A novel three-dimensional network-based stearic acid/graphitized carbon foam composite as high-performance shape-stabilized phase change material for thermal energy storage

https://doi.org/10.1016/j.compositesb.2021.109318Get rights and content

Highlights

  • Graphitized carbon foam (GCF) is obtained with gradient hierarchical porous surface.

  • Large loading capacity and high thermal conductivity of the GCF is achieved.

  • A good interfacial bonding between the GCF and stearic acid (SA) is observed.

  • A three-dimensional network-based shape-stabilized SA/GCF composite is prepared.

  • The composite phase change material has a good thermal stability and reliability.

Abstract

Three-dimensional porous carbon materials have received extensive attention as supports for shape-stabilized phase change materials (PCMs). In order to improve the loading capacity, thermal conductivity and encapsulation performance for PCMs, a three-dimensional graphitized carbon foam (GCF) was developed with gradient hierarchical porous surface. The GCF was successfully prepared by pyrolysis of nano-magnesium oxide/epoxy resin mixture followed by surface treatment through a carbon-thermal reaction of Fe2O3. Using the GCF prepared at 1200 °C (GCF-1200) as a support for stearic acid (SA), a novel three-dimensional network-based SA/GCF composite was achieved as shape-stabilized PCM. The results show that the GCF-1200 has a large SA loading capacity of 84.66 wt% without any liquid leakage. The prepared SA/GCF-1200 composite exhibits a good interfacial bonding between the GCF-1200 and SA without obvious phase separation in its fracture surface. The composite possesses a high compressive strength of 9.45 MPa increasing by about 3.02-fold compared with the GCF-1200, and meanwhile has a significantly improved thermal conductivity of 1.012 W/m K by 4.36 times that of pristine SA. In addition, the melting and freezing enthalpy for the composite was measured as 181.8 and 182.7 J/g, respectively, which corresponds to a thermal storage efficiency of up to 99.9%. More importantly, it presents excellent thermal reliability and chemical stability without evident changes in enthalpy after 200 thermal cycles. Therefore, the composite has a great potential for thermal energy storage applications.

Introduction

Nowadays, energy structure is still dominated by non-renewable energy sources like fossil fuels [1]. Due to problems such as limited reserves and over-exploitation [2,3], energy depletion and environmental pollution have become important factors restricting the current social development to some content [4]. Therefore, it has become an urgent challenge to develop clean, high-efficiency, and renewable new energy and improve energy utilization efficiency as well [5]. Phase change materials (PCMs), inexpensive with high energy storage density [6], can achieve the purpose of storing or releasing heat energy and regulating temperature by means of absorbing or releasing a large amount of heat energy from the external environment [7]. Consequently, they have broad application prospects in the fields of waste heat recovery, building energy conservation, solar energy utilization, aerospace and electronic equipment heat dissipation [8,9]. Among PCMs, the solid-liquid PCMs feature low phase transition temperature, large latent heat of phase transition and small volume change during the phase transition [[10], [11], [12], [13]]. According to the chemical composition, they can be divided into inorganic, organic and composite solid-liquid PCMs. With the merits of high latent heat of phase change, no supercooling, no corrosion, no volume effect, and good chemical stability, organic PCMs, such as stearic acid (SA), paraffin wax, polyethylene glycol, fatty acid and its derivatives [[14], [15], [16], [17]] are widely used in thermal energy conversion systems. However, the problems of liquid seepage and low thermal conductivity in the application process still exist [18]. Currently, some shape-stabilized composite PCMs with high thermal energy storage performance have been prepared through incorporation of organic PCMs into support materials [19]. For the prepared composite PCM, the organic PCM is encapsulated in the support material, effectively reducing the liquid seepage of PCM and thus improving its shape stability during the phase change process [20]. In addition, the loading capacity and thermal conductivity of the support material affect the energy storage density and thermal transfer efficiency of the as-prepared composite PCMs, respectively. Therefore, the supporting material of PCM is hoped to have large loading capacity, high thermal conductivity and good encapsulation performance [21].

