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Article

Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage

by
Ajiv Alam Khan
1,
Syed Mohd Yahya
1,* and
Masood Ashraf Ali
2
1
Sustainable Energy and Acoustics Research Lab, Mechanical Engineering Department, Aligarh Muslim University, Aligarh 202002, India
2
Department of Industrial Engineering, College of Engineering, Prince Sattam bin Abdulaziz University, Alkharj 11942, Saudi Arabia
*
Author to whom correspondence should be addressed.
Sustainability 2023, 15(1), 516; https://doi.org/10.3390/su15010516
Submission received: 8 October 2022 / Revised: 23 December 2022 / Accepted: 24 December 2022 / Published: 28 December 2022
(This article belongs to the Special Issue Sustainable Developments and Innovations in Manufacturing)
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Versions Notes

Abstract

:
PLUCISE A82 (PW82) is considered one of the best phase change materials as it is economical, commercially viable, and eco-friendly. Unless there is a great need to optimize the number of parameters to investigate encapsulated PCMs with good performance, for the effective and practical applications of organic phase change materials, it is required to enhance their thermal conductivity. In this study, efforts were made to increase the thermal properties of phase change materials by seeding different nanoparticles. The direct synthesis method, in which the mixing of nanoparticles in paraffin wax (PW82) takes place, is used for the production of NEPCM. Differential scanning calorimeter and heat conduction experiments were used to evaluate the effect of variable concentration of nano-encapsulation on thermal storage and heat conduction characteristics of nano-enhanced PCM. The thermal storage feasibility was also determined. In this study, titania (TiO2), Ti3C2/MXene was mixed in PW82 in 0.1, 0.2, and 0.3 wt.%. The investigation was also carried out for hybrid nano-enhanced PCM in a hybrid combination of (TiO2), and Ti3C2 (MXene) in PW82, used in wt.% concentration of 0.1, 0.2, and 0.3. Doping of titania and MXene improves the specific heat capacity of PCM. For doping of 0.3 wt.% of TiO2–Ti3C2 in PCM, the specific heat is improved to 41.3%. A maximum increment in thermal conductivity of 15.6% is found for doping of TiO2–Ti3C2 0.3 wt.%. The dissociation temperature of this prepared nano-enhanced PCM increases by ~6% for 0.3 wt.% weight fraction. Therefore, this study demonstrates that the doping of TiO2 and Ti3C2 with PW82 to form a new class of NEPCMs has significant scope to enhance the thermal storage capacity of organic paraffin.

1. Introduction

Energy is one of the most important factors for the sustainable growth of any nation. A large portion of energy demand globally is met with the help of conventional energy sources, i.e., fossil fuels, derivatives of petroleum and coal, etc. However, the use of fossil fuel as an energy source impacts the environment very badly. Therefore, scientists and researchers are now trying to invent new sources of energy, and find solar energy as one of the best substitutes for fossil fuel. As solar energy is mainly comprised of thermal energy, it is a great task to store solar thermal energy and preserve energy sources and thermal systems [1], because there is a very low-temperature difference during thermal energy absorption and release. Hence, a latent heat storage system may act as a very good mode of solar thermal energy storage. In this method of latent heat storage, the absorption and release of energy take place due to the phase change of the thermal energy storage material [2].
A number of investigations were carried out by many researchers to investigate the best PCM for latent heat storage [3,4,5,6]. Due to the high capacity of latent heat storage, PCMs are widely used for solar thermal energy storage in various fields, such as the development of smart textiles, and the construction, defense, space, and automotive industries, etc. Recently, many researchers investigated the application and use of PCMs for the cooling and heating of buildings. PCMs are also used to maintain a pleasant temperature in automobiles [7,8,9,10]. Hence, researchers these days focus on PCMs to use them as thermal energy storage [11]. Parker et al. [12] used PCMs as thermal protection for electronic devices.
Even though PCMs have many advantages for use as thermal energy storage, they have a very low thermal conductivity, which creates a great problem for the charging and discharging of the PCM during the load change [13]. This acts as a great obstacle for scientists and researchers to use PCMs commercially. To overcome this problem, researchers carried out many studies to enhance the thermal conductivity of PCMs. One of the most frequently used methods popular among researchers is the doping of some metal or non-metal in PCMs [14,15,16,17]. Other methods to enhance the rate of heat transfer are by using fins [18,19] or fibrous material [20,21,22,23], replacing simple material with expanded or porous material [24,25,26,27,28], and incorporating nano-capsules [29,30,31], which are also used to enhance the charging and discharging rate of PCM.
However, the high density of metals and non-metals as compared to PCMs and the large surface area of doping particles leads to the sedimentation of doped particles at a very fast rate, which reduces the performance enhancement of the thermophysical properties of PCMs by doping particles. The advent of nano-technology helped overcome the problem of the large surface area. With the latest techniques of nano-technology, the size of doped metals or non-metals can be reduced to nano-size. Hence, suspension performance of doped particles is enhanced due to an increase in the specific area of nano-sized particles. To achieve desirable thermophysical characteristics, many researchers used carbon nano-tubes [32,33] as additives, carbon nano-fibers [34,35] Al2O3, Fe3O4 & SiO2 nanoparticles [36,37,38,39,40], TiO2 (titania), silica (SiO2), and ZnO [41], etc. The investigation shows the remarkable change in thermophysical properties of PCMs. Jioa et al. [42] divided the typical rectangular thermal energy storage unit into several partitions (1, 2, 4, and 8). Due to increased thermal networks or enhanced local natural convection, increasing the cavity partitioning and fins shortens the melting time of the PCM. MXenes has drawn significant research attention because of its varied chemical structure and outstanding physicochemical characteristics. To capture thermal energy for effective use, solar energy must be converted to electrical or thermal energy [43]. Electrical efficiency grows by about 34% with two PCMs [44]
However, the above literature survey reveals some studies have been carried out to characterize the TiO2 and MXene nanoparticles to study various morphological and chemical characteristics [45,46,47,48,49], while many studies were conducted to enhance the thermophysical properties of PCMs by using other nanoparticles. However, very few studies have been performed so far by using hybrid nano-PCMs to enhance the thermal conductivity of the PCM. To the best knowledge of the authors, no study has been conducted to investigate the effect of doping of TiO2 and MXene on the thermophysical properties of PCMs, In this study, we used hybrid nano-fluid, which is the combination of TiO2 and Ti3C2 in PW82, and investigated its effect on the thermophysical properties of PCMs.

