Thermally Conductive Phase Change Composites Featuring Anisotropic Graphene Aerogels for Real‐Time and Fast‐Charging Solar‐Thermal Energy Conversion

Abstract

Phase change materials (PCMs) have triggered considerable attention as candidates for solar‐thermal energy conversion. However, their intrinsic low thermal conductivity prevents the rapid spreading of heat into the interior of the PCM, causing low efficiencies in energy storage/release. Herein, anisotropic and lightweight high‐quality graphene aerogels are developed by directionally freezing aqueous suspensions of polyamic acid salt and graphene oxide to form vertically aligned monoliths, followed by freeze‐drying, imidization at 300 °C and graphitization at 2800 °C. After impregnating with paraffin wax, the resultant phase change composite (PCC) exhibits a high transversal thermal conductivity of 2.68 W m−1 K−1 and an even higher longitudinal thermal conductivity of 8.87 W m−1 K−1 with an exceptional latent heat retention of 98.7%. When subjected to solar radiation, solar energy is converted to heat at the exposed surface of the PCC. As a result of the PCC's high thermal conductivity in the thickness direction, heat can spread readily into the interior of the PCC enabling a small temperature gradient of <3.0 K cm−1 and a fast charging feature. These results demonstrate the potential for real‐time and fast‐charging solar‐thermal energy conversion using phase change materials with tailored anisotropy in their thermal properties.

Engineering the Thermal Conductivity of Functional Phase‐Change Materials for Heat Energy Conversion, Storage, and Utilization

“…To achieve the a fast charging of the solar‐thermal energy storage materials, Min et al developed graphene aerogel and paraffin wax‐based anisotropic and highly conductive phase change composites ( Figure a) . The developed composite materials exhibited high transversal thermal conductivity (2.68 W m −1 K −1 ) and an even better longitudinal thermal conductivity (8.87 W m −1 K −1 ).…”

“…g) The time period is taken for completing the charging of PCC0 and PCC8. a–g) Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

Silver Attached Graphene-Based Aerogel Composite Phase Change Material and the Enhancement of Thermal Conductivity

“…There are many types of PCMs, including organic PCMs such as paraffin [ 1 , 2 , 3 ] and inorganic PCMs such as inorganic salt hydrates [ 4 , 5 ]. However, all of them have the problem of low thermal conductivity, which leads to low efficiency of phase change and the phenomenon of overcooling and overheating [ 6 , 7 , 8 , 9 , 10 ]. In addition, they are prone to leakage in the absence of containers and other encapsulation conditions [ 11 , 12 ].…”

Graphene Modified Montmorillonite Based Phase Change Material for Thermal Energy Storage with Enhanced Interfacial Thermal Transfer

“…In the past decade, thermal management has become emerging subject and attracted tremendous attention form fundamental research and industrial applications [1]. As part of thermal management systems, thermal energy storage technology has received significant interest due to its crucial role in the solar thermal technology and building energy conservation [2].…”