MOF-Templated N-Doped Carbon-Coated CoSe₂ Nanorods Supported on Porous CNT Microspheres with Excellent Sodium-Ion Storage and Electrocatalytic Properties

Three-dimensional (3D) porous microspheres composed of CoSe₂@N-doped carbon nanorod-deposited carbon nanotube (CNT) building blocks (CoSe₂@NC-NR/CNT) can be successfully synthesized using CNT/Co-based metal-organic framework (ZIF-67) porous microspheres as a precursor. This strategy involves the homogeneous coating of ZIF-67 polyhedrons onto porous CNT microspheres prepared by spray pyrolysis and further selenization of the composites under an Ar/H₂ atmosphere. During the selenization process, the ZIF-67 polyhedrons on the CNT backbone are transformed into N-doped carbon-coated CoSe₂ nanorods by a directional recrystallization process, resulting in a homogeneous deposition of CoSe₂@NC nanorods on the porous CNT microspheres. Such a unique structure of CoSe₂@NC-NR/CNT microspheres facilitates the transport of ions, electrons, and mass and provides a conductive pathway for electrons during electrochemical reactions. Correspondingly, the composite exhibits a superior dual functionality as both an electrocatalyst for the hydrogen evolution reaction (HER) and an electrode for sodium-ion batteries (SIBs). The CoSe₂@NC-NR/CNT microspheres exhibit a small Tafel slope (49.8 mV dec^-1) and a superior stability for HER. Furthermore, the composite delivers a high discharge capacity of 555 mA h g^-1 after 100 cycles at a current density of 0.2 A g^-1 and a good rate capability for SIBs.