2. Materials and Methods

2.1. Materials

We procured the organic phase change material (PLUSICE 82) from Phase Change Material Product Ltd. Company (UK). No pre-processing of material was carried out, i.e., we directly used the material in the received form. The organic PCM A82 has the following thermophysical properties: melting point of 82 °C, specific heat capacity at 25 °C is 2.21 KJ/kg-K, volumetric heat capacity is 1878 KJ/m3-K, and mass density is 850 kg/m3. This PCM PLUSICE A82 is also known as PW82 paraffin wax. The nanoparticles to be used, MXene and titania, were purchased from SRL Lab India. Figure 1 illustrates the TEM and SEM images of MXene nanoparticles. The images clearly show that the shape of MXene nanoparticles is tubular in shape, which is the requirement to increase the thermal conductivity. Figure 2 shows the TEM and SEM images of TiO2, which are spherical. Tubular or planar particles have more surface area than spherical particles of the same volume. Hence, MXene should be more effective as compared to titania.

2.2. Preparation of Nano-PCM

Three samples of nano-PCM were prepared by having three different wt.% concentrations (0.1, 0.2, and 0.3 wt.%) of Ti3C2 in PW82. The microbalance (Explorer series, EX224, Ohaus) with ±0.0001 measuring uncertainty was used to measure mass values of MXene flakes (0.06 g) and PW82 (59.940 g). The calculated amount of PW82 and MXene was used to prepare PW82/MXene in which MXene was in 0.1 wt.% age. The paraffin wax (59.940 g) was heated with the help of a hot plate (RCT BASIC, IKA) in the beaker, volume of 150 mL. The hot plate temperature (RCT BASIC, IKA) was maintained at 100 °C, and for the purpose of melting and homogenizing, PW82 was left on the hot plate for about 15 min. When a homogeneous liquid of PW82 was obtained in the beaker, then 0.06 g of MXene flakes was added. The mixture of liquid PW82 and MXene was adequately stirred with the help of a magnetic stirrer at 500 rpm. During the mixing of liquid PW82 and MXene, the beaker was kept closed with the lid of aluminium foil. This is to prevent the formation of an air bubble during stirring by a magnetic stirrer. This stirring process ran for about 2 h continuously. In this study, the concentration of nanoparticles was limited to 0.3% wt.% because MXene is a very costly material, so it was not possible to use a high concentration, due to the high experimentation cost involved. The authors in this research tried to ascertain the usability and effectiveness of MXene. This study revealed that in future research, higher concentrations of MXene may be investigated.
Similarly, the preparation of nano-PCM of TiO2 and hybrid NEPCM of TiO2 and Ti3C2 was carried out by a two-step method. The calculated amount of TiO2 required according to weight% (0.1, 0.2, and 0.3 wt.%) was calculated and doped in the calculated amount of PW82. To prepare hybrid NEPCM, the mono NEPCM of TiO2 and MXene was mixed in equal amounts and stirred adequately with a magnetic stirrer at 500 rpm, along with heating in a closed beaker with an aluminum foil lid.

2.3. Thermal Conductivity Measurement

The KD2 Pro device (Decagon Devices Inc, Pullman, WA, USA) was used to perform the measurement of the thermal conductivity of nanoparticles/PW82 composites, the line diagram of the device is shown in Figure 3. The working of the KD2 Pro is based on a transient linear heat source comprised of a sensor and microcontroller unit. The sensor of the KD2 Pro has lengths and diameters are 100 mm and 2.4 mm, respectively. The L/D ratio was kept high to nullify the tip effects of the sensor. To record the temperature and to heat the samples, the same sensor was used; hence, the sensor, along with acting as a heater during the flow of current, also measured the temperature for a certain period. The measurements of the conductivity of the samples were carried out at the ambient temperature of the laboratory. Before starting the experimentation to measure the thermal conductivity, the thermal equilibrium of the samples and environment were ensured. Five experiments were performed for each sample, and then the mean value of these samples with a standard deviation of 0.5% was used as the final result. The accuracy for the measurements in ranges 0.2–4 W/mK and 0.1–0.2 W/mK is taken as ±10% and ±0.02 W/mK, respectively.
The thermal characteristics, such as latent heat, solidification temperature, melting point temperature, etc., were found by conducting DSC analysis of the samples (Shimadzu Corporation, Kyoto, Japan). The Figure 4 illustrate the line diagram of DSC analyzer. The samples for differential scanning calorimetry were made from the nanoparticles/PW82 composites powder particle in weight of about 5 mg each. The weighing of the powdered composites samples was carried out with 0.01 mg precision electronic scale (Shimadzu Corporation, Japan). The specimen samples for DSC were prepared as a result of powdered composites being placed and pressed together with a lid in a special aluminum beaker. The high-purity standard indium sample was used for the calibration of the DSC instrument. The DSC of the samples were performed at the rate of 10 °C/min cooling or heating in the temperature range of 30 °C–120 °C. For each sample, three experiments were carried out, and then the average of these three results with a standard deviation of 1% was taken as a final result. The temperature accuracy and sensitivity of DSC are taken as 0.1 °C and ±1%, respectively.