In recent years, the porous carbon materials, with three-dimensional network structure, high electrical/thermal conductivity, low density and high chemical stability [22,23], have been developed (mainly including graphene foams, carbon nanotube foams and carbon foams) and received extensive attention as supports to prepare three-dimensional network–based shape-stabilized composite PCMs. However, for most of graphene foams and carbon nanotube foams, the as-prepared composite PCMs generally exhibit unsatisfactory thermal storage performance. This can be mainly attributed to their discontinuous three-dimensional network structure formed by point, face or edge contacts, thus leading to high thermal/electrical contact resistance [24]. In addition, the preparation costs of these two kinds of foams are relatively high, which would limit their further application in the field of phase change energy storage [25]. Carbon foam (CF) is a kind of lightweight porous carbon material with interconnected continuous three-dimensional network structure [26]. For this reason, it has been considered as a promising support for fabrication of three-dimensional network-based shape-stabilized composite PCM with both high thermal storage performance and good shape stability [27]. More importantly, graphitized carbon foams (GCFs) usually possess high thermal conductivity and good chemical compatibility with organic PCMs [28]. However, most GCFs still confront the main problems like smooth pore wall, large pore size and relatively high bulk density when used as organic PCM supports [29]. This would lead to low energy storage density and liquid seepage of as-prepared composite PCMs. In addition, their high preparation costs also restrict the further application for thermal energy storage [30]. Presently, a series of fruitful works have been carried out on the catalytic graphitization of resin-based CFs or the surface treatment of cell walls for increasing their micro/mesopores content [31]. Compared with conventional GCFs, these GCFs usually exhibit larger micro/mesopore content, lower bulk density and lower preparation cost; consequently, the as-prepared composite PCMs exhibit better leakage-prevention performance and higher energy storage density [32]. Nevertheless, it is still necessary to further enhance their loading capacity and thermal conductivity as well as encapsulation performance for organic PCMs.

There is a contradiction between improving their loading capacity and increasing thermal conductivity for GCFs [33]. It is generally accepted that the thermal conductivity of CF increases with the increasing of its bulk density whereas the loading capacity decreases [34]. In order to achieve both high thermal conductivity and large loading capacity, the prepared CFs should have high graphitization degree and low bulk density with high open-cell ratio. In addition, the encapsulation performance of CF is closely related to both the cell structure and the interfacial bonding between organic PCM and cell walls [35]. It is well-known that the ideal spherical cell structure of CF is beneficial to the effective encapsulation of PCM, which could act as hollow sphere structure with desired encapsulation performance [36]. Also, the strong interfacial bonding may provide good encapsulation performance of CF for PCM, mainly depending on the microstructures of its cell walls [37]. Hence, how to design and prepare a kind of CF with desirable structure is the key for achieving high-performance shape-stabilized PCMs. In previous works, a CF with well-developed three-dimensional network structure was fabricated by pyrolysis of nano-magnesium oxide (nano-MgO)/cyanate ester resin composite [38]; meanwhile, the nano-MgO particles could act as a template for the growth of graphene layers during the pyrolysis [39]. In addition, considering that there exist large numbers of bubble-like bulges with through holes on the cell walls of the prepared CF, a gradient hierarchical porous surface could be obtained by a subsequent surface treatment of the cell walls. This would favor the achievement of good interfacial bonding between PCM and the CF. In this work, a three-dimensional graphitized carbon foam (GCF) was developed with gradient hierarchical porous surface. The GCF was prepared by pyrolysis of nano-MgO/epoxy resin mixture followed by surface treatment through a carbon-thermal reaction of Fe2O3. After that, a novel three-dimensional network-based composite PCM was achieved with excellent thermal energy storage and leakage-prevention performance by the incorporation of SA into the as-prepared GCF.

Section snippets

Materials

Ferric nitrate nonahydrate (Fe(NO3)3·9H2O), stearic acid (SA) and dichloromethane (CH2Cl2) were provided by Sinopharm Chemical Reagent Co., Ltd. Nano-MgO dispersion with a concentration of 20 wt% was supplied by Henner New Material Co., Ltd. Bisphenol A epoxy resin (E−51) was purchased from Jinliyuan curatorial Co., Ltd. Bismaleimidodiphenyl methane (BMDM) and diaminodiphenylmethane (DDM) were purchased from Fengguang Chemicals Co., Ltd. All reactants were analytical grade and used without

Morphology and structural characterization of CF and GCFs

FESEM images of the surfaces of the prepared CF and three GCFs (GCF-1000. GCF-1200, and GCF-1400) are illustrated in Fig. 1a–d, exhibiting that they all have well-developed three-dimensional network structure. As shown in Fig. 1a, the CF possesses spherical-shaped pore structures with an average pore size of 300 μm, which can be attributed to the self-foaming characteristics of epoxy resin; also, a large number of pores with an average pore size of 200 nm can be observed on its pore walls, due

Conclusion

This work presented an approach for the fabrication of high-performance shape-stabilized composite phase change materials (PCMs). For preparing the composite PCMs, a three-dimensional graphitized carbon foam (GCF) was developed with gradient hierarchical porous surface. The GCF was successfully fabricated by pyrolysis of nano-MgO/epoxy resin mixture followed by surface treatment through a carbon-thermal reaction of Fe2O3 pyrolyzed from Fe(NO3)3. On this basis, a novel three-dimensional

CRediT authorship contribution statement

Renquan Wu: Conceptualization, Methodology, Investigation, Writing – original draft, Formal analysis, Characterization. Wei Gao: Investigation, Formal analysis, Characterization. Yunhong Zhou: Investigation, Formal analysis. Zhuqi Wang: Investigation, Resources. Qilang Lin: Conceptualization, Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by the National Natural Science Foundation of China (Grant No. 51872049).

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