In-situ deposition preparation of n-octadecane@Silica@Polydopamine-doped polypyrrole microcapsules for photothermal conversion and thermal energy storage of full-spectrum solar radiation

Abstract

Phase change materials （PCMs） play an essential role in utilizing solar energy. However, there exist inherent defects of pure PCMs, such as low solar energy utilization efficiency and easy leakage. In this work, we successfully prepared a novel type of n-octadecane@Silica@Polydopamine-doped polypyrrole photothermal phase change microcapsules (SCN@PAP micro-PCMs), contained n-octadecane (n-OD) as the core material, silica as the intermediate layer, and polydopamine and polypyrrole composite (PDA-PPY) as the wall material. The microcapsules' morphology, chemical structure, photothermal and thermal storage properties, and thermal stability were investigated. This study confirmed that polydopamine (PDA) doping positively regulates the optical properties of polypyrrole (PPY). The PDA-PPY(PAP) was uniformly deposited on the surface of n-OD@SiO2 phase change microcapsules (SCN micro-PCMs) in granular form with the appropriate doping ratio. Further, tuning the ratio of SCN micro-PCMs to PAP and pyrrole (PY) to dopamine (DA) could endow SCN micro-PCMs with good photothermal properties and retain high thermal storage properties. When the mass ratio of PY: DA = 1:0.032 and SCN: PAP = 6:1, the prepared SCN@PAP micro-PCMs exhibited high photothermal conversion efficiency up to 97.31%, with a melting enthalpy of 145.3 J/g. The enthalpy value decreased by less than 1 J/g after 100 heating and cooling cycles demonstrating excellent thermal energy storage cycling stability. The SCN@PAP micro-PCMs are expected to be promising in promoting the efficient utilization of solar radiation.