2.4. Specific Heat Measurement

In this experimental study, the measurement of specific heat of PW82/(MXene + TiO2) nanocomposites was carried out with the help of DSC-1000/C (Linseis, Selb, Germany). This DSC instrument (Figure 4) has a very high resolution of about 0.03 μW. The measurement of thermal conductivity was performed by using a crucible of 40 μL, made of aluminium. The measurement was carried out for the temperature range 25 °C to 250 °C at 10 °C/min heating rate. These samples of nanocomposite were closed in an airtight aluminum crucible of capacity 40 μL under the atmosphere of nitrogen with a 20 mL/min flow rate. The calorimetric precisions and temperature repeatability are taken as ±1% and ±0.1 °C, respectively.
Four calibrated samples of zinc, lead indium, and tin were used; each was provided by the supplier for calibration of enthalpy and temperature for the DSC analysis of our sample. The specific heat (Cp) value obtained experimentally was well-matched and comparable with the value of specific heat given by the supplier. For the measurement of the specific heat of the PW82/(MXene + TiO2) nanocomposites, one uniform protocol was adjusted to ensure the accuracy of results.

2.5. Thermal Stability Analysis

Perkin Elmer TGA 4000 apparatus was used to carry out the thermogravimetric analysis (TGA) of the PW82/(MXene + TiO2) nanocomposites. An alumina crucible of volume 180 μL, capable of withstanding temperatures up to 1750 °C under the atmosphere of nitrogen of maximum possible purity with a flow rate of 19.8 mL/minute at 2.6 bar pressure, was selected for the analysis of the samples. The samples of 20 mg of PW82/(MXene + TiO2) nanocomposites were heated with rate of heat 10 °C/min, and temperature of the samples was raised from 30 °C to 800 °C. The obtained data were analyzed using Pyris Software.

3. Results and Discussion

3.1. Morphological Analysis

TEM and SEM images of TiO2 and MXene nanoparticle-based NEPCM are given in Figure 5. The TEM image of NEPCM TiO2 clearly shows that the nanoencapsulation in wax is achieved properly. The spherical-shaped TiO2 nanoparticles produce better encapsulated NEPCM. Similarly, the SEM image of MXene NEPCM indicates that there is some wrinkling and stretching of Mxene in paraffin wax. Hence, the laminar shape of MXene is better for enhancing the thermophysical properties of PCMs.

3.2. Thermal Conductivity of MXene and Titania

The variation in the coefficient of thermal conductivities for pure PW82 and PW82/nanoparticle composites for different mass fractions of nanoparticles is given in Figure 6. The coefficient of thermal conductivity for pure PW82 is found to be 0.307 W/m-K. The low thermal conductivity of PW82 is due to low phonon transfer and low frequency of vibrations of the molecules. When nanoparticles are added in PW82, which have more frequency of vibration, this then leads to an increase in the phonon scattering of the nanocomposites, and, hence, the thermal conductivity of the nanocomposites improves greatly.
From the graphs of thermal conductivity variation with the variation in mass fraction of nanoparticles in PW82, it can easily be concluded that the thermal conductivity of the nanocomposite increases. It is seen that the improvement in thermal conductivity is more for MXene than the TiO2 nanoparticles for the same doping. The improvement in thermal conductivity of PW82 composites loaded with 0.1, 0.2, and 0.3 wt.% TiO2 nanoparticles is found as 2.28%, 2.6%, and 3.25% respectively. However, its behavior is more prominent with the addition of MXene flakes (Ti3C2) with PW82, resulting in a 5.21%, 9.12%, and 12% increment in thermal conductivity at the same concentration, respectively. By combining titania and MXene flakes with PW82, it is observed that the rate of increment is higher than individual combinations with PW82, and the maximum enhancement at 0.3 wt.% is found to be 15.63% in comparison to paraffin wax PW82. The metal oxide nanoparticles have spherical shapes, while carbon-based nanoparticles have tube shapes or a two-dimensional planar structure. Hence, the thermal conductivity of the nanocomposite within PW82 is enhanced due to the high surface-to-volume ratio of the nanocomposites, which develop a network that allows good phonon scattering in PW82 PCM. It can be said that metal oxide nanoparticles are spherical, while carbon-based nanoparticles are tube-shaped or a two-dimensional planar structure. It can be said that the shape causes enhancing in thermal conductivity within the PW82 because nanoparticles with a high surface/volume ratio form a network that allows better phonon scattering in the PW82.

3.3. Thermal Storage Capacity of Titania and MXene

Figure 7 illustrate the specific heat capacity of pure paraffin wax with titania, MXene, and hybrid PCM/(TiO2 + Ti3C2) nanocomposites. The specific heat capacity (cp) of any thermal system is considered one of the best parameters for the assessment, calculation, and design of the systems [44]. The thermal heat storage capacity of pure organic paraffin (PW82), PW82/TiO2, PW82/Ti3C2, and the hybrids of both nanocomposites were examined by using DSC analysis. It is observed from the results that the specific heat increases little at low concentrations of nanoparticles. At the same time, its value surges rapidly when loading is increased to 0.3 wt.% for all nanocomposite samples at 25 °C. However, at 250 °C temperature, this behavior is somewhat different, with large initial increments in specific heat at low concentration, whereas the increment rate is low at higher loading of nanoparticles.
It Is evident from the obtained data that the specific heat of pure phase change material increases when the temperature of the material is raised. The physics behind the increasing Cp value with an increase in temperatures can be explained and understood because of the higher rotational, vibrational, and translation energy of molecules at high temperatures. Hence, average molecular energy of substances increases with heating or raising the temperature of the substances, which enhances the energy storage capacity [44]. At 25 °C and 0.3 wt.% loading, the increment in the value of cp of nanocomposites are 2.48%, 3.13%, and 3.4% for PW82/TiO2, PW82/Ti3C2, and PW82/(TiO2 + Ti3C2,), respectively. The maximum enhancement of 4.13% is achieved at 250 °C and 0.3 wt.% loading for PW82/(TiO2+ Ti3C2). This is due to the higher amplitude and lower natural frequency of the vibrations of the surface areas atoms, due to which bonds between the atoms act as springs. Due to the high surface area of two-dimensional materials and the high surface energy of the organic pure paraffin atoms, this phenomenon may result in the interface interaction of atoms (C–H bonds). The enhancement in the specific heat capacity of hybrid nanocomposites may be due to this enhanced interaction of the atoms in the surface area.

