Metal−organic framework (MOF)-derived composites of transition metal oxides and porous carbon show great potential for energy storage applications. Selenylation is an effective strategy to improve the electrochemical properties of electrode materials. A facile one-step derivation and selenylation of MOFs is proposed here to obtain CoSe 2 nanoparticles embedded into an N-doped carbon skeleton material (CoSe 2 /NC). Moreover, the composite is directly grown on nickel foam as nanosheet arrays, rather than on other materials as powders. The CoSe 2 /NC electrode with special construction exhibits a high capacity of 120.2 mA h g −1 at 1 A g −1 and an excellent cyclic ability of 8% loss after 10,000 cycles. An asymmetric supercapacitor CoSe 2 /NC-NF//AC displays a maximum energy density of 40.9 W h kg −1 at 980 W kg −1 . Moreover, the device has demonstrated that it can successfully charge a mobile phone. The outstanding performance indicates promising potential of CoSe 2 /NC-NF electrodes for supercapacitors.

HIGHLIGHTS • A freestanding MXene-derived defect-rich TiO 2 @reduced graphene oxides (M-TiO 2 @rGO) foam electrode was fabricated. • M-TiO 2 @rGO presents fast Na + storage kinetics due to capacitive contribution. • M-TiO 2 @rGO foam electrode displays a capacity retention of 90.7% after 5000 cycles.

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Transition metal selenides are widely considered as good electron conductor materials, showing bright prospect in energy storage and conversion. However, binary metal selenides as supercapacitor electrode materials are rarely reported. Herein, a simple and binder-free hydrothermal method is employed to grow hierarchical urchin-like MnCo-selenide on nickel foam. The unique hierarchical microstructure, synergetic effect, and excellent conductivity enable the electrode exhibit outstanding supercapacitor performance compared with counterpart oxide and sulfide, including high specific capacitance (1656 F g–1 at 1 A g–1) and extraordinary cycle performance (8.2% capacity decline after 8000 cycles). Additionally, the asymmetric supercapacitor (ASC), employing MnCo-selenide and AC as anode and cathode, exhibits remarkable energy density of 55.1 Wh kg–1 at 880 W kg–1, confirming the as-prepared urchin-like MnCo-selenide is a satisfactory material for the energy storage system.

Large surface area, high electrical conductivity, and abundant channels have been recognized to favor faradic capacitors, but their realization at the same time by a facile preparation process is still a great challenge.