Photo- and magneto-responsive highly CNTs@Fe3O4 Glauber's salt based phase change composites for energy conversion and storage

Abstract

As a crucial component in phase change heat storage systems, phase change materials have demonstrated remarkable application potential across diverse fields, such as solar energy storage systems, magnetic induction energy conversion, and storage. This research reports a high-performance photomagnetically driven composite phase change materials. The photomagnetic response unit was fabricated via the hydrothermal coprecipitation method by in-situ loading of Fe₃O₄ nanoparticles onto carbon nanotubes (CNTs@Fe₃O₄). Subsequently, it was integrated with the Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O eutectic salt to synthesize the composite PCM heat storage material.Experimental findings indicate that the composite incorporating 2.5 % CNTs@Fe₃O₄ exhibits nearly zero subcooling (ΔT = 0.1 °C), a thermal conductivity as high as 1.0230 W/(m·K), a significant latent heat of phase transformation (melting enthalpy of 253 J/g and solidification enthalpy of 218 J/g), and an enthalpy retention rate of 94.8 % after 1000 thermal cycles. The Fe₃O₄ endows the material with excellent magneto-thermal conversion performance. Specifically, at a 2.5 % doping content, the temperature increase within 240 s in an alternating magnetic field can reach 67.2 °C through the Néel/Brownian relaxation mechanism. Additionally, the CNTs carrier enhances the photothermal conversion efficiency to 94.5 %. This material combines high thermal conductivity, cycle stability, and dual-field (optical/magnetic) driven heat storage capabilities, thus demonstrating significant application potential in multifunctional thermal energy storage.