3.4. Thermal Reliability and Stability of PW82 with MXene and Titania

In the application of energy storage, thermal stability for a long duration is the primary requirement for every thermally enhanced composite. The viability of any composite for use as thermal energy storage is demonstrated by investigating the stability of thermal conductivity. The thermal conductivity and phase change enthalpy of 0.3 wt.% PW82/(TiO2 + Ti3C2) composites for heating/cooling cycles for up to 150 cycles are shown in Table 1. The results from the table clearly show that the thermal conductivity and phase change enthalpy of the composite do not vary more than 1% for these mentioned heating/cooling cycles. This motivates the researchers to use PW82/(TiO2 + Ti3C2) composites in energy storage applications.
The TGA analysis is carried out to investigate the long time thermal stability of the pure phase change materials (PW82) and hybrid phase change material/(TiO2 + Ti3C2) nanocomposites. The TGA analysis of pure PCM (PW82) and hybrid PCM/(TiO2 + Ti3C2) nanocomposites samples of mass loss with the temperature are shown in Figure 8. The heating rate 10 °C/min for the initial mass of ~15 mg for each sample is maintained for obtaining the TGA results. Figure 8 shows that the pure phase change material (PW82) shows maximum mass loss behavior of about 70% in the temperature range 285 °C and 425 °C. The results obtained are similar to the investigation reported by Tang et al. [50]. Due to the low weight fraction of (TiO2 + Ti3C2) nanoparticles in the phase change material, the mass loss of nanocomposites is not effected on a large scale by nanoparticles. Therefore, the decomposition of nanocomposites almost acts as the decomposition of pure PCMs. When the weight fraction of nanoparticles in nanocomposite reaches up to or beyond 0.3% wt.%, then a remarkable increase in the thermal stability of PCMs is observed [51]. In the temperature range of 30 °C to 302 °C, no significant degradation in hybrid (TiO2 + Ti3C2) nanomaterial is noticed. Within the temperature range of 30 °C to 302 °C, the negligible mass loss of hybrid (TiO2 + Ti3C2) nanomaterial due to temperature rise is observed [52].
The stability of the pure PCM lasts until its decomposition. In this temperature range, the PCM decomposes into its constituent parts and microcapsules. After the resultant components are decomposed, the microcapsules degrade more progressively. Perhaps such a slow disintegration might result due to the formation of a more resistant shell [53]. Thus, it can be concluded that nanocomposite samples hybrid (TiO2 + Ti3C2) in paraffin wax have excellent thermal stability at temperatures below 302 °C. This is a desirable feature for nanocomposites in thermal energy storage applications [50].

3.5. Estimation of Enthalpy and Melting Point of Various Nanocomposites

Figure 9 and Figure 10 show the thermogram curves for the PW82 and PCM/(TiO2 + Ti3C2) nanocomposites. These curves were obtained as a result of differential scanning calorimetry analysis composed of melting and solidification. The thermogram curves obtained during solidification and melting are known as exotherm and endotherm curves, respectively. The peaks on the exotherm and endotherm curves show the phase change of the PCM. By analyzing these curves, melting temperature and solidification temperatures were obtained. Table 2 shows the data obtained by DSC for enthalpy and melting/solidification temperature of the nanocomposites developed by doping of nanoparticles in PCMs. The solidification and melting temperatures of pure PW82 are 68.9 °C and 70.8 °C, respectively, which show very good similarity with the data provided by the supplier of the pure phase change material [54]. The melting DSC characteristics of the PCM were obtained by analysis of the endotherms. The solidification and melting of PW82 begin at 70.8 °C and end at 88.7 °C, which are also known as the onset melting and endset melting temperatures of the PCM, respectively. The latent heat (Hm) of melting is measured as the area under the endotherm peak. The latent heat of melting from the curve is obtained as 175.6 J/g.
The thermograms of the nanocomposites loaded with carbon-based nanoparticles and metal oxide between the range of 0.1 wt.%–0.3 wt.% are found to be quite similar to the clean PW82, with a slight exception in the case of the MXene-doped nanocomposite. Accordingly, for all the nanocomposites based on the type of nanoparticle and their mass concentration, there is very little change in the melting/solidification temperatures. The melting point temperature of the nanocomposite obtained by adding MXene (Ti3C2) to pure PW82 is raised slightly from 70.8 to 71.8 °C for the highest concentration of MXene (Ti3C2) (0.3 wt.%). The very small change in melting point temperature of the nanocomposite is noticed due to the interface connection between atoms of the pure PCM (PW82) with high surface energy and nano-sized particles of Ti3C2 with a high surface area. The slight raising of the melting point temperature proves the discussed mechanism of enhancement of the specific heat (cp), which is in-line with the results reported by Navid et al. [55] for hybrid NEPCM of MXene–silver.
The melting point temperature of PW82/Ti3C2 with doping concertation of 0.1 wt.% is 70.9 °C and for 0.2 wt.% is 71.5 °C. It is concluded from the results of the DSC analysis of the samples that the endothermic energy of nanocomposites reduces with the doping of MXene nanoparticles in paraffin wax. This indicates that the energy released during the melting point occurs, and heat transfer increases at this crucial point. Almost a 3% standard deviation is estimated for the measurement of enthalpy. However, the data recorded for enthalpy of PW82/Ti3C2 for the weight concentrations of 0.1%, 0.2%, and 0.3% wt.% are 100.75 J/g, 110.15 J/g, and 122.35 J/g, respectively. From the results, it can be observed that for the lower mass fraction of 0.1% wt.% of MXene (Ti3C2) flakes causes less endothermic activity, resulting in lower enthalpy. The performance of nanocomposites indicates that a higher mass fraction of Ti3C2 flakes creates stronger crystallinity; therefore, the thermal energy storage capacity of the nano-encapsulates improves remarkably for this crucial point. The greater potential of interactions between nanoparticles and base fluid molecules compared to that of base material molecules is the cause of enthalpy enhancement. We see a decrease in latent heat of melting/solidification for the case when the metal oxide is used (TiO2) with PW82. However, for MXene flakes and the hybrid nanocomposite, an increasing trend is observed. It is interesting to note that the latent heat of NEPCM is lower than that of the base PCM, which is in line with the earlier results reported by Zeng et al. In this work, the DSC analysis of the paraffin wax proves that the latent heat of the phase change material decreases with the addition of MWCNT. Figure 9 represents the thermogram of the hybrid nanocomposite. It is observed from the plot that melting point increases with the loading of nanoparticles while the onset of solidification temperature decreases, which is similar to the results reported by researchers numerically as well as experimentally for NEPCM of different nanoparticles [56,57,58], meaning solidification is advanced. The trend of latent heat is similar to MXene with a little decrement in its values.
Further, doping different nano-additives with varying doping concentrations changes the exothermic and endothermic curves. The doping of nanomaterials reduces the peaks of endotherms and exotherms, and, hence, the phase change temperature of melting is reduced. Table 2 shows the results obtained with the help of DSC analysis of the nano-enhanced PCMs for the solidification and melting of different nanoparticles with different wt.% concentrations.

