Photo- and magneto-responsive highly graphitized carbon based phase change composites for energy conversion and storage

Abstract

Phase change material (PCM) as latent heat storage unit shows great potential in various scenes, including solar energy storage system and magnetically induced energy conversion and storage. But insufficient optical activity and electromagnetic response capability seriously hinder its wider applications. Herein, we reported an advanced high-performance photo- and magneto-driven composite phase change material (CPCM), where metal-organic framework (MOF) derived magnetic highly graphitized carbon (MGC) served as a fast-charging photo- and magneto-responsive supporting skeleton, and octadecanol (ODA) acted as a latent heat storage unit. In graphitic structure, there were numerous sp2 carbon atoms and π electrons. Under solar irradiation, heat is quickly discharged by lattice vibration resulting from π-π∗ transition and subsequent electron-phonon coupling in highly graphitized carbon. Moreover, in situ anchored magnetic cobalt nanoparticles contribute to another exothermic effect triggered by light and alternative magnetic field owing to its surface plasmon resonance (SPR) and eddy current effect, respectively. Additionally, cobalt nanoparticles can also serve as the heterogenous nucleation sites to promote the crystallinity of ODA molecules, thus profiting the increase of phase change enthalpy. Therefore, our developed cobalt-decorated highly graphitized carbon based photo- and magneto-responsive CPCM synergistically reached an enhanced photothermal efficiency of 88.1%, thermal energy storage capacity of 131.14 J/g, and excellent thermal cycling stability and reliability after undergoing multiple charging-discharging cycles, showing great potential in latent heat storage, solar and magnetic energy harvesting.