) admixing a first monomer and a second monomer to form a monomer composition;(b) admixing a polymerization agent with the monomer composition, wherein the polymerization agent initiates polymerization, forming a pre-polymer;(c) admixing the pre-polymer with a pre-vitrimer and a photoinitiator to form the SMV.

39. The method of claim 38, wherein the first monomer comprises diphenyl carbonate.

40. The method of claim 38, wherein the second monomer comprises di(trimethylolpropane).

41. The method of claim 38, wherein the polymerization agent comprises tris(2-aminoethylamine).

42. The method of claim 38, wherein the pre-vitrimer comprises tris((2-(acryloyloxy)ethyl) isocyanurate (TAI).

43. The method of claim 38, wherein the photoinitiator comprises diphenyl(2,4,6- trimethylbenzoly)phosphine oxide (TPO).

44. A SMV synthesized by the method of claim 38.

45. The SMV of claim 44, wherein the SMV absorbs atmospheric water, atmospheric carbon dioxide, or both.

46. The SMV of claim 44, wherein the SMV experiences changes in electrical resistivity resulting from changes in relative humidity.

47. The SMV of claim 46, wherein electrical resistivity of the SMV decreases with an increase in relative humidity.

48. The SMV of claim 44, wherein absorption of atmospheric carbon dioxide changes with a change in external temperature.

49. The SMV of claim 48, wherein absorption of atmospheric carbon dioxide decreases with an increase in external temperature.

50. The SMV of claim 44, wherein the SMV remains solid between at least 25 °C and 80 °C.

51. The SMV of claim 44, wherein the SMV substantially retains its original shape between at least 25 °C and 80 °C.

52. The SMV of claim 44, wherein the SMV has a tensile strength of from about 0.05 to about 10.0 MPa.

53. The SMV of claim 44, wherein the SMV is optically transparent.

54. A structure comprising the SMV of claim 44.

55. The structure of claim 54, wherein the structure comprises a hollow box.

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