Nat. Commun. 8, 1478 (2017)

The storage of solar energy using the phase change of a material, for example, the melting of a solid into liquid, is often a slow process due to the thermal properties of the material involved. Now, Zhongyong Wang and colleagues have reported a means to speed up the process and increase the amount of stored energy by a factor of approximately three by magnetic control of optical absorber distribution. The authors use Fe3O4@graphene nanoparticles in a paraffin host. The graphene component of the nanoparticles yields strong optical absorption of the solar radiation while the Fe3O4 enables magnetic manipulation. Once the surface of the composite material is melted by photothermal conversion, the nanoparticles in the liquid are attracted to a side wall by a magnet within a few seconds. This removal of the optical absorbers allows better penetration of light deeper into the material allowing greater deposition of solar energy.