Carbon aerogel based composite phase change material derived from kapok fiber: Exceptional microwave absorbility and efficient solar/magnetic to thermal energy storage performance

Abstract

Herein, we report a facile yet efficient strategy for fabricating a carbonized kapok fiber aerogel (CKF) based composite PCM , by incorporating magnetic guest of Fe 3 O 4 nanoparticles and encapsulating thermal energy guest of lauric acid (LA). The obtained LA/CKF@Fe 3 O 4 composite PCMs (CPM) shows an ultrahigh latent heat of 97.5% that of LA. Besides, the integration of Fe 3 O 4 contributes to the CPM with excellent microwave absorption performance by achieving an optimal balance between the impedance matching and the high loss characteristics. The minimum reflection loss for CPM-30 is −17.3 dB at 8.4 GHz within thickness of 5.5 mm, far exceeding the practical demand of −10 dB. Furthermore, the CPM can also realize efficient solar/magnetic to thermal conversion . To the best of our knowledge, this is the first example of carbon aerogel based composite PCM prepared by facile yet renewable method that also exhibits ultrahigh thermal energy capacity, enhanced thermal conductivity , superior microwave absorption property and efficient solar/magnetic to thermal conversion performance. This study paves a way for designing of high-performance composite PCMs with numerous energy storage forms and functions by extending the reported system to other natural microtubules and functional guests. In addition to the highly efficient utilization of solar irradiation, the composite PCM is also able to convert magnetic energy into thermal energy. Similarly, the CPMs were subjected to an alternating magnetic field to estimate the magnetic to thermal energy conversion performance. The temperature evolutions were detected using an infrared thermometer in real-time, as illustrated in Fig. 7d. Upon electromagnetic excitation, the temperatures of the CPMs increase rapidly owing to the magnetothermal effect of the Fe 3 O 4 nanoparticles. It is clear that the heating rate of the CPMs increase gradually with increasing Fe 3 O 4 contents. As excitation time increases, an inflection point is observed in the temperature-time curve, demonstrating that the harvested magnetic energy is converted into thermal energy and stored in the form of latent heat. The higher magnetic to thermal conversion efficiency of sample with high Fe 3 O 4 content may be attributed to the synergistic effect of their relatively low latent heat, large thermal conductivity, optimal impedance matching, and high loss characteristics. Upon the excitation being switched off, the temperatures of CPMs drop immediately to the freezing point of LA, and an obvious freezing plateau appears between 41 and 37 °C, indicating that the stored latent heat is released due to the normal crystallization of LA. These results reveal that the novel CKF@Fe 3 O 4 host matrix can effectively absorb solar and electromagnetic energy, thereby convert them into thermal energy, then dispatch this energy to the surroundings through the interpenetrating 3D network of carbon microtubules, and successfully store it in the form of latent heat through the phase transition of embedded PCM. Thus, the novel carbon aerogel based CPMs in this study is a multifunctional energy harvester and is expected to have broad application in solar/magnetic energy conversion and storage.