Two-dimensional porous CeO₂@Co₃O₄ sheet-like heterostructures for high-performance aqueous hybrid supercapacitors

Two-dimensional (2D) heterostructures have attracted a great deal of attention in electrochemical energy storage (EES) due to their unique structure and superior performance. Here, we demonstrate a simple and facile hydrothermal method to prepare 2D porous CeO₂@Co₃O₄ sheet-like heterostructures assembled by 3D nanoflake array as basic building units. In the synthesis, a cerium and cobalt acetate mixed solution was obtained via the reaction of the mixed solutions of cerium nitrate and cobalt nitrate with sodium hydroxide (NaOH) and acetic acid (HAc), respectively. Then the obtained solution was transferred to a Teflon-lined stainless steel autoclave. The obtained CeO₂@Co₃O₄ composite sheets display unique 2D/3D structures, high surface area, and high electroactive sites. As electrode materials for supercapacitors (SCs), compared with single-metal oxides of CeO₂ and Co₃O₄, the CeO₂@Co₃O₄ composite sheets with Ce/Co of 1 : 1 reached a specific capacity of 1027.95 C g^-1 (1856 F g^-1) at 1 A g^-1 in the three-electrode system and 83.79% of its initial capacity after 10 000 cycles. In addition, a assembled hybrid device (CeO₂@Co₃O₄//AC) with CeO₂@Co₃O₄ (positive electrode) and activated carbon (AC, negative electrode) achieved a high energy density of 42.28 W h kg^-1 at a power density of 809.15 W kg^-1 and a long cycle life of 88.42% capacity retention after 10 000 cycles. This strategy not only explores a high-performance electrode material for EES but also provides an alternative route for the synthesis of 2D heterostructures.