4. Conclusions

In this study, NEPCM is prepared by direct synthesis. The varying amount of TiO2 and Ti3C2 nanoparticles and their hybrids are mixed in pure paraffin wax (PW82). The thermal properties of nanocomposites, as well as pure paraffin, are measured by conducting thermal conductivity measurement and DCS analysis. The thermal storage capacity of pure paraffin wax, nanocomposites of TiO2 and Ti3C2, and hybrid nanocomposite of TiO2–Ti3C2 are measured in the 25–250 °C temperature range. This temperature range is selected by maintaining the maximum operation temperature as no more than the decomposition temperature of the PCM. It is observed that the hybrid nanocomposite of TiO2–Ti3C2 nanoparticles in the PCM with a weight concentration of 0.3 wt.% shows maximum enhancement in specific heat capacity, which is 33.4% and 41.3% at temperatures 25 °C and 250 °C, respectively. The improvement in thermal conductivity of the hybrid nanocomposite (PCM/TiO2–Ti3C2) for weight fraction 0.3 wt.% is ~15%. The melting point of the hybrid nanocomposites increases with increasing the doping concentration of nanoparticles in the PCM, and for 0.3 wt.%, it is found to be 73.1 °C. The melting point of pure paraffin wax is 70.8 °C, and for nanocomposites of TiO2 and Ti3C2 for weight concentration 0.3 wt.% are found to be 71.3 °C and 71.8 °C, respectively. The DSC analysis shows that the endothermic enthalpy of hybrid NEPCM of TiO2–Ti3C2 decreases. The endothermic enthalpy of the pure paraffin wax is ~175.6 J/g. Enthalpy values of hybrid nanocomposites for the weight concentrations of hybrid of TiO2–Ti3C2 in paraffin wax 0.1, 0.2, and 0.3 wt.% are ~80.7, ~87.8, and ~95.4 J/g, respectively. This reveals that the energy released during melting and the transfer of heat is improved at this crucial point. The long-term performance analysis for thermal conductivity of the prepared hybrid nanocomposites PW82/TiO2–Ti3C2 recommends the use of the nanocomposite in proposed applications even for more than 20 thermal cycles because of its appreciable thermal reliability. The final degradation temperature of nanocomposite PW82/TiO2–Ti3C2 is 397 °C in volume fraction of 0.3 wt.%. The thermal analysis also shows that the PCM should be doped homogeneously and uniformly with nanoparticles to achieve long-duration thermal stability of the nanocomposite (PW82/TiO2–Ti3C2). From the above results, it can be concluded that PW82/TiO2–Ti3C2 composites can be used efficiently as thermal energy storage. The impacts of the number of layers, thickness, and size analysis are of significant interest for future studies because of the higher performance of the hybrid TiO2–Ti3C2 nanomaterial when used as a nanofiller to build PCM nanocomposites with improved thermal storage and thermal conductivity. It is also necessary to measure thermal conductivity at higher temperatures to observe how it changes with temperature.

