Design and fabrication of flower-shaped MnCo2O4.5/CoSe/MnSe2 heterostructures via incomplete selenization for high-performance cathodes of supercapacitors

Transition metal oxides or selenides have been widely used in electrode materials for supercapacitors. And the formation of heterostructures between the two different materials can further realize high-performance electrode materials and high-energy density supercapacitor. Therefore, in our work, the novel reaction method of incomplete selenization makes the electrode material have both oxides and selenides, and the prepared heterostructured composite material has excellent electrochemical performance. Herein, the nickel foam (NF)-supported flower-shaped manganese‑cobalt-oxide-selenide composite heterostructures self-assembled from the heterogeneous nanorods consisting of MnCo₂O_4.5, CoSe, and MnSe₂ components were designed and fabricated via a facile, adjustable, incomplete selenization of the hydrothermal derived manganese‑cobalt hydroxide (Mn-Co-OH) precursor (named as Mn-Co-O-Se-x, where x represents the feed mass ratio between selenium powder and precursor, which is 5, 10, and 20, respectively). The optimized Mn-Co-O-Se-5 composite exhibits a high specific capacitance of 3424 F g⁻¹ at a current density of 1 A g⁻¹. After 10,000 cycles at 20 A g⁻¹, the discharge capacitance is 103.7% of the first value, demonstrating superior cycle stability. Moreover, the assembled Mn-Co-O-Se-5//activated carbon (AC) asymmetric supercapacitor (ASC) device delivers maximum energy density and power density at 112 Wh kg⁻¹ and 16,000 W kg⁻¹ and shows good cycling stability with a capacitance retention of 98.7% after 10,000 cycles at 10 A g⁻¹, demonstrating promising prospects for application in supercapacitors.