Solvothermal synthesis of hollow Fe₃O₄ sub-micron spheres and their enhanced electrochemical properties for supercapacitors

Uniform hollow Fe₃O₄ sub-micron spheres (HFOS) with particle size ranging from 350 to 450 nm have been fabricated by a controlled solvothermal synthesis with ferric chloride hexahydrate as sole iron source and sodium dodecylbenzenesulfonate (SDBS) as a surfactant. The suitable addition of SDBS has been proved to promote the formation of monodisperse Fe₃O₄ hollow particles with narrow size distribution. Good intrinsic magnetic properties including high saturation magnetization of 80.1 A·m² kg^-1 and very low coercivity of 7.3 Oe are observed in these HFOS due to their high purity and spherical morphologies. The electrochemical studies have revealed that these high-purity monodisperse HFOS exhibit high specific capacitance of 294 F g^-1 at 0.5 A g^-1 and good cycle stability with a maintenance of about 90.8% original capacitance after 500 charge/discharge cycles. The excellent electrochemical properties for these HFOS can be attributed to their high purity and large specific surface area resulting from their hollow structure, which promises their big potential application for high-performance supercapacitors.