Author Contributions

Formal analysis, S.M.Y.; Data curation, A.A.K.; Writing—original draft, A.A.K.; Writing—review & editing, S.M.Y. and M.A.A.; Supervision, S.M.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Dincer, I.; Rosen, M.A. Thermal Energy Storage: Systems and Applications; John Wiley & Sons: Hoboken, NJ, USA, 2021. [Google Scholar]
  2. Agyenim, F.; Hewitt, N.; Eames, P.; Smyth, M. A review of materials, heat transfer and phase change problem formulation for latent heat thermal energy storage systems (LHTESS). Renew. Sustain. Energy Rev. 2010, 14, 615–628. [Google Scholar] [CrossRef]
  3. Nkwetta, D.N.; Haghighat, F. Thermal energy storage with phase change material—A state-of-the art review. Sustain. Cities Soc. 2014, 10, 87–100. [Google Scholar] [CrossRef]
  4. Kenisarin, M.M. Thermophysical properties of some organic phase change materials for latent heat storage. A review. Sol. Energy 2014, 107, 553–575. [Google Scholar] [CrossRef]
  5. Liu, M.; Saman, W.; Bruno, F. Review on storage materials and thermal performance enhancement techniques for high temperature phase change thermal storage systems. Renew. Sustain. Energy Rev. 2012, 16, 2118–2132. [Google Scholar] [CrossRef]
  6. Rathod, M.K.; Banerjee, J. Thermal stability of phase change materials used in latent heat energy storage systems: A review. Renew. Sustain. Energy Rev. 2013, 18, 246–258. [Google Scholar] [CrossRef]
  7. Jamekhorshid, A.; Sadrameli, S.M. Application of phase change materials (PCMs) in maintaining comfort temperature inside an automobile. World Acad. Sci. Eng. Technol. Int. J. Chem. Mol. Nucl. Mater. Metall. Eng. 2012, 6, 33–35. [Google Scholar]
  8. Mondal, S. Phase change materials for smart textiles—An overview. Appl. Therm. Eng. 2008, 28, 1536–1550. [Google Scholar] [CrossRef]
  9. Hosseini, M.J.; Rahimi, M.; Bahrampoury, R. Experimental and computational evolution of a shell and tube heat exchanger as a PCM thermal storage system. Int. Commun. Heat Mass. Transfer. 2014, 50, 128–136. [Google Scholar] [CrossRef]
  10. Soares, N.; Costa, J.J.; Gaspar, A.R.; Santos, P. Review of passive PCM latent heat thermal energy storage systems towards buildings’ energy efficiency. Energy Build. 2013, 59, 82–103. [Google Scholar] [CrossRef]
  11. Farid, M.M.; Khudhair, A.M.; Razack, S.A.K.; Al-Hallaj, S. A review on phase change energy storage: Materials and applications, Energy Conversion. Managament 2004, 45, 1597–1615. [Google Scholar]
  12. Parlak, M.; Sömek, K.; Temel, Ü.; Yapici, K. Experimental investigation of transient thermal response of phase change material embedded by Graphene nanoparticles in energy storage module. In Proceedings of the 2016 15th IEEE Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), Las Vegas, NV, USA, 31 May–3 June 2016; pp. 645–651. [Google Scholar] [CrossRef]
  13. Fan, L.W.; Khodadadi, J.M. Thermal conductivity enhancement of phase change materials for thermal energy storage: A review. Renew Sustain. Energy Rev. 2011, 15, 24. [Google Scholar] [CrossRef]
  14. Marin, J.M.; Zalba, B.; Cabeza, L.F.; Mehling, H. Improvement of a thermal energy storage using plates with paraffin–graphite composite. Int. J. Heat Mass. Transf. 2005, 48, 2561. [Google Scholar] [CrossRef]
  15. Zhang, Y.P.; Ding, J.H.; Wang, X.; Yang, R.; Lin, K.P. Influence of additives on thermal conductivity of shape-stabilized phase change material. Sol. Energy Mater. Sol. Cells 2006, 90, 1692. [Google Scholar] [CrossRef]
  16. Wang, J.F.; Xie, H.Q.; Xin, Z.; Li, Y.; Chen, L.F. Enhancing thermal conductivity of palmitic acid based phase change materials with carbon nanotubes as fillers. Sol. Energy 2010, 84, 339. [Google Scholar] [CrossRef]
  17. Cai, Y.; Wei, Q.; Huang, F.; Gao, W. Preparation and properties studies of halogen-free flame reardant form-stable phase change materials based on paraffin/high density polyethylene composites. Appl. Energy 2008, 85, 765. [Google Scholar] [CrossRef]
  18. Shatikian, V.; Ziskand, G.; Letan, R. Numerical investigation of a PCM-based heat sink with internal fins. Int. J. Heat. Mass. Transf. 2005, 48, 3689. [Google Scholar] [CrossRef]
  19. Gharebaghi, M.; Sezai, I. Enhancement of heat transfer in latent heat storage modules with internal fins. Numer. Heat Transf. A 2008, 53, 749–765. [Google Scholar] [CrossRef]
  20. Hu, J.; Yu, H.; Chen, Y.M.; Zhu, M.F. Study on phase-change characteristics of PET–PEG copolymers. J. Macromol. Sci. B 2006, 45, 615. [Google Scholar] [CrossRef]
  21. Karaipekli, A.; Sarı, A.; Kaygusuz, K. Thermal conductivity improvement of stearic acid using expanded graphite and carbon fiber for energy storage applications. Renew. Energy 2007, 32, 2201. [Google Scholar] [CrossRef]
  22. Wang, M.R.; Kang, Q.J.; Pan, N. Thermal conductivity enhancement of carbon fiber composites. Appl. Therm. Eng. 2009, 29, 418. [Google Scholar] [CrossRef]
  23. Chen, C.; Wang, L.; Huang, Y. Electrospun phase change fibers based on polyethylene glycol/cellulose acetate blends. Appl. Energy 2011, 88, 3133. [Google Scholar] [CrossRef]
  24. Sari, A.; Karaipekli, A.; Alkan, C. Preparation, characterization and thermal properties of lauric acid/expanded perlite as novel form-stable composite phase change material. Chem. Eng. J. 2009, 155, 899. [Google Scholar] [CrossRef]
  25. Karaipekli, A.; Sari, A. Capric–myristic acid/vermiculite composite as form stable phase change material for thermal energy storage. Sol. Energy 2009, 83, 323. [Google Scholar] [CrossRef]
