Formation of carbon coated yolk-shelled Fe3O4-CeO2 hollow spheres toward remarkable performance supercapacitors

Yolk-shelled hollow structures with unique structural features are incredibly attractive for energy storage systems. Here we present a self-template strategy to prepare carbon coated yolk-shelled Fe3O4-CeO2 hollow spheres. First, yolk-shelled Fe-Ce glycerate precursors are designed by a solvothermal method. Afterward, the carbon coated yolk-shelled Fe3O4-CeO2 hollow spheres are eventually synthesized via calcinations the obtained precursors in Ar. Such unique structures endow the Fe3O4-CeO2 with abundant inner cavities, large surface area and more electroactive site. As electrode material for supercapacitors, a large capacity of 430 C g−1 is obtained at 2.0 A g−1, and it can be as high as 198.4 C g−1 even at 20 A g−1. Moreover, it also takes outstanding rate capability and superior cycling durability (only 5.2 % capacity reduction over 5000 cycles at 6.0 A g−1). Furthermore, a quasi-solid-state flexible asymmetric supercapacitor device is constructed by Fe3O4-CeO2 cathode and activated carbon anode. The device manifests a high energy density of 46.6 Wh kg−1 at 2.0 A g−1 (versus 1650 W kg−1 power density). Even at 15 A g−1, the energy density is still 21 Wh kg−1 with 12,441 W kg−1. We envision that this work not only explores a promising electrode material for supercapacitors, but also provides an alternative avenue to prepare yolk-shelled hollow structures toward energy storage applications.