  26. Kim, S.; Drzal, L.T. High latent heat storage and high thermal conductive phase change materials using exfoliated graphite nanoplatelets. Sol. Energy Mater. Sol. Cells 2009, 93, 136. [Google Scholar] [CrossRef]
  27. Li, J.L.; Xue, P.; Ding, W.Y.; Han, J.M.; Sun, G.L. Micro-encapsulated paraffin/high density polyethylene/wood flour composite as form-stable phase change material for thermal energy storage. Sol. Energy Mater. Sol. Cells 2009, 93, 1761. [Google Scholar] [CrossRef]
  28. Zhao, C.Y.; Lu, W.; Tian, Y. Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs). Sol. Energy 2010, 84, 1402. [Google Scholar] [CrossRef] [Green Version]
  29. Hawlader, M.N.A.; Uddin, M.S.; Khin, M.M. Microencapsulated PCM thermal energy storage system. Appl. Energy 2003, 74, 195. [Google Scholar] [CrossRef]
  30. Sari, A.; Alkan, C.; Karaipekli, A.; Uzun, O. Microencapsulated n-octacosane as phase change material for thermal energy storage. Sol. Energy 2009, 83, 1757. [Google Scholar] [CrossRef]
  31. Chen, Z.H.; Yu, F.; Zeng, X.R.; Zhang, Z.G. Preparation, characterization and thermal properties of nanocapsules containing phase change material n-dodecanol by miniemulsion polymerization with polymerizable emulsifier. Appl. Energy 2012, 91, 7. [Google Scholar] [CrossRef]
  32. Shaikh, S.; Lafdi, K.; Hallinan, K. Carbon nano additives to enhance latent energy storage of phase change materials. J. Appl. Phys. 2008, 103, 094302. [Google Scholar] [CrossRef] [Green Version]
  33. Wang, J.F.; Xie, H.Q.; Xin, Z. Thermal properties of paraffin based composites containing multi-walled carbon nanotubes. Thermochim. Acta 2009, 488, 39. [Google Scholar] [CrossRef]
  34. Cui, Y.; Liu, C.; Hu, S.; Yu, X. The experimental exploration of carbon nanofiber and carbon nanotube additives on thermal behaviour of phase change materials. Sol. Energy Mater. Sol. Cells 2011, 95, 1208. [Google Scholar] [CrossRef]
  35. Elgafy, A.; Lafdi, K. Effect of carbon nanofiber additives on thermal behavior of phase change materials. Carbon 2005, 43, 3067. [Google Scholar] [CrossRef]
  36. Ho, C.J.; Gao, T.Y. Preparation and thermophysical properties of nanoparticle-in paraffin emulsion as phase change material. Int. Commun. Heat Mass. Transf. 2009, 36, 467. [Google Scholar] [CrossRef]
  37. Khan, A.A.; Danish, M.; Rubaiee, S.; Yahya, S.M. Insight into the investigation of Fe3O4/SiO2 nanoparticles suspended aqueous nanofluids in hybrid photovoltaic/thermal system. Clean. Eng. Technol. 2022, 11, 100572. [Google Scholar] [CrossRef]
  38. Arasu, A.V.; Mujumdar, A.S. Numerical study on melting of paraffin wax with Al2O3 in a square enclosure. Int. Commun. Heat Mass. Transf. 2012, 39, 8. [Google Scholar] [CrossRef]
  39. Teng, T.-P.; Yu, C.-C. Characteristics of phase-change materials containing oxide nano-additives for thermal storage. Nanoscale Res. Lett. 2012, 7, 611. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  40. Pfleger, N.; Bauer, T.; Martin, C.; Eck, M.; Wörner, A. Thermal energy storage—Overview and specific insight into nitrate salts for sensible and latent heat storage. Beilstein. J. Nanotechnol. 2015, 6, 1487–1497. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  41. Teng, T.P.; Lin, B.G.; Yeh, Y.Y. Characterization of heat storage by nanocomposite -enhanced phase change materi-als. Adv. Mater. Res. 2011, 287, 1448. [Google Scholar] [CrossRef]
  42. Jiao, F.; Bai, D.; Du, J.; Hong, Y. Numerical investigation on melting and thermal performances of a phase change material in partitioned cavities with fins for thermal energy storage. J. Energy Storage 2022, 56, 106022. [Google Scholar] [CrossRef]
  43. Solangi, N.H.; Mubarak, N.M.; Karri, R.R.; Mazari, S.A.; Jatoi, A.S.; Koduru, J.R.; Dehghani, M.H. MXene-based phase change materials for solar thermal energy storage. Energy Convers. Manag. 2022, 273, 116432. [Google Scholar] [CrossRef]
  44. Wang, X.; Ma, B.; Wei, K.; Si, W.; Kang, X.; Fang, Y.; Zhang, H.; Shi, J.; Zhou, X. Thermal storage properties of polyurethane solid-solid phase-change material with low phase-change temperature and its effects on performance of asphalt binders. J. Energy Storage 2022, 55, 105686. [Google Scholar] [CrossRef]
  45. Viana, M.M.; Soares, V.F.; Mohallem, N.D.S. Synthesis and characterization of TiO2 nanoparticles. Ceram. Int. 2010, 36, 2047–2053. [Google Scholar] [CrossRef]
  46. Jastrzębska, A.M.; Karwowska, E.; Wojciechowski, T.; Ziemkowska, W.; Rozmysłowska, A.; Chlubny, L.; Olszyna, A. The Atomic Structure of Ti2C and Ti3C2 MXenes is Responsible for Their Antibacterial Activity Toward E. coli Bacteria. J. Mater. Eng. Perform. 2018, 28, 1272–1277. [Google Scholar] [CrossRef]
  47. Low, J.; Zhang, L.; Tong, T.; Shen, B.; Yu, J. TiO2/MXene Ti3C2 composite with excellent photocatalytic CO2 reduction activity. J. Catal. 2018, 361, 255–266. [Google Scholar] [CrossRef]
  48. Saber, D.; El-Aziz, K.; Felemban, B.F.; Alghtani, A.H.; Ali, H.T.; Ahmed, E.M.; Megahed, M. Characterization and performance evaluation of Cu-based/TiO2 nano composites. Sci. Rep. 2022, 12, 1–14. [Google Scholar] [CrossRef]
  49. Deka, P.P.; Ansu, A.K.; Sharma, R.K.; Tyagi, V.V.; Sarı, A. Development and characterization of form-stable porous TiO2/tetradecanoic acid based composite PCM with long-term stability as solar thermal energy storage material. Int. J. Energy Res. 2020, 44, 10044–10057. [Google Scholar] [CrossRef]
  50. Tang, B.; Qiu, M.; Zhang, S. Thermal conductivity enhancement of PEG/SiO2 composite PCM by in situ Cu doping. Sol. Energy Mater. Sol. Cells 2012, 105, 242–248. [Google Scholar] [CrossRef]
  51. Gao, R.; Hu, N.; Yang, Z.; Zhu, Q.; Chai, J.; Su, Y.; Zhang, L.; Zhag, Y. Paper-like graphene-Ag composite films with enhanced mechanical and electrical proper-ties. Nanoscale Res. Lett. 2013, 8, 32. [Google Scholar] [CrossRef] [Green Version]
  52. Shen, J.; Shi, M.; Yan, B.; Ma, H.; Li, N.; Ye, M. One-pot hydrothermal synthesis of Ag-reduced graphene oxide composite with ionic liquid. J. Mater. Chem. 2011, 21, 7795–7801. [Google Scholar] [CrossRef]
  53. Bayés-García, L.; Ventola, L.; Cordobilla, R.; Benages, R.; Calvet, T.; Cuevas-Diarte, M. Phase change materials (PCM) micro-capsules with different shell compositions: Preparation, char-acterization and thermal stability. Sol. Energy Mater. Sol. Cells 2010, 94, 1235–1240. [Google Scholar] [CrossRef]
  54. Phase Change Materials; Products Ltd. Company, 2011.
  55. Aslfattahi, N.; Saidur, R.; Arifutzzaman, A.; Abdelrazik, A.S.; Samylingam, L.; Sabri, M.F.M.; Sidik, N.A.C. Improved thermo-physical properties and energy efficiency of hybrid PCM/graphene-silver nanocomposite in a hybrid CPV/thermal solar system. J. Therm. Anal. Calorim. 2020, 147, 1125–1142. [Google Scholar] [CrossRef]
  56. Hajizadeh, M.R.; Selimefendigil, F.; Muhammad, T.; Ramzan, M.; Babazadeh, H.; Li, Z. Solidification of PCM with nano powders inside a heat exchanger. J. Mol. Liq. 2020, 306, 112892. [Google Scholar] [CrossRef]
  57. Sheikholeslami, M. Numerical modeling of nano enhanced PCM solidification in an enclosure with metallic fin. J. Mol. Liq. 2018, 259, 424–438. [Google Scholar] [CrossRef]
  58. Kaviarasu, C.; Prakash, D. Review on Phase Change Materials with Nanoparticle in Engineering Applications. J. Eng. Sci. Technol. Rev. 2016, 9, 26–36. [Google Scholar] [CrossRef]
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Figure 1. TEM and SEM images of Ti3C2 (MXene flakes).
Figure 1. TEM and SEM images of Ti3C2 (MXene flakes).
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Figure 2. TEM and SEM images of TiO2 nanoparticles.
Figure 2. TEM and SEM images of TiO2 nanoparticles.
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Figure 3. Line diagram of thermal conductivity setup for PCM: (a) KD Pro thermal analyzer, (b) test section, and (c) circulating water bath.
Figure 3. Line diagram of thermal conductivity setup for PCM: (a) KD Pro thermal analyzer, (b) test section, and (c) circulating water bath.
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Figure 4. (a) Line diagram of DSC apparatus; (b) DSC apparatus.
Figure 4. (a) Line diagram of DSC apparatus; (b) DSC apparatus.
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Figure 5. TEM and SEM images of (a) TiO2 NEPCM, (b) MXene NEPCM.
Figure 5. TEM and SEM images of (a) TiO2 NEPCM, (b) MXene NEPCM.
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Figure 6. Thermal conductivity data of hybrid PW82/(TiO2 + Ti3C2) nanocomposite as a function of nanomaterial loading.
Figure 6. Thermal conductivity data of hybrid PW82/(TiO2 + Ti3C2) nanocomposite as a function of nanomaterial loading.
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Figure 7. Specific heat capacity of pure paraffin wax with titania, MXene, and hybrid PCM/(TiO2 + Ti3C2) nanocomposites.
Figure 7. Specific heat capacity of pure paraffin wax with titania, MXene, and hybrid PCM/(TiO2 + Ti3C2) nanocomposites.
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Figure 8. TG analysis of pure organic PCM (PW82) and hybrid PCM/(TiO2 + Ti3C2) nanocomposites.
Figure 8. TG analysis of pure organic PCM (PW82) and hybrid PCM/(TiO2 + Ti3C2) nanocomposites.
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Figure 9. The thermogram curves of PW82 nanocomposites: (a) TiO2; (b) Ti3C2.
Figure 9. The thermogram curves of PW82 nanocomposites: (a) TiO2; (b) Ti3C2.
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Figure 10. The thermogram curves of PW82/(TiO2 + Ti3C2) nanocomposites.
Figure 10. The thermogram curves of PW82/(TiO2 + Ti3C2) nanocomposites.
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Table
Table 1. Variation in thermal conductivity and phase change enthalpy of paraffin wax organic/MXene (Ti3C2) + TiO2 with no. of cycles.
Table 1. Variation in thermal conductivity and phase change enthalpy of paraffin wax organic/MXene (Ti3C2) + TiO2 with no. of cycles.
Heating/Cooling Cycles0102030405075100150
Thermal conductivity (W/m-K)0.3550.3540.3520.3540.3530.3510.3530.3540.352
Phase change enthalpy (J/g)95.4094.2594.1894.8695.2295.3395.1094.9895.15
Table
Table 2. Thermal specifications of NEPCM obtained from DSC analysis.
Table 2. Thermal specifications of NEPCM obtained from DSC analysis.
PCM TypeConcentration (wt.%)Tm (°C)Hm (J/g)Ts (°C)Hs (J/g)
PW82---70.8175.668.9159.4
PW82 + TiO20.171.0165.268.7155.10
0.271.2158.468.1148.25
0.371.3150.567.6142.62
PW82 + Ti3C20.170.9100.7570.195.75
0.271.5110.1569.5105.10
0.371.8122.3568.2120.13
PW82/TiO2 + Ti3C20.17180.768.5075.49
0.272.587.867.3382.75
0.373.195.466.4390.22
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Khan, A.A.; Yahya, S.M.; Ali, M.A. Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage. Sustainability 2023, 15, 516. https://doi.org/10.3390/su15010516

AMA Style

Khan AA, Yahya SM, Ali MA. Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage. Sustainability. 2023; 15(1):516. https://doi.org/10.3390/su15010516

Chicago/Turabian Style

Khan, Ajiv Alam, Syed Mohd Yahya, and Masood Ashraf Ali. 2023. "Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage" Sustainability 15, no. 1: 516. https://doi.org/10.3390/